LIMIT SWITCH FOR AUTOMATIC GATE APPLICATION; THE BENEFITS

A limit switch is absolutely crucial for gate safety and accessibility, for both swinging and sliding automatic gates. The limit switches provide additional protection and comfort by automation as part of an automatic gate control system.

This smart design is the reason why an automatic gate will not close when your car is in the way, and why it will automatically start to open when a car approaches. It also allows for proper closing or opening of the gate all the way and also at the right time, even without a human operator.

System of Operation of a Limit Switch

A limit switch is a kind of sensor that senses an object’s absence or presence; its location, velocity, and range of motion; or end of flight. The electromechanical system consists of an actuator which is attached to a series of contacts such as a knob, arm, lever, plunger or roller. When an entity comes into contact with the actuator, an electrical interaction is indicated for the device to make or split.

Limit switches are used in a wide range of control systems, from household appliances to heavy duty machines, due to their efficiency, longevity and ease of use.

For example, when you open the fridge door, what makes the light come on is a limit switch. That’s what lets the garage door opener realize when the door is fully closed and immediately stops the engine. In swinging or sliding gates used in facilities such as, apartment complexes, parking garages and office buildings, a limit switch can automatically tell the gate when to open and when it is fully closed, thereby disabling the motor.

Characteristics of a Limit Switch

Examining the number of advantages that limit switches offer there are some key considerations. There are many specific forms of switches, owing to their use in so many different applications.

• Dimensions: Limit switches are available in a variety of sizes, enabling installation anywhere desired.

• Actuator type and actuator movement: Actuator type relates to the physical mechanism which sends electrical instructions to stop the machine in response to the motion. Actuator movement can be just linear, linear multi-direction or rotary multi-direction.

• Environmental requirements: oil, snow, dirt or other harsh conditions may affect the needed type of switch.

• Electrical specs: The primary electrical factor is the current cap which defines the configuration of the limit switch within the electrical system of the machine.

• Building material: From aluminum to plastic and advanced products that can survive destructive or radioactive environments, housing materials are accessible to match the particular needs.

You can find two common limit switch contact styles which are normally closed (NC) and normally open (NO). Specialized switches are also available designed to work at extreme low / high temperatures and with differing mechanical life cycles. A part of the benefit of the intelligent design of the limit switch is its flexibility.

Conclusions on Benefits of Limit Switch

Such relatively small components play an enormous role in automatic gate performance, protection and affordability. They are very reliable, need low amounts of electrical energy and have a long service period. With such an adaptive automation system, you can serve more customers, quicker and with less expenses and services associated with it. They are thus an essential component of commercial and residential operations for a wide variety of automatic gate applications.

BASICS OF A MOLDED CASE CIRCUIT BREAKER

A molded case circuit breaker literally protects a miniature circuit breaker from excess load currents. They are also used in appliances where an adjustable trip setting may be desired. A molded case circuit breaker is often abbreviated as MCCB. It is more flexible than a plug-in breaker because it can be used over a wide range of frequency and voltages. The trip setting of this type of breaker can also be adjusted to any desired value and its amperage rating could be up to 2500A. It does three main things.

  1. It protects against overload conditions.
  2. It protects against basic electrical faults such as a short circuit.
  3. It can be used for switching a circuit on and off.

Due to the fact that molded case circuit breakers are flexible in their current and voltage requirements, they can be used for a wide range of purposes. Whether it is a low-power use or high-power use, an MCCB will do the job. Molded case circuit breakers are used in so many industries.

Operating principle of an MCCB

A molded case circuit breaker works like other circuit breaker types. It uses the principle of magnetism and thermal properties of substances. The way this device guides against faults is different from how it protects against overload or excess currents. For fault protection, it uses the principle of electromagnetic induction. On the other hand, it uses a thermal mechanism to guide against overload or excess current condition. If you need to trip the breaker manually, you can make use of a disconnection switch.

Some areas of application of a Molded case circuit breaker

MCCB’s are used for the following:

  1. To protect main electric feeder
  2. To protect a capacitor bank
  3. Generator protection
  4. Welding protection
  5. Motor protection
  6. When an adjustable trip setting is needed.

THE A-Z OF MACHINE AND COMBUSTION SAFETY

The chances of an accident happening in a manufacturing company are very high. In fact, statistics show that the manufacturing industry leads the pack when it comes to accidents and injuries. These figures are still high despite all efforts the regulatory body is putting into correcting this anomaly. Most of the accidents are caused by poor work tools and bad equipment.

The regulatory body comes up with new policies year after year just to sanitize the workplace and ensure compliance with safety rules and guidelines.

Why does manufacturing disobey safety rules and guidelines?

There is something about humans not acting until danger is imminent or something goes wrong. Basically, most safety managers only react to accidents, they are not proactive. They do not look for ways to prevent these incidents from happening. Another cause of accidents is cause assumption. When a new machine is purchased, most workshop managers assume everything is alright without running proper tests or checking the parts. Just so you know, a machine, whether new or old must meet all safety requirements.

Risk Assessment

The minimum requirement guiding the use and operation of any piece of equipment is stated in the safety standards of the regulating body. By risk assessment, we mean trying to identify probable causes of danger and working on them. To access a piece of equipment for risks, you must evaluate its operational state and functionality state. You must take note of factors like how long it takes for the machine to start, and how long it takes it to stop. If you notice any anomaly, you must take the necessary steps and make critical decisions to block every loophole. This is called “uncovering gaps in protection.” As far as risk reduction strategies are concerned, there are different options available and various ways to go about it. However, the end goal is to ensure the workplace is safe for everybody.

