Best way to run feeder 350 feet underground?

LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I just got a call to price running a feeder from a garage with a 200a panel to a barn to supply a 30a, 120v RV outlet.

There is presently a 20a circuit, but I don't yet know the wire size used. Even #10cu would be iffy with voltage drop.

I would probably recommend #6cu or larger al wire for the distance, and also suggest a 4-wire feeder for future use.

The main question is whether to go with PVC and wires, which would be a bear to pull vs going with direct-bury wire.

Between underground feeder like URD or mobile-home feeder, what are the functional differences between the two?

Thank you as always.
 
Not sure what your actual load is but for the minimum conductor size I ran these through the Southwire VD calculator and got these numbers for:

120 volts, 350', 3% VD, Copper conductors, (Aluminum conductors):
30 amps-#1/0 (#3/0)
25 amps-#1 AWG (#2/0)
20 amps-#2 AWG (#1/0)
15 amps-#4 AWG (#2 AWG)
10 amps #6 AWG (#3 AWG)
 
Thank you for that, Rob.

Correct, RV outlet.

The customer is correctly concerned that the existing 20a lighting feeder is inadequate.

I now know I want MHF, not URD, and I plan to suggest 2-2-2-4 al, such as this:

nassaunationalcable.com

2-2-2-4 Aluminum Mobile Home Feeder Cable

Shop 2-2-2-4 Aluminum Mobile Home Feeder Cable, 100 Amps, 600V, rated for wet/dry locations at 90°C. Sunlight-resistant, NEC & UL listed, with durable XLP insulation. Order now.
nassaunationalcable.com nassaunationalcable.com

Additional opinions welcome.
 
At that distance I would install at least a 1.25" PVC even if you choose to go with a direct burial cable assembly . An open ditch now is not going to be open later. As a matter of fact, I would probably install a water line too
 
there's only 5 cents a foot difference, about half the voltage drop on the aluminum, and easier to direct bury.

#10 is showing 19.9% drop on a 350' with 30a @ 120v.
#2 alum urd triplex is showing 5.37% drop on the same.

nassau national cable is showing 2-2-4 (stephens) aluminum urd at $1.40/foot
they are also showing 10/2 UF cable at ...... $1.45/FOOT.

i'd bury the #2 aluminum direct bury. (assuming you're not in rocky area) it's cheaper, and has 1/4 the voltage drop.
 
infinity said:
I know nothing about RV's, what size load would one expect on a 30 amp circuit?
Click to expand...
Impossible to know. Most have a typical 120/240 panel (even though no 240V loads, usually) but when they use the 120V/30A adapter, both buses get connected to the single ‘hot’. Those rooftop ACs draw 12A. So a large RV with 2 ACs can draw 24A just for AC. The rest is mostly lights and maybe a TV. Until they start bringing portable, electric kitchen appliances, then anything’s possible.
 
LarryFine said:
I may be able to sell him on $1K for wire, but probably not $3.5K for conduit.
Click to expand...
Where are you buying your conduit? 350' of 1.25 is less than $500.00. I agree that the customer probably doesn't want to spend that either
 
infinity said:
I know nothing about RV's, what size load would one expect on a 30 amp circuit?
Click to expand...
Used on smaller/older travel trailers. Mostly runs on propane, even the frig. About the biggest load they have is a 120V/15A AC unit.

The bigger RV's use NEMA 14-50's.
 
I would use PVC, but we have rocky soil. I wouldn't even think of going smaller than 2" on #2 for that length of pull. I would also be inclined to use steel sweeps. If you have sandy soil, I would toss it right in the ditch.

I would be inclined to pipe it, get the cable on a reel, set it up, and pull it in with rope with a truck. Do 20' at a time with someone feeding.
 
Would it make more sense to run a 240 volt circuit and use a transformer at the 120 volt end? That would have a big impact on wire size and voltage drop.
 
busman said:
I would sell the 2" PVC.

Mark
Click to expand...
Yep.
If they like the smaller RV with 30A, they may want to upgrade to a larger unit at 50A.

But it depends on why they want this outlet in the first place. Are they living in the unit, or is it for packing/unloading, or maintenance/storage.
 
infinity said:
Would it make more sense to run a 240 volt circuit and use a transformer at the 120 volt end? That would have a big impact on wire size and voltage drop.
Click to expand...

You might also be able to use the existing underground feeder using 240V and a transformer.
The transformer would draw some current under no load, but it would probably be mostly reactive power from the magnetizing current. I think most utilities only bill residential customers for real power, with the energy usage in kWh.
 
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