breaker size

Status
Not open for further replies.

ceb58

Senior Member
Location
Raeford, NC
Help a brain dead fellow out. I will be installing some electronic devises at a correctional facility. These devises are mounted on poles around the outside of the facility ( 4 poles ). Each devise must have a dedicated 120v circuit and has a load of 4 amps. Here is the problem. By the voltage drop calculations 2 of those circuits ( 460ft, 560ft ) must be # 6 THHN and the other 2 ( 1640 ft, 1740ft )must be #3 THHN due to the distance from a UPS panel inside of the prison to the devises. I think I can land the #6 on a SP 30 but unsure of the #3. Only other option is to put a short pig tail on the wire and land on 20 amp SP breaker.
No way to do transformers on the yard.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
At the panel you probably could go as high as a #8 on a 20A breaker. Get a butt splice with set screws or a Polaris connector and splice the larger wire on. That short of a piece you could even just use #12. I don't know about your devices but you may have to splice down there too.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
4 Amps of current draw causing that much of a VD to require #6??? Methinks you calculated something wrong. At 600ft I get a 6.75% drop using #12 wire. 6.75% drop is 112VAC at the device. On the longer one I get 7.6% drop using #8, so still over 110V.

Is it that sensitive? Most devices are +-10% and many things are actually designed for 115V when used on a 120V circuit. Check your specs and calcs again.
 

ceb58

Senior Member
Location
Raeford, NC
4 Amps of current draw causing that much of a VD to require #6??? Methinks you calculated something wrong. At 600ft I get a 6.75% drop using #12 wire. 6.75% drop is 112VAC at the device. On the longer one I get 7.6% drop using #8, so still over 110V.

Is it that sensitive? Most devices are +-10% and many things are actually designed for 115V when used on a 120V circuit. Check your specs and calcs again.

I used the voltage drop calculator from Mikes home page allowing for only a 3% voltage drop.
 
Status
Not open for further replies.
Top