Wrapping Up!

The safety of lives and property within a workplace or workshop is very important. In fact, it is paramount. Therefore, all hands must be on deck. If any machine looks bad or does not operate as it should, it is better to fix it before making use of it. Otherwise, things could go wrong and people will get hurt. Safety is one of the key components of workshop practice.

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EVERYTHING YOU SHOULD KNOW ABOUT CONTROL INTERFACE ERGONOMICS

It is not uncommon to see computers with a mouse. This mouse usually has some buttons and each button has its importance and relevance. There is also a scroll wheel between these two buttons, and this scroll wheel makes it easier for us to navigate a webpage with ease.

The push button and switch performs a similar function in a machine control interface. This makes it easier to operate the machine. Hence, less effort is required. A selector switch allows us keep track of rotational movements, while an emblematic push button allows us to keep track of linear movements. So, are there any reasons to choose one over another?

  1. A selector switch makes it possible to ascertain the status of your machine interface even if it is not in a working condition. So, if you want good visibility of status, the selector switch should be your choice.
  2. With a selector switch, we can assume total control even when wearing gloves than we would do with a push button. This is because the surface area of a push button is typically small albeit there are a few that have been designed with large heads.
  1. If you are thinking about the possibility of navigating a machine or piece of equipment without necessarily looking at it, a selector switch may fit the bill. This is because a selector switch usually has a large handle. Hence, it is easier to locate without focusing your eyes on it.
  1. As far as the speed of actuation is concerned, the push button has an advantage. This is because it can be used repetitively as it only requires the movement of any of the fingers. On the other hand, a selector switch has to be turned, and twisting of the wrist is required.

E-STOP BUTTONS, PUSH BUTTONS, AND OTHER BUTTON TYPES

Buttons are everywhere. Almost all products have buttons. However, the importance and relevance of these buttons outweigh each other. Also, these button types are more popular than each other. Push buttons and emergency stop buttons are the most popular of all button types. They are found in different equipment and machineries. They also have sub-divisions albeit the way and manner they are produced remains the same. Also, our company is known for producing top-quality electromechanical products such as switches as buttons. In fact, many other companies patronize us due to our impressive service delivery and quality of our work.

OUR RANGE OF PRODUCTS

Our list of products is extensive and exciting. They include but are not limited to the following:

The principle of operation of these products differs from each other. This means that there is a unique product for every situation, need, or company.

PUSH BUTTON

This is another type of switch. Usually, this button is embedded on a pad. They are designed for manual use, i.e. they are made to be operated by hand. The Push Button is used in conjunction with electromagnetic equipments. It comes in different design patterns, shapes, and sizes.

 TYPES OF PUSH BUTTONS

 Push Buttons are of different types. However, it is important to state that all types can be used with electromagnetic equipment. Some of the most popular types are:

  • 25 inch Mushroom Plunger with Spring Latch
  • 00 inch Plastic Plunger
  • Flat Chrome Plunger Push Button Switches
  • Push Button Switches with Larger Mounting Pattern
  • 25 inch Metal Mushroom Plunger
  • 25 inch Mushroom Plunger with Shield and Weatherproof
  • 25 inch Push Button with Key Lock
  • 00 inch Push Button with Key Lock

The aforementioned types are all single plunger switches. We are also specialists in producing double plunger switches that can be used for larger equipment or wider application.

WHY DO YOU NEED A PUSH BUTTON?

Push buttons provide an extra layer of safety as far as operating equipment is concerned. Machines and other equipment that cannot shut down on their own can make use of push buttons. The importance of a push button cannot be overemphasized. So, when there is need to operate a large machine, it is okay to have a push button on standby because anything could break or fail to work at any point in time. It is often said that one of the basic principles of engineering is to make sure there is a way to turn off any equipment that was put in operational mode. In other words, do not start what you cannot stop. So, a push button is needed for safety and as an extra measure of precaution. 

WHAT IS AN EMERGENCY STOP BUTTON?

An emergency stop button is also called an E-stop button. However, it is used when there is need for immediate action or when a machine or piece of equipment needs to be stopped as fast as possible. It is not uncommon to see a heavy machine breakdown or start to malfunction. In a time like that, there should be a way to halt the operation of the machine instantly and that is what an E-stop button does. The design of an E-button is such that it fits with the equipment on which it is used so that it looks like they were produced together. E-buttons are installed to reduce the risk of accidents.

WRAPPING UP!

Different buttons have their areas of application. Since safety is important in every workplace, investing in either a push button or an E-stop button would be a wise move. However, it would be wiser to have both since they are not expensive or pricey.

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CONTROL WIRING – TYPES OF SWITCH, SELECTOR SWITCH, PUSH BUTTON, TOGGLE, ETC.

Types of switch

Any device which could be used to distrupt/interrupt electrons circulating within a circuit is known as electrical switch. Essentially, switches are binary devices: they are either entirely on (“closed”) or totally off (“open”). There are a lot of different kinds of switches and in this chapter we will discuss some of those forms.

Although it may seem odd to discuss this basic electrical subject at such a late stage in this book series, I do so because the following chapters address an older field of digital technology focused on mechanical switch contacts rather than solid-state gate circuits, and the undertaking needs a thorough understanding of switch types. Understanding the function of switch-based circuits while also mastering solid-state logic gates helps make both topics easier to understand and it sets the stage for an improved learning experience in Boolean algebra, the digital logic circuit mathematics.

