Stop Voltage drop

Dansos

Senior Member
Location
PA
this is specifically for a single phase application. Other than upping the wire size, what other things can we do to account for voltage drop when running long runs underground?
Ex. We need to run feeders approx 800’ underground to a separate building.Customer wants a 100A MLO panel installed.
If I wanted to have these feeders running off a 100A breaker, what can I do other than up the wire size?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
. . . what can I do other than up the wire size?
Raise the voltage. Voltage drop is dependent on circuit resistance and current. If you raise the voltage, you lower the current.

Insulation is cheaper than conductor. Step up to 480 or 600 volts at the origin, and back down to 120/240 at the terminus.
 

tom baker

First Chief Moderator
Staff member
Very nice drawing!
And to the OP, is it really a 100 amp load? Or they just want power for plugs and lights?
I had a request for a 20 amps 800 ft @ 120 V... it got pretty expensive, Honda EUI 2 KW generator did the trick and could be used elsewhere.
I had used the Sq D mini power zones, for long runs, 240 to 480, then 480 to the power zone, it has a pri disconnect, xfrm and panel, 2 ground rods and you are done.
 

GoldDigger

Moderator
Staff member
Raise the voltage. Voltage drop is dependent on circuit resistance and current. If you raise the voltage, you lower the current.

Insulation is cheaper than conductor. Step up to 480 or 600 volts at the origin, and back down to 120/240 at the terminus.
And don't forget that the benefit is actually doubled. If you double the voltage you cut the current in half so you have 1/2 the absolute voltage drop. But since the nominal voltage is doubled, the percentage voltage drop is actually 1/4 of the original.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
this is specifically for a single phase application. Other than upping the wire size, what other things can we do to account for voltage drop when running long runs underground?
Ex. We need to run feeders approx 800’ underground to a separate building.Customer wants a 100A MLO panel installed.
If I wanted to have these feeders running off a 100A breaker, what can I do other than up the wire size?
What kind of building? How big is the load?
 

Dansos

Senior Member
Location
PA
It is def not gonna be a load of 100A. Without walking through and counting things I’m gonna air on caution and say 40A would be more then enough.
So...... would I just run the 2AL but derate the breaker?
 

Dansos

Senior Member
Location
PA
What kind of building? How big is the load?
It is a cabin that is used as more of a second home. No electric appliances except fridge. Couple lights and some outlets. Only item that will draw anything is a septic pump system WITH 16FLA
 

winnie

Senior Member
Only item that will draw anything is a septic pump system WITH 16FLA
Watch out for the starting current here. If you size the system for reasonable voltage drop with a motor's full load current, the voltage drop can be excessive when the motor is starting.

It might pay to have a more expensive vfd controlled motor to eliminate this transient, rather than using larger conductors.

-Jon
 

11bgrunt

Senior Member
Location
TEXAS
Here is an efficient way to do this. Clever and yet code compliant.
I have seen this done with two padmounts and primary cables. The 240-600 transformers and cable will be a cheaper install.
Depending on the utility, a contractor can build a circuit for much less than the new utility electric service charge out to 800'. The handicap is that the customer becomes responsible for all maintenance cost associated with equipment past the utility meter point.
 

Dansos

Senior Member
Location
PA
Well anything less than 1/0 cannot be ran in parallel correct?
I think just picking a comfortable amperage that’s owner will want up there and derating the breaker is going to be our best option for this project. Thank you for all the info on the topic though guys!!
 

LarryFine

Master Electrician Electric Contractor Richmond VA
. . . at 480V a #4 would work.
Then it's even better at 600v. Or, use the voltage ratio to extrapolate the 600v figure if you want even smaller.

So, compare the cost to do the run with #2-0 to the cost with #4 (or #6?) and two transformers.

I have the feeling the latter will be less expensive as well as more electrically efficient.
 
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