20A Outlet Wiring: 10 ga THHN Stranded/Solid?

[Oxjockey]

OK, I've done all my calcs and I want to run (2) 20A circuits through my conduit. In order to run 4 or more conductors in conduit, you have to de-rate by 80% which means running 10 ga THHN. I'd run a single neutral, but you can't with GFCI outlets, only a double pole 20A GBCI breaker, which Square-D doesn't make.

Problem: Where can I get solid 10 ga THHN? I tried Home Depot and they only have stranded, which works I guess, but is a PITA to work with. Solid would be a lot better.

Anyone?

Bryan

[BillaVista]

In what way do you find stranded a PITA? Just when making the terminations?

depending on the size of your conduit and how many 90* turns etc. i would have thought pulling 4 10ga wires through the conduit would be a monsterous PITA??

If you're set on solid - check your applicable codes to see if it's prohibited to run NM cable wires in conduit, and if not, you could always rip some 10 ga NM cable to provide your solid conductors

[u2slow]

How about you pull 3 wires into the conduit with a junction box on the end.

From the junction box, split off with separate neutrals and install your outlet boxes and GFI plugs.

If GFI's didn't work this way, you would need separate neutrals at your service entrance. :rolleyes:

[threadkiller]

You can get solid wire at an electrical supply house. OR you can pull stranded wire through the conduit and make some solid wire pigtails to tie into your outlets.

Nah, fuck it! You're wiring TWO outlets! Sprout some balls and make the stranded work. GFI's aren't a bitch to wire up!

[willyswanter]

Use the stranded, it is much easier to deal with in junction boxes... 10ga solid isn't too bad but try #2! Anyway, when you make your connections to your outlets use crimp spade terminals. Crimp them on to the end of the stranded and clamp them down with the screw terminals on the side of the outlets. Nice, neat, and effective :D

[Oxjockey]

Use the stranded, it is much easier to deal with in junction boxes... 10ga solid isn't too bad but try #2! Anyway, when you make your connections to your outlets use crimp spade terminals. Crimp them on to the end of the stranded and clamp them down with the screw terminals on the side of the outlets. Nice, neat, and effective :D

Now that's a good idea.

I could make the stranded work, but I'm not confident in the connections. It's like the screws on the 20A outlets aren't large enough to safely accomodate the 10ga, nevermind stranded.

Edit: The Leviton 20A outlet only accomodates up to 12ga wire, so use of 10ga would technically be a code violation. I can't win. :crybaby2:

I'll stop at Graybar on the way home.

Thanks all! :beer:

[Just-fabricate-it]

Are you sure #12 won't work? I have a 1990 NEC and in table 310-16 (ampacities for insulated conductors not more than 3 in a raceway) shows #12 THHN copper good for 30A (but a footnote says no larger than a 20A breaker). It also shows #12 TW good for 25A. If you derate either of those by .8 you still have 20A (or more) capacity. If I'm missing something here sorry for confusing the situation.

[Oxjockey]

Are you sure #12 won't work? I have a 1990 NEC and in table 310-16 (ampacities for insulated conductors not more than 3 in a raceway) shows #12 THHN copper good for 30A (but a footnote says no larger than a 20A breaker). It also shows #12 TW good for 25A. If you derate either of those by .8 you still have 20A (or more) capacity. If I'm missing something here sorry for confusing the situation.

No! That's a great point! I've seen charts that list 30A rating, but others listing 20A. Of course, the 12ga is only supposed to be used for 20A, so am I derating based on that value or the actual "rating" which can be 30A as you mentioned?

I have 4 conductors in the raceway, 2 hots, 2 neutrals, 1 ground (obviously not a conductor). What pisses me off is the requirement to derate without any concern to fill. I could have a 2" conduit here, but hey, you still have to derate 80% for 4 conductors. :shaking:

[Eric]

What pisses me off is the requirement to derate without any concern to fill. I could have a 2" conduit here, but hey, you still have to derate 80% for 4 conductors. :shaking:


What you are forgetting is that conductors can get hot. When you put the conductors in a conduit, they are touching each other and are no longer in free air with 360* cooling. When you bundle conductors, they get hotter than single conductors. This is why you need to derate them.

According to 1999 NEC 310-16 (ratings) and 310-15 (deratings)

IF you use 12AWG stranded 75*THHN, it is good for 25A in conduit with 3 conductors and 20A derated (25x0.8) with 4-6 conductors.

If you use 12AWG stranded 90*THHN, it is good for 30A in conduit with 3 conductors and 24A derated (30x0.8) with 4-6 conductors.



If you want to use stranded wire and ring lugs, you need to get spcial outlets that are ring lug compatiable. This is what we use at work all the time. These are more expensive, but you don't have to worry about fitting bigger wire into the terminal clamps.

[Oxjockey]

What you are forgetting is that conductors can get hot. When you put the conductors in a conduit, they are touching each other and are no longer in free air with 360* cooling. When you bundle conductors, they get hotter than single conductors. This is why you need to derate them.