The simplest type of switch is referred to as contact block, where the action of an actuating mechanism brings two electrical conductors into contact with one another. Some switches are more complicated, comprising electronic circuits that are capable of turning on or off based on some perceived physical stimuli (such as magnetic field or light). In any scenario, the final output of any kind of switch will be (at least) a pair of wire-connection terminals which are either bound by the internal communication mechanism (“closed”) of the switch or not linked together (“open”).

Any switch intended to be operated by a human is generally referred to as a hand switch, and it is made in several varieties:

Toggle switches

A lever which is angled in one of two or more positions actuates the toggle switches. A toggle switch is one example of a popular light switch which is used in household wiring. Most toggle switches are designed to come to rest at any of their lever positions, and some will have an internal spring mechanism that will return the lever to some kind of normal position allowing what is termed “momentary” operation.

Pushbutton switch

The push-button switches are two-position devices that are controlled with a push and release button. For momentary action, of the push-button switches have a spring mechanism internally which returns the button to its  “unpressed,” or “out,” position. With every press of the button, several push-button switches will turn on or off alternately. Some push-button switches will remain in their “pressed” or “in” position till the button is pulled back out. Normally, this type of push-button switches does have a mushroom-shaped button for quick push-pull operation.

Selector switch

This type of switches are actuated with some sort of rotary knob or lever to select one of two positions or more. Compared to the toggle switch, selector switches can either stop at any of their positions or have spring-return mechanisms for momentary activity.

Joystick

A joystick switch is controlled by a lever which can move in more than one direction. One or more of the mechanisms for switch contact are actuated based on how far and which way the lever is pushed. On the switch symbol is the circle-and-dot notation which shows the direction of the joystick lever motion needed to actuate the contact. Joystick hand switches are widely used for operating cranes and robots.

Many switches are designed specifically to be controlled by a machine’s action, rather than by a human operator’s hand. Such motion controlled switches are commonly referred to as limit switches, as they are often used to restrict a machine’s motion by shutting off the actuating control to a device if it goes too far. Limit switches are of several types, as with hand switches:

Lever actuator limit switch

These limit switches closely resemble selector hand or rugged toggle switches equipped with a lever driven by the system component. The levers are often tipped with a small roller bearing which prevents the lever from getting worn off by repeated contact with the part of the machine.

Proximity switch

Proximity switches detect either a magnetic or high frequency electromagnetic field approaching a metallic system component. Simple proximity switches use a permanent magnet to control a sealed switch mechanism while closing the system component (usually 1 inch or less). More sophisticated proximity switches operate like a metal detector, energizing a wire coil with a high-frequency current, and measuring the amplitude of that current electronically. If a metallic (not inherently magnetic) part gets close enough to the wire, the current increases, and the control circuit goes off. The proximity switch symbol shown here is of the electronic type, as shown by the diamond-shaped box circling the switch. A non-electronic limit switch and the lever-actuated limit switch have the same symbol.

The optical switch, containing a photocell and a light source, is another type of proximity switch. The position of the machine is sensed either by a light beam interruption or by reflection. Often, optical switches are effective in protection systems, where light beams can be used to identify workers approaching a dangerous area.

The monitoring of various physical quantities with switches is necessary for many industrial processes. These switches may be used to sound warnings, signaling that a process variable has surpassed standard thresholds, or they may be used to shut down systems or facilities when those variables have reached unsafe or harmful rates. There are different types of process switches:

Speed switch

These switches detect a shaft’s rotational speed either through a centrifugal weight device installed on the shaft or through some kind of non-contact sensing of shaft motion such as magnetic or optical.

Liquid pressure or Pressure switch Gas may be used to actuate a switch function if that pressure is applied to a bellow, diaphragm, or piston, which transforms pressure to mechanical force.

Temperature switch

The “bimetallic strip” is an inexpensive temperature sensing mechanism: a thin strip of two metals, joined back to back, with each metal having a different thermal expansion rate. Differing levels of thermal expansion between the two metals allow it to bend when the strip heats or cools. Then, a switch contact mechanism can then be actuated by the bending of the strip. Many temperature controls use a brass bulb packed with either a gas or liquid, with a tiny tube linking the bulb to a switch that detects heat. The gas or liquid expands as the filament is heated, creating an increase in pressure which then stimulates the switching mechanism.

Liquid level switch

A floating body may be used to actuate a switch mechanism when the volume of liquid in a tank increases past a certain point. If the liquid is electrically conductive, the liquid itself may be used as a conductor for bridging at the appropriate depth between two metal probes embedded in the tank. The conductivity strategy is typically applied through the conductive material, with a specific relay configuration caused by a small amount of current. In most situations, moving the circuit’s full load current through a liquid is inefficient and risky.

The amount of solid materials such as animal feed, coal, wood chips or grain in a hopper, bin, or a storage silo can also be detected by the use of specially designed level switches. A typical design for this usage is a small paddle wheel, placed at the desired height into the bin which is turned gradually by a small electric motor. The material stops the paddlewheel from spinning once the solid material fills the bin to this height. The small engine’s torque response then trips the switch mechanism. One other design utilizes a metal prong shaped “tuning fork,” placed into the bin at the desired height from the outside. The fork is vibrated by an electronic circuit and the magnet / electromagnetic coil assembly at its resonant frequency. When the bin fills up to that height, the solid material dampens the fork force, the vibration intensity and/or frequency shift that the electronic circuit senses.

