500 mcm or 600 mcm

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Mike LE

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Why must a 600 MCM conductor be used for 3 or more sets of parallel conductors if the calculated load is less than the 3 500 MCM rated at 380 amperes each. I have never really been clear on this. Reference 240.4 Could you please clarify this?
 
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Welcome to the forum.:)

Basically because the next size up rule of 240.4(B) is limited to devices of 800 amperes or less.

As far as why the NEC choose 800 amperes for the limit I am not really sure.

Chris
 
I think one reason could be that the jump in standard size ocpd's starts to get larger.

800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, etc.
 
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