500 mcm or 600 mcm

[Mike LE]

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?

 

[raider1]

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

 

[benaround]

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.