40 amp breaker7/14/2023 ![]() ![]() #10Cu is good on a 30A circuit.Īs for the electrician's "mistake" I don't see the problem. So you use Al-rated Polaris connectors to pigtail to #10 Cu, which will fit without trouble. For instance if you wisely chose 4 AWG Aluminum for your 400' long-run 30A dryer circuit, neither the 30A breaker nor socket will accept #4 nor aluminum. In that case you need to simply pigtail to an intermediate size or metallurgy. The only speedbump with the "any size or larger" is a very much larger wire may not physically fit on the breaker or panel lugs. Good call, since some better stoves/ranges want 50A or even 60A, and #6 is good for all that. On a 40A circuit you are allowed to use any cable 8 AWG or larger.Ħ AWG is larger than 8 AWG, so you are ducky-doo with the #6. What you have there is a 40A circuit, because it is breakered 40A per instructions. 50A - and unless the cooktop instructions actually say it is OK to do so, you need to stick with 40A, even if the wire can handle 50A. But that is not necessarily the case for 40A vs. Any normal plug-in 15A device can use a 20A receptacle. For example, a circuit consisting of 12 AWG wire and 15A duplex receptacles can use a 15A breaker (perfect match for the individual receptacles) or 20A breaker - OK because of the wire size (15A would only need 14 AWG) and a special exception for 20A circuits that allows for multiple 15A receptacles instead of 1-or-more 20A receptacles, and the 15A receptacles are designed to allow 20A passing through. It is possible to have multiple valid breaker sizes. And you can't use a larger breaker because the device is not rated for that - i.e., it expects to have the protection provided by a 40A breaker in order to handle any faults in a safe manner. ![]() You can't use a smaller breaker (probably safe, but you would get frequent nuisance trips which are inconvenient at best and lead to unsafe operation at worst if you (or a future owner) ends up "fixing" it later in an unsafe manner). So if the cooktop calls for a 40A breaker then you must use a 40A breaker. The device needs to be protected by an appropriate size breaker which is determined by the design of the device and is part of the UL (or equivalent) listing for the device. ![]() You could even use a 15A breaker on 6 AWG wire - strange but nothing unsafe about it. For example, a 30A breaker on 8 AWG wire, a 15A breaker with 12 AWG wire (which can also use a 20A breaker), etc. But it can include lots of different things. That includes the very typical 50A (instead of 55A) for 6 AWG. But you can always use a smaller breaker - it will be 100% safe. 40A is the largest breaker you can normally use for 8 AWG copper. 55A is the largest breaker you can normally use for 6 AWG copper. Larger wire (which is a lower # due to the way wire sizes are named) can use a larger breaker. The breaker needs to be sized to protect the wire and the device. ![]()
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