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I have a 40 yr old home with circuit breakers. While looking for the breaker to turn off a circuit (I was replacing a light switch), I found that two breakers, on the same side of the bus, but separated by a few other breakers, both disconnect the circuit. To be clear, I am telling you that I can turn off either one of these to kill the hot wire in the switch box. The only thing I can think of here is that somehow one of the breakers is feeding the other. I've never seen a circuit behave like this.

This is similar to the other thread on this site about "Two breakers switches control the same thing" except in my case, I have the opposite result: either of the two breakers will kill the circuit.

Is there any reason this may have been done on purpose? Is this allowed by code?

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Close the breaker panel, put up a "Here Be Dragons" sign and call an electrician. You've left the realm of DIY. Seriously. When stuff like this happens, you just can't safely predict what's going on. –  Chris Cudmore Jun 26 '13 at 14:20
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For some older breakers, same side is the same bus but most modern ones have the feed crisscross so a 220v double breaker is side by side on the same mounting rail. Is it possible you have a 220v circuit you're lookin at. (Voltage remarked is based off of US voltages) –  Jason Jun 26 '13 at 15:43
    
The breakers control a simple 110v lighting circuit (US). There are some ganged 220v breakers that are on one side of the panel, but the two that I am speaking of are separated by several other breakers. Also, I just did some research and found out that the brand of circuits and panel that I have (Federal) is dangerous and needs to be replaced. –  Jerry Jun 26 '13 at 16:13
    
I would suspect that they needed replaced beside the assertion that you just made :) –  Some Free Mason Jun 27 '13 at 17:07
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2 Answers 2

That could be a split bus panel, meaning that there are two sets of power distribution buses. It used to be allowed by something called the "6 handle rule" (which allowed up to six of them in a service panel) back when circuit breakers cost a small fortune.

They were wired like this:enter image description here

And might look like this: enter image description here
Note the gap in the breaker buses at center where there are no breakers, but you can see heavy black wires connecting to the right end of the secondary buses.

The cables from the meter connect at right (which would conventionally be the top of the panel) and feeds the six double breakers. Five of them feed directly to heavy loads: range, water heater, dryer, baseboard heaters, etc. The top-left double ganged breaker feeds the second bus in the left half of the photo.

In this configuration, any circuit fed from the lower bus would be shut off if either its own breaker were switched off, or the feed breaker—which also shuts off almost everything in the building.

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If you can't figure it out from the picture, check to see if any OTHER circuits go off when you flip one of the two breakers in question, especially if one of them is larger than the other. This would prove that you've got a split bus configuration. –  Michael Kohne Aug 25 '13 at 3:00
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The break circuit must be using stair case schema to turn off the light. It works like a XOR gate in digital logic, the switches should be in opposite position to close the circuit.

You got to short circuit one switch to get rid of this configuration.

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No. The OP stated that both switches must be on for the circuit as a whole to be on. Could you add a diagram to explain what you mean? –  Niall C. Jul 29 '13 at 23:26
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