Using 10ga thhn with 12ga Romex

[Overlord66]

I have 220 irrigation pump that was wired wrong and needs to be corrected. I have 1'' conduit from the garage to the the pump room. The circuit was wired with 12ga romex from the panel until the pull head that leads outside. I planned on using 12ga thhn in the conduit all the way to the pump. My dad showed up with 4 brand new spools he had laying around. When I looked at them they are 10ga.

This is a 20 amp circuit can I use the 10ga thhn in the conduit or should I go buy 12ga.

Also what is the fill rate if I use 10ga? Could I add another 10ga 110 circuit to the conduit with out over filling it?

 

[rockwithjason]

you can use one of the ten gauge romex in that one inch pipe for sure. two might get hard to pull. i would have to do a calculation to see if two cables would be an overfill

 

[OccupantRJ]

Use the 10 gage. You'll have less voltage drop.

 

[MrMark]

No problem there, it is actually way better for voltage drop on a long run to use the 10. It must continue to be protected at 20 though.

There are conduit fill calculators on the internet, electrician2.com, for example. I'm sure you can add your additional circuit to the conduit fix wise, but be sure to look up derating for more than 3 current carrying conductors in a conduit.

 

[Dennis93]

Yes, the 10 is better for you, but make sure you have enough room in the conduit. Is it solid or stranded, stranded is a lot easier to pull but I'd go with a solid for its better performance.

Better question is how was it wired wrong, seems like you are just replacing wire with newer wire. You can't put Romex in conduit, so seems like it was wired correctly?

 

[MrMark]

So long as he's not in a wet location or buried with that conduit to the pump it's OK to have the nm in the conduit.

 

[Overlord66]

It was never in conduit. They ran direct burial 12/3 from the garage to the under the deck (6" below ground") up the concrete wall, draped under the joists and into the pump relay. They also ran it in 3/4 conduit where it was exposed on the back of the garage and since it wouldn't fit in the conduit they stripped one of the conductors out.

It wasn't necessarily wrong. It was sloppy and not water tight. The wiring for our septic lift station was even worse.

 

[theoldwizard1]

THHN is not rated for direct burial. Not certain, but even in undergound conduit I think you need THWN.

 

[Overlord66]

The new conduit I ran is not buried. It just runs under the deck and is attached to the joists. Its kind of an interesting room in that it's not water tight because the deck is it's roof but it has 10 foot concrete walls on three sides.If I could figure out a cheap way to add a ceiling I would love to make it water tight.

 

[rburke65]

I believe that you will be fine with the #10s in the 1" conduit for the pump as well as the extra 120 volt circuit.

 

[Norcal]

Most THHN is also rated as THWN , make sure the grounding conductor is also 10 AWG & should be good to go, You cannot undersize the grounding conductor when the ungrounded conductors are upsized, the applicable code section is NEC art 250.122(B).

 

[RickP]

Its kind of an interesting room in that it's not water tight because the deck is it's roof but it has 10 foot concrete walls on three sides.If I could figure out a cheap way to add a ceiling I would love to make it water tight.

A roof of corrugated metal or plastic would work. If the walls go all the way to the deck, you could install individual roof panels in between the joists - there are some DIY systems like that on the market.

 

[RickP]

Its kind of an interesting room in that it's not water tight because the deck is it's roof but it has 10 foot concrete walls on three sides.If I could figure out a cheap way to add a ceiling I would love to make it water tight.

A roof of corrugated metal or plastic would work. If the walls go all the way up to the deck, you could install individual roof panels in between the joists - there are some DIY systems like that on the market.

 

[Charles (in GA)]

Yes, the 10 is better for you, but make sure you have enough room in the conduit. Is it solid or stranded, stranded is a lot easier to pull but I'd go with a solid for its better performance.

Better question is how was it wired wrong, seems like you are just replacing wire with newer wire. You can't put Romex in conduit, so seems like it was wired correctly?

No difference in performance of stranded vs solid. Romex is quite legal in conduit so long as it is not a wet location. Wet loc would be underground or outdoors.

I would not hesitate to use it in conduit outdoor so long as it is not exposed to direct water or rain and conduit was PVC.

 

[Dennis93]

See ive always read that solid is less prone to overheating, and a lot harder to screw up. I try to use solid whenever pulling it isn't an issue. Romex is NOT legal in conduit here in VA unless the conduit is open and just used to pass through something and provide added protection, i.e. when going under a house through the brick or something of that nature. I would go ahead and use THHN/THWN like you're supposed to and since that's what you have. And yes, most are rated THHN/THWN. Sometimes not on the wire but on the spool or description.