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I was trying to locate the circuit breaker for an outlet in my garage and found a truly baffling setup. Two breakers control the same outlet (both plugs). After some head scratching, I opened the breaker box and found (see pic) breaker 4 (20 amp) wired to the outlet as expected but breaker 34 (30 amp) wired to breaker 4. Why would this be done? It was obviously intentional and possibly setup for a freezer. Is this safe and in anyway an accepted practice?

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Thanks everyone for the help! I know enough to keep from getting electrocuted and this just didn't meet the logic test. I'll be checking the wiring and hopefully this is the only work they attempted.

Niall C.
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John Miele
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    Do both the breakers stay set? By my math those breakers should be on opposite legs, which should create a 240V wire warmer. – Tester101 Apr 03 '15 at 01:47
  • @Tester101 If that were the case, there'd be an open circuit between the two legs and both breakers would pop. I think his numbers must be wrong. – BlueRaja - Danny Pflughoeft Apr 03 '15 at 05:37
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    @BlueRaja-DannyPflughoeft That's what I said. But it would be a *closed* circuit (or short). Well... At least it would be closed for a millisecond, until one of the breakers tripped or the wire burnt up. – Tester101 Apr 03 '15 at 10:00
  • Are they in parallel, or are they in sequence? Because that makes a difference, no? So `Main -> B4 -> [Outlet, B34]` or `Main -> [B4, B34] -> Outlet`? – Jan Fabry Apr 03 '15 at 14:02
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    If it is a 3 phase panel (and with at least 17 rows, it might be - it's a big panel either way) then it's on the same phase. Personally I'd like it if my garage had a 3 phase panel, wouldn't you? – Adam Davis Apr 03 '15 at 19:14
  • @AdamDavis: I don't have any 3 phase motors, so I'd rather have 240 volts in 2 phase vs. 208 volts at 3 phase. – wallyk Apr 07 '15 at 03:51

4 Answers4

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As @Ecnerwall says, definitely not safe / legal / advisable.

My guess is that the guy kept tripping breaker #4 (maybe too many power tools in the garage?) and decided to share the load with another breaker by adding the extra wire. Approximately half of the current will flow through each breaker, effectively creating a 40 amp breaker.

EDIT: in fact it's possible / likely that the wires on that circuit were regularly carrying more than 20 amps. Wherever possible you should inspect the wiring, including all outlets on that circuit, to see if there are any signs of melted insulation or other damage. If you find any indication of heat damage I think it would be prudent to rip out the entire circuit and rewire it, since there may be damaged insulation in the walls just waiting to catch fire.

Hank
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  • It's possible that they guy did not want a 40 Amp breaker, but a 30 Amp breaker, i.e. intended the 20 Amp breaker to be left switched off. Perhaps the 20 Amp breakers was used originally, and the wire was too short to reach the bottom breaker, so he 'extended' it, intending breaker 4 never to be switched on. Obviously still not safe / legal / advisable, but *very slightly* less silly than breakers in parallel. – abligh Apr 04 '15 at 09:27
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    @abligh -- you can wirenut in most panels these days, so there's no reason at all for such ugly hackery. – ThreePhaseEel Apr 06 '15 at 03:28
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Alright, now that you found the blatant 240.8 violation:

240.8 Fuses or Circuit Breakers in Parallel. Fuses and circuit breakers shall be permitted to be connected in parallel where they are factory assembled in parallel and listed as a unit. Individual fuses, circuit breakers, or combinations thereof shall not otherwise be connected in parallel.

I'd grab a copy of the 2014 NEC, call up any electrician friends you have, and invite them over for a Code-violation Easter-egg hunt. I think it'll be a blast :D

ThreePhaseEel
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    I can hardly imagine situations where even a factory should be allowed to do that. – Russell McMahon Apr 03 '15 at 18:46
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    @RussellMcMahon, I don't know what the use-case would be, but if there is one, you can bet that the factory-assembled unit would be _labelled_ for that use-case. Labelling means a lot to regulators. – Solomon Slow Apr 03 '15 at 21:37
  • @jameslarge I agree. I'm not questioning the power of regulatory approval :-). Just, as an EE, the idea of cascading cutouts is "interesting". Say breaker1 is the most weak-kneed and trips at say 2 x I_rated. If both are equally sharing the load then breaker2 is seeing 2 x Irated and wondering whether to trip when current jumps to 4 x Irated and its mind is made up. Operation would be very much faster than the time for the 1st trip. In many cases 4 x rated current is no great problem - which is where the designers benison is a very good idea. – Russell McMahon Apr 03 '15 at 23:47
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    If only I had an electrician friend... Where would you find one of these that accepts payment in beer? – John Miele Apr 04 '15 at 00:36
  • @RussellMcMahon You can't readily buy (much less bend) wire listed for much over 450A, so you are forced into using multiple wires and fusing each individually. Our panel is built to do this with 2 fuse sites per leg. "Never happen in residential" you might say, but a friend already has two 200A main panels (one for his heat pump) and wants to add two 180A on-demand water heaters. – Harper - Reinstate Monica Aug 04 '16 at 18:37
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Uh, NO!!! That was a hamfisted moronic code violating idiot wiring job done by a guy who said "hold my beer and watch this!"

Rip it out and look around for other work this guy may have done while three sheets to the wind.

Ecnerwal
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4

Two breakers on the same circuit that are not clipped or otherwise mechanically forced to trip at the same time... doesn't seem like a good idea.

Best case: Someone upgraded the wires/fixtures on the circuit to handle the extra load but didn't want to reconfigure the panel.

Worse case: Someone got tired of resetting the breaker and/or unplugging his garage grow op or garage full of beer fridges and decided to burn his house down instead.

Good catch on you. Make some smores before you fix it. Mmm, basement panel smores.

John
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