40 Amp Circuit Wire Guage Question

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  #1  
Old 06-23-13, 08:13 AM
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40 Amp Circuit Wire Guage Question

I was just looking at an existing 40 amp circuit that goes to an outlet box. There is a 40 amp dual 240vac circuit breaker with a black and a red #8 AWG THHN connected to the circuit breaker that goes to the outlet box. There is a green #10 AWG THHN wire that goes along with the red and black # 8 s to the box. Should I change out the green wire for a #8 awg conductor? I do recall something about 240 circuits that allow a smaller ground conductor but cannot find the reference.
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Old 06-23-13, 08:19 AM
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Table 250.122 is the chart used for sizing grounding conductors. For up to a 60 amp circuit size a #10 copper will work. There is no need to change what you have.

It is not based on the voltage.
 
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Old 06-23-13, 09:22 AM
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Thanks for looking it up and the quick response. I guess I will need to find some other excuse for a trip to the big box store.
 
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Old 06-23-13, 10:45 AM
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Are you sure that wiring is 240 volts in that box. 240 volts can be very dangerous to work with. I highly recommend a meter purchasing trip to the big box store.

Already have a meter ? ..... you're stuck home


But you know......we are men and we don't require a reason to buy tools and the like.
 
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Old 06-23-13, 10:48 AM
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Got several meters. On my way to pick up some PVC pipe for a drainage project. Yes, one can always invent a task that requires a trip to the big box stores. We even have two directly accross the street from each other.
 
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