100 Amp Sub-Panel Question on Wire Guage

[harborremodel]

I've been working on adding a sub panel to my shop. I have a two pole 100amp sub panel. I'm looking for someone to explain a bit of how load is distributed in the sub panel the two poles.

I know that for 100 amps i need at least #3 awg THHN copper to handle the load but my question is about how that load is distributed. If i have a two pole 100amp breaker in the main panel feeding my two pole 100amp sub panel isn't the potential amp load distributed evenly between the poles? If i'm drawing 30 amps on a two pole breaker in the sub-panel is that 30 amps of draw being evenly distributed into two 15amp loads on each pole?

I'm already going to run 3awg copper for both hots and the neutral but i want to understand the theory behind how this works. Anyone who feels like putting on their professor hat would be greatly appreciated.

 

[Snoonyb]

When you remove the dead front panel, from the subpanel you'll see the primary bussbars alternate side to side, sometimes in a graduated, opposing "S's", or opposing single strand ladders.

However balancing the loads is a function of you determining what is fed from where.

Don't forget your ground.

 

[bud16415]

I’ll take a stab at it and the above information is correct. The voltage potential is between the two hot legs when you put a meter on the two hots you read 240v and between ether hot and neutral you will only see 120v.

When you attach a 120v breaker it takes one spot and is between one of the hots and neutral. A 240v breaker takes two adjacent spots and because the power zig zags from side to side as mentioned above the breaker connects to both phases and neutral.

I’m not an electrician and I hope the information is correct. Others in the trade will be along with more info.

 

[JoeD]

With a 30amp 240v load each of the 120v hot legs carry half the current

Incorrect. Each of the hot wires carries the full current

 

[bud16415]

Joe is correct in a 2 wire 240v circuit placing an amp meter over one of the wires will show the full amps. Placing it over both wires will show zero amps as they will be canceling, As there is no neutral. In a 3 wire 240v the only amps that will me measured on the neutral is the unbalanced load of some 120v draw from one leg or the other. In that case you will measure two different amounts on each leg.

Sorry for the confusion and I will correct my post.

 

[JoeD]

Hot wires always carry the full load amps of whatever device is operating on the circuit.
If there is a shared neutral involved with two hots then the neutral only carries the difference in current between the two circuit loads.