The 2008 National Electrical Code (NEC) makes it a little confusing. This formula is also no longer applicable for today's panels. For panelboards not manufactured as 'lighting & appliance' panelboards, there is no limit to the number of circuit breakers allowed. 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. Here's an old formula for determining how many circuits are allowed in the Class CTL panelboard being inspected this formula is helpful to use when inspecting older electric panels without clear labeling inside the 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. The use of tandem circuit breakers is a perfectly acceptable practice, as long as the panelboard is designed for tandem circuit breakers and they're installed in locations within the panelboard where they're allowed. Because of this, they're often referred to as 'cheaters.' 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. You'll also hear them called 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 adaptation of an article I wrote for the ASHI Reporter, which was published in February of 2011.įirst, a quick definition. Today I'll set the record straight as to when tandem circuit breakers can be used. Confusion abounds over the use of tandem circuit breakers in panelboards, even among electricians and electrical inspectors.

Homeline tandem 15 amp breaker