what size wire for my 220v outlets?

[Jim Ketron]

I need some help on ? size wire to run
I already have 12-2 wire for the 120v runs
what amps do most 220v shop tools use
some of the tools that Im thinking of geting in the future(220v)Grizzly cabinet saw I think it pulls 18amps and a larger DC 15 amps and a AC ? on the amps.
Jim

[Dennis Peacock]

I need some help on ? size wire to run
I already have 12-2 wire for the 120v runs
what amps do most 220v shop tools use
some of the tools that Im thinking of geting in the future(220v)Grizzly cabinet saw I think it pulls 18amps and a larger DC 15 amps and a AC ? on the amps.
Jim

Jim,

Most 220V tools require a 30 Amp circuit. That means you'll need to run a 10-2 w/grnd to the outlet. 10-2 copper wire is normally good for up to 40 Amps on start loads and will sustain 35 Amps on constant load. All my tools that are 220V run easily on 10 guage wire. I even have my cyclone on 10 guage wire and it peaks at 42 Amps under start loads with no problems here.

Just in case you need to know:
12-2 w/grnd is good for up to 20 Amps.
14-2 w/grnd is good for up to 15 Amps.
10-2 w/grnd is good for 30 to 35 Amps.
#8 Aluminum is good for 40 Amps.
#6 Aluminum is good for 50 Amps.
#4 Aluminum is good for up to 70 Amps.
1 Aught Service Cable is good for 100 Amp service
4 Aught Service Cable is good for 200 Amp service.

Extension cords are good for almost everything!!! :eek:

[Steven Wilson]

I need some help on ? size wire to run
I already have 12-2 wire for the 120v runs
what amps do most 220v shop tools use
some of the tools that Im thinking of geting in the future(220v)Grizzly cabinet saw I think it pulls 18amps and a larger DC 15 amps and a AC ? on the amps.
Jim

20A 220v circuits will handle most 3hp or less motors, 30A will handle most 5hp motors. Wire sizes (excluding derating for various reasons) would be 12ga and 10ga respectively. Besides wire sizes you will need to be aware of box fill and most likely conduit fill restrictions. I suggest that you get a copy of the NEC and read up on branch circuit wiring.

[Steve Stube]

I used a minimum of 12 - 3 w/g for my 220 volt outlets. I ran 8 or 10* - 3 w/g for the 5 HP compressor ckt. and spotted in 4 more 40 Amp 220 boxes for other 5 HP equipment (now that is real 5 HP motors the 28 Amp @ 220V kind). Welder outlets are wired with 6 - 3 w/g.

Black and Red wires carry your 120V each, White the netural (or return of any unbalance) and the ground(bare wire) is available as an equipment ground.

I have been watching your shop come together and enjoying the updates with photos, looks great!

*I had posted 10 gage originally but now I think maybe it was 8 - I will check it out tomorrow. It's late and my memory has gone south.

[Rob Russell]

Jim,

Most 220V tools require a 30 Amp circuit. That means you'll need to run a 10-2 w/grnd to the outlet. 10-2 copper wire is normally good for up to 40 Amps on start loads and will sustain 35 Amps on constant load. All my tools that are 220V run easily on 10 guage wire. I even have my cyclone on 10 guage wire and it peaks at 42 Amps under start loads with no problems here.

Just in case you need to know:
10-2 w/grnd is good for 30 to 35 Amps.


Dennis,

FYI, #10 is limited by the NEC to a 30 amp breaker. A breaker will carry around 10x rated current for startup loads, unless it's a "long" start in which case you need a HVAC-rated breaker.

Jim,

If you're planning on running #10, do yourself a favor and use the largest boxes you can. I don't know if you're planning to sheetrock, but the 4 11/16 x 4 11/16 2 1/8 seems cavernous until you're trying to stuff a bunch of stiff wire into it. Give yourself the extra room.

If you're running conduit, you need to pull individual conductors. 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.

Rob

[Bob Hovde]

[QUOTE=Steve Stube]I used a minimum of 12 - 3 w/g for my 220 volt outlets. I ran 8 or 10* - 3 w/g for the 5 HP compressor ckt. and spotted in 4 more 40 Amp 220 boxes for other 5 HP equipment (now that is real 5 HP motors the 28 Amp @ 220V kind). Welder outlets are wired with 6 - 3 w/g.

