How To Determine When To Use Tandem Circuit Breakers

There is normally a confusion when it comes to the use of tandem circuit breakers within the panelboards. This confusion also faces electricians and electrical inspectors too. In this post, we want to explain things into detail and make sure that you will no longer be confused.

A summarized definition

A tandem circuit breaker is referred to as a double circuit breaker that occupies the space of a single circuit breaker or panelboard. You might have heard some electricians calling it a duplex, twin, half-height, slimline, wafer breaker, half-inch or double depending on where you come from. While the tow-pole circuit breaker is connected to two poles, a tandem breaker doesn’t.

A tandem circuit breaker allows you to connect two circuits on a panelboard by occupying a single circuit breaker space. They are normally applied after the panel has been filled to its maximum capacity with standard circuit breakers. Due to this, they are normally called cheaters.

Does this mean that installing them is cheating? No, it is not. The installation of tandem circuit breakers is just an acceptable practice as long as the panelboard is designed to be used for tandem circuit breakers and they can be installed in any locations that are mounted with panelboards.

How does a home inspector determine if the tandem circuit breaker is allowed into the panelboard that they are inspecting? There are several ways to do so.

The class CTL panelboards

The panelboards should comply with the UL standard 67, which needs all lighting and appliance panelboards to comply with Class CTL (Circuit total Limiting). There is an old formula that is used to determine the number of circuits that can be installed in the class CTL panelboard that is being inspected. This formula is essential to use when you are inspecting an older electric panel that has no proper labeling inside the panel. You will have to take the amperage of the panelboard and multiply it with the number of poles, and then divide it by 10. This sounds a bit complicated but it is just simple. Let us take an example so that you can understand.

Let us use 100 amp panelboard as an example that will make you understand

100 Amp X 2 Poles = 200 then 200/10 = 20

As based on this formula the maximum number of circuits that can be used in a 100-amp 120/240-volt panelboard is 20. When it comes to panelboards not manufactured as lighting and appliance panelboards there are totally no limits to the number of circuits breakers that are allowed. Note that this formula is no longer applicable in today’s panelboards.

There is a confusion that is created by the 2008 National Electrical Code (NEC). The previous versions of the NEC were limiting the maximum number of circuits in a lighting and appliance panelboard to 42. The 2008 edition of the NEC dropped the lighting and appliance panelboard section, but the NEC 408.54 states that “A panelboard must be offered with physical means in order to prevent the installation of extra overcurrent devices than the specific number which the panelboard was designed, listed and rated to handle.

The manufacturers still specify the maximum number of circuit breakers that are allowed and should also offer the rejection feature so it has to prevent the application of tandem circuit breakers where they are not allowed.

The class CTL panelboards have different ways of preventing class CTL tandem circuit breakers from being applied in locations where they are not meant to. This is what is known as the rejection feature.

The tandem circuit breakers are manufactured like this so as to prevent people from improper use although this does not stop everyone from doing so.

When it comes to panels that were manufactured before the adaption of the class CTL standard, the non-Class CTL tandem circuit breakers are accepted to be connected as replacement circuit in breakers only. The non-Class CTL tandem circuit breakers are not designed with a rejection feature, unlike the Class CTL breakers. As it is clearly labeled on the side of all circuit breakers, such circuit breakers that were manufactured before the adaption of the class CTL standard are not allowed. Sometimes it is difficult for home inspectors as the markings are not usually visible after being installed, and the home inspectors cannot pull out the breakers to try to figure it out.

Does the panelboard accept tandems?

Now as we have discussed the general guidelines for tandem circuit breakers, let us now look at the means that home inspectors or electrical inspectors use to determine when the tandem breakers are accepted in different panelboards.

The version of the panelboard                             

The version or part number of the electric panelboard normally shows whether or not the electric panelboard is designed in a way that it can allow tandem breakers and how many of them can be used. Here are some few examples:

  • The G3040BL1200 contains 30 spaces and allows a total number of 40 circuits. You can use up to 10 tandem circuit breakers.
  • The G3030BL1150 has 30spaces and 20 circuits are accepted. You can use up to 8 tandem circuit breakers.
  • The BR1212B100 consists of 12 spaces and has a total of 12 circuits that are allowed. No tandem circuit breakers are allowed.
  • The HOMC20U100C consists of 20 spaces and has a total of 20 circuits that are allowed. No tandem breakers that are allowed.

This will help you as it has simplified the pattern.

What is the major concern when it comes to circuit breakers?

When tandem circuit breakers are applied in areas where they are not accepted, they could lead to an improper physical connection with the connection bar within the panelboard which can lead to a fire outbreak. The tandem circuit breakers also raise the total load upon the bus bars within the panelboard; this requires the home inspectors or electricians to use their common sense.

In case home inspectors or electricians identify tandem circuit breakers that are installed in an improper location, they will normally recommend repairs to be made. In case the bus bars of the panelboard has been destroyed or altered in any way to allow the installation of tandem circuit breakers, the panelboard must be replaced. There is absolutely no way that can help the home inspectors determine if the bus bars have been destroyed without having to remove the circuit breakers. This is something that they are not allowed to do.

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