Lone Crapshooter

I am working on 4 480 volt heaters origionaly installed in 1948 and they seemed to work fine until we installed the correct fuses.
They are single phase connected line to line on a 3 phase 30 amp disconnect. The heaters are 4500 watt @ 480 volt each so the way I figure they would pull about 9.5 amps each.
What I wanted to do is is repull the circuit with #8 THHN take all 3 phases down to each group and have BROWN and YELLOW feed the heaters and ORANGE be common to both heaters.
This arrangement would be the same for both groups of heaters.
Then I got to thinking why not pull 6#10 three for each group and hook them up in the same fashon.
My question is if each heater pulls 9.5 amp how much current would be on the ORANGE or common wire. With the first setup would it be 0 amps 18 amps or around 30 amps at the disconnect.
Also I would like to know how you figure this problem.
THANKS

BryanMD

To make the example simpler lets pretend there are only 3 heaters... being fed evenly and equally: A&B to #1; B&C to #2; C&A to #3... OK?
Now what do you have?

And why is the orange common?

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March 2010: On the road with my RV. California is first primary destination then it is off to Eastern OR, Northern ID and Western MT for drycamping and fly fishing until Labor Day.