Black and Red wires carry your 120V each, White the netural (or return of any unbalance) and the ground(bare wire) is available as an equipment ground.

Now I'm confused. :confused: I understand the 20amp/30amp break, but not the 10/2 - 10/3 break. I assume that's for 1-phase vs. 3-phase motors. When will the average home shop need the 10/3 (3-phase) service? I also don't understand why Dennis went from copper to aluminum. I was planning on 6ga copper for my 60 amp service (80 ft from the house panel to the separate garage).

Bob

[Jim Becker]

Bob, the copper vs aluminum decision is often made for cost reasons on thick service cables...aluminum is less espensive but is also physically larger. Some special care is also required when terminating it relative to corosion prevention. Also, the "10/3" designation has nothing to do with 3-phase. It's just an indication that the cable has three conductors plus a ground...usually...the exception being "cord" material off the roll at the home center where it has two conductors plus ground. If you buy "Romex" cable designated as 10/2 (or 14/2 or 12/2), it will have two conductors plus a ground. X/3 "Romex" will have three conductors plus a ground. Most 240v equipment we use in our shops only requires two conductors plus ground. A third conductor (typically used as the "neutral"), if available, isn't used for those devices but would be necessary for a dual voltage situation where something on the device requires 120v, such as a clock, timer or light. Please note that some localities require that x/3 cable be pulled, even if the third conductor is not needed for the application.

Jim K...I'd suggest you pull 10 guage cable for your 240 volt circuits just to cover yourself for future tool purchases. The cost difference is negligable! While most things run fine on 20amp, it really depends on the tool. My MM16 is using a 20amp circuit as is my TS and Lathe. But the "aircraft carrier"-like FS-350, with it's 4.8hp motor requires a 30amp feed. With 10 guage wire, you can easily upgrade (or downgrade) the circuit to or from 30amp by changing the breaker, outlet and plug(s) at any time...that beats pulling new wire any day!

[Dennis Peacock]

I also don't understand why Dennis went from copper to aluminum. I was planning on 6ga copper for my 60 amp service (80 ft from the house panel to the separate garage).

Bob

Bob,

I'm an Ex-electrician. We always ran the "big wire" in aluminum due to the cost. So I quoted you what I ran in 500+ houses. Stove, dryer, HVAC unit and all got aluminum wire. The rule we used was provided by our inspector: If you use Aluminum wire, you must go one size larger in wire guage. I personally would run everything in copper, as what I did in my own shop. I didn't like aluminum wire then and I don't like it today.

Check the service cable on your house going to your panel and the wire going from your meter-base to the pole (commercial power source). You will find "aluminum wire". ;)

[Rob Russell]

... Stove, dryer, HVAC unit and all got aluminum wire. The rule we used was provided by our inspector: If you use Aluminum wire, you must go one size larger in wire guage. I personally would run everything in copper, as what I did in my own shop. I didn't like aluminum wire then and I don't like it today. ...



Cheaper is right, especially with copper prices cranking up recently. There are a number of cases now where you need to go up 2 gauges to get the matching ampacity out of aluminum that you do copper (ex. 100 amps @ 75 degrees [typical residential breaker terminal temp rating] = #3 copper but #1 aluminum).

The other problem with aluminum is oxidation. A lot of DIY'ers don't use antioxidant on the exposed aluminum so you can get corrosion over time at your connection points (and that's a bad thing). All the big box stores carry OxGard or a similar antioxidant. It comes in a little tube that you spread on/work into the exposed aluminum (I used a glue brush on the OxGard when I ran aluminum SER for my subpanels).

[Bob Hovde]

Thanks Jim and Dennis,

It's starting to come back, now . . . :rolleyes: I think 10/2 in my (separate) garage is fine - no appliances there.

Bob

[Ken Garlock]

Bob, ....

Check the service cable on your house going to your panel and the wire going from your meter-base to the pole (commercial power source). You will find "aluminum wire". ;)

Dennis, it is my understanding that aluminum wire is used up to your meter because electric utility companies are not required to abide by the NEC, and/or local regulations, rather by what the federal govt. allows.

I was told by a Texas licensed electrician that the only city in Texas that permits the use of aluminum wire in residential construction is San Antonio. Copper is clearly better for house wiring, and I don't believe the cost savings is worth the potential fire risk due to a bad junction.

That is my story, and I am sticking by it. :D

[Chris Padilla]

Jim,

I'm putting #10 EVERYWHERE in my garage remodel. A 500' spool at HD is $50 and I have black, white, red, and green. These are all stranded, not solid core, too.

