This is referred to as a “rejection feature”. Rejection featuresĬlass CTL panelboards have different methods of preventing class CTL tandem circuit breakers from being used in locations where they’re not allowed. The 2008 version of the NEC removed the “lighting & appliance” panelboard designation, however, NEC 408.54 says “A panelboard shall be provided with physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and listed.” Manufacturers still list the maximum number of circuit breakers allowed and must provide a rejection feature to help prevent the use of tandem circuit breakers where not allowed. Previous editions of the National Electric Code (NEC) limited the maximum number of circuits in a lighting and appliance panelboard to 42. I don’t have to spend my time studying panel diagrams in this case.Ģ008 to today: For the newest panels, you simply go with what the manufacturer tells you, and the labeling is usually clear. As a home inspector, this is helpful because if I look at a 100 amp panel with 20 spaces, I immediately know that the panel doesn’t allow tandem breakers. For panelboards not manufactured as “lighting & appliance” panelboards, there is no limit to the number of circuit breakers allowed. A 150-amp panel would allow a maximum of 30 circuit poles, and a 200-amp panel would allow a maximum of 40 circuit poles. It sounds complicated, but it’s not - let’s use a 100-amp panelboard as an example:īased on this formula, the maximum number of circuits allowed in a 100-amp 120/240-volt panelboard is 20. Take the amperage of the panelboard, multiply by the number of poles, and divide by 10. This formula is helpful to use when you’re inspecting older electric panels without clear labeling inside the panel. Not for CTL assemblies.”ġ965 to 2008: Here’s an old formula for determining how many circuits are allowed in Class CTL panelboards made during this time period. These breakers will be labeled “For replacement use only. In these cases, it’s possible that tandem circuit breakers are allowed in every space in the panel. Sometimes the panel has clear labeling, but usually is doesn’t on these old panels. Pre-1965: Old panels that predate the CTL standard didn’t have a hard and fast rule for the number of circuit breakers allowed. To help determine if tandem breakers are allowed, first consider the age of a panel. Panelboards must follow UL Standard 67, which requires all lighting and appliance panelboards to be Class CTL (Circuit Total Limiting). How does a home inspector determine whether tandem circuit breakers are allowed on the panelboard they’re inspecting? There are a number of ways to do so. It’s perfectly fine to use tandem circuit breakers on any panelboard that’s designed for tandem circuit breakers, provided they’re installed in the proper locations. Because of this, they’re often referred to as “cheaters.”ĭespite the misnomer, this is not cheating. The next photo shows an older style tandem breaker found in Square D panelboards.īecause tandem circuit breakers allow for two circuits to be installed on a panelboard in a one circuit breaker space, they’re typically used after a panelboard has been filled to capacity with standard circuit breakers. The photo below shows a 60-amp two-pole circuit breaker at the top, then a 15-amp tandem circuit breaker (highlighted), then a 20-amp tandem circuit breaker (highlighted), then a 20-amp single-pole circuit breaker at the bottom. While a two-pole circuit breaker gets connected to two different poles at a panelboard and has a common trip or a handle tie for simultaneous disconnecting of two poles, a tandem breaker does not. People also refer to them as duplex, slimline, twin, half-height, half-inch, double, and wafer breakers, depending on local customs. A tandem circuit breaker is a double circuit breaker that takes up the space of a single circuit breaker on a panelboard. This is an updated version of an article I wrote for the ASHI Reporter back in 2011.įirst, a quick definition. I’ll explain what they are, when they can be used, and how a home inspector can figure all of this out. Today I’ll set the record straight on tandem circuit breakers.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |