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I live in a high rise apartment built in the '70s (USA), and this afternoon we suddenly lost all power to just our unit. After some investigation we found that the main disconnect (70A) powering our unit had tripped. When I looked into our own load center, the oven/range breaker (50A) was also tripped.

We weren't doing anything unusual - the oven was on and some lights, but we've often had the dishwasher/lights/hair dryers/etc. running simultaneously. I find it strange that both the 50A and the 70A tripped simultaneously. Does anyone know why this can happen?

If it's relevant, I have installed some LED light bulbs into dimmers that are not for LEDs (on different circuits from the oven/range circuit) and some of them were on at the time. Doesn't seem like that should be relevant but it's the only thing I can think of.

UPDATE - found the root cause! It turns out the range and the cooktop were combined together in a box in the cupboard with wire nuts and then a single line was run to the 50A breaker. Wires in one of the connections melted the plastic and shorted, tripping the breaker.

Currently we have only the cooktop connected, as there's significant work required to bring the unit up to the current code (last remodel was 10 years ago). They'll have to move the panel outside of the closet and increase the size as all the current spaces are doubled up.

Photo of the carnage - thank you to the poster who told me to keep the breaker shut off! enter image description here

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  • 50A and 70A are amperage rating? It's seems kinda insane to have such a high amperage at a flat. In Czech Republic we have usually 16-25A depeding if you have electric water heater or not... – jnovacho Jul 13 '20 at 11:15
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    @jnovacho Those numbers are perfectly normal for the US, where everything is on half the voltage (120V, thus twice as much current for the same power) and only split-phase system (thus just two legs 240V apart, not three phases with 400V between them). A 3x16 A feed for an electric range would be standard in Europe, and that's basically the equivalent of a 50A 240V breaker in the US. So, nothing insane here. – TooTea Jul 13 '20 at 13:11
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    @jnovacho wait until you see a 200A disconnect. – Eric Hauenstein Jul 13 '20 at 13:17
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Very simple: Massive power overload from the oven.

The 70A and 50A tripping at the same time means:

  • Problem is past the 50A. Since that has just one appliance, we know the source of the overload.
  • Since 70A tripped, must be greater than 70A, which of course is also greater than 50A.
  • Since breakers are generally designed with a thermal trip curve to avoid trips from motor startup and similar short surges, this was likely far more than 70A, because if it was 71A it would trip the 50A quickly but not the 70A.

My guess is an element (oven or cooktop) failed but short circuited along the way, tripping the breakers.

I'd be extremely wary of turning on the 50A (the 70A is fine) without getting the oven checked by a professional first. If you're in a rental, call the landlord.

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    Yup. When a calrod element fails, consider yourself lucky that it failed hard enough to trip the breaker. I've had an oven element make a loud pop and proceed to arc in a messy and dramatic way without tripping the breaker. I was really happy that I was there in the kitchen to hear the funny noise and look though the oven window at a molten mess in progress so I could shut the oven off. 50A will support quite a bit of pyrotechnics before it trips. – Ecnerwal Jul 12 '20 at 10:41
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    @Ecnerwal And it can really screw up the oven shell. – JACK Jul 12 '20 at 12:06
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    @GeorgeAnderson I don't think this makes electric more dangerous than gas. I'd much rather have my range catch fire than my whole house explode. – Joseph Sible-Reinstate Monica Jul 12 '20 at 17:42
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    @JosephSible-ReinstateMonica Electric and gas each have their own rare but serious problems. For electric, it is an element or other failure causing arcing/melting/fire. For gas, there are two very different problems: fire and explosion. Fire if something spills or otherwise gets into the flame that shouldn't - this can happen with electric too, but I'd argue much easier with gas. Explosion is an entirely different problem - that happens if you have an actual pipe leaking gas (very rare) or a burner "on" but not ignited and gas leaks for a relatively long time and then... – manassehkatz-Moving 2 Codidact Jul 12 '20 at 17:57
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    @manassehkatz-Moving2Codidact Agreed. My comment was a bit tongue in cheek, but I didn't know electrical elements could short out like that. And yes, it's easier to catch something on fire with gas range top than electric by far (I've had to throw away a couple of pot holders and towels due to that!). – George Anderson Jul 12 '20 at 18:02

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