Liquid flow switch

Inserted in a pipe, a flow switch will detect any liquid or gas flow rate that exceeds a certain level, usually with a small vane or paddle that is pushed by the flow. Other flow switches are designed as differential pressure switches, measuring the pressure drop over a pipe-built restriction.

Another kind of level switch is the nuclear switch, ideal for detecting solid or liquid materials. Composed of a radiation detector and a radioactive source material, both are mounted for either liquid or solid material over the diameter of a storage vessel. Any material height above the level of the detector/source arrangement will reduce the radiation strength that reaches the detector. This decrease in detector radiation may be used to activate a relay mechanism to provide a switch contact for vessel level measurement, alarm point, or even control.

Both source and detector are outside the vessel, and there is no intrusion except for the radiation flux itself. The radioactive sources used do not pose any immediate threat to maintenance or operations staff as they are fairly weak.

Usually, there is more than a way of implementing the switch to serve as an operator control or monitor a physical process. For any application, there is usually no single “perfect” switch, although some obviously show some advantages over others. Switches have to be intelligently adapted to the task for reliable and efficient operation.

• REVIEW:

• The switch is an electrical device. It is usually electromechanical and is used to control the continuity between two points.

Hand switches are powered with human touch.

• Limit switches are machine movement driven.

Process switches are activated by some physical process changes (temperature, flow, level, etc.).

Switch contact design

A switch may be built with any mechanism putting two conductors into contact with each other in a regulated manner. This can be as easy as having two copper wires to meet each other through the action of a lever or by moving two metal strips into direct contact. Nevertheless, a proper switch design must be reliable and rugged, and avoid the possibility of electrical shock posed to the user. Industrial switch designs therefore are never that basic.

The conductive components used for making and breaking the electrical connection in a switch are called contacts. Contacts are made primarily from silver or silver cadmium alloy, the conductive properties of which are not significantly impaired by oxidation or surface corrosion. Gold contacts have the greatest resistance to corrosion, but are reduced in current-carrying capacity and may be “cold welded” when combined with high mechanical force. The switch contacts are driven by a system that guarantees even and square contact for optimum reliability and minimal resistance, whatever the metal preference.

Contacts like these can be built to accommodate extremely large quantities of electric current, in some cases up to thousands of volts. The limiting factors for the ampacity of the switch contact are:

• Sparking triggered by opening or closing contacts;

• Voltage over open switch contacts (potential of jumping current across the gap).

• Heat produced by the current from metal contacts (while closed).

The exposure of the contacts in the standard switch contacts to the surrounding atmosphere is a major disadvantage. This is usually not a problem in a good, tidy, control-room setting. But most industrial conditions aren’t so innocuous. The existence of corrosive chemicals in the air will cause the contacts to prematurely deteriorate and fail. The risk of regular contact sparking which causes flammable or explosive chemicals to ignite is even more worrying.

When there are such environmental concerns, certain forms of contacts for small switches may be considered. These other contact types are sealed from outside air contact and therefore do not experience the same exposure problems as standard contacts do.

The mercury switch is one common type of sealed-contact switch. Mercury is a metallic element and it is liquid at room-temperature. Being a metal, it has outstanding conductive characteristics. It can be put into contact within a sealed chamber with metal probes (to close a circuit) as it a liquid simply by inclining the chamber so that the probes are on the bottom Most commercial switches use small mercury-containing glass tubes that are tilted one way to open the contact, and tilted another way to close it. Such systems are an excellent alternative to open-air transfer connections anywhere environmental exposure issues are concerned, apart from the problems of tube breakage and spilled mercury (which however is a toxic material), and sensitivity to vibration.

There, in the open position, a mercury switch (often referred to as tilt switch) is shown where the mercury is seen to be out of contact with the two metal contacts and also at the other end of the glass bulb: the same switch is shown in the closed position. Gravity also holds the liquid mercury in contact with the two metal contacts, ensuring electrical stability from one to the other: Mercury switch contacts are inefficient to create in large sizes, so you will typically find these contacts rated at no more than 120 volts and no more than a few amps. Of course, there are variations but these are some common limits.

Another type of sealed-contact switch is the magnetic reed switch. As with the mercury switch, the contacts of a reed switch are found within a sealed tube. Unlike the mercury switch that utilizes liquid metal as the contact medium, the reed switch is essentially a pair of very small, magnetic, metal strips (hence the term “reed”) that are brought into contact with each other by adding a strong magnetic field outside the sealed loop. The magnetic field source in this type of switch is typically a permanent magnet, which is pushed by the actuating mechanism closer or further away from the tube. This form of contact is usually measured at lower voltages and currents than the normal mercury switch, due to the small size of the reeds. Usually, reed switches tolerate vibration better than mercury contacts though, because there is no liquid inside the conduit to splash about.

