220 sub panel wiring

[franksinatra]

Hello all, Great forum.

Im currently finishing my basement in my split foyer home and one of the walls seperates my garage and basement. My main box is on this wall. I want to run 220 out to the garage and I need to figure out what size wire(s) I need. Because my wall is currently open, I figured this is the time to do it. I have 150 coming in to the main panel. I have 10 openings for additional circuits. I will be using the 220 for a table saw, welder and a compressor along with a few lights. Only 1 will be used at any 1 time but the lighting will be constant. I will be installing a sub panel in the garage and Im thinking of running 80-100 amp circuit. I figured it was better to go above my needs now instead of wishing I had more in the future but I dont want a huge overkill. My run will be 15 feet max to the panel and Im thinking of running 2 220 outlets from there. I was told to run 4 gauge wire but I was shocked at the size and figured I would ask everyone here. I have also been reading and noticed some people are running the cables through conduit. Is this necessary? I wont be installing the wires just running them so I can finish my wall this week and an electrician friend of mine will be hooking it up. Any thoughts? Thanks and I really enjoy the forum. Grant

 

[MXtras]

When it comes to electrical, you will never get into trouble going too big but you can get into trouble fast if you go too small.

I do not have my NEC code book in front of me so I can not say what code is but 2 Ga sounds comfortably adequate. Check code first.

Also - oversizing your wire is a good way to reduce voltage drop (increased amperage draw). In your case of a 15' run, it's not as big of an issue but it is something to keep in mind.

Scott

 

[mike944]

2Ga copper should be good for 100A, on your short run.

If you use a pre-manufactured Service Entrance type cable then you don't need conduit. If you have 4 separate wires, then you will need a conduit.

If you don't use a conduit, you'll probably need some of those nail-protection plates if you're going to be drilling holes through wall studs to run the cable. Unless you can maintain at least 1.5" between the drilled hole, and BOTH faces of the stud, you need to protect the hidden cable against nails and screws when you hang the drywall. Unless you have 2x6 studs, you'll never achieve the 1.5" with a cable that large.

 

[Charles (in GA)]

For feeders other than main feeders, NEC table 310.16 is the appropriate reference for cable sizing. a #4 copper cable is, at best, capable of 95 amps. This is using 90c rated wire and no temperature correction. If ambient temps above 86f are to be encountered anywhere along the length of the cable, a correction factor, which derates the cable, need be applied. Depending on the type of wire used, the amp rating of #4 copper could be as low as 70 amps.

You will need to carry four wires to the subpanel, two hots, a neutral, and a separate ground. Code will not allow for the neutral and ground to be shared on a feed to a sub-panel.

In the subpanel, the ground (earth) bar should be bonded to the metal subpanel cabinet, using the provided screw or strap. The Neutral should NOT be bonded or connected in any way to the metal cabinet or the gound bar, it should remain isolated and insulated from all other conductors in the cabinet.

If you can find #3 copper, it is capable of 110 amps at best and 85 amps at worst, depending on the type of cable used. #2 copper will serve for up to 130 amps and at worst 95 amps.

If you elect to use aluminum wire, you will need 2 or 1 or 1/0 depending on the actual type of cable used.

Refer to the NEC 2005 for the table listed above.

You could use a jacketed cable containing all four wires and as someone has stated, staple it to the studs and if routed thru studs, use protective metal plates on the studs where the cable passes thru.

You may if you wish, run conduit from one panel to the other and pull loose cables in such a conduit. It would need to be fairly large, at least 1-1/4" or possibly 1-1/2" depending on if PVC or EMT is used. There is really no reason to run the conduit however, assuming you will cover the wires with sheetrock or other wall coverings. If left exposed, you would need to use conduit.

Charles

 

[mike944]

For feeders other than main feeders, NEC table 310.16 is the appropriate reference for cable sizing.

I knew somebody was bound to chime in with proper references.......

 

[franksinatra]

Thank you, I dont need 100 amps, just thought I might as well run more than I need while the wall is open. My friend just brought me some ( I think)service entrance cable with Aluminum wire. It reads 3 CDRS 1awg / 1CDR 3awg. Im guessing thats the 2 hots and neutral at 1awg and the ground at 3awg? How many Amps will that allow me? Also is there any difference in sub panel boxes and breakers? Im looking at the home and industrial units at home Depot. The guy said theres not much difference other than the orange flag on the industrial breakers and the metal hook ups in the back, oh and the slightly smaller size. Any reason a person should go with one or the other? Thanks again. Grant

 

[Charles (in GA)]

I prefer Siemens panels, second to that but just as good, GE panels. Murray is actually a Siemens, Cutler-Hammer is probably good but the oddball breakers are a real turn off. Square D is a good product, but again, the breakers are peculiar to Square D and there are features about them I really do not like. Square D also markets a Homeline, which is a cheap line that is also incompatable with others.

My best suggestion is to see what kind of panel you have now in the house, and use the same brand. This will make breakers interchangeable from one to the other. You won't go out and buy one for a new circuit in one panel and realize you got confused and that it only fits the other one.

This is a jacketed cable, I hope? If it is four individual wires twisted together it is USE or USE-2 and would need to be in a conduit. Is the wire marked on the jacket in some other way, such as SE, USE or USE-2? NEC table 310.15(B)(6) is sizing for service entrance, service laterals, and feeder conductors acting as main power feeders, it is not suitable for sizing the wires in this particular situation but lists SE, USE, and USE-2 in #1 AWG Aluminum as suitable for up to 110 amps. The reason I reference this, is that NEC table 310.16 only addresses USE-2 aluminum wire and shows that #1 is good for 115 amps at full rating. Don't forget temp derating if needed (which it sounds like you don't need to worry with, as the wires will not be in an attic).

If you use Aluminum wire, make sure you use a supply circuit breaker that is marked for AL wire (most are) and that the sub panel you are feeding is also marked for AL cable (again, most are), and use anti-corrosive paste for aluminum wire, woring it well into the strands on the ends.

Charles

 

[MXtras]

Also - whether you use AL or copper, torque the lugs at each connection and then re-check the torque a week or so later (power off, of course). Both the copper and AL will migrate under the initial torque and the connection will loosen up - it's the nature of the materials. I have noticed that after they are torqued the second time, they will hold torque well.

If you use AL, check the connection condition and lug torque every couple of years. I have seen some bad things happen with AL wiring - don't let any of it happen to you.

Scott