250MCM for 21.7 amps? Voltage drop calc must be wrong?

[Bri22]

I am a little flustered because the size of wire I'm coming up with for my load seems ridiculous.

21.7 Amp total load
120 volt single phase
1317 foot run
PVC conduit
3.09 Voltage drop


I come with 250MCM!!? I never had a run that long but thats that just doesn't seem right.... All I am powering is two arm gates and a little control equipment. The engineer somehow came up with 58 amps (I don't know how) and has me running parallel 250MCM!
Am I going crazy or are the calculations correct?

Thanks for your time!

 

[iwire]

Raise and lower the voltage with transformers.

 

[topgone]

I am a little flustered because the size of wire I'm coming up with for my load seems ridiculous.

21.7 Amp total load
120 volt single phase
1317 foot run
PVC conduit
3.09 Voltage drop


I come with 250MCM!!? I never had a run that long but thats that just doesn't seem right.... All I am powering is two arm gates and a little control equipment. The engineer somehow came up with 58 amps (I don't know how) and has me running parallel 250MCM!
Am I going crazy or are the calculations correct?

Thanks for your time!

Your calculations seems fine to me.
250MCM @ 21.7 amps, 1317 feet, VD = 3.06 volts
350MCM @ 58 amps, 1317 feet, VD = 0.39 volts

 

[GoldDigger]

Your calculations seems fine to me.
250MCM @ 21.7 amps, 1317 feet, VD = 3.06 volts
350MCM @ 58 amps, 1317 feet, VD = 0.39 volts

Check for typos and edit?

 

[don_resqcapt19]

Your calculations seems fine to me.
250MCM @ 21.7 amps, 1317 feet, VD = 3.06 volts
350MCM @ 58 amps, 1317 feet, VD = 0.39 volts

The online calculator that I use gives me a drop of 2.5 volts for 21.7 amps at 1371 feet on 250 kcmil copper.

I get a drop of 4.8 volts for 58 amps at 1371 feet using 350kcmil copper

I use this calculator. (you have to scroll down to get to the calculator)

 

[Bri22]

Your calculations seems fine to me.
250MCM @ 21.7 amps, 1317 feet, VD = 3.06 volts
350MCM @ 58 amps, 1317 feet, VD = 0.39 volts

Okay, thanks. Glad I didn't screw up my calculations. Never would of guessed I'd need that big of wire for the small load.

 

[Bri22]

The online calculator that I use gives me a drop of 2.5 volts for 21.7 amps at 1371 feet on 250 kcmil copper.

I get a drop of 4.8 volts for 58 amps at 1371 feet using 350kcmil copper

I use this calculator. (you have to scroll down to get to the calculator)

Nice calculator, makes it easy! Thanks for the quick reply.

 

[ptonsparky]

Now that you have the VD figured, refer back to post 2.

 

[ActionDave]

Okay, thanks. Glad I didn't screw up my calculations. Never would of guessed I'd need that big of wire for the small load.

I don't understand where 58A comes from if the load is 21.7.

Use a 230V motor and let you acceptable voltage drop be ten percent and you should be able to use a more reasonable wire size for this application with no drop in performance.

 

[Bri22]

Raise and lower the voltage with transformers.

Thanks for the suggestion, I was thinking the same after I figured the wire size but questioned myself because it didn't seem possible it could be correct. If I run 480/277 out there to a small weather proof transformer I'd have more wires but they would be much smaller. Using Don's suggested online calculator I come up with.

6 AWG with a 3.2 voltage drop?

480 volt 3-phase
1317 feet
21.7 amps

Did I do that correctly?

Thanks so much for your help BTW!

 

[iwire]

I would seriously look at kicking it up to at least 480 volt and run the numbers again.


You posted while I was typing.

 

[Bri22]

Now that you have the VD figured, refer back to post 2.

Got it, Thanks! Working 80+ hours a week I'm about brain dead.