I'm also running everything through 3/4" flex conduit (so far!) and plan to keep only 4 wires per conduit if I can help it so I don't get nailed too hard by the deregulation that Rob points to above. 4 #10s pull nicely through the 3/4" flex.

I'm also running #10 everywhere because I didn't want to purchase rolls of #12 or #14...too much money and too many rolls to deal with.

Yes, I'm discovering that the flex is a pain and while it flexes...it doesn't flex as much as I would have liked it to in certain situations (I'll update my "Padilla's Garge Gut/Remodel thread soon). It is also kinda painful to cut but I'm getting the hang of it.

I'm mainly putting flex in for future upgrade (or downgrade) ease in my shop. I plan to run a few empty conduits here and there with some empty junction boxes here and there, too.

All my boxes are the large 4 11/16" x 4 11/16" x 2 1/8" and all will get 5/8" mud rings.

I plan to multi-wire each 120 V box (2 duplex plugs, each on a different circuit but on the same breaker so 1 duplex plug will get a black hot and the other will get a red hot). Keep in mind you only need 1 white (nuetral) for this wiring scheme and of course, the green ground.

If you plan to use the 240 V twist-locks, I highly suggest you mount the boxes very, very well. Those plugs put some strain on the outlet due to weight just hanging there as well as effort to plug in and out.

[Rob Russell]

... so I don't get nailed too hard by the deregulation that Rob points to above ...



Umm - derating ??? ;) Note that it's 4 or more current-carrying conductors. The grounding conductor doesn't count.

I agree with the rest of your post. A quick tip. When working with stranded wire, twist it counter-clockwise before forming a loop to go around your terminal screws. It'll stay tighter. http://www.fadzter.com/smilies/thumbsup_old.gif

Rob

[Chris Padilla]

:D Okay, deRATING! I knew there was something funny about that when I typed it out! :D

Thanks for the tip on the derating and green wire...I should be in good shape then.

I planned to get those outlets that are back-wired (I think that is the correct term) and you just insert the wire and clamp down on it...no loops to make. Very, very nice.

[Rob Russell]

I planned to get those outlets that are back-wired (I think that is the correct term) and you just insert the wire and clamp down on it...no loops to make.

If you're talking about the true back-wired receptacles, where the side terminal screw is part of the clamping mechanism and tightening the side screw also tightens the clamp on the back-wire - that's fine.

If it's a back-stab receptacle where you push the wire into a hole and a spring plate holds the wire in - you don't want to use those. The spring plates can loosen up over time, the connections heat up and cause fires.

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.

Rob

[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.

---------------------------------------------------------------

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 (http://www.jhlarson.com/ind_table.htm), 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.


==================================================





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. http://www.fadzter.com/smilies/bash.gif

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 :rolleyes: ). 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.... :D I just backed off and I ask him questions here.... :D ;)

[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.

[Rob Russell]

Does each wire running into a box need to be cut and wire-nutted?
No. You can have conductors that pass through a box without terminating in the box.



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?
Yep. See above.



Should I put a service loop in those wires even though they aren't cut?
You don't need to. Being the somewhat anal type about things like that, I'd probably use some of the plastic cable clamps to keep the "through" wires tucked to the sides of my boxes. I know how much you like pictures, so what I mean are these things.
http://www.mcmaster.com/catalog/110/gfx/small/8876tc1s.gif



Am I making sense here?
As much as you ever do. :D

==========================================

Back to derating, and some background info:

From NEC table 310.15(B)(2)(a):
<table border="1" width="50%">
<caption>Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable</caption>
<tr><th width="25%">#Current Carrying Conductors</th><th width="25%">Derating Factor</th></tr>
<tr><td>1 - 3</td><td>100% (no derating)</td></tr>
<tr><td>4 - 6</td><td>80%</td></tr>
<tr><td>7 - 9</td><td>70%</td></tr>
<tr><td>10 - 20</td><td>50%</td></tr>
</table>

Unadjusted Ampacity for #10 THHN/THWN @90&deg; = 40 amps.