According to 1999 NEC 310-16 (ratings) and 310-15 (deratings)

IF you use 12AWG stranded 75*THHN, it is good for 25A in conduit with 3 conductors and 20A derated (25x0.8) with 4-6 conductors.

If you use 12AWG stranded 90*THHN, it is good for 30A in conduit with 3 conductors and 24A derated (30x0.8) with 4-6 conductors.



If you want to use stranded wire and ring lugs, you need to get spcial outlets that are ring lug compatiable. This is what we use at work all the time. These are more expensive, but you don't have to worry about fitting bigger wire into the terminal clamps.


I understand that completely, but I also think the larger available airspace with increased surface area should be considered. I think derating should be based on percentage of fill, personally, but I don't write the code. :D

I assume the 12ga 30 ampacity is a raceway rating, so I'm going to go with the 12ga solid 90*C wire, 4 ccc's in 1/2" conduit. Derated to 24A and because they're general use outlets, I'm happy to round down to a 20A OCD.

Sounds good?

[teajay]

Square D QO? A 2pole GFI is made...
Part # QO220GFI
http://www.aplussupply.com/break/sqd/qo/qo.htm
Then use 2 #12 hots, and 1 #12 neutral... You're good to go. Sure, a fault blows the other side too, but no biggie.

[Oxjockey]

Square D QO? A 2pole GFI is made...
Part # QO220GFI
http://www.aplussupply.com/break/sqd/qo/qo.htm
Then use 2 #12 hots, and 1 #12 neutral... You're good to go. Sure, a fault blows the other side too, but no biggie.


Looks like it has the arc arrestor, too? It's only $150! :eek:

Thanks, I looked but couldn't find one. :beer:

[u2slow]

You only need the two neutrals (actually "return" conductors) in that conduit if you are using two separate single-pole GFI breakers. This way has 4 current carrying conductors so you have to derate and increase your wire size.

You won't need to de-rate if you run a single neutral and use GFI plugs. You will only have 3 wires in the conduit (ok, 4 if you count the ground), and only the two "hots" are considered current carrying.

[Oxjockey]

You only need the two neutrals (actually "return" conductors) in that conduit if you are using two separate single-pole GFI breakers. This way has 4 current carrying conductors so you have to derate and increase your wire size.

You won't need to de-rate if you run a single neutral and use GFI plugs. You will only have 3 wires in the conduit (ok, 4 if you count the ground), and only the two "hots" are considered current carrying.

I just wound up wiring with 12 ga solid. I have two GFCI outlets, both 20A. Maybe some day I'll put in more outlets. :flipoff2: I think a 30A 220v is in my near future. Maybe some lights.

Thanks all! :beer:

[TJ Jim 6]

Sorry to jump in so late on this one, at this point it's only FYI.
1. THWN is what you want to pull, 90* rating
2. If you are installing conduit, oversize it, you can avoid derating.
i.e. 1/2" go to 3/4"
3. The only reason to pull #10 on a 20A circuit would be to compensate for voltage drop over a long distance.
4. If using RMC, IMC or EMT the conduit is the ground.
5. #12 can be used on a 30A motor circuit.


You can share the neutral for both GFI's just wire into the line side of the GFI's ONLY, and tail out the neut. at one recepticle. This way only one will trip.

Also, always check with your local electrical inspector, The NEC(NFPA 70) is the bare minimum, your area may have an additional electrical code.

Jim

[Oxjockey]

Sorry to jump in so late on this one, at this point it's only FYI.
1. THWN is what you want to pull, 90* rating
2. If you are installing conduit, oversize it, you can avoid derating.
i.e. 1/2" go to 3/4"
3. The only reason to pull #10 on a 20A circuit would be to compensate for voltage drop over a long distance.
4. If using RMC, IMC or EMT the conduit is the ground.
5. #12 can be used on a 30A motor circuit.


You can share the neutral for both GFI's just wire into the line side of the GFI's ONLY, and tail out the neut. at one recepticle. This way only one will trip.

Also, always check with your local electrical inspector, The NEC(NFPA 70) is the bare minimum, your area may have an additional electrical code.

Jim

I hate to disagree with what appears to be a professional, but:

1. THWN is what you want to pull, 90* rating
2. If you are installing conduit, oversize it, you can avoid derating.
i.e. 1/2" go to 3/4"
3. The only reason to pull #10 on a 20A circuit would be to compensate for voltage drop over a long distance.
4. If using RMC, IMC or EMT the conduit is the ground.
5. #12 can be used on a 30A motor circuit.

1) Isn't THHN rated at 90* in dry locations?
2) Derating will happen based on the number of conductors in the raceway; max % fill is based on conduit size
3) Derating occurs because I have 4+ cccs in a raceway.
4) Possibly, I've also grounded at the outlets
5) I thought you had to up the demands by 125%? Doesn't really matter, I don't have any dedicated motor circuits in the garage.

If I'm wrong, it's healthy for me to find out why, but I'm trying to accurately representing what I've found out in the last few weeks.

