Voltage Drop

[tpcblack]

Pricing a project that specs the following:

- Supply a 2P/30A Breaker
- Run 1200' of 1" Sch40 PVC w/ 3 #10 & 1 #10 G
- Feed 100A Panelboard w/ 2P/30A Main, 2 1P/20A, 6 Spares.
- From this panel feed Irrigation control Module drawing 1A.

Since the panel will initially only draw 1A, VD will not be an issue but at 1200', #10's are not going to get you anywhere near 30A without significant VD.

Here's the question: Is it LEGAL to install this in this manner given that when installation is completed there will only be 1A load on the panel but knowing that it has a 30A potential that could damage a larger load due to VD?

Thanks.

 

[raider1]

There is no NEC requirement that we take into account voltage drop for a circuit.

What you are installing would be NEC compliant.

Chris

 

[winnie]

This looks like a job for "upsell man"!

They wouldn't want 30A breakers and a panel with extra spaces if they didn't want the flexibility to increase the load. However with the wire size specified they can only draw about 5A before they hit a 5% voltage drop.

I would quote as specified, and then offer 1.5" conduit, and larger conductors as an upsell.

-Jon

 

[Dennis Alwon]

I would let the clients know the situation and try to get an upgrade if possible. Unfortunately, even at 3 amps and that distance you would need a #8 to stay within the FPN of 3%.

 

[ceb58]

I would let the clients know the situation and try to get an upgrade if possible. Unfortunately, even at 3 amps and that distance you would need a #8 to stay within the FPN of 3%.

MH vd calculator has it a 3/0Cu for 30 amp. The other way would be to step it up and then step it back down with transformers.

 

[winnie]

Pure design issue, but given that this is a 120/240V feeder, I would calculate the voltage drop relative to a 240V load rather than a 120V load.

My reasoning is that if they actually need a full 3600VA, that would likely be balanced across the 2 legs.

-Jon

 

[Dennis Alwon]

MH vd calculator has it a 3/0Cu for 30 amp. The other way would be to step it up and then step it back down with transformers.

I didn't say for 30 amps. I said at 3 amps you would need a #8 and that is using 240V in the calculator.

The online calculator I used calls for 2/0 at 30 amps for sp 240 volts

 

[ron]

Who enforces the Energy Code in your jurisdiction?
Is it the International Energy Code or ASHREA 90.1 or both?
Look about 1/2 way down the link below
http://www.iaei.org/magazine/?p=211

 

[dbuckley]

If it does go ahead as specc'd, I'd be tempted to put a label on the panel to the effect that the feeder is rated for 5 amps maximum load before voltage drop becomes an issue.

 

[tpcblack]

Thanks everyone. I appreciate the help.

It sucks when you know how something should be done correctly but you also know that if you bid it that way you would never get the job.

 

[ceb58]

I didn't say for 30 amps. I said at 3 amps you would need a #8 and that is using 240V in the calculator.

The online calculator I used calls for 2/0 at 30 amps for sp 240 volts

Dennis, I didn't say you said 30 amps I was throwing in the 30 amp calculation by the OP's statement of 30amp not your 3 amp #8 calculation. Now get ready for the snow