Breaker Breaker

EAM44June 10, 2013

Hi All - I am in need of you expertise. Any feedback would be welcomed.

I hired an electrician to move two outlets in the kitchen, the 240 for the oven, and the 120 for the fridge. In the process he noticed that the wiring for the oven are (forgive me) 30A wires, and the breaker they're connected to is a 50A breaker. That breaker also services my electric cooktop. He recommended I change the breaker to a 30A breaker, although he said that if the cooktop and ovens were on at the same time it could trip the breaker. Why would I want to do this?

He did note that the oven wires, in place for over 40 years, were flexible and in good shape and that nothing seemed wrong but the mismatch. If I understood him correctly, he said that the oven would burst into flames before the breaker would trip (I get that part, 50>30) but why would the oven "pull" more than 30A through those wires?

He's coming back tomorrow to finish the job. Should I leave things as they are, or should I change the breaker? Thanks for the input.

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If the wires are rated for 30 amps, the breaker may be no larger.
Drawing excessive current through the wires causes the wires to overheat. This could result in the wire's insullation melting which in turn could create an electrical arcing and sparking situation and a fire inside the walls.
I'd reverify with him, and maybe someone else, too, that these are indeed #10 wires (the size for a 30 amp circuit for an electric clothes dryer) as that is unusually small to be found for this application. Has he given you a price for a new circuit with a #6 wire cable?

    Bookmark   June 10, 2013 at 5:30PM
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Breakers are for emergencies. The problem is not about routine usage of the appliance, but what happens in case of a short, either in the wiring or inside the appliance. If something shorts out and draws more than 30A, the wires overheat inside the wall and cause a fire before the breaker trips. That's where your problem lies.

    Bookmark   June 10, 2013 at 5:34PM
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If the oven and the range share the same breaker, is it possible that the breaker has #6 (50 amp) wire and somewhere else the #10 (30 amp) wire is split off?

    Bookmark   June 10, 2013 at 8:56PM
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Thank you all. tox, great explanation.

randy - I was hoping you were right about this. Alas, the wire coming out of the relocated box (breaker is off, of course) is labeled

"Hafield Hatvinol 10 type TW 600V"

I found the Nehring electrical wire specs for type TW 600V and their stranded 10 wire is rated for 30A in a conduit. CRUMBS.

I took a moment to look up my dream ovens, and the single oven would be fine with 30A service. The double ovens would need 50A. Maybe I should get a quote for re-wiring.

weed - interesting, and possible. I know the electric cooktop is on the same circuit. Would this make things
1.) less of a problem?
2.) more difficult to fix?

Thanks again for trying to help!

    Bookmark   June 10, 2013 at 9:02PM
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"Breakers are for emergencies. The problem is not about routine usage of the appliance, but what happens in case of a short, either in the wiring or inside the appliance. "

Umm, not exactly.

Breakers prevent overloading of wires, either short term or under a fault condition.

There ARE applications that breakers provide ONLY short circuit protection (like motor only circuits, welder circuits, and other equipment that has built in protection that prevents it from overloading the conductors in normal use).
The common household breaker is a thermal-magnetic breaker.

It allows overloads for seconds to minutes (the thermal trip portion) often up to a few hundred percent of the rating while providing a very fast turn off (the magnetic trip portion) for faults (short circuits).

The magnetic portion may not come into play until 500% to 1000% of the breakers rating.

This post was edited by brickeyee on Wed, Jun 12, 13 at 10:03

    Bookmark   June 12, 2013 at 10:02AM
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