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split bus


Chad Fabry
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I don’t know the actual history behind them, but I’m sure it wasn’t the original intent of the 6-throw rule, which I believe was to ensure a reasonable number of disconnects grouped together in one place to allow quick service disconnect.

I suspect it went as follows…

Some bright spark at FPE or Zinsco, or whichever company did it first, read the rule and had an “Eurekaâ€

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The disadvantages are that the homeowner may not understand how to shut off power to the lighting (120V) circuits, and that even after doing so, the 240V circuits are still energized. Often in older homes the panels are poorly labeled, and sometimes additional single pole breakers have been added in the upper (240V) section, which should be reserved for double pole breakers (maximum of 6). The added circuit(s) in the upper section would still be energized after the homeowner thinks they have shut off power to the lighting circuits.

Having a single main disconnect is a big improvement.

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I agree; there is no advantage for consumers, only disadvantage. Truth be told, this is just one of those "because we can" things that never should have been allowed (like backwiring devices).

I'm of the opinion that a single main should be required for residential service equipment, period. That would be the simplest and safest situation for consumers.

Brian G.

Maybe Someday [:-indiffe

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Originally posted by Chad Fabry

Thanks guys.

The reason for their existence has always eluded my common sense radar and I've never bothered to find out why they were made.

That's one more thing checked off my list of "Things to do before I die."

The design precedes breaker panels. The fuse panels of the previous era were mostly a "split bus" design. The simplest of these had a "lighting main" and a "range" main. When breakers came along, the manufacturers just mimicked the fuse panels that already existed.

- Jim Katen, Oregon

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