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The sizing of conduit systems that wire has to be pulled into is dependant on the physical size of the conductor being drawn into the conduit. The second governing factor is the conductor count of the specific conductor that is needed. A 500 MCM copper conductor with an insulation factor of 90 degrees C is rated at 430 amps.

This is where the conductor count is need by the service, as to whether the service is single or three phase. In this specific case, the electrical code will allow both single and three phase installations to use the same size conduit.

A maximum total of four 500 MCM conductors can be drawn into a 78 mm diameter conduit.

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Q: What size conduit for 400amps?
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