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Older, split bus type panel.The left side 2 pole 50 amp breaker is a main, for lighting. The breakers above the split are usually for 2 pole breakers; refer to the "six breaker" rule.

Next time take a few minutes to study the panel diagram of the split bus panel, which will show exactly how the busbar is configured.

BTW, does anyone have a guess as to when manufacturers stopped making this type of panel?

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As Neal & Mike explained, it's a split bus panel. No breakers were removed, the panel came from the manufacturer like that with the two copper wires leading from the lighting main to the lower set of bus bars.

Like Mike said, they're very common. I suspect he's right about 1984 being the cutoff point, though I don't happen to own the '84 edition. (The '81 edition allowed them, the '90 edition didn't.)

In your picture, the two single-pole breakers above and to the right of the split don't belong there. For one thing, they bring the number of disconnects up to 7 while the maximum is supposed to be 6. For another, they change the nature of the upper section from a "power panelboard" to a "lighting and appliance branch-circuit panelboard". The former can have 6 disconnects, but not the latter. So those two circuits really need to be moved to the lower section.

For more on this topic, you can check out sections 408.30 - 408.41 in the 2005 NEC.

- Jim Katen, Oregon

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Originally posted by Les

I thought it was "six hand movements"?

Sort of. The requirement is talking about six "disconnects". It then goes on to specify that these disconnects can be either "switches or circuit breakers". Then, later, it specifies that the the switches or circuit breakers must be activated by not more than six "operations of the hand" in the particular case of multi-wire circuits.

Here's the relevant portion of 230.71.

230.71 Maximum Number of Disconnects.

(A) General.the service disconnecting means for each service permitted by 230.2 or for each set of service-entrance conductors permitted by 230.40, Exception Nos. 1,3,4, or 5, shall consist of not more than six switches or sets of circuit breakers, or a combination of not more than six switches and sets of circuit breakers, mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. There shall be not more than six sets of disconnects per service grouped in any one location.

Now, the section that references "operations of the hand" (in my opinion, a truly bizarre phrase) immediately follows the section I quoted above. It's a strange one.

230.71 (B)Single-Pole Units. Two or three single-pole switches or breakers, capable of individual operation, shall be permitted on multiwire circuits, one pole for each ungrounded conductor, as one multipole disconnect, provided they are equipped with handle ties or a master handle to disconnect all conductors or the service with no more than six operations of the hand.

Can these people use an editor or what?

- Jim Katen, Oregon

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