Voltage Drop Help

[tampascl]

First off, I have read a boatload of posts here in the forum on this subject, and I'm only more confused! I've also looked at about a half dozen online voltage drop calculators and that still has me scratching my head The calculators ask me what voltage is (120 vs 240), but which do I choose, since i have some things that run on each?

Here is my situation: My pole barn is 210 feet away from my 200-amp service and meter pole. The pole barn has an upstairs 1,000 square foot "man cave" that will have its own A/C unit, lights, computer, etc., in addition to the barn's compressor (220v), lights, and normal outlets throughout. My hope is to use 4/0 4/0 4/0 2/0 aluminum mobile home feeder wire and not experience any dimming lights or problems with my computer when my A/C or compressor turn on. Please help. The electric company wants nearly $4,000 for them to run underground service to a new meter, but they also said I'm fine installing a subpanel off the current service, but they would not be responsible for voltage drops (and won't give me advice on what wire to use).

 

[kd3pc]

with your needs as described, you are talking about an almost 2,000 sq ft home and garage. 200 Amp service will almost be required to do what you want.

If you only have a 200 Amp service at the house/pole....you are going to need another one, or a heavier service/parallel service from the power company, to handle this new building.

MH feeder you describe, should handle your loads, but depending on where you are located and soil type, it may be more cost effective to spend the money for the Power Company to do it. It will be labor intensive.

 

[rockwithjason]

if the panel is 240 then you use the 240 number

 

[Rookie2]

Your fine. but the highest breaker allowed to subfeed your pole barn is 80amps I believe. Some of these other guys are more up on code.

 

[Mr. T]

if the panel is 240 then you use the 240 number

I'm not 100% certain but I was under the impression that you're supposed to use actual metered voltage at the source for voltage drop calculations?

 

[LXCam]

The first thing you need is the total sum of the connected load. Find the values for your larger equipment and total them up. Most likely all these such as air compressor, welder, AC, etc are 240 volts. Add another 30 amps to the mix for misc loads such as lighting and general receptacle stuff. Then use a calc or pm me the information and I'll do the calc for you.

 

[wyliesdiesels]

First off, what loads do u have in the house? WH, dryer, what size ACs, electric heat, etc etc... This is the pertinent info that is missing!

 

[tampascl]

I think most of my confusion deals with the "load current" or "current at the end of cable run." It sounds like I should total up the amps that I would use in a max situation, rather than just plug in the total amperage of the panel. In other words, if I were running it to a 100 or 200 amp sub panel, I've been plugging 100 or 200 amps into the calculator, which always returns much larger conduit. So what I should be plugging in to the calculator is the sum of the a/c unit, compressor, and couple of lights or other things I'm running at the same time, which might only be half the amps of the service panel. Correct?

 

[wyliesdiesels]

My phone is about to die but after i get it charged i will do the calcs and post the formula i use...

What loads do u have in your house?

 

[LXCam]

I think most of my confusion deals with the "load current" or "current at the end of cable run." It sounds like I should total up the amps that I would use in a max situation, rather than just plug in the total amperage of the panel. In other words, if I were running it to a 100 or 200 amp sub panel, I've been plugging 100 or 200 amps into the calculator, which always returns much larger conduit. So what I should be plugging in to the calculator is the sum of the a/c unit, compressor, and couple of lights or other things I'm running at the same time, which might only be half the amps of the service panel. Correct?

Ah ya

 

[justsam]

As Wylie is pointing out, it is more an issue of not starving your existing house, than providing power to your pole barn. With the cable and loads you mentioned I would not expect an issue with excessive voltage drop.

Yes you add up what you suspect are concurrent loads, not the load rating of the panel.

 

[tampascl]

Thanks everyone..this helps immensely!

 

[wyliesdiesels]

So to wrap this up u didnt state what size in HP your compressor is nor what size your AC is....

@ 210' with the 4/0 wire u mentioned and a 100a load your voltage drop will be about 1.8% or 4.2volts if u have 240v to start with at your house....

SO how much of your 200a service does your house use? What loads does your house have?

 

[Speedy Petey]

with your needs as described, you are talking about an almost 2,000 sq ft home and garage. 200 Amp service will almost be required to do what you want.

Really? You came up with this simply from what he described?
I don't really agree. This is not nearly a 2000 sq/ft home and garage. Not even close. In fact, it's not even a home. He made no mention of a kitchen or even a bathroom.

 

[Speedy Petey]

Your fine. but the highest breaker allowed to subfeed your pole barn is 80amps I believe.

HUH?? Where'd you hear this one?

 

[Speedy Petey]

tampascl, please listen to Wylie in this thread. He's asking you the right questions.

 

[wyliesdiesels]

HUH?? Where'd you hear this one?

I blew by that comment faster than a freight train...no merit to it whatsoever!