[Gummi Bear]

Sorry to jump in so late on this one, at this point it's only FYI.
1. THWN is what you want to pull, 90* rating
2. If you are installing conduit, oversize it, you can avoid derating.
i.e. 1/2" go to 3/4"
3. The only reason to pull #10 on a 20A circuit would be to compensate for voltage drop over a long distance.
4. If using RMC, IMC or EMT the conduit is the ground.
5. #12 can be used on a 30A motor circuit.


You can share the neutral for both GFI's just wire into the line side of the GFI's ONLY, and tail out the neut. at one recepticle. This way only one will trip.

Also, always check with your local electrical inspector, The NEC(NFPA 70) is the bare minimum, your area may have an additional electrical code.

Jim

1. THHN/THWN is indeed rated at 90*, however, you can only assume it's rating as being good for 75*. There are NO UL approved 90* terminals anywhere, and you must calculate based upon the lowest degree rating in a given circuit (typically the terminations)

2. Oversizing the conduit doesn't do shit for the derating, the code specifies conductors in a raceway, it doesn't care what size it is.

3. True, however, some jobs it is spec to pull #10 neutrals (becoming more and more common in the digital age) I do a lot of 'super neutral' systems, where you have a 200% neutral (grounded conductor) in your distribution panelboard (typically serving IG receptacles, or UPS loads)

4. Also true (per 250.118-2,3,4), however, most spec and municipalities will require you to pull a seperate grounding conductor. It is considered good practice to do so.

5. You need to read up on article 430 before coming up with stuff like that, it's a reckless statement. That is extremely subjective, learn the 5 steps to properly protect a motor and its circuit.

OX,
in the future, if you'll do some looking, Pass & Seymour, Hubbel, and the other major manufacturers make receptacles with saddle clamps (pressure plates) for wire terminations rather than the typical wrap-around-the-screw termination. This is the same type of term that better GFI's commonly come with. They accept #14 to #10 wire.

http://www.passandseymour.com/images/products/5262I.jpg

Personally I don't like using things like fork terminals at an outlet, it's a pain int the ass, and if you ever service it, or add to that circuit, they're difficult to deal with. For the cost of the terminals, and the labor to fart around with them, I'd rather buy a quality receptacle, and be done with it.

It is common trade practice to use #12 wire for a 20A circuit, don't sweat it. If someone really wants to nitpick, you'd have to derate for your ambient temperature, as well as the number of conductors in raceway, or number of jacketed cables in a bundle (and number of conductors in a jacketed cable if there are more than 3).

[speedaholic]

I found a little trick to help me with stranded wire at terminations and always passes w/ inspector. Don't remove all of the insulation from the wire when stripping, just slide it down about a 1/2" and wrap it around the terminal screw. Now you don't have and loose wires, there still in a neat bundle.

[teajay]

Ox: $150 a breaker a bit steep? Sure is... (wasn't actual advice... more like pointing out your initial point)

On Gummi's last point, I generally always try to use the outlets with the saddle clamps. They're very fast to install, dont fatigue the conductors while going around the screw, and sure beat the cheapies for quality.

[TJ Jim 6]

[QUOTE=Gummi Bear]1. THHN/THWN is indeed rated at 90*, however, you can only assume it's rating as being good for 75*. There are NO UL approved 90* terminals anywhere, and you must calculate based upon the lowest degree rating in a given circuit (typically the terminations)

2. Oversizing the conduit doesn't do shit for the derating, the code specifies conductors in a raceway, it doesn't care what size it is.

3. True, however, some jobs it is spec to pull #10 neutrals (becoming more and more common in the digital age) I do a lot of 'super neutral' systems, where you have a 200% neutral (grounded conductor) in your distribution panelboard (typically serving IG receptacles, or UPS loads)

4. Also true (per 250.118-2,3,4), however, most spec and municipalities will require you to pull a seperate grounding conductor. It is considered good practice to do so.

5. You need to read up on article 430 before coming up with stuff like that, it's a reckless statement. That is extremely subjective, learn the 5 steps to properly protect a motor and its circuit.

Sorry, I was out of town.
2. You are correct, and I stand corrected.

5. I misspoke on this one, I shoud have said, 30A overcurrent protection due to to start-up current to keep the breaker from tripping every time it starts.

Jim

[tippy99888]

Dam Gummi, I thought I'd get to have some fun then I got to your thread and seen you had it all wrapped up. Good job. I think the "super" neutral came about from people thinking they know what their doing. Just because the neutrals get tied together at the panel, doesn't mean you can grab the first white wire you see and use it. I also run a ground wire, I hate seeing the pipe used as the ground. I've seen too many shabby installs conduit is barely in the coupling or where the pipe gets hit or bent and isn't connected at all. Had an electrician at a sister plant die from a lack of ground. He was merely changing the tubes in a flouresent light when his number was called. The light was near a heater of some sort, and the heater was installed with SOW cable instead of liquid tight (lazy install). For some reason the SOW had a broken ground wire, (maybe it was used I don't know, not the point) But one of the leads in the heater was shorting to ground the whole time and when he brushed up against the heater he was the path to ground through the light, and got fried.