what size wire for my 220v outlets?

[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.

Am I making sense here?

As much as you ever do.

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

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? 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?

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.

[Rob Russell]

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

Chris, you're not good yet!

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.

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?

[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.