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What are common problems with split-bus electrical panels?
Tuesday, November 23, 2021
A split-bus panel has a gap in the bus bar(s), and requires that all the breakers in the upper bus bar (mains) be shut off to disconnect all power. One breaker in the upper bus bar disconnects the circuits in the lower bus bar. It is an older panel design that has not been produced since the 1980s. The three defects we commonly see with split bus panels are:
1) Not all the main breakers are clearly marked. The little stickers that are required to denote which breakers must be thrown to shut off all power have fallen off over time.
2) A panel with six main breakers, each of which is 240-volt, has had one or more 240-volt breakers changed out for two 120-volt breakers, pushing up the number of necessary switch-throws in the top cluster to shut off all power to more than the maximum six allowed. The panel shown below takes 9 switch-throws to shut off all power.
3) Most split-bus panels date back to the 1950s and ‘60s. After that, their popularity waned and the last ones were manufactured in the mid-1980s. So most of the original circuit breakers are now past the their estimated 40- to 50-year functional lifespan.
If you have a split bus panel in your home and are not planning on replacing it anytime soon, consider at least replacing the original breakers as a safety upgrade. Arc Fault Circuit Interrupter (AFCI) breakers are now code-required for most replacement circuits, and will provide an extra level of fire protection—which is especially important in a home with older wiring. They detect any arcing or sparking in wiring that become frayed, damaged, or deteriorated, and trip to cut off the circuit—on top of the normal circuit breaker duty of tripping when too much current is flowing through the wires.
Up to six main disconnects grouped together in the same main panel continued to be allowed until the 2020 edition of the National Electrical Code, but we rarely see more than one main breaker in a panel today. Go to our article Are split-bus electrical panels illegal? for more details.
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