You can run up to (3) 30 amp/240v circuits through a run of conduit, wired with #10 THHN/THWN.
You can run up to (10) 20 amp/120v circuits through a run of conduit, wired with #10 THHN/THWN.
You can run up to (3) mixed 30 amp/240v and 20 amp/120v circuits. It's only 3 because the 240v circuits(s) can only withstand 80% derating.
Put 8 CCC's in a conduit and you're looking at 70% derating which would drop the ampacity of the #10 to 28 amps. That's no problem for the 120v/20 amp circuits, but that causes a problem for the 30 amp 240v circuit. To further confuse things, there is a rule that says you can round up to the next standard breaker size (which would be 30 amps), even if the derated ampacity is 28 amps. That means you could run (4) 30-amp circuits with wire derated to 28 amps but protected by a 30 amp breaker. Confused yet? :confused: If you run a multiwire circuit, the neutrals don't count. If you're running in a basement or garage where you need GFCI for the 120v receptacles, you need separate neutrals which do count. Confused now? :D

The simplest thing would probably be to run 2 sets of conduit. Run 1 for 120v circuits and 1 for 240v circuits. You could run basically as many 120v circuits as you need in the "120v conduit" and up to (3) 30-amp/240v circuits in the "240v conduit". I say (3) 240v circuits because an AHJ can't argue that you've exceeded the derated ampacity of the #10, even if 240-3(b)(1) let's you. You could do the install so the conduit runs are close to each other with your outlet boxes in neat clusters.

Figure out how many circuits you want to run and we'll talk what size conduit you should run.

Holler if any of this doesn't make sense.

Rob

[Chris Padilla]

Sounds good (and scary) Rob! Thanks for taking the time and effort to post this...I really appreciate it! :)

[Rich Konopka]

keep going Guys this is interesting reading :)

[Chris Padilla]

Ask some more questions, Rich! :) I think I'm good. :D

[Rob Russell]

Ask some more questions, Rich! :) I think I'm good. :D

Chris, you're not good yet! http://www.fadzter.com/smilies/spanka.gif

You haven't identified how many circuits you want to run. Conduit fill could be an issue and force you to upsize, depending on what size conduit you're planning to run.

Rob

[Rich Konopka]

Ask some more questions, Rich! :) I think I'm good. :D
I don't have any real tough questions ... I'm just reading the thread and it is something that I will be wrangling with if I ever finish my other projects. I have limited electricity in the shop now. However, I just had a new 100amp sub panel installed and will be getting ready to do some wiring. I plan on doing the rough wiring and have my electrician do the final hookups.

My biggest question/challenge is where to begin from a design perspective. I think I have the lighting down. The more the better, alternate circuits, eight footers, and emergency lighting from the main panel.

Outlets, I plan on quads every 4 ft around the bench areas. I also plan on having multiple 240's scattered throughout.

When I lay out the outlets I am going to use 3/4" plastic conduit. How many outlets can I string on one circuit? 3,4,5?

Any ideas,pointers,links on the design aspects would be great !

[Chris Padilla]

Rich,

You need to figure out what the current load will be on that circuit and that will determine how many things you can have plugged in and running at the same time.

I'm sure the NEC bible has some table or numbers for this but I don't know them. It also relies on your ability to predict your future needs.

Odds are good that you will only be running 1 maybe 2 120 V appliances (tools) at the same time. In that case, you could almost have as many as you want.

Look around your house and note your current set-up. How many outlets are on a circuit in your home? That will give you a place to start. I think 3-5 is perfectly safe.

For the quads, I'd multi-wire them, which gives you two circuits per run/box.

Think about dedicated circuits, too. For example, my dust collector will get it's own 240V/30A circuit. Some folks like to put their air-compressors on dedicated outlets, too. If you have an A/C or furnace, that might work best on its own circuit.

Fun, eh? :D

[Rob Russell]

There is no limit on the number of receptacles you can have on a residential 120v circuit.

The only real NEC restrictions on a circuit would come if you have continuous loads, and that's highly unlikely in a home workshop.

FYI, you could effectively run up to (5) 120v circuits through 3/4" schedule 40 PVC conduit if you're pulling #12 THHN/THWN. That's going to be a lot to pull through a 3/4" conduit, though. If you really want that many separate circuits, I'd run 1" - you get a lot more room.

[Richard Blaine]

There is no limit on the number of receptacles you can have on a residential 120v circuit.

Check with the local permitting authority. In my neck of the woods, they limit you to 13 outlets on a single 20 amp circuit. Obviously, they don't expect you to be using them all at one time, and I doubt you will in your home shop. The extra outlets are there for convenience.

