Community Forums

dsilva · 12-07-2012, 06:34 PM

Hi don't really know how to post but here goes. I want to put in175ft. of 8/3wire underground,from my house panel to a 30 amp post hook-up I read where 8/3 is rated as 55amps. I know that I will lose some in 175 ft.my question is will i still have 30 amps or better, can some tell me. There won't be anything else on that line and I will come off a 40 amp breaker. Hope some one can hel me.
thanks.

dsilva

rsha · 12-07-2012, 06:38 PM

It's not amps you need to worry about. Voltage drop will be you problem. 8/3 seems like a little small for that distant. Might want to check the code.

Pusherman · 12-07-2012, 06:49 PM

Good plan to use the larger wire to prevent the voltage drop. But it should still be 'fused' at 30A for the breaker size, not 40A.

Note: If your motorhome has a 30A 3 wire service, then technically you need 2 conductors with ground. In other words, 10/2 with ground, or in your case of running the longer length, 8/2 with ground. If you have a 50A service, then it's a different story. You need 3 conductors with ground, as technically it's a 240V service. Amperage will determine the size of the wire.

Going up one size for your distance is a good idea.

WeatherTodd · 12-07-2012, 07:02 PM

Voltage Drop Calculator

Workshop · 12-07-2012, 07:10 PM

Here is another Voltage Drop Calculator. Looks like you will need at least a #6 for that length. As stated above connect with a 30 amp breaker.

dsilva · 12-07-2012, 07:15 PM

Quote:

Originally Posted by Pusherman

Good plan to use the larger wire to prevent the voltage drop. But it should still be 'fused' at 30A for the breaker size, not 40A.

Note: If your motorhome has a 30A 3 wire service, then technically you need 2 conductors with ground. In other words, 10/2 with ground, or in your case of running the longer length, 8/2 with ground. If you have a 50A service, then it's a different story. You need 3 conductors with ground, as technically it's a 240V service. Amperage will determine the size of the wire.

Going up one size for your distance is a good idea.

are u guys saying I need 10/3 wire. i will be hooking up to a 30 amp cord
from the post to the M.H. no washer dryer. I know I can't run 2 A.C. on 30 amps.I will use it to charge the battries while its parked in the barn and not have to turn off the fridge. Thanks for ur replies Pusherman and rsha

jfran304 · 12-07-2012, 07:22 PM

Why don't you install a 50 Amp hookup instead of the 30 Amp? It will cost you a little more but then you will be able to run everything in the coach.

Jon

PEJ · 12-07-2012, 08:00 PM

#6 is still not enough at 30 amps, but more importantly you need a licenced electrician.

vsheetz · 12-07-2012, 08:17 PM

I would run three wires and a ground - leaving the 4th wire unused or configured as a MWBC (multi wire branch circuit = provides for two 120v circuits) for now - and allowing for converting to 50 amp service in the future. Three #6 current carrying (white/black/red) plus one #10 ground (green), all THHN assuming in conduit.

How is this going to get there? If trenching should be 18" deep in conduit to meet code in most places. If only 120v circuit can be 12" deep. Direct bury is 6" deeper. Conduit is highly recommended -easier/cheaper to dig, can pull to change or add wires in the future. Direct bury cable is cheaper. Trenching is easy to do - hire a couple day workers to do it, give them a 4" trenching shovel and a digging bar.

Whether you need a licensed electrician depends on your local requierments. Here in SoCal I can pull a owner builder permit and do it all myself. If you do need or want a electrician to do it - do the trenching and wire running yourself, then have the electrician just do the hook-ups at either end.

LandKinaMoho · 12-07-2012, 09:20 PM

Can you say CODE. Trench inspection, conduit , backfill etc Permit. Just sayin.

bluepill · 12-07-2012, 09:52 PM

dsilva: If you are only charging batteries and running an LP/Electric fridge, you will probably only be using about 15 amps, not the full 30. This assumes that you can limit your charger/converter to 10 amps input (many have this ability to adjust) and your fridge draws 4 amps. With the charger and fridge off, you would use about 14 amps on a single A/C unit rated at 13,500 BTU.

I have used a 15 amp circuit to power my MH as described above, and it has worked fine.

Calculation below:

1 conductors per phase utilizing a #8 Copper conductor will limit the voltage drop to 3.03% or less when supplying 15.0 amps for 175 feet on a 120 volt system.
For Engineering Information Only:
40.0 Amps Rated ampacity of selected conductor
0.7421 Ohms Resistance (Ohms per 1000 feet)
0.052 Ohms Reactance (Ohms per 1000 feet)
4.8 volts maximum allowable voltage drop at 4%
3.625. Actual voltage drop loss at 3.03% for the circuit
0.9 Power Factor

Skip426 · 12-07-2012, 09:56 PM

Quote:

Originally Posted by LandKinaMoho

Can you say CODE. Trench inspection, conduit , backfill etc Permit. Just sayin.

X2. If anything goes wrong, remember " Murphy , and his law " the first thing any insurance company is going to look for is a permit, the second is a way not to pay a claim.

vsheetz · 12-07-2012, 10:47 PM

Agree - having things such as this properly permitted and inspected is a must.

Here is a great resource forum for home improvment activities. I have done a whole house renovation, detached 24x30 workshop, and several other projects with excellent advice from the good folks here. All with owner builder permiting and inspections. DIY Chatroom - DIY Home Improvement Forum