General-purpose switch contact voltage and current levels are commonly found to be higher on any specified switch or relay if the electrical power being transferred is AC instead of DC. The explanation for this is the tendency of an alternating-current arc over an air gap to self-extinguish. Due to the fact that 60 Hz power line current ceases and reverses direction 120 times per second, there are many ways for an arc’s ionized air to lose adequate temperature to avoid conducting current, to the extent where the arc will not restart at the next voltage level. However, DC is a steady, constant movement of electrons that tends to keep an arc even smoother over an air gap. Therefore, by switching a specified value of the direct current, switch contacts of any kind cause more wear than for the same amount of alternating current. When the load has a significant amount of inductance, the issue of switching DC is amplified, as there will be very strong voltages produced through the contacts of the switch when the circuit is opened (the inducer will do its best to maintain circuit current at the same magnitude as when the switch is closed).

Contact arcing can be reduced with both AC and DC by inserting a “snubber” circuit (a resistor and capacitor wired in series) in parallel with the contact, such as this: a sudden rise in voltage across the switch contact induced by the contact opening will be tempered by the charging operation of the capacitor (the capacitor countering the rise in voltage through drawing current). The amount of current discharged through the contact whenever it closes again is limited by the resistor. If the resistor was not present, the capacitor could actually make the arcing worse during contact closure than the arcing during contact opening without a capacitor! While this extension to the circuit tends to reduce contact arcing, it is not without disadvantage: a prime factor is the probability of a broken (shortened) resistor / capacitor combination supplying electrons with a route to pass through the circuit at all times, even if the contact is open and the current is not needed. The threat of this malfunction, and the extent of the resulting consequences, must be weighed against the enhanced contact wear without the snubber circuit (and eventual failure of the contact).

One thing which is not new is the use of snubbers in DC switch circuits: this has been practiced by automobile manufacturers on engine ignition systems for years, reducing arcing across the switch contact “points” in the supplier with a tiny capacitor called a condenser. As any technician will tell you: the service life of the “points” of the distributor directly depends on the operation of the condenser.

With all this talk about minimizing switch contact arcing, one might assume that for a mechanical switch, less current is always better. This isn’t always so, however. A small amount of intermittent arcing will work out great for the switch contacts, because it protects the contact faces from corrosion and small amounts of debris. The contacts may tend to accumulate undue resistance if a mechanical switch contact is worked with too little current and may fail prematurely! This minimum amount of electrical current that is required to sustain mechanical switch contact in good health is called the wetting current.

In a properly designed system, the wetting current rating of a switch is normally well below its maximum current rating, and also well below its normal operating current load. Nonetheless, there are situations where the contact a mechanical switch may be needed to manage currents regularly below usual wetting current limits (for example, when a mechanical selector switch has to open or close an analog electronic or a digital logic circuit where there is an extremely small current value). Gold-plated switch contacts are highly recommended to be listed in those applications. Gold will not corrode like other metals as it is a “noble” metal. As a consequence, such contacts have extremely low current wetting criteria. Regular contacts with the silver or copper alloy will not provide effective operation when used in this low-current service!

REVIEW:

• Reed switches are another form of sealed-contact system, the contact being created by two thin metal “reeds” inside a glass tube, coupled by an external magnetic field effect.

• Mercury switches use the liquid mercury metal slug as a moving contact. Shielded in a glass tube, the spark of the mercury contact is shielded from the outside world, rendering this form of switch ideally suited for atmospheres that host potentially explosive vapors.

• The parts of the switch responsible for making and breaking electrical synchronization are considered the “contacts.” Usually made of corrosion-resistant metal alloy, contacts are designed to meet each other by a process that helps to maintain proper alignment and spacing.

• Switch contacts suffer from DC switching more than AC. This is due primarily to the self-extinguishing nature of an AC arc.

• To reduce contact arcing, a resistor-capacitor network called a “snubber” may be connected in parallel to a switch contact.

• The minimum amount of electric current needed to carry a switch contact to be self-cleaned is called wetting current. This value is normally far below the maximum current rating for the switch

The make/break sequence and “normal” state of contact

Any kind of switch contact can be configured such that the contacts “close” (establish continuity) when actuated, or “open” (interrupt continuity) when actuated. In switches that have a spring-return function in them, the spring returns it to a direction with no applied force. This direction is known as the normal position Then contacts open in this position are normally called open, and contacts closed in this position are normally called closed.

The normal position, or condition, for process switches is what the switch is in when there is no process control over it. One easy way to figure out a process switch’s usual state is to find the switch status as it lies uninstalled on a storage shelf. Definitions of “normal” process switch situations are as follows:

Pressure switch: When the pressure applied is zero

Speed switch: shaft not spinning

Level switch: empty bin or tank

Flow switch: Zero flow of liquid

Temperature switch: ambient temperature

One important thing to do is to distinguish between the “normal” state of the switch and its “normal” use in the operational process Consider the example of a liquid flow switch that acts as a low-flow alarm in a system of cooling water. The cooling water system’s natural or properly functioning state is to have a fairly constant coolant flow through this pipe. If we want to close the contact of the flow switch in case of a lack of coolant flow (for example, to complete an electrical circuit that triggers an alarm siren), we would like to rather than use a flow switch with normally-open contacts use one with normally-closed contacts. The contacts of the switch are forced open when there is sufficient flow through the pipe; when the flow rate decreases to an abnormally low point the contacts revert to their usual (closed) state. Thinking of “normal” as the process’s usual state could be confusing, so be careful to always think of the “normal” state of a switch as that in which it is as it is sitting on a shelf.

