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When was the maximum of six switches or breakers first required for the main disconnect in a house electrical system?
Wednesday, July 11, 2018
Every residential electric service needs a “main disconnect,” which is usually a single breaker, set apart at the top (or bottom) of the panel from the cluster of distribution breakers. But a main disconnect does not have to be a single breaker. The National Electric Code (NEC) allows up to six circuit breakers or switches, grouped together, to be the main disconnect. In other words, it is acceptable to take up to six switch-throws to shut off all the power to a home.
The current rule allowing a maximum of six breakers or switches grouped together or in a single enclosure first appears in the 1937 edition of the NEC. Each switch or breaker must be clearly marked as a MAIN DISCONNECT, as in the photo above, which shows the top area of a “split bus” panel with identifying stickers down the center. These panels typically had four or six breakers for the main disconnect and were only manufactured from the mid-1960s to the mid-1980s. To read more about split bus panels, see our blog post ”What is a split bus electric panel?”
Although up to six breakers can still be used as a main disconnect today, we rarely see more than one. Also see our blog post Why are old electrical components not always "grandfathered" as acceptable by home inspectors?
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