Grounding wire

Hey we just got a cnc machine to play with it needs a 50amp 480 vac service.

I know it needs 6awg wire, I know where to find this in the code book.

I think it needs 10awg ground wire but I don't remember can someone point me in the right direction of where to look in the NEC code book.

I don't have my NEC handy to give you the exact section and subsection and paragraph but section 250 covers grounding.

Table 250.122 for grounding of raceway and equipment. For your 50A breaker, that puts you at a 10 AWG as you thought.

Remember that if your ungrounded conductors are increased in size (for example, for voltage drop), then your ground needs to be increased proportionately also. (250.122(B))

joeparrish said:

Hey we just got a cnc machine to play with it needs a 50amp 480 vac service.

I know it needs 6awg wire, I know where to find this in the code book.

I think it needs 10awg ground wire but I don't remember can someone point me in the right direction of where to look in the NEC code book.

Click to expand...

Your 6AWG statement appears to coorespond to the main feed.
And that would be correct, but only if the ambient temp was always below 96 degrees. For 96 and above, you'd need 4AWG. This is if you use the 60 degree column of 310-16, which you are supposed to use if the current is less than 100 amps (UL rule, USA).

Dont forget to run a calc for voltage drop vs wire length.

Dan Bentler