 

[iwire]

Thanks for the suggestion, I was thinking the same after I figured the wire size but questioned myself because it didn't seem possible it could be correct. If I run 480/277 out there to a small weather proof transformer I'd have more wires but they would be much smaller. Using Don's suggested online calculator I come up with.

6 AWG with a 3.2 voltage drop?

480 volt 3-phase
1317 feet
21.7 amps

Did I do that correctly?

Thanks so much for your help BTW!

If you only need single phase at the gate just run 480 single phase. You would only need two hots and an EGC.

 

[Bri22]

I don't understand where 58A comes from if the load is 21.7.

Use a 230V motor and let you acceptable voltage drop be ten percent and you should be able to use a more reasonable wire size for this application with no drop in performance.

Thanks man. I have no clue where he came up with 58A.

I really appreciate the quick replays from everyone!

 

[JFletcher]

Welcome to the forum. With almost a quarter mile run, yes, you need at least 250MCM for 3% or less VD at 120V, 21.7A load, or 350MCM for aluminum.

If you use transformers to 480V, and can live with 10% VD (actually 8.23), you could go as small as #8 wire.

Given the long run and fairly low load, a pair of 480/120V 3kva transformers with smaller wire would be more economical than the larger conductors.

 

[Bri22]

If you only need single phase at the gate just run 480 single phase. You would only need two hots and an EGC.

I only need single phase. The two gate arms are 120 volts and I need to instal a quad receptacle for the security co. for their cameras and com equipment.

Oh yea, two hots and a EGC, that makes sense. I guess all the transformers I have wired have been 3 phase so I din't think of that. I'll just have to find the right transformer. I don't know why the supposedly "smart engineer" didn't think of that!

If I could ask one more question since you are being so generous? Could you help me out with the voltage drop calculation on that? I'm going to give it try right now and see if I can figure it out.

I really appreciate your help BTW!

 

[GoldDigger]

I only need single phase. The two gate arms are 120 volts and I need to instal a quad receptacle for the security co. for their cameras and com equipment.

Oh yea, two hots and a EGC, that makes sense. I guess all the transformers I have wired have been 3 phase so I din't think of that. I'll just have to find the right transformer. I don't know why the supposedly "smart engineer" didn't think of that!

If I could ask one more question since you are being so generous? Could you help me out with the voltage drop calculation on that? I'm going to give it try right now and see if I can figure it out.

I really appreciate your help BTW!

Try using the calculator at http://www.southwire.com/support/voltage-drop-calculator.htm
See what you get.

 

[JFletcher]

1 conductors per phase utilizing a #10 Copper conductor will limit the voltage drop to 3.11% or less when supplying 5.4 amps for 1317 feet on a 480 volt system.
For Engineering Information Only:
30.0 Amps Rated ampacity of selected conductor
1.1417 Ohms Resistance (Ohms per 1000 feet)
0.05 Ohms Reactance (Ohms per 1000 feet)
24.0 volts maximum allowable voltage drop at 5%
14.925. Actual voltage drop loss at 3.11% for the circuit
0.9 Power Factor

 

[ActionDave]

I come up with #4 at 240V.

You guys go out and buy some transformers, disconnects, and some fuses, I'm gonna check the shop and see if there is enough 4AWG if not I'll use 6AWG and take Friday off since I didn't spend two days wiring up transformers.

 

[Bri22]

Welcome to the forum. With almost a quarter mile run, yes, you need at least 250MCM for 3% or less VD at 120V, 21.7A load, or 350MCM for aluminum.

If you use transformers to 480V, and can live with 10% VD (actually 8.23), you could go as small as #8 wire.

Given the long run and fairly low load, a pair of 480/120V 3kva transformers with smaller wire would be more economical than the larger conductors.

Thanks for the welcome! Number 8 (or even 4 or 6 for that mater) vs 250MCM for almost quarter mile... It would be silly to consider 250MCM! I have no clue how this engineer got his degree.

Thanks for your help!