Shop Wiring

[JSUPreston]

I just showered after finishing the rewiring of my shop. I inherited a 20x20 block building when I moved into the house 4 years ago. Had a new roof put on two weeks ago. I have a 30 amp 240 coming off the main breaker at the house to a sub in the shop. At the sub, it becomes 2 30 amp 120s. I got the cheap hammer drill from HF, and it worked like a champ for mounting boxes and 3/4 pvc conduit to the walls. I wired everything with 10/2 3 wire 10 gauge wire. Went through 150', and I still need about another 15' for one more outlet. The voltimeter tests every jack at 110/120, so it looks good. Just got a lot of cleaning up to do before I can get on my project list for the year.

I know I'm rambling, but I am "plumb wore out" from pulling, twisting and cutting wire, and I just had to brag to someone about finally finishing this up. It only took me 3 days over a span of a month to get it done.

[Tim Clark]

Sounds like you've worked your tail off.

I mean to offend you but,

What do you have in your shop that needs a 30 Amp circuit?

You might have saved a few bucks on wire by running 12-2 (20 Amp) and 14-2 (15 Amp) wire instead of 10-2 for everything. That would have given you 2 or 3, 20 amp circuits with 1-3 outlets each (a dedicated circuit for the TS and maybe the compressor) for your bigger tools. You can have multiple tools that you'll only run one at a time plugged into the same circuit. And 3-4 15 Amp circuits with 3-4 outlets each for your smaller hand tools and one circuit for your light fixtures.

Remember, you can run more circuits than the main breaker capacity as you will not be using the full capicity all at once. It all depends on the load requirements for your shop of course but it just seems like you have way larger wire and breakers than you need in your branch wiring. Also, you should size the branch circuits to the equipment you'll be using on them. A 30 amp breaker won't protect a 20 amp tool as it will trip much later than the properly sized breaker (and wire) would. The load ratings should be on a tag or plate attached to every tool.

Also, you should have a 30 amp breaker in the main panel to feed your shop sub-panel. It sounded like you tapped straight off your main breaker (big no-no and fire hazard). If the 30 amp breaker in the sub-panel fails (unlikely, but it happens) there isn't anything else protecting the shop feed from overloads. It could melt and start a fire without ever tripping the 100 or 200 amp main..

We like your company here and want to keep you around.

Be safe.

[gjat]

Good Job!

As a person with 25 years in electrical construction as a project manager and estimator, you did exactly right. (But Mr. Clark is right if you don't have a means of 'disconnect protection' at the point you tap off the main! That defeats the safety of #10).
Oversize the conductors and undersize the breakers is the SAFEST, though not the most economical thing to do. You also have options to split circuits, etc. In my opinion, using 10awg wire is a value call where the value is in safety. It's also easier, faster, and cheaper to not wear eye protection or not paint the red line.

[just4funsies]

Always better to oversize the wiring, because you never know what you'll have there in the future. One caution: metering out the outlets at 120vac will tell you if they're connected, but is not an indication of ampacity (current-carrying capacity). Your wiring sounds plenty big, but if you ever trip a breaker, you may have a power cord or connection going bad (such as from a dissimilar (aluminum/copper) metal connection, or similar. It's just a good idea not to assume anything from an unloaded meter reading.

You definitely should have a disconnect at your tap from the house main.

[JSUPreston]

I used the 10-2 because the electrician that ran the new wire from the house to shop said that I needed it to carry the load. Since I bought a 100' spool of it, it made sense to me to go ahead and use it up. When I ran out in the middle of the second circuit, I decided that I should just go ahead and finish it out with more 10-2.

All the decisions were based on what the hired electrician told me. The main panel on the house has a 240 30 amp breaker. The breaker box that was already in the shop was a 2 breaker 120 30 amp box. As far as multiple circuits go, I have the lights and a very small A/C and a couple of outlets on one circuit (in case I need to plug in a battery charger, etc). The miter saw, planer, jointer and BT3100 will share the other circuit. I never use more than 1 power tool at a time, so the 30 amp capacity will probably do.

Also, remember that I am a little limited as to what I do, not only financially, but also the fact that I don't own the property (yet). You wouldn't believe the rats nest of wiring I replaced! A single 15 amp 120 was the feed, and then there were two fuse boxes, some grounded, some non grounded wiring, all of different gauges. Some of the wire was cloth insulated, the others standard off the shelf. Whatever my wife's grandfather picked up cheap (or free). I'm not an electrician myself, and I did a lot of reading before making the decisions I did when I rewired, but even I knew the old stuff wasn't safe. Even if I didn't do everything exactly 100% the ideal way, I'm still much better off than I was before.

Given y'all's imput, should I downsize my subpanel breakers to 20 amp? Also, I am considering the idea of a cutoff mouted either on the outside of the shop or just before the sub inside the shop. Fortunately, the sub is right inside the door of the shop, so unless there was a problem right inside the door, I think I could get to the panel fairly quickly.

[gjat]

Not yet, but maybe. Need more info.
So the feed to the shop, from the house, is 10/2 (w/ ground?) and it is fed from a 30 amp breaker in your house's main panel?

[maxparot]

For those that think that oversizing the wiring is of value here is something to consider:
All electrical components are designed with at least 20% safety margin when used according to NEC code. So this means using the right wire in the correctly sized circuits provides for both safety and economy.
It is best to follow codes it allows for people with the proper knowledge to do their jobs. Engineers design, Electricians install, DIYer ask lots of questions and then emulate good electricians.

[Tim Clark]

You do have the right size breaker at the main panel and that was the biggest Q I had.

Since you already had the 10-2 it makes sense to use what you have.

If it were me I would have some 20 (and maybe some 15) amp breakers on the branches in the shop. But that's just me. I spent just enough time as an electrician's apprentice to pick up the basics. There are others here with far more knowledge and experience than me and I respectfully defer to them when it comes to safety issues.

Be safe

[scorrpio]

I recall how spent I was after a full day of struggling with a 6/3+G UF-rated cable. I got 60amps running to a sub in an outbuilding, and 6/3 in heavy insulation is a bear to work with. I am still not done with it as for now it sits in a conduit above ground, waiting for warmer days when I can dig a trench and bury it. The subpanel is a 100amp workshop kit from Lowes, a great deal. For $50, you get a 12-space box with separate insulated neutral and ground buses, a pre-installed 100 amp main breaker and four 20 amp breakers. I have a 60amp at the main panel. The oubuilding already had lights off a different circuit on main, I left them that way. I wired four 20-amp 120V circuits off the sub, using 12/2+G to run them: a dedicated one for DC/shop vac, a dedicated for heater/ventilation, one for several 20amp outlets - each in a single box, reserved for major power tools, and one for a bunch of regular outlets two per box, for low-amp accessories. I still need to tidy it all up though - for now, the wires are attached with ties to some screwed-in eyelets, I need to properly hide everything into conduits...

[Curly Qsawn]

Got me thinking...

I’m doing some rough concept thinking about the wiring in my garage so I can add some better tools. This isn’t going to be a DIY job, but I like to know what I’m getting into. My question relates to 220v outlets. I know I can have multiple outlets on a circuit, but all I’ve ever seen are single outlets – not like 110v where you could have a 4 outlet box. Is that the only way 220v boxes work, is a single outlet, meaning I’d have to wire to each outlet I wanted? I think I’m wondering if there is such a thing as a multiple outlet box for 220v?

[scorrpio]

The rule of thumb is that 220V in residential USA is usually reserved for high-powered appliances which generally have to live on a dedicated circuit - and have a dedicated outlet positioned next to them. Because of that, 220V outlets are usually one per box.

[JSUPreston]

Scorrpio, is this the one you mentioned? http://www.lowes.com/lowes/lkn?actio...G1K&lpage=none

If so, I may get that and replace the current subpanel. The one I have now is limited to two circuits, which is why I wired the way I did.

Thanks for the heads up.

[LarryG]

My question relates to 220v outlets. I know I can have multiple outlets on a circuit, but all I’ve ever seen are single outlets – not like 110v where you could have a 4 outlet box. Is that the only way 220v boxes work, is a single outlet, meaning I’d have to wire to each outlet I wanted? I think I’m wondering if there is such a thing as a multiple outlet box for 220v?

There's no code prohibition against having more than one 220V outlet on the same circuit. You just have to consider the maximum total load at any given time, the same as you do with 110V. I have this setup in my shop ... I have one 220V outlet for my band saw, and five feet away is another 220V outlet for my jointer. Both are on the same circuit. Mine is a one-man shop so both tools never run at the same time, but even if they did it would be okay because it's a 15A circuit and the two tools only draw about 10A combined.

If you want multiple 220V outlets at the same physical location, you'll need to use a gang box that will hold however many outlets you want.

[Tim Clark]

I don't know if there's a "duplex" outlet specifically for 220V. You can however loop from one box to another (that's how my electric heat sys is wired).

You could check into ganging a box (same as a multi-switch/outlet box in your house) to have two or more outlets in one box. Just be very aware of your loads if you do.

It sounds like you're having an electrician do it so ask lots of Qs before he/she starts the work.

[gjat]

Electrical devices and their enclosures are designed according to potential heat generation. This is a factor of voltage and amperage. There aren't 'duplex' 220v outlets because they would not be NEC legal in a single gang box. You'd have to use a larger box and put them beside each other in a double gang box.