electrical line load loss 1

[mcb48]

I have a 15KW generator that feeds a 5 hp 220v water pump. I would like to run an underground line about 200 yards to a remote building to run a light, a 1/4 hp air pump, and a trickle charger for a 12 v battery.

I was told to use #6 underground line and that should give me enough amps for what I need. Can anyone verify this please.

Thanks

 

[busbar]

Roughly, expect to see 3% (of 120V) drop on a 1200-ft loop of ~6.1-amp load if copper, or ~3.7 amperes for aluminum. (Expect the lamp to flicker quite noticeably when the motor starts.)

 

[jims99]

mcb,

Based on your proposed loads you should be fine.

Quick and rough calculations, with assumptions:
1/4hp @220vac is about 3 amps
2 x 100W light bulbs: ~ 1 amps
Charger: 1 amp
Total: 5 amps.

#6 wire is rated around 70 amps so obviously you have plenty of margins here.
Voltage drop for 400 yards (round trip) is about 2.5 v (based on 0.4 ohms/1000 ft), that’s about a 1% drop, so again you’re fine here. (generally accepted is drop<3%).

I need to emphasize the importance of meeting electrical codes (type of wire, conduits, protection devices, and so on and so on…)

Hope this helps.

jim s.

 

[dspDad]

If your pump is close to the generator, and this run of 200 yards is for a few small appliances, then #6 is overkill and you should design for a 15 or 20 amp circuit.

Also, if you use a GFI (probably required, but I don't know your specifics), then place the GFI near the load in the remote shed. Placing it near the generator will cause it to trip extraneously when the ground is wet, etc, because there is a significant amount of leakage in long lengths of buried cable.

 

[boiler84]

Voltage Drop Calculation:

------------------------------------------------------------ For a 120/240 Single phase cricuit and a 600 foot run. Assuming you can handle a 3% voltage drop a #6 AWG. Aluminum Triplexed UD cable will provide for a load of 8 AMPS. If you set it up for a 15 AMP service you will want to go with #2 AWG. Always remember upsizing the conductor will provide for future growth or increased loading while more efficiently utilizing the energy as the conductor will not dissipate energy in the form of heat as it will operate at a lower temperature.

If you prefer Copper you could go with #4 AWG USE singles that can be direct buried and will provide for 15 amp service. I hope this helps

 

[dspDad]

I agree with the line size calculations for 3% voltage drop and going with #6 or larger is a reasonable and conservative solution. If the voltage drop needs to be controlled, and cost is a non-factor, wire size should be pulled from the tables.

In any system, there is going to be a bottle-neck or a weakest link, and in the system described, the (small) generator/ (big) pump will determine the system performance.
A common design flaw is design for the a future that never arrives. It is usually less expensive to have very modest over-design and plan to rework the system if the requirements change. This depends completely on how likely and how expensive an upgrade will be.

If this is a cabin in the woods, which it sounds like, then future load increases are unlikely, and the quality of the power is already poor. Spec'ing large guage wire won't add much except cost.

When your pump kicks on, you're going to have large voltage drops due to motor starting current, and in a backup or temporary power system, (unlike a home or business) flickering lights are a non-issue.

On the other hand, if you think that a utility hookup is in your future, or that the outbuilding may turn into a spare bedroom, then go conservative. If it was my barn, I'd probably use #8 instead of #4, knowing that I could run a battery charger but not a mig welder.

This also sounds like a 110 system, not a 220, so whether you choose #4, #6 or #8, make sure its 3 wire plus ground, not 2 wire plus ground.