Subpanel installation questions

[Roland Coppens]

I’m planning on a wiring upgrade for my garage woodworking shop and some miscellaneous questions have arise that I was wondering if I could get some help with. (Cross-posting note: Some of these have been posed on another forum as well. I'm just trying to cover my bases.)

Here’s some background information:
- I’m in Alberta, Canada
- I’ll be getting the permits and doing the work myself, calling for inspection when finished
- I have a copy of P.S. Knight’s ‘Electrical Code Simplified Book 1 2006-2010’
- I have previously done some basic electrical work, but nothing approaching the complexity of this project
- My garage is attached to my house and is insulated, drywalled and heated (though usually only to ~5-10C when not being used)
- I plan on using surface mountings in the garage for this project.
- My main panel is in my basement and is 100A.
- While my basement is finished, most of the wiring for this project will mercifully be able to run through an insulated but undrywalled storage room. Only about 15’ or so will need to be routed through a finished area. Given the situation and some planned future renovations, I’ll be opening a portion of the ceiling for this portion of the run.
- In order to pass into the garage, the line will need to pass through the concrete basement wall.
- Based on information I’ve collected to this point the plan is to #6 cable from the main panel to the subpanel in the garage.
- The main panel will have a 60A double pole breaker and the subpanel in the garage is rated at 100A (but not because that ampacity is required – I just found that the 100A panel was less expensive and easier to find)
- I plan on GFCI protection for each circuit (either on the first receptacle in a circuit, or at the breaker if needed)

So, knowing that here are my questions:

1. Will the #6 cable coming through the basement wall into the garage fit into ½” conduit or would ¾” be required for this bit?

2. I'm a little be-dazzled with all the 'loomex', 'THHN', 'THWN', 'NM', 'Romex', 'SER', 'NMW, 'NMWU',' in the stuff I've been reading. I'm pretty sure what's needed for the circuits off the subpanel in the garage is 12-2 loomex (but confirmation on that wouldn't hurt). What I'm not sure about is what kind of rating/description/three-or-four letter acronym the #6 cable feeding the subpanel is supposed to have. Any help sorting this out would be helpful.

2. In terms of passing through from the basement cement wall into the garage, are there special requirements? I’m aware that the cable mustn’t be surrounded by insulation so will be careful about that part, but am just curious if conduit passing through from the garage side into the basement for a small distance (say 12” maybe) is sufficient. The conduit would run continuously from the garage side of the basement wall up into the subpanel.

3. Rule 12-518 of the 20th edition of the Canadian Electrical Code states that where cable is run on the surface of the wall and within 59" from the floor the cable must be protected from mechanical damage with wood or similar molding. Most of the planned circuits off the subpanel will be in & around this height. Regardless of whether or not they don’t require protection, I plan on using conduit. I’m having trouble getting solid information however, whether PVC conduit is permissible in this application or not? I’d rather use PVC than EMT if possible because of the cost and ease of working.

4. Two of the planned circuits will be dedicated, being used with just one tool/device in mind (for example one for my dust collector and one for my welder). I was wondering if it’d be possible to have the cables for these circuits share conduit with cable for other circuits. Rule 4-004(10) contemplates cables in continuous contact. Can cable for other circuits run inside the conduit carrying one or both of the cables for these circuits? Would the ampacity of the conductors need to be derated as a result? (The code talks about wires inside walls being in continuous contact but doesn't seem to discuss this issue as relates to conductor inside conduit.)

5. If, as mentioned in question 2, I rout cable for multiple circuits in one conduit, what is the recommended method for passing