My new 30 amp (240v) oven tripped a 50 amp breaker, and now will not heat. The warranty repair is happening, but here's my question: should I just put in a 30 amp breaker to protect the oven from breaking? (Note, I'm not worried about the wiring -- everything is rated for 50 amps)
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4I don't know the law, but I'll point out that the oven wouldn't trip the breaker if the oven wasn't already broken. The breaker doesn't cause the oven to break.– Stack Exchange Supports IsraelCommented Nov 3, 2020 at 12:35
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Is this oven the only appliance on the circuit?– ThreePhaseEelCommented Nov 4, 2020 at 3:23
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yes it's dedicated– curiousCommented Nov 4, 2020 at 15:33
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What does the appliance labeling and instructions tell you about correct wire and breaker size? Reason I ask is NEC 110.3(B) absolutely requires you to obey labeling and instructions, because those are the conditions under which the appliance was UL-certified. Note that you're always allowed to use larger wire, so #8 or #6 or even #00 on a 30A breaker is fine.– Harper - Reinstate MonicaCommented Nov 4, 2020 at 22:27
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1 Answer
Actually there is a code reference for breaker sizes in this case.
The reference table is on NEC 210.24 ,, 210.21.B.2 & B.3 show the tables.
A 30 amp device is a bit vague if the device draws 30 amp it could be on a 40 amp protected circuit, but not normally a 50.
In this case we would check the mfg instructions. I have found a few cases where the mfg designed the oven for use on a 50 amp circuit.
The circuit breaker is to protect the wiring but the code also limits the maximum size breaker in article 422.11.E.3 to 150% of the devices rated current. if the oven had a true draw of 30 amps a 45 amp breaker would be the maximum size. If the device only draws 24 amps and is rated for a 30 amp circuit a 40 amp breaker would be allowed if the device has no maximum stated.
If the device states 30 amp max OCPD that value can not be exceeded no mater how large the wire is.
So depending on the mfg requirements I would change the breaker to the recommended size because some mfg’s will do anything to get out of a warranty repair. Two large of a breaker would not cause a fault but could allow much more damage to happen and some use any reason to deny a repair.
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Thank you Ed. The installation specifically says: Electrical Supply grounded, 240/208 VAC, 60 Hz Service 30 amp dedicated circuit and I take it that this is not a proper install under massachusetts 2020 codes: which is based on NFPA 70, 2020 edition?– curiousCommented Nov 4, 2020 at 15:35
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I would change the breaker size. With a new device (stove) code doesn't require updating to 4 wire if you have 3 but the breaker itself is not the correct size for the mfg instructions. I have seen a warranty claim denial because the instructions were not followed , wow your state is 1 of 4 to have adopted the 2020 code.– Ed BealCommented Nov 4, 2020 at 15:52
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do you know the article reference in the 2020 code? is it exactly the same (150%)?– curiousCommented Nov 5, 2020 at 15:03
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The 2020 reference is 422.11.E.3 , it is rare for them to change code references although it happens. I did look it up just to make sure on page 464 of the handbook. It’s the same page in the 2017 book also.– Ed BealCommented Nov 5, 2020 at 16:05