Question for electricians

[MNBobcat]

I need to run 300 feet of electric wire. I was wanting to run a 20 amp (single phase) circuit. Actual power use should be well below 20 amps but I prefer to plan for more than I currently need.

Usually I run 12/2 romax for a 20 amp circuit. Using a voltage drop calculator, it looks like even a 10/2 might be on the small side.

What do you guys recommend?

Also, I can go direct burial as its going 3 feet deep. We do have gophers but I don't think they go that deep. Not sure though.

 

[techman]

Voltage drop is what you can tolerate. For simple power tools, 5% would be okay. Other gear might not be so tolerant. If you plan to draw much less than 20 amps, do a voltage drop calculation at the expected current.

As for direct burial, it is allowed, but for the price of PVC conduit, I would not direct bury. Conduit offers another layer of protection against mechanical (or mammalian) damage as well as better moisture/water protection over a longer time. If you look at the price difference of standard wire vs. UF cable (req'd for direct burial) the additional price for the conduit is minimal. Also with conduit, if you go a size up, you never know what you hight want to add in the future with regard to other wires.

paul

 

[LD1]

Yep, you really need to know what the end of line amperage draw is going to be.

If you plan on using a full 20 amps, and want to stay over 110v, you need 8ga. BUT, if you cut the EOL current draw to 10 amps, you can use 12ga and still stay over 110v.

Which brings me to my next thing. Check your source voltage. I have seen someplaces that incoming voltage from the power company is only 115-116V. Which would give you less wiggle room. I have 121-122 comming in at my house,which is a good thing for long runs to start with an extra volt or two.

 

[EddieWalker]

What are you going to power? I used 12/2 for the lights at my front gate that is a 700 feet run. The lights only need a few amps, so voltage drop isn't a big deal.

Eddie

 

[MNBobcat]

I'm powering an irrigation control box for my vineyard. I imagine the required amps are quite low. However, I also plan to install a GFI outdoor outlet for plugging in radios and whatever. At some point, I may tie into it for a yard light too.

I'm thinking of putting it in conduit. This is considered a wet location. I'm trying to figure out if I need to use THWN in the conduit. Apparently romax or NM-B isn't rated for wet locations.

 

[bdeboer]

THWN is a correct wire for this application, will also be easier to pull.

 

[MNBobcat]

Is a dual rated THHN the same as a THWN in terms of being used in a wet location?

 

[LD1]

I dont see what you list ever pulling more than 10 amps. which would be okay with 12ga. But for 10ga isnt a ton more expensive, and allows a little more leeway. 8ga makes a bigger price jump but would be needed for full 20A.

What was your source voltage BTW??

 

[MNBobcat]

Initially its going to be plugged into the 115v connection on my generator. After I trench another feed line over to where the generator is sitting then it will hook to that line. That line would be about a number 0 or number 1. My generator sits near the pump. The vineyard is 300 feet away.

I've decided on pulling three #8 dual-rated THHN in conduit for the 300 foot run.

 

[LD1]

I'd fire up the generator and see what the voltage is. 115v could mean anything from 110-125. IF it is indeed 115v output, even 6ga wire would put you UNDER 110v if pulling the max of 20a