When applying the derate to conductors based on the number of current carrying conductors in a raceway I know you can use the 90 degree column if using THHN. I understand all of that. This does not effect the sizing of the overcurrent device correct? If your load requires a 20 amp circuit then a 20amp circuit it is, but after derating you might have to use a #10 thhn conductor. Am I understanding this correctly?
Derate conductors
- Thread starter JdoubleU
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- Occupation
- Licensed Electrician
You are on the right track. The breaker, not the size of the wire determines the circuit.
In many cases, the load determines the required minimum circuit ampacity... breaker rating can't be less than noncontinuous plus 125% continuous load. That said, the breaker rating determines the circuit rating... but be cautious when adding load to any circuit rated 800A or less. The conductor ampacity can be as low as the next lower standard breaker rating +1 and the load cannot be any greater than that value, regardless of the circuit rating.
kwired
Electron manager
- Location
- NE Nebraska
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- EC
I agree with Smart$, the load determines what is needed for both the conductor size as well as minimum overcurrent protection level.
About the only time we figure it on the overcurrent device is for general purpose lighting and receptacle circuits where there is no fixed load(s). Then we typically do figure the circuit can be loaded to either 15 or 20 amps depending on what breaker is supplying the circuit.
About the only time we figure it on the overcurrent device is for general purpose lighting and receptacle circuits where there is no fixed load(s). Then we typically do figure the circuit can be loaded to either 15 or 20 amps depending on what breaker is supplying the circuit.
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