wiring design

I'm trying to put together a wiring design for the new shop. I already have a separate circuit dedicated to lighting. I'm trying to decide what to do about the circuits to run the tools. I figure on running two 120V/20A circuits for the smaller stuff. Additionally, I figure on running two 240V/30A circuits. I plan to put the dust collector on one, and the other tools on the other. The dust collector is packed away in a box at the moment, so I can't take the specs off the motor (and I can't find them online), but I'm quite sure a 30A circuit will handle it. I was able to take the motor specs off the other devices: table saw (230V/8.6A), jointer (230V/7.1A), and band saw (230V/6A). I don't plan to run more than one of these other units at the same time. Frankly, I could probably do 20A on the 240V circuits, but I just think 30A would give me more flexibility in the future if I ever needed to plug in something that needed extra current. The longest run would be no more than 45 feet. I'm open to comments on the above.
As for the wiring itself, I think I'm looking at running 3 - #12 wires for the 120V circuits (2 hots and a shared neutral) and 4 - #10 wires for the 240V circuits (4 hots). No ground as we are required to use metal conduit around these here parts. Based on the conduit fill chart, I'm looking at roughly 25% fill with 3/4" EMT. Any reason to bump that to 1"?
Any comments on this plan?
todd
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"todd" wrote:
> I'm trying to put together a wiring design for the new shop.
You will save money by standardizing on #10AWG for 30A circuits and #12AWG for 20A circuits.
This will allow you to buy full spools of wire to get best price.
Dedicate a 2P-30A C'bkr for each load. If you do this up front, you will have taken future expansion into consideration.
If down the road you buy added equipment, then is the time to consider sharing a receptacle, not now.
Start with a 12/24 load center equipped with a 60A Main.
12/24 translates into 12 full size c'bkrs or 24 half size c,bkrs.
I'd use 1/2 size c'bkrs.
Load the panel full of 2P-30A c'bkrs, then fill remaining spaces with 1P-20A c'bkrs.
C'bkrs are a relatively low cost item and the price is only going to go up.
If code will alow you, run 3/4" plastic conduit, otherwise you are stuck running thin wall.
Use double gang boxes and install 2 gang, 20A, duplex receptacles every 8-10ft or closer if the spirit moves you. (This provides 4 outlets/gang box)
Use double gang boxes for the 240V-30A receptacles. You will appreciate the wiring space.
Running a neutral with the 240V circuits is optional.
It all depends if you need a 120V circuit for the equipment you are using.
DON'T try to double up runs to save some conduit. Sooner or later, it will come back to bite you.
Run individual conduit runs.
Good luck and have fun.
Lew
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All sounds good to me.

Yes -- it will be *much* easier to pull the wires through 1", or even 1-1/4", EMT than through 3/4".

Sounds like you've done your homework pretty well.
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Doug Miller (alphageek at milmac dot com)
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Sounds pretty good. My comments: -about "shared neutral" on your 120 volt circuits. That neutral has to carry full load current, so it should NOT be shared. You could get away with a "shared" green wire, but you arent'using one.
-It's the 240 volt curcuits where you could "share" a neutral (or go down a size). I suggest that you DO run a neutral to those boxes. One of these days you may buy a 240 volt appliance of some sort that also uses 120 volts, like maybe for a control circuit or a fan. Then you'd need the neutral.
You didn't say how big your shop is, but I'd consider 120 volt receptacles every 6 feet, and at 4' height. Every other receptacle would be on a different circuit. It there more than one door to the shop? Consider 3-way light switches.
Pete Stanaitis -----------------------------------------------
Doug Miller wrote:

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That is incorrect. On a properly installed shared-neutral circuit, the neutral conductor carries the *difference* between the currents on the two hot conductors, not their sum. For example, if one side is pulling 12A, and the other 4A, the current in the neutral conductor is 8A, *not* 16A.
"Properly installed" means with the two hot conductors connected to *opposite* legs of the 240V service via a double-pole circuit breaker.

Phooey. It's not even needed on the 240V circuits.

Incorrect again. The neutral conductor in a branch circuit is not permitted to be downsized. The *grounding* conductor is, on circuits rated 40A and higher, but not the neutral.

Not too many woodworking machines fall into that category...
--
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Doug Miller (alphageek at milmac dot com)
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All good advise above. But consider putting in even MORE outlets. I have one every 8 feet (length of conduit) around 3 walls, one for 120vac, one for 220vac. And about every other day I wish for an outlet halfway between! All tools are on rollers except the table saw, so they get moved around as need be. Guess what limits their move???
As to height, I put mine at chest height or a little higher. Why reach down???
One other thing. I'm always needing more 120vac outlets near the main workbench. I have a 4 plug outlet, one for a heater, one for a radio, one for a lamp, leaving a single one for Skill saw, power drill, belt sander, shop vac, and whatever else I come up with. Wish I had put in a 50 plug outlet!
Hope this helps.
Regards.....
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I hate this practice. It's good if you're the one that ever touches the wiring, but it sucks if someone else gets into the box and assumes neutrals for every branch circuit. For a home application, the cost savings in sharing neutrals is so negligible that it's almost stupid to go this route. All it takes is someone to get inside the box - even a licensed electrician, and move a breaker and all bets are off. Just run the neutral for each branch.

I'm betting that what he meant here was to downgrade the circuit instead of what it looked like - reduce the wire size.
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-Mike-
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Anyone who assumes two neutrals for a circuit that comes off of one double-pole breaker shouldn't be working on AC wiring anyway. :-)

Which is one of the reasons I specified using a double-pole breaker: precisely to eliminate the possibility of moving one side of the circuit to the same leg as the other side.
The other reason is that with a double-pole breaker, it's not possible to kill only one side of the circuit (and unknowingly leave the other side live, when doing maintenance).

Dunno -- looked to me like he meant reduce the wire size, and that's a no-no.
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Doug Miller (alphageek at milmac dot com)
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D'oh! Can you believe I read your comments and somehow only saw the statements preceeding "Properly installed...". Must be an age thing or sumptin'.

Of course, I would have to have actually seen that in order for it to register.
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I'll have to challenge this one Doug. That's not a lot of wire to pull through 3/4". I'm not even sure 1" or 1 1/4" would be any easier. At the fill he's going to experience in 3/4", he's really only dealing with the force of pulling the strands. That will be the same regardless of the conduit diameter.
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Not really. The wires aren't going to just lay straight in the conduit; they're going to assume a spiral shape, and there will be friction against the conduit walls. The bigger the conduit, the easier it is to pull the conductors. 1-1/4" is probably overkill, but for the modest difference in price between 3/4" and 1" conduit, I'd use the larger one and save myself some effort.
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Doug Miller (alphageek at milmac dot com)
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Todd, To the advice you've already gotten, I'll add a suggestion to put a couple of receptacles in the ceiling over your workbench or assembly area. It's so much better than having cords running across the floor to reach the middle of the room.
DonkeyHody "In theory, theory and practice are the same, but in practice they are not."
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At least TWO breakers for lighting, and "used" lights shared between them. That way if the lights go out, there's still enough light to see which way to move your hand away from the business end of whatever you're using.
I also put a bank of nightlights on EACH of my ckts; can tell at a glance which is on or not on. Plus, created a Master Switch just outside the door; when I leave the shop, NOTHING is powered except lights of one ckt. Takes a few relays, but not hard to install, especially during the design stage. And, it has a key-lock switch (kids around).
Pop`
todd wrote:

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Check your box fill requirements before you decide to run everything in one conduit unless you like the look of extension boxes.
Mike M
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