Ask Me Help Desk - Cable sizing for a 110' run @ 50 amps

Quote:

Originally Posted by Spool

I'm installing an outdoor spa approx 110' from the main disconnect. I've installed 11/4" pvc conduit to a jct box approx half way to the 50Amp gfi disconnect. I'd like to know what size power cable to use before I finish the conduit.
I have enough #4 for 4 runs to the jct box. From there I'd like to use #6 to finish the run. Is this possible having a gfi to wire to? Otherwise should I use #4 for the complete run or what gauge wire?

Thanks for your input.

Are you going to have a 220 volt pump and electric heater? Any other use of 120 volt power out there?

You can run 3 #4 wires for the main power, and then use a #6 or #8 ground wire, and hook this up to a 50 or even 60 amp circuit breaker. I would use #4 wire all the way. This way you can upgrade the circuit breaker to 70 amps anytime.

Your expected voltage drop will be less with #4 wire too. That is a long distance. Depending on the voltage at the inlet, you might need a voltage booster transformer for the motor. The electric heater does not need to run on 220 volts, it can run on 200 or even 190, it will just take longer to heat up.

I live in a home that is about 200' from the main electric meter, and they installed #8 wire to a 30 amp circuit breaker feeding my appliances. I am at 120 volts with nothing on, it drops to 106 when I turn on the microwave (about 13 amps). When I run my air conditioner - 13 amps, I use a voltage booster that is rated at 12 volts, so I get 132 volts with nothing on, and 118 - 120 volts when the A/C is running.

The voltage booster is fine for motors, and the motor will run cooler. However a electric heating element will draw many more amps if run on higher than normal voltage, and the electric 220 volt heater will still heat, even if run on 150 volts, just the amperage will be much lower, and total wattage much lower.

So a 4,000 watt 240 volt electric heater element run on 120 volts will only draw 8.3 amps and consume 1,000 watts per hour, while at 240 volts it would have used 16.6 amps and drawn the rated 4,000 watts. At 4 KW, it will last 8-10 years in normal use, at 120 volts, it will probably last 20 - 30 years, unless corroded or covered with calcium, or other debris.

The ground wire can be undersized by 2 nominal wire sizes, while the neutral conductor must be the same wire size as the other conductors.

1-1/4 pipe is a little tight for the 4 wires you planned on installing. I would wait until you try to pull in some of that #4 wire before installing the remaining piping, as you might have to upgrade all of it to 1-1/2" or 2" pipe to make pulling around bends easier.

How deep is the piping buried? Steel pipe will not be damaged very easily, even if close to the surface, or run along a wall or above ground, but plastic pipe really should be buried deep enough that a roto tiller going down 10" will not get close to that piping. Most times I would recommend it being buried more than 18" below grade.

Utility company in my area buries it's piping 48" below grade, so it will not get hit while the homeowner is trying to plant a tree, build a wall or something.

Did you call Dig Alert? Call them first, they will be able to tell you if there is a buried natural gas line, water line, or more dangerous to you, a buried electric company line.

At my buddy's house, he was putting in a brick wall. He found out that the tract of homes had a 12,000 volt electrical line buried under his front lawn, it was shown on the plans as being on the other side of the street, but ended up being installed on his side of the street. It was something like 60" below grade, so he would not have dug that deep, but still if a contractor with a backhoe had dug into that line, it would have killed him, and the neighborhood would have been without power for a couple of days too!

Good luck on your project.

You will probably get a better response by asking this question in the "Electrical" section, as not to many electricians will be answering questions about spa's, where more questions have to deal with how many PPM chlorine is safe and desired.

Fred.