We are installing a Cooktop that calls for a 40amp circuit. I was given 6AWG wire (instead of the 8AWG wire I asked for) by mistake. The electrician saw the 6AWG wire (that I had already run) and used a 50amp breaker. The Cooktop installer requires that the breaker be 40amp. My electrician was concerned that using the larger 6AWG wire would lower the resistance therefore affecting the amps; he cited Ohm's law. He has refused to change the breaker from 50amps to 40amps for fear of damaging something or affecting safety. I thought the amp requirement was dictated by the device (it asks for 40amps) and the 40amp breaker would ensure that 40amps is all that it would get. Does anyone know of any dangers/issues if using a smaller breaker with 6AWG wire?
Electrical – Can a 40amp breaker be used safely and without issue with a 40amp device on 6AWG wire
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Best Answer
Your "electrician" is not one of the brighter bulbs in the pack.
The 40A is to protect the wiring and the device.
If the wiring is AT LEAST 8Ga then it's adequate to protect the wiring. It also protects 6Ga, (or 500 MCM for that matter) just fine, and it properly protects the device at the end of the wire just fine.
"Ohms law" has squat to do with this. You could have a cooktop located 3 feet from the breaker panel and connected with 8 Ga or one located 100 feet from the panel and connected with 6 Ga - the 8 Ga would have (much, about 20 times) lower resistance, because of the wire length. Upsizing wire for longer runs on heavy circuits is actually quite normal. As stated, not a particularly knowledgeable electrician you have there.