The symbol for switches varies depending on the intent and actuation of the switch. A normally open switch contain contact is designed in such a way that it indicates an open connection ready to shut when it is actuated. In comparison, a switch that is normally closed is designed as a closed connection that when actuated, opens. Remember the following symbols: Each switch contact also has a common symbol, representing the contact points within a switch with a pair of vertical lines. Normally open contacts are marked by non-touching lines while normally closed contacts are defined with a bridging diagonal line between the two lines. Compare the two:

When actuated, the switch seen on the left will close and open while in the normal state (un-actuated). Once actuated, the switch on the right opens and is closed in the normal (non-actuated) position. When switches are described with these common symbols, the type of switch should typically be indicated in text next to the symbol immediately Please note the icon on the left should not be mistaken with a capacitor’s. If a capacitor requires to be depicted in a diagram of control logic, it will be shown as follows:

 ————

In regular electronic symbology, the above figure is intended for polarity-sensitive capacitors. The capacitor symbol is used for every type of capacitor in control logic symbology, even when the capacitor is not prone to polarity, so as to clearly differentiate it from a normal-open switch contact

A further design aspect must be addressed for multiple-position selector switches: that is, the process of breaking old connections and making new connections as the switch is pushed from position to position, the moving contact reaching numerous stationary contacts in sequence

————————————

The selector switch shown above moves the common contact lever to one out of five different positions, to connect wires numbered 1 to 5. The most popular design of a multi-position switch like this is one such that contact is interrupted with one place before contact is made with the next position. This design is known as break-before-make. For example, if the switch was placed at position number 3 and turned slowly in the clockwise direction, the contact lever would shift off the position number 3, getting the circuit to open, going to a position between numbers 3 and 4 (both circuit paths open), and then touching position number 4, and getting the circuit to close.

There are situations where full opening of the circuit attached to the common wire at any point in time is unacceptable. A make-before-breakswitch mechanism can be designed for such an operation, in which the movable contact lever essentially bridges between two contact positions (between number 3 and number 4, in the scenario above) as it moves between positions. The concession here is that, as the selector knob is rotated from position to position, the circuit must be able to manage switch closures between neighboring position contacts (1 and 2, 2 and 3, 3, and 4, 4 and 5). Here is such switch:

 ———-

If movable contacts with stationary contacts can be put into one of many positions, such positions are sometimes referred to as throws. Often, the number of movable contacts is called poles. The selector switches seen above would be defined as “single-pole, five-throw” switches with five stationary contacts and one moving contact.

If two identical five-throw, single-pole switches were mechanically coupled in such a way that they were operated by the same mechanism, the whole assembly will be called a “double-pole, five-throw” switch:

————————————————————————————————————————————————————————————————————

With process switches, this is the uninstalled state it is in while sitting on a shelf.

Some common configurations of switch and their abbreviated descriptions:

REVIEW:

  • An open unactuated switch is called normally-open switch. An unactuated closed switch is referred to as normally-closed. The terms “normally-closed” and “normally-open” are sometimes abbreviated as N.C and N.O., respectively.
  • The general symbol for N.C. and N.O.
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  • Multi-position switches can be either make-before-break or the very common one, break-before-make.
  • The switch “poles” refers to the number of moving contacts whereas the switch “throws” refers to the amount of stationary contacts per moving contact.

Contact “bounce”

In a single, clean instant, when a switch is triggered and contacts touch each other under the actuating force they are expected to maintain continuity. However, though, switches do not achieve exactly this aim. Because of any inherent elasticity in the mechanism and/or contact materials, and mass of the moving contact, contacts will “bounce” for a period of milliseconds upon closure before coming to full rest and providing unbroken contact. Switch bounce is of no concern in many applications: it matters little if a switch regulating an incandescent lamp “bounces” for a few cycles whenever it is actuated. Since the warm-up time of the lamp exceeds considerably the bounce duration, there will be no irregularity in the activity of the lamp.

Nevertheless, if the switch is used to send a signal with a quick response time to an electronic amplifier or to some other circuit, contact bounce may cause very visible and undesired effects:

A closer look at the oscilloscope monitor shows a rather hideous set of makes and breaks when the switch is triggered one time:

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When, for example, this switch is used to transmit a “clock” signal to a digital counter circuit, so that each pushbutton switch is intended to raise the counter by a value of 1, what will happen then is that the counter increments (by several counts) each time the switch is actuated. Since mechanical switches also interface in modern systems with digital electronic circuits, switch contact bounce is a frequent feature of the architecture. Somehow, it is necessary to eliminate the “chattering” created by bouncing contacts, so that the receiving circuit has a smooth, crisp off / on transition:

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Switch contacts can be debounced in several different ways. The most straightforward method, is to address the problem at its core: the switch itself. Here are some ideas for the design of minimal bounce switch mechanisms:

  • Reducing the kinetic energy of the moving contact. This reduces the impact force when it comes to rest on the stationary contact, thus reducing the bounce.
  • Use the stationary contact(s) with “buffer springs” so that they are able to rebound and softly absorb the impact force from the moving contact
  • Build the “wipe” or “slide” contact switch rather than the direct impact. Sliding contacts are used in “knife” switch designs.
  • Dampen the action of the switch mechanism using the shock absorber” device for air or oil.
  • Using sets of contacts in parallel, each slightly different in mass or contact gap such that when one is rebounding off the stationary contact at least one of the others is still in firm contact.
  • Get the contacts “wet” in a sealed environment with liquid mercury. When initial contact is made, mercury “surface tension should maintain continuity of the circuit although the moving contact may bounce off the stationary contact multiple times.

