Parallel Conductor Sizing

[Chad Evans]

Can someone help me out with this… Apparently sizing of parallel conductors has slipped my mind. Is there a general rule of thumb or formula? Thanks for any assistance in advance!

 

[infinity]

#1/0 is the minimum size you can run in parallel. EGC in each raceway just be full sized.
Someone will follow up with the rest of the rules.
Welcome to the Forum.

 

[Chad Evans]

I should probably word my post better. How do you determine the ampacity of say 2 500 kcmil in parallel versus a single 500 kcmil?

 

[don_resqcapt19]

I should probably word my post better. How do you determine the ampacity of say 2 500 kcmil in parallel versus a single 500 kcmil?

Assuming the sets of 500 kcmil are in separate raceways simply add the ampacities. If they are in a single raceway, you will have to apply ampacity adjustment based on the number of current carrying conductors in the raceway.
For your application of two sets of 500 kcmil, the code ampacity would be 760 amps. The rule in 240.4 would permit the parallel run to be protected at 800 amps.

 

[Chad Evans]

Thanks! As usual I’m trying to make things complicated. I appreciate the help.

 

[winnie]

In this case you are not crazy to wonder if things are more complicated than you remember.

Under the NEC, for parallel installation of building wiring, we simply add ampacities, as @don_resqcapt19 notes.

But this simple addition is not always the case. Two examples I can think of where there are specific formulas involved are bus bars in large panels and underground duct banks where heat from one raceway affects other raceways.

Jon

 

[masterinbama]

#1/0 is the minimum size you can run in parallel. EGC in each raceway just be full sized.
Someone will follow up with the rest of the rules.
Welcome to the Forum.

The EGC rule is probably the one that's missed the most.

 

[ggunn]

Assuming the sets of 500 kcmil are in separate raceways simply add the ampacities. If they are in a single raceway, you will have to apply ampacity adjustment based on the number of current carrying conductors in the raceway.
For your application of two sets of 500 kcmil, the code ampacity would be 760 amps. The rule in 240.4 would permit the parallel run to be protected at 800 amps.

Once the required OCPD gets to be greater than 800A you can't use 240.4 any more.