Voltage Drop to Barn

[jelmlinger]

Hi Gentlemen,

Here's the scenario: Barn is 350' from house... Customer said they just needed lights and plugs so I buried #2 URD between them. Now they are talking making an apartment in the barn, i.e. more load!

Am I wrong in thinking that I'm only gonna get 20 amps out there at best?

And just for fun, what are the risks of feeding this wire from a 100A breaker? My thought is that if they have a load that with voltage drop pulls 90 some amps but less than 100 amps, just for arguments sake, isn't there a fire hazard risk of burning up the wire before the breaker trips?

One last question since it's been a few years since I've had this class... when calculating this, I would use 120v because that's what I have per leg, correct? Yes, it's ultimately a 2P 240v circuit, but 120v per leg, so vd calc should use 120 here I believe??

Thank you guys. Stay safe.

 

[electrofelon]

Hi Gentlemen,

Here's the scenario: Barn is 350' from house... Customer said they just needed lights and plugs so I buried #2 URD between them. Now they are talking making an apartment in the barn, i.e. more load!

Am I wrong in thinking that I'm only gonna get 20 amps out there at best?

And just for fun, what are the risks of feeding this wire from a 100A breaker? My thought is that if they have a load that with voltage drop pulls 90 some amps but less than 100 amps, just for arguments sake, isn't there a fire hazard risk of burning up the wire before the breaker trips?

One last question since it's been a few years since I've had this class... when calculating this, I would use 120v because that's what I have per leg, correct? Yes, it's ultimately a 2P 240v circuit, but 120v per leg, so vd calc should use 120 here I believe??

Thank you guys. Stay safe.

Generally you use 240 volts for the calc. Sometimes you may want to also look at the drop with 120 volts in case one large 120 v load is run without anything on the other phase, like say a large 120 motor, but usually things will balance out enough so that there shouldn't be much 120v load on the feeder.

I would have gone bigger for an apartment, but I think that will still work fine. I get about 4% vd with 50 amps. Just stay away from any on demand electric water heating or a bunch of electric heat

 

[paradox413]

First of all, you should use single phase equation with 240V as voltage level for voltage drop calculations.
And for residential, you can try to use 5% as the VD limit if you were using 3% for branch circuits. Because the house service entrance VD can be ignored (if the distance is short enough). Probably won't give you much spares. Just a thought.

 

[electrofelon]

First of all, you should use single phase equation with 240V as voltage level for voltage drop calculations.
And for residential, you can try to use 5% as the VD limit if you were using 3% for branch circuits. Because the house service entrance VD can be ignored (if the distance is short enough). Probably won't give you much spares. Just a thought.

I usually don't put too much stock in VD percentages, perhaps unless it's a known consistant load. It's more about choosing a realistic value for the current and a judgement on how long and frequently that current will actually exist. For a residential application, I wouldn't have an issue going quite high with percent VD using like 50-60 amps where that would likely occur for just a minute or two a few times a week or month, and would probably be resistive loads anyway.

 

[paradox413]

I usually don't put too much stock in VD percentages, perhaps unless it's a known consistant load. It's more about choosing a realistic value for the current and a judgement on how long and frequently that current will actually exist. For a residential application, I wouldn't have an issue going quite high with percent VD using like 50-60 amps where that would likely occur for just a minute or two a few times a week or month, and would probably be resistive loads anyway.

Totally understood. It depends on the specific scenario. We probably need to put some stock in this case because of the future apartment loads.