Again, as others have said, make dedicated circuits for the big tools whether or not they are 220v and run a couple of 20A circuits for hand held tools. You may also wish to run a couple of 15A circuits for you lights rather than use 20A -- the #14 is a little easier to work with and it will provide quite a bit of lighting before you need to upgrade to 20A.

[Chris Padilla]

I'm running some 8/3 from the main panel to my new A/C. The 8/3 was leftover from the old A/C run so I figured, what the hey, this is pricey stuff! The new A/C will be in a different spot but either way, the 8/3 will run under my house in the crawl space to reach its final destination.

Since I'm running 8/3, I wanted to tap-off that line and run some lights/outlets under the house to make future crawls easier on me.

I happen to have a sub-panel that I just pulled out from my garage that I was thinking to run the 8/3 into under the house.

My question:

What is the maximum size breaker I could put into the main panel to feel the sub-panel over the 8/3? My HVAC guy says the new A/C will need a 40 A breaker.

Could I put a 50 A in the main (yes, I have one laying around doing nothing), and a 40 A in the sub? I was then going to put in a 15 A in the sub, too, for lights and a couple outlets. Or, could/should I put a 40 A in the main and another 40 A in the sub? If memory serves, I think #8 handles 40 A max.

Being that I want to put a sub-panel in a crawl space, are there any special rules for mounting the panel? I was thinking to mount it in between joist bays but facing down. Or, perhaps I could hang a sheet of plywood and mount it more "normally" facing...maybe even make it "swing down" or something a bit fancy?

Thoughts?

[Rob Russell]

Chris,

Ignoring voltage drop, #8 can be protected with a 50 amp breaker - if you're running something like BX. If you're running NM, you can only use a 40 amp breaker. This is because of a temperature restriction on NM. If you are running BX, you could put in a 40 amp breaker in the 50 amp subpanel.

Now, to installation. You need a "working space" that is 30" wide x 3' deep x 6.5' tall. There are some special situations, but face down, between the floor joists in a crawlspace doesn't meet the NEC requirements and isn't likely to pass muster with the AHJ for an exception. You can ask, but don't be surprised if they say no. I'd seriously come up with plan B.

If your crawlspace is dirt floor, it's probably considered a "damp location" in your area, and that means you can't run normal NM. If you have a concrete floor in the crawspace, it's a "dry location" like a normal basement. If in doubt, check with your AHJ.

FYI, you will need a light near the subpanel.

It may be easiest just to run the 8/3 to the A/C and give up on making that a subpanel.

Rob

[Chris Padilla]

Rob,

Thanks for your comments. I see "sub-panels" all the time that don't meet the spacing requirements you just outlined. Take, for example, a single or double breaker small box used for shut-off near an A/C.

I guess my question is what is defined as a sub-panel and must meet those dimensions? The sub-panel I'm thinking to use is, I believe, a 70 A one. It has room for 8 breakers.

My crawlspace is a dirt floor but I would say it is far from damp!! It is dry as a bone under my house and I'm not in a flood plain, either.

Hmmm, there is another place I could put the sub-panel and that is the under-the-stairs space I have in my garage. However, it is not likely to meet the dimensions you outlined above either although it would be normally oriented and in a dry location. Hmmm.....

think, think, think...think, think, think.... (sorry, too much Winnie the Pooh...my kid is in love with the DVDs we have....)

[Rob Russell]

I see "sub-panels" all the time that don't meet the spacing requirements you just outlined. Take, for example, a single or double breaker small box used for shut-off near an A/C.


That's because that little thing you called a "shut-off' is really a disconnect and isn't being used to feed any other load than the A/C.



I guess my question is what is defined as a sub-panel and must meet those dimensions? The sub-panel I'm thinking to use is, I believe, a 70 A one. It has room for 8 breakers.

Hmmm, there is another place I could put the sub-panel and that is the under-the-stairs space I have in my garage. However, it is not likely to meet the dimensions you outlined above either although it would be normally oriented and in a dry location.

Think "panelboard" used to feed branch circuits. That's where I'd worry about the working space. It is possible that the working space requirements apply to something as small as a disconnect and that AHJ's routinely ignore the reqs. I can't speak to that and, at the moment, can't chase down the code to see if that section applies to disconnects too.

If you're stuck for a place - ask your AHJ what they will allow. Another alternative is to put the subpanel outside, just use a weatherproof enclosure. They make 'em.