Sizing for Voltage Drop

[Little Bill]

I have a couple of requests/questions concerning voltage drop.
Would someone check me on this please?

Need to run a 208V, 70A single phase circuit 425'. The feed will come out of a 208/120V 3 Ø panel.
According to the calculator I used I would need to use 2/0 to keep voltage drop to 3% and be able to have 70A available.

Now since I increased the ungrounded conductors, I need to increase the EGC.
According to my calculations I will need a 2/0 EGC.:weeping: Does that sound right?

circ. mils of 2/0 is 133100
circ. mils of #4 is 41740

133100/41740=3.18
3.18 x 41740 =132733
2/0 would be closest to 132733 (133100)

What size grounded (neutral) conductor would be needed?

The loads are just one machine that pulls 35A @ 208V and doesn't need a neutral. The others are 120V for a couple of receptacles and maybe some lights. So any increase in neutral would just be max 40A load @ the 425' distance.

 

[augie47]

I show a 2/0 being required but only if you calculate it on a full 70 amp load. The 35 amp load would only require a #2 so choose your poison depending on the load you wish to use in your calculation.
Your 70 amp circuit would normally have a #10 equipment ground so your 3.18 multiplier
would be X 10380 (#10 cirmil) or 33008 or a #4
Since you have various loads I assume this is a feeder and 215.2 would required the neutral to be no smaller than the equipment ground

 

[Little Bill]

I show a 2/0 being required but only if you calculate it on a full 70 amp load. The 35 amp load would only require a #2 so choose your poison depending on the load you wish to use in your calculation.
Your 70 amp circuit would normally have a #10 equipment ground so your 3.18 multiplier
would be X 10380 (#10 cirmil) or 33008 or a #4
Since you have various loads I assume this is a feeder and 215.2 would required the neutral to be no smaller than the equipment ground

Thanks, that's what I get for trying to figure this late at night!
I was using #4 for the original EGC instead of #10!:slaphead:

 

[luckylerado]

I would need to use 2/0 to keep voltage drop to 3%....

Shouldn't you be looking for 2%?

 

[Little Bill]

Shouldn't you be looking for 2%?

I don't think so unless I know the branch circuit(s) is already 3%.

 

[luckylerado]

I don't think so unless I know the branch circuit(s) is already 3%.

so it is not a feeder?

 

[Little Bill]

so it is not a feeder?

It is a feeder.
Generally you look for 5% vd total between feeder & bc. I don't see a 3% drop in my bc so I'm just shooting for 3% for the feeder.

 

[iwire]

Shouldn't you be looking for 2%?

I would be willing to bet that there is no code requiring Bill to shoot for any target.

In many areas voltage drop is up to the installer.

 

[don_resqcapt19]

Shouldn't you be looking for 2%?

That is up to the designer....there are no NEC requirements for voltage drop for this application.

 

[Little Bill]

I would be willing to bet that there is no code requiring Bill to shoot for any target.

In many areas voltage drop is up to the installer.

That is up to the designer....there are no NEC requirements for voltage drop for this application.

No requirement, just the owners wanting their machine to have enough voltage.