Shop subpanel

[Mike Holbrook]

Ok I have been to Lowes and came up with more questions instead of parts.

What I found at Lowes was a 100 amp Load Center, which I think is similar or the same as a sub-panel. I think I discovered why this gets more expensive than one might think. 100 amp wire to run between my 200 amp Basement panel and the 100 amp shop panel is $.80 - $1.00 per foot. Lowes also had a diagram for a shop sub-panel but they showed an even larger panel (150 amp). 100 amps sounded like over kill to me, as I can not imagine having a machine or several machines pulling that much all at once in a one man shop. The smaller Load Centers had only a few circuits on them though.

My goal was to have:1) individual circuits wired for powerful machines: a couple 220 and several 120 2) a ground fault circuit to use with the sharpening equipment (water stones) and 3) a couple circuits with just a few outlets on each. I do not think that several of these machines will be running at the same time though.

I was sort of looking for a panel that could hold a minimum of 8 circuits (hopefully more) with a lesser total amp rating. I was thinking of running 10 gauge wire on all the individual machine circuits and the shared circuits.


I am wondering what others here have used to set up their shop sub - panel. Maybe my thought process is flawed or maybe Lowes or Home Depot are not the best places to get electrical supplies of this type. I am especially concerned that the cheap outlet boxes I find at these places seem cramped with 12 gauge wire, I imagine they will be next to impossible with 10 gauge.

[Jim Becker]

You can use a 100a, 150a or 200a panel ("load center") for a 100a subpanel...it's the space you are looking for for your circuits. How you feed it determines what is available from a power standpoint. I kinda think that 100a is a good way to go as long as your main panel can support it...and by that I don't mean physically, but electrically. You may want to have/pay for a consult from a qualified electrician on that before you buy anything.

My shop building has a 200a panel and a 200a feed in buried 2" conduit. The shop doesn't need that, but the cost difference was not that great and it means the building is ready for renovation/finishing of the second floor in the future including a heat pump. (Service to the property is 400a)

Be sure that whatever panel you end up with has room to grow in case you decide to add additional circuits in the future. You need spaces to do that.

[Jeff Sudmeier]

I am especially concerned that the cheap outlet boxes I find at these places seem cramped with 12 gauge wire, I imagine they will be next to impossible with 10 gauge.
Mike,

Try to find more of a building supply or electrical contractors supply place. Home depot is pretty catered do DIY's. For this reason, I have not seen the larger, deeper outlet boxes there. However, at the local housing supply, you can pick up the extra deep boxes. These things are about 3 inches deep, compared with about 2 for standard boxes. It should help you out.

[Brad Olson]

For your receptacle boxes, NEC actually specifies how many cu. in. are required based on the # of wires in the box and the receptacle. Look at these charts before you choose your boxes. I can't remember what the size for 10g wire is, but I know for 12g, 18 cu. in will do most things and if you get to past two pairs of wires plus ground you have to go to 22 cu. in. boxes.

If you are getting feeder (THHN?) at about $1 per foot, that is about right. Remember you'll need 4 wires if you shop is attached and if it isn't attached grounding depends on if there is a conductor path between the structures. So you are looking at about $4 per foot plus conduit.

[Ken Garlock]

Mike, three additional points-

Make sure you are getting a SUB PANEL. A sub panel will have separate, unconnected neutral and ground busses. The only place you are allowed to connect the ground and neutral together is at the main service panel where the utility company wiring enters the building.

Second - There are two types of panels, the Square-D Q series, and others. BTW, Square-D makes other series that are not label as Q series boxes, you don't want those.

Third, to properly supply a 100 amp sub panel, you will need 2 gauge wire. IF you use UF type for direct burial, you need 1 gauge.

I just finished running a 10-3 plus ground circuit this week. The borg has that cable for about $66 per 100 ft.

[Mike Elo]

100 amp is usualy plenty. The big box stores will have the best prices if they have what you need. HD should have the deep boxes but you never know. No matter what you do, the wire from you main to you sub panel is going to be a little pricey. Now for the preaching........... Get in contact with the Dept. of Labor and industries or whoever is in charge of electrical inspections in your area. It won't cost you anything and they should be happy to answer your questions. And they will tell you exactly how to do it right and safe. They will probably have specific instructions on how to ground the sub panel and how to handle the neutral bus and the ground bus inside the sub. This is a simple process but there is a right way to do it and they will help you with this. I have seen many many home shops done wrong and there is realy no reason to guess when it comes to adding sub panels. Like I said it's realy simple but there are a few particulars when you add a sub panel. Good luck, Mike.