Each of these solutions compromises some element of switch efficiency for limited bounce, and designing all switches with limited contact bounce in mind is unpractical. Attempts made to minimize the contact’s kinetic energy may result in a small open-contact distance or a slow-moving contact, which reduces the voltage that the switch can accommodate and the amount of current it can interrupt Although non-bouncing, sliding contacts often create “noise” (abnormal current induced by irregular contact resistance during movement) and suffer from more mechanical damage than normal contacts.

Multiple parallel contacts provide fewer bounce, but only more cost and switch complexity. The use of mercury to “wet” the contacts is a very effective means of reducing the bounce, but it is sadly restricted to low-ampacity switch contacts. Also in mounting position mercury-wetted contacts are usually limited, because gravity may trigger the contacts to bridge inadvertently if they are positioned the wrong way.

If re-designing the switch system is not a solution, mechanical switch contacts can be externally debounced, utilizing supplementary circuit components to modify the signal. For example, a low-pass filter circuit connected to the switch output can minimize the voltage / current fluctuations produced by the contact bounce:

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Switch contacts can be electronically debounced using hysteretic transistor circuits (high or low-state “latch” circuits) with built-in time delays (known as “one-shot” circuits), or two inputs that are  controlled by a double-throw switch.

HOW IS A FUSE BOX DIFFERENT FROM A BREAKER PANEL

We all know that not all houses were built at the same time. What this means that there are different types of electrical appliances and they all vary in age and features. Two of the most common components of are the electrical system in a house are the breaker panel and fuse box. So, what are they and what do they do?

Fuse Box

The fuse box and breaker panel are very similar in the way they operate and the things they do. Primarily, they split electric currents into different circuits and places where they are needed within a household. Also, they stop the flow of current whenever they detect excess current.

Usually, a fuse box contains a metal filament that permits the flow of current. Whenever, there is overcurrent condition, the filament will melt and electric power will be disrupted. This is what is commonly regarded as a “blown fuse”. Unlike a circuit breaker that can be reset, a blown fuse will have to be replaced. Although fuse boxes are efficient, they have many disadvantages and this led to the introduction of breaker panels.

The major drawback is that fuses have to be replaced almost every now and then. They are not in any way convenient. Apart from that, they cannot be used together with AFCI’s and GFCI’s. Fuse boxes are also a huge fire risk. This is because a bigger fuse is needed to compensate for higher demands for electricity. The more the fuse size is increased, the higher the risk and dangers involved.  

A Breaker Panel

The principle of operation of breaker panels is different from fuse boxes. Whenever overheating occurs, it has a unique way of handling it and halting current flow. It either uses the principle of bimetallic strip or solenoid to execute this task. We already know that both are based on temperature difference and difference in expansion of two distinct metals. When the breaker goes off, you only have to return the switch to the “ON” position. This is an advantage the breaker has over the fuse. The fuse would burn and have to be replaced. Unlike a fuse box, a breaker panel can work with AFCI and GFCI outlets. It also permits more load and electrical appliances than a fuse box. Generally, a breaker is safer than a fuse box. The risk of fire outbreak is lesser or non-existent. Apart from that, a breaker panel allows you to meet the modern electrical demands in residential and industrial buildings.

So, if what you have is a fuse box, you may want to consider replacing it with a breaker panel. Using a breaker panel may also mean you have to change some wires and outlets in the house. That is really not a problem, a qualified electrician can fix that and make your breaker work seamlessly with a GFCI and AFCI outlet.

WHAT TO KNOW BEFORE PAYING FOR A LOAD CENTER

Another name for the load center is the breaker panel. It is the heart of your home’s electrical system. It is responsible for distributing electrical power gotten from the source to all parts of your home. Apart from that, it offers protection to all outlets and circuits since this is where all the circuit protection of the home resides.

There are too many types and brands of load centers in the market today. This has made it more difficult to make a choice or purchase any of the products. We are here to eliminate your worries.

However, before you splash the cash on any load center, there are a few factors that you should put into consideration. One of the first things you should do is to seek counsel from an experienced electrician or electrical engineer on requirements and specifications. This will give you an idea of which type or brand suits your needs. An experienced electrician will advise you based on factors like the amperage capacity, as well as circuit variations (whether 1-pole or 2-poles).

Main Breakers vs. Main Lugs Panels

A main breaker is like a router. It determines whether there would be electric power in a house or not. If you need to shut down power supply into the house, you do so from a main breaker. Once it is turned off, there would be no flow of electrical power into that household. A main breaker also offers protection from overcurrent and short-circuits conditions.

The most popular service disconnect in residential buildings is a Main Breaker. It could either be indoor or outdoor. However, it is mostly placed in a load center. As said earlier, when you switch off the main breaker, there would be no power to any of the circuits within the house. That does not mean there is no current in the wires that feed the breaker. These wires are still hazardous. So, it is best to keep a distance from them.

On the other hand, there is no main breaker in a main lugs load center as it contains only lugs. Another name for a main lug load center is “sub-feed panel.” The installation of this device could be done adjacent to a main panel. This allows us have additional circuits when the main breaker panel is not empty. Another way of installing a main lugs load center is to set it up far away from the main panel. This means there would be a local disconnection for the appliances and circuits that are in some parts of the house like the garage or store.

Indoor Load Center vs. Outdoor Load Center

A load center can either be used indoor or outdoor. This is to ensure all electrical appliances have access to them. The major difference is that the outdoor type can withstand harsh weather conditions. So, if you live in a place where rainfall and snow is predominant, you may want to choose an outdoor load center.

Ampacity

This is the yardstick for measuring all load centers. Ampacity is the maximum permissible current that a load center has been constructed to accept. It is important to know about it since it directly or indirectly influences the ampacity needed in your house.  You should know about it before making a main breaker choice. The load or power requirement of an household can be computed in different ways. If you do not know what your power requirements are, seek counsel from a qualified electrical engineer or electrician. Usually, the convention is 200A for newer homes and 100A for older homes. If the house is very large and it is expected that there will be high demand for electricity, a 400A-service may be the ideal option. 

Types of Breakers

There are different types of breakers and they all have their unique strength and importance. The most popular types are the standard circuit breakers. Ground Fault Circuit Interrupters (GFCI), and Arc Fault Circuit Interrupter (AFCI).

Basically, a standard circuit breaker prevents excess currents from making its way into the wiring system. We all know how dangerous this could be. In fact, it is one of the most common causes of a fire outbreak in most houses. It also has the ability to offer protection from short circuit conditions. 

On the other hand, an Arc Fault Circuit Interrupter (AFCI), helps to guide against arcing. We all know how dangerous arcing can be if not prevented. It can lead to a fire outbreak and electrocution. 

Ground Fault Circuit Interrupters (GFCI) does almost the same thing as an AFCI albeit its primary role is to guide against electrocution and electric shocks. It de-energizes the circuit anytime it senses current leakage.

The Dual Function Circuit Breaker (DFCB) combines the qualities and properties of a GFCI and AFCI. So, it is able to guide against electrocution and fire outbreak. To know what type of breaker to use for a particular part of the house, you must be familiar with the local electrical code. We also have another category of breakers called Tandem breakers. Just as the name suggests, they can work in tandem with other breaker types.

Circuit Breakers

In residential buildings, breakers are designed to be used in 12/240V single phase outlets. Usually, a circuit breaker is rated in amperes. The ideal specification is for the current rating of the surrounding wires that are linked to the breaker to exceed or equal the current rating of the breaker. Do not attempt to use a breaker whose ampere rating exceeds that of the installed wiring.

HOW MUCH OF AN ISSUE IS IT IF MY ELECTRIC PANEL DOES NOT HAVE A MAIN BREAKER?

The answer to this question is probably “NO”. In some cases, issues may arise but because the installation of electric panels is not mostly done by inexperienced persons, it is a rare occurrence to see an electric panel without a main breaker.

There are times when it looks like there is no main breaker, but logically there is one. The aim of this article is simple, to explain this point so that someone without prior knowledge of electricity understands what is been discussed. Real Estate agents and other professionals need to understand the ideas and concepts behind an electrical panel so that when it is been discussed, they would not seem lost.

The first and most important point is this, if there is a means of sending power to a home or household, there has to be a way of shutting it down. This is the basic principle of engineering; you do not start what you cannot stop. Without a main disconnect breaker, it would not be possible to shut down power supply to a household. Usually, the Main Disconnect Breaker is found in the electrical service panel. A fuse can do an equal job, the only problem is that it gets blown anytime there is a power surge or irregular current. Therefore, the frequency of replacement is high.

WHERE IN MY BUILDING CAN LOAD CENTERS AND PANELBOARDS BE LOCATED?

It is common for space for electrical panels and equipment to be dedicated in a commercial building. Read about the requirements:

A compartment that contains overcurrent equipment such as fuses or circuit breakers is called a panelboard (which could also be called load centre).

It is common to reserve space for electrical panels and appliances in a commercial building. A commercial building will often have a main room for major electrical services and also, on other floors, smaller electrical rooms.

A requirement of the National Electrical Code requires is ‘‘clear space” which is to provide easy access to the overcurrent equipment and provide adequate space for repair and review, referenced as working space around the panelboard. Working space can differ, as shown in the diagram below, based on the voltage of the electrical equipment and related structures and walls.

Dedicated work room needs to be provided before and right above the panelboard. The working space width in front of the device must be at least 30″ or the equipment width, whichever of the two is greater. The working space also stretches vertically from the floor or grade to a minimum height of 6-1/2′ or equipment height, whichever is greater. Such specifications are given for in National Electrical Code article 110.26 and Table 110.26(A)(1).

Local codes also may determine acceptable dimensions of work spaces.  For example, the City of Austin requires the vertical extension of the working space from the floor to the structure beyond the NEC’s 6 -1/2″requirement.

It is not common for a space to be dedicated for installing an electrical panel in residential facilities. Therefore panelboards are often installed in single-family homes in basements or garages. The panels are often mounted in dormitories or halls of apartments or condos. Article 240.24 describes the positions where panel boards may not be placed, and therefore by default, overcurrent equipment.  The code states that panel boards may not be placed in the vicinity of readily ignitable content (such as wardrobes), toilets, over stairs, in plumbing walls, or near to sinks or plumbing fittings.  Furthermore, the code is diligent to state that the panel boards be placed in a readily accessible spot, implying that the highest circuit breaker’s top cannot be over 6’7″AFF or from the workstation. There are also local codes limitations on the locations of panelboards.

Installation of panelboards may be outdoors or indoors. Panelboards have to be built using the correct NEMA classification for the setting they are being used in. Indoor panelboards usually have the NEMA 1 classification whereas outdoor panelboards generally have the NEMA 3R ranking.