Electrical Code Question

January 8, 2007 8:51 PM

One residential electrical junction box with wires coming into it from two different circuit breakers, is this to code or completely whack?

I just had the displeasure of shocking myself while trying to figure out why the furnace isn't turning on.

In my utility closet there is a junction box with two switches and two outlets. My furnace has not been running and I've tracked this down to the switch for the furnace that only seems to want to be on when I put pressure on it while in the on position. Assuming it was a loose wire or bum switch, I cut the breaker that shut off the light controlled by the other switch at this box (after some trial and error as everything is inconveniently unlabeled in the fuse box) and thought that I would be safe to open the box but then got zapped by live wires on the switch for the furnace. So one switch (for the gas furnace) is controlled by a separate circuit breaker than the other switch and the two outlets all in one junction box. I have since now found both circuit breakers in the electrical panel for this box now but stopped poking around at the problem.

While this setup is not intuitive, is it to code? Should I just replace the faulty switch or hire an electrician to look at the faulty wiring?

This is in Washington, DC if jurisdiction matters. It looks like DC bases its electrical codes from the National Electrical Code with some amendments, so general knowledge and experience is appreciated. It's a forced air gas furnace with an electric blower motor.

And I'm not an electrician, so forgive me if I have the terminology all wrong. Extra points for gentle corrections.

posted by peeedro to home & garden (8 comments total)

Gas + confusing electrical panel = Call a furnace repairman. They will have the proper tools to repair your furnace whether it is electrical or otherwise.

Always, always test the circuit with a voltage detector or multimeter even after flipping the breaker. You may have flipped the wrong one as you quickly (and luckily) discovered.
posted by Roger Dodger at 8:56 PM on January 8, 2007

This isn't code legal in Canada for exactly that reason. The simplest thing to do (if the wiring coming into the box allows) is to install a box divider.
posted by Mitheral at 9:48 PM on January 8, 2007

Alternatively you could gang the breakers together (so that if one is shut off the other is too) but this may require moving breakers around in the service panel and not all breakers are gangable.
posted by Mitheral at 9:51 PM on January 8, 2007

I live in Texas and that is certainly not to code. I doubt that would be expensive to correct though. It will probably involve moving breakers as stated earlier.
posted by jlstitt at 9:57 PM on January 8, 2007

...thought that I would be safe to open the box but then got zapped by live wires on the switch for the furnace

This is precisely why that sort of thing isn't allowed. You're lucky you didn't hurt yourself worse. In the future, get yourself a non-contact current tester before working on potentially shocking subjects. These little beauties are easy as hell to operate—just wave them around the lines that might be energized, and they'll give off a nice audible/visual warning so you don't accidentally electrocute yourself.
posted by Civil_Disobedient at 5:10 AM on January 9, 2007

I'm pretty sure having multiple branch circuits in a single box isn't explicitly forbidden by the NEC. A common thing to do in kitchens is to have two circuits coming into the same box each feeding one side of a duplex outlet (with the little ear broken off so the two sides are actually separated). It's also common for the box containing the switches for a large room to have two or more circuits inside.

Hot wiring looks just like dead wiring. Always use a tester before touching.
posted by oats at 9:00 PM on January 9, 2007

Kitchen outlets will be ganged together, either a single double pole breaker or two singles with a cross bar.
posted by Mitheral at 10:33 PM on January 9, 2007

Oops, you're right--technically they're a 120/240 circuit.

I still couldn't find anything in the American Electrician's Handbook that forbade multiple branches in a box.
posted by oats at 7:56 AM on January 10, 2007