Smith

[Smith]

Hello,

On a 120v/20amp circuit, installing two 120v/6amp fans, one at 100' and the other at 200' from electrical panel. My question is, can we use one circuit with #10 wire to feed both fans for this install. The calculations for #10 wire is good for 12 amps for 100' and 6amps for 200'. Would this be correct?

 

[charlie b]

I confirm your methodology and your results. Welcome to the forum.

 

[GoldDigger]

Your calculation for the far end voltage drop is not correct if the two fans share a common run of wire.
Instead of using 6A at 200' you need to *add* the drops for 6A at 100' and 12A at 100'.
Now if the drop for 12A at 200' is OK, then you would not need to do the other calculation.
If you run one fan 100' in one direction and the second fan 200' in the opposite direction, then your calcs would be appropriate.

Tapatalk!

 

[cpinetree]

I use an excel calculator "Voltage Drop Calculator for Segmented Circuit",
I think was provided by someone on this site, but I can not attach it. Send a pm and I'll email it to you.

It looks like #12 would be fine. see screen shot below: 3.83% at the end (assuming your ok with 5%, and your starting voltage is 125v)

 

[Smart $]

If you want to use one size wire, another way to do the voltage drop calculation is to use the values for the load center of the circuit...

http://books.google.com/books?id=aB...a=X&ei=Iw5QU7PGEa6-sQS31YDoAg&ved=0CC0Q6AEwAA

 

[charlie b]

Instead of using 6A at 200' you need to *add* the drops for 6A at 100' and 12A at 100'.

That is what I did, and that is what I thought the OP meant. My results were 3 volts for the first 100 feet at 12 amps, and 1.5 volts for the second 100 feet at 6 amps. The total VD is therefore 4.5 volts, or 375%. So please tell us, "Smith," whether that was your approach?

 

[cpinetree]

I use an excel calculator "Voltage Drop Calculator for Segmented Circuit",
I think was provided by someone on this site, but I can not attach it. Send a pm and I'll email it to you.

It looks like #12 would be fine. see screen shot below: 3.83% at the end (assuming your ok with 5%, and your starting voltage is 125v)

Found where I got this: http://forums.mikeholt.com/showthread.php?t=141401

Thanks Electron_Sam78 email: samandholly6@yahoo.com

 

[Besoeker]

That is what I did, and that is what I thought the OP meant. My results were 3 volts for the first 100 feet at 12 amps, and 1.5 volts for the second 100 feet at 6 amps. The total VD is therefore 4.5 volts, or 375%. So please tell us, "Smith," whether that was your approach?

Would you need to take account of the starting current of the fans in question?

 

[GoldDigger]

Would you need to take account of the starting current of the fans in question?

Only if the VD would be large enough to cause problems with starting. Not super likely unless the fans were axial and had to start against a back pressure and back flow of air.
As for NEC, starting current and the resulting VD are only officially considered for fire pumps.

 

[Smith]

Smith

The conduit leaves the panel then after 100' this is where the first 120v/20amp receptacle will be placed for the first fan to plug into. Then from that 4's box the conduit will continue down to the final receptacle which will feed the last fan at 200' from panel. So I would calculate 12amps for the first 100' & then 6amps for the remaining 100'??? I just wanted to make sure that by pulling #10 THHN wire this would be the correct conductor size.

 

[GoldDigger]

The conduit leaves the panel then after 100' this is where the first 120v/20amp receptacle will be placed for the first fan to plug into. Then from that 4's box the conduit will continue down to the final receptacle which will feed the last fan at 200' from panel. So I would calculate 12amps for the first 100' & then 6amps for the remaining 100'??? I just wanted to make sure that by pulling #10 THHN wire this would be the correct conductor size.

That is the calculation that Charlie B actually ran for you, and it came out OK.
Yes.