View Full Version : Wiring for a 1HP Irrigation Well/Pump

06-09-2007, 03:04 PM
I'm having a sprinkler system installed soon, and want to get a head start on wiring the 1 HP pump, which is about 40 feet away from the main panel. I know I need to get a pump-start-relay and an irrigation-controller (probably using Hunter supplies for the whole project). The relay and controller will be indoors and 5 feet away from the panel.

So once the 18" deep trench is in place, exactly what cable/wire do I need and does it have to be in a conduit? I'm thinking I need a 20amp breaker, 10/2 cable, and low voltage sprinkler wire from the controller to the pump relay. Am I on the right track?

Bob NH
06-09-2007, 06:19 PM
18" deep with 240 Volts requires conduit (nonmetallic ok). NEC Table 300.5. You should be able to get by with 1/2" conduit. You can pull a string through it with just a vacuum cleaner pulling a light string with a light bunch of plastic grocery bag on it. Then pull a heavier line with the string.

12 AWG is ok for a 1 HP motor 45 ft from the panel.

You should use THWN. Stranded is easier to pull. The standard wire found at HD is usually rated for both THHN and THWN. If you are wiring only the 240 Volt pump then you will need a Black, Red, and Green. You can get by with two black instead of black and red. If you choose cable instead of single conductors you need UF B, but that will be harder to pull and probably more expensive. You would probably need 3/4" conduit to pull the UF, and some lubricant. Unless you have a lot of elbows you should be able to pull the THWN without lubricant, or use a little corn starch or generic brand of "personal lubricant".

For the pump relay, I like to use a "Definite purpose contactor". A 20 Amp rated 2-pole is about $14 at Grainger. I usually use at least a 30 Amp which is $20. They are stock no 5B131 and 5B124 respectively for the ones with 24 Volt coil. Your controller probably puts out 24 VAC to the coil so you will need a contactor with a 24 VAC coil. You need to be sure the controller puts out enough current to actuate the contactor.

The contactor is open frame so you will need to put it in some kind of box. You should be able to find one at HD. You might be able to find a big junction box that will hold it.

You will need terminal adapters to adapt the conduit to the boxes, elbows for the conduit unless you want to learn how to bend it with a heat gun, cement, and maybe a piece of liquid tight flex to connect to the pump.

06-10-2007, 09:03 AM
Thanks for all the info. The guy installing the sprinkler system may provide his own relay, but if he doesn't then I'll get the one at Grainger.

I'll go to HD or Lowe's and check on the conduit, 12 AWG, and liquid tight flex. It's a very straight line from the panel to the pump, with only 2 elbows: one going up from the ground and one into the house. I could probably use a few sections of 10' pvc rigid conduit -- this would make it really easy to get the wire through. I'll wait until it's trenched out, then decide.

Thanks again.

Bob NH
06-10-2007, 12:03 PM
PVC rigid is what you want for the underground run. You only need the flex if you want to make it easy to connect to the motor.

HD usually sells a short piece of flex with fittings on both ends. That piece costs less than 2 fittings. If you buy that, and a piece of longer flex if you need it, you can take the fittings off the short flex and put them on the longer piece.

To connect the flex fitting to the conduit you will need a female terminal adapter for the conduit. It may come with the small flex unit.

06-10-2007, 07:46 PM
Got it. I'll definately use rigid pvc then, and the short flex to connect to the motor only. That makes sense, and it's probably the easiest way to do it.

I'm familiar with indoor stuff, and I wired an entire basement of outlets by running two circuits. I was at HD today and noticed that UF B is recommended for outdoors, but it doesn't require conduit unless there's a chance one might cause damage with a shovel. That's a little odd. There's always that chance. I'm tempted to use the UFB without conduit, but I'd have trouble sleeping if I did that. So I won't.

Anyway, is it safe to use the indoor wire as long as it's in a sealed conduit? I know THWN is water resistant but is it rated for outdoors?

Bob NH
06-11-2007, 06:15 AM
A conduit underground is always considered a wet environment. You must use a wire that is rated for wet conditions, such as THWN. THWN is ok for outdoor applications.

You can't legally put NM (Romex) in a conduit.

Almost all THHN is also rated THWN or THWN-2.

06-12-2007, 12:25 PM
OK, that makes perfect sense to me. I should be good to go now. I'll use THWN or UFB (& conduit) from the pump to the relay, and since the relay and controller will be indoors, Romex from the relay to the panel. It's only about 5 feet to the panel, so I'll probably have enough THWN.


06-18-2007, 06:25 PM
Can you see the pump from the panel? (line of sight)

If not, you need a disconnect like on your AC unit.

PS....NO UF....ever. PVC and thhn/thwn

PS PS. Ground/bond EVERYTHING !!

No such thing as "too safe".

06-19-2007, 08:34 AM
Yes, safety is important. Everything is grounded and in place. I put the connections near the well in an above-gound water-proof box. The whole system works perfectly.