[greg kurtock]

I recently installed a 100A Seimans sub panel purchased at Lowes. It was a buss panel, did not have it's own main breaker (which is what you want for a sub, the breaker needs to be in the main panel anyway). It had 18 or 20 slots, cost something like $25. The 100A breaker for the main panel to feed the sub was actually more expensive. I figure you should buy at least double the number of slots you think you need. Remember, those 220v breakers take two slots.

You need to match wire guages, recepticles and breaker sizes to the load that will be using the circuit. I read a lot around these kind of forums where people frequently oversize the circuit. More circuits which are more closely matched to the loads is better, ideally the breaker should be 125% of the load. You can oversize the wire gauge if it's a longer run to minimize voltage drop, but an oversized breaker defeats one of it's main purposes (protect an overloaded motor).

Most importantly, please talk to an electrician before trying to tackle this yourself. Be wary of the "free" advice on this and other boards, I've seen plenty of bad advice floating around.

Greg

[Stephen Dixon]

When I added a subpanel in my basement, I used a 24 circuit, 100 amp, Main breaker panel, I have 3 220 circuits, and 5 120 circuits. I recommend an individual circuit for each 220v tool, plus each tool that starts or runs automaticly or runs when other tools are running, ie. dust collectors, air compressors, unit heaters/furnaces/air conditioners, etc., and at least 2 general purpose recepticle circuits, and at least 1 circuit for lighting that is seperated from the recepticles. You can have an unlimited number of outlets on a circuit in a residence, so there is no need to add a lot of individual circuits for general purpose circuits, I like 2 or possibly 3 circuits for that, but no more. In my shop I have 16 quad outlets, 1 every six feet around the shop, on 2 circuits.

Steve

[Chris Padilla]

Mike,

I just finished up rewiring my whole garage. I was lucky in that I was able to pull directly from the main panel (service entrance if you like) although I did go ahead and install a sub-panel as well.

I used the large 4 11/16" sq. metal electrical boxes. You *may* have to visit an electrical warehouse to find proper mudrings for them as HD is limited in mudrings for that larger sized box but you can cram a lot in there and it is nice and roomy for your hands anyway. I ran ALL my garage stuff with #10 because I didn't want to deal with various gauges. I also put just about everything in 3/4" flex conduit where I could.

Everyone here seems to be against the Square-D HOM series--I always see the Q stuff from Square-D being recommend. I used the HOM style panel and associated breakers with no problems and I think they are cheaper anyways. In fact, the style of breakers for my whole house are the HOM style.

I bought a 100-A 8-slot panel but I didn't need many slots to begin with nor much current so I fed it with some 6/3 Romex (max of 50 A) and I use it for 1 240 V/30 A, 2 120 V/15 A, 2 120 V/20 A, and 1 240 V/30 A for the A/C.

[Mike Elo]

There is some excelent advice on this string but be careful. Here are just a couple tips.
Use a GFCI recept. to feed the recept's where your portable tools will be used.
(GFCI's don't provide overcurrent protection. Circuit breaker do. GFCI's protect you not your tools.)
The circuit breaker primarily protects the wires. (A 20 amp circuit breaker is not going to protect your battery charger for you drill motor that's plugged into it.)
It's impossible to match your wire sizes to what you will have plugged into any given outlet.
The NEC states clearly and simply that a 15 amp breaker will feed #14 awg wire.
A 20 amp will use #12. And a 30 amp a #10. That helps keep it simple as well.
You might here talk about voltage drop in long runs of wire. (It would have to be a realy big shop for this to be a concern. You might hear talk about more 220 volt outlets because your machines run better on 220 vac. This one is a big misconception. There is no advantange to running machines @ 220 vac. at all. At least until they get to be of larger horsepower and then they only savings is in the size of the wires on that circuit.
There are ways to wire your shop and it will work, and there are ways to wire you shop and it will be right and safe. Mike.