what size wire for my 220v outlets?

[Chris Padilla]

Rob,

Correct--back-wired. I did some research on the Leviton website and that is where I learned about them. They are rated for #10-14 wire so I'm in good shape as I plan to use either the commercial or industrial style.

I'm shocked back-stab outlets are legal to use....

[Jim Becker]

I suspect you're talking about the true back-wired devices, for example the Leviton commercial or industrial specification grade ones. Those are rated for #10 solid or stranded conductors in the back-wire holes. You do need to make sure the receptacles you buy are rated for #10 stranded, because that's what you're using. I don't know if all back-wire receptacles are rated by the manufacturer for #10 stranded. Probably are, but it's worth checking.

I always use the Leviton commercial grade for this feature (I hate having to twist wire around a screw if I can avoid it), even in the house...and learned early on to re-tighten them after tightening them! Sometimes, they don't go all the way snug the first time even though they seem tight. The ones I used from the 'Depot worked fine with a #10 as I re-used a #10 cable in the kitchen renovation for a 120v circuit to the gas range that was originally the feed for the old 240v cooktops that went "bye-bye"...

[Chris Padilla]

Jim,

When I purchased my twist-lock 240 V/30 A plugs, I noticed how nice it was to wire up and so I went searching to see if 120 V (15/20 A) outlets had such features. I tell you I wasn't looking forward to wraping #10 around those screws.... Leviton's website had everything I wanted!

[Paul Downes]

All of my machines with the exception of my compressor only require a 20 amp breaker. Therefor I am running 12-2 for all of these circuits, excepting the compressor circuit which is aluminum wired for a few days more until I pull in 10-2 copper for it. Aluminum is not desirable because of the oxidation issue. I also would think that in an outdoor building such as my pole barn, the aluminum would see more temperature fluctuations that could increase both the chances of oxidation and lossening of wire fasteners. It's not worth the risk of a loose/oxidized connection building up heat and burning the place down.

My understanding is that the only need for 12-3 or 10-3 is when a machine requires a control feed of 110 volts. I'm not sure but the only time I might need this is perhaps on a power feeder? I am using the 12-2 because I had a 500ft spool handy. I checked with my master electrician buddy and he said it was more than adaquate, concidering the length of the runs.

[Donald Hofmann]

In my shop I ran 12 guage for my 220V outlets. My biggest motors are 3 hp on the Unisaw, planer, and cyclone.
If I had excessively long runs, I would run 10 guage from the breaker panel to a junction box, and then from there make two or three runs to my outlets using 12 guage.

I typically have about 3 outlets per circuit breaker. Being a one man shop, I don't expect to run more than one tool at a time, other than my Oneida 2hp commercial which is on a separate outlet.

[Jim Ketron]

Thanks Men I have around 40' of 10-3 wire a sparktrician gave me today on the jobsite.
I also have 300' of #6 stranded wire (another sparky gave me) I was going to put a 50 amp box in and I didn't think it would be enough.
I also have about 125' of #2 aluminum (4 wire) direct bury( another free-be) I have done some research on the net most say not to use it for 100 amp service so I may use a 100 amp box and try to find a 90 amp breaker to run my sub panel from the house.
Jim

[Chris Damm]

http://www.jhlarson.com/ind_tables/calc_wiresize.htm

[Rob Russell]

http://www.jhlarson.com/ind_tables/calc_wiresize.htm

Be really careful using that calculator. It gives you theoretical ampacities which don't necessarily apply to what we'd need to install. The fine print at the bottom of that page sez:

This Calculator will determine the minimum size conductor needed based on a 3% Voltage Drop. It does not take into consideration other factors such as minimum ampacity based on the National Electrical Code Table 310-16. (Allowable ampacities of conductors). Consult The NEC for further details.

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I do use the JH Larson site as a handy reference and have posted it here before as a useful tool. Go to Tools for the Trades, which is the main page and select Allowable Ampacities of Insulated Conductors.

If you look in there, to use some of Jim's examples from above (use:

• #6 copper is good for 65 amps
• #2 aluminum is good for 90 amps.

Check out the link for3 Wire Residential Single-Phase Services. You'll see that #2 aluminum is good for a 100 amp service. There has been a considerable amount of discussion on a couple of the electrical boards I lurk on about how unclear the NEC is about which table to use for determining conductor size for a subpanel feeder. Jim's approach of using a 90 amp breaker is certainly the safest approach. FYI Jim, you can get a 90 amp breaker on ebay for way less than you'll get it locally if you're patient.

Rob

[Jim Ketron]

Im having a hard time finding a 90 amp breaker at HD or L but I have a few electrical supply places to look for them $$$
I have seen the talks about the 100 amp and #2 aluminum on several diff electrical forums. like the old saying better safe than sorry.

Im going to start runing wires this weekend in the new shop. hope to get in there in a few weeks!
Jim

[Rob Russell]

Jim,

Another approach is to run the #2 UF and use a 75 amp breaker. You can always "under-breaker" the wire. If you use the aluminum, don't forget to get some OxGard to put on the ends.


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With conduit, you also need to worry about derating because of an ampacity adjustment factor ifyou have more than 3 current-carrying conductors (CCC's) in a raceway (conduit). Put simply, that means if you have (2) 240v, 30-amp circuits pulled through the same conduit - that's 4 CCC's which means an adjustment factor of 80% from table 310.15(B(2)(a). That means, to get a 30 amp circuit, you'd need to pull #8. Conduit is nice for expansion, but it can get tricky.

I goofed on my earlier post. I used the right table, wrong column, when I chose the ampacity for #10 THHN/THWN that we are derating. When derating conductors for bundling, we can use the column with the highest rated ampacity for that conductor. THHN/THWN is the typical individual conductor we'd pull, and we'd use the 90 degree column ampacity ratings. In that case, #10 THHN/THWN has an ampacity rating of 40 amps. So, even at derating to 80% based on 4-6 current carrying conductors in a raceway (conduit), #10 would be good for 32 amps.

The bottom line is that you could run (3) 30-amp 240v circuits through a single conduit using #10 THHN/THWN. You could fit the (6) current-carrying conductors + 1 grounding conductor in 3/4" PVC conduit. If I were running that much I'd use 1" to make the pulling easier if the runs were long.

Sorry for the earlier goof.

Rob

[Chris Padilla]

Geeeeez, ROB!!! What are we payin' ya for???? This might make my life easier now that I can pack a few more circuits into 1 conduit.

Let me ask you this: Does each wire running into a box need to be cut and wire-nutted? In other words, could I just run wires through a box as a means to get elsewhere for that particular circuit and have them go straight through? Should I put a service loop in those wires even though they aren't cut? Am I making sense here?

[Rob Russell]

Chris,

I'll think about that - may need to check a coupla code sections. My gut answer is it's no problem to have the wire running straight through, though.

Rob

[Steven Wilson]

In other words, could I just run wires through a box as a means to get elsewhere for that particular circuit and have them go straight through?

You can run wires straight through. IIRC you only count one of the ground wires though. You'll want to look this up in the NEC (you do have a copy ). If you do this you'll need to take into account the volume of the box, volume of the receptical plate, number of wires, wire guages, and number of recepticals. There is a formula that you need to follow. In general you'll want to have the largest box that you can find and the receptical plate with the most volume, otherwise the box fill calculation will be the limiting factor and not the size of the conduit. This is also where running 10ga wire for everything (20A and 30A circuits) will bite you.

[Chris Padilla]

Well, I'm using the largest boxes I can find and those are the 4 11/16 x 4 11/16 x 2 1/8 inches so that will help. On top of that will be a 5/8" mudring.

I suppose for certain boxes that may contain a fair amount of wires, I could drop down to the 4" box but use 1 1/2" extender rings unless the 4 11/16" boxes come with 1 1/2" extender rings. I haven't ever seen any but I have yet to visit a real electrical supply house. HD and my local h/w store are the only places I've visited. In fact, I have only found 4 11/16" 1/2" mudrings at these places...nothing else.

Copy of the NEC? Uh, yeah, Rob has my copy and he said something about "cold dead fingers" and "prying" and such.... I just backed off and I ask him questions here....

[Steven Wilson]

Chris, I'm not sure about using the extender rings. If you look at some of the receptical plates you'll see a volume number stamped on them (such and such cuft). You add the volume of the box plus the volume of the receptical plate and that gives you the volume you have to work with. If you don't have a copy of the NEC then go to the library and look it up. Better yet, Xerox a copy of the two or three pages that you'll need and then file it away. IIRC, you can run (2) 20A, 12ga circuits and (1) 30A, 10ga circuit through 3/4" conduit with a large box and a receptical plate that takes a 20A or 30A twist lock receptical just fine. You can also run (2) 30A circuits, but not (3) 30A circuits or (2) 20A and (1) 30A circuit.