Wiring over long distances Voltage Drop

[600SL]

My current situation for wiring my garage requires feeds up to 145'. for my 240V lines that does not appear to be an issue since my 6 conductor #10 ga per conduit run will be capable of delivering it's derated max current of 24 amps with under 3% voltage drop.

However my 4 conductor #10 per conduit run will not be capable of delivering it's derated max current of 24 amps. The best it can do is 11 amps with under 3% voltage drop and 19 amps with 5 % VD.

Shortening the 120V line to 2 75' runs, which is very difficult will increase its capability to a more acceptable 22 amps with 3% VD.

The question is how acceptable are these numbers. Since I have seen people with twice the size garages as mine I would like to know how this situation is dealt with. Do I need to increase my wire size to #8ga for the 120V circuits.

Is 5% too much VD?

This data was calculated here.
http://www.paigewire.com/pumpWireCalc.aspx

 

[sberry]

Mine is big and has 5 sub panels fed with number 2 alum. Very short secondary circuits.

 

[theoldwizard1]

Is 5% too much VD?

IMHO, no.

Remember that 5% drop is at max current. How likely are you to be operating at the max current ?

What is the VD at about 75% of max current ?

 

[600SL]

IMHO, no.

Remember that 5% drop is at max current. How likely are you to be operating at the max current ?

What is the VD at about 75% of max current ?

75% of max current 15 amps will be ~ 4%, 55% 11 amps is ~ 3%. Plus for this run there will be ~ 9 wire nut splices along the way.

 

[ForceFed70]

Also - measure you line voltage. While this may change, it'll help you decide. Most equipment is designed for 115 volts, if you've got the full 120V (my place often measures 123V per leg) then you've got an extra 4% to work with.

 

[nehog]

My current situation for wiring my garage requires feeds up to 145'. for my 240V lines that does not appear to be an issue since my 6 conductor #10 ga per conduit run will be capable of delivering it's derated max current of 24 amps with under 3% voltage drop.

However my 4 conductor #10 per conduit run will not be capable of delivering it's derated max current of 24 amps. The best it can do is 11 amps with under 3% voltage drop and 19 amps with 5 % VD.
...

Are you saying you are running multiple circuits to a detached building?

 

[theoldwizard1]

Also - measure you line voltage. While this may change, it'll help you decide. Most equipment is designed for 115 volts, if you've got the full 120V (my place often measures 123V per leg) then you've got an extra 4% to work with.

Don't count on the power company to provide that 123V continuously !

 

[theoldwizard1]

Are you saying you are running multiple circuits to a detached building?

Yeah, I ust re-read that !

6 conductor #10 ?

4 conductor #10 ?

 

[justsam]

Having read the OP's build thread I know this building, 30x48, has a main panel, and separate meter feed.
http://www.garagejournal.com/forum/showthread.php?t=230835

His reference to 4 conductors or 6 conductors has to do with the number of current carrying conductors in the conduit, and any associated de-rating required.

I am not understanding the distances involved unless there is some reason that outlets must be fed from only one direction away from the main panel location. If that is the case it may easier or cheaper to establish a subpanel at the other end of the building.

As has been mentioned by others, I would not be too concerned about a 5% voltage drop because of how infrequently the circuit would be loaded to maximum. If you do know of one location where this might occur, such as a table saw with high starting current, then wire it accordingly.

 

[GarageWarrior]

BTW, in a pinch you can get a 10% buck/boost transformer to make-up for voltage drop on long runs.

10% buck/boosters are commonly used in commercial tanning booths to go from 208 to 230 volt and will also work fine with 120 power (so you get 132V before the drop) . Used ones can be had really cheap at auctions, as most guys don't know what to do with them.

A little while ago I needed to do power-washing about 200' away from the outlet and couldn't get the pump running due to too much voltage drop - added buck/booster and was back in business

 

[600SL]

Having read the OP's build thread I know this building, 30x48, has a main panel, and separate meter feed.
http://www.garagejournal.com/forum/showthread.php?t=230835

His reference to 4 conductors or 6 conductors has to do with the number of current carrying conductors in the conduit, and any associated de-rating required.

I am not understanding the distances involved unless there is some reason that outlets must be fed from only one direction away from the subpanel location. If that is the case it may easier or cheaper to establish a subpanel at the other end of the building.

As has been mentioned by others, I would not be too concerned about a 5% voltage drop because of how infrequently the circuit would be loaded to maximum. If you do know of one location where this might occur, such as a table saw with high starting current, then wire it accordingly.

Yes there are 120V 4 conductors in one conduit and 6 240V conductors in a separate conduit running thee perimeter of the building from one direction only. With the current limited space above the garage doors already claimed by three conduits for welder compressor and exterior lighting going around that direction if challenging but certainly not impossible and it would bring the maximum length down to about 80'. So if its not going to cause problems going one direction is preferred.

Then of course if I do find I have to bite the bullet and go over the garage doors there really is no work wasted since that conduit would end up picking up the same conduit on the other side of the garage. Its just a matter of getting through the gauntlet.

 

[wyliesdiesels]

Why not just put a subpanel in on the opposite end of the garage and shorten your branch circuits. It will be cheaper than running all that copper around!

 

[600SL]

Why not just put a subpanel in on the opposite end of the garage and shorten your branch circuits. It will be cheaper than running all that copper around!

How so. All that copper will still need to run the perimeter of the building. Same number of feed to stager the receptacles. Plus I will also need some heavy copper to get to the sub panel. It would reduce the gage requirements but would that pay for a sub panel and the wiring to it.

 

[wyliesdiesels]

How so. All that copper will still need to run the perimeter of the building. Same number of feed to stager the receptacles. Plus I will also need some heavy copper to get to the sub panel. It would reduce the gage requirements but would that pay for a sub panel and the wiring to it.

Al wire for the feeder to the subpanel is a lot cheaper! If youre handy with excel u could figure out if its cheaper. THHN wire adds up quick!

 

[600SL]

Al wire for the feeder to the subpanel is a lot cheaper! If youre handy with excel u could figure out if its cheaper. THHN wire adds up quick!

I can do this in my head. 2000 ft of 10 ga $400. 2000 ft of 12 ga $260 + 240 ft of 1 AGW AL $102 = $362. + subpanel, breakers, and 80 ft of 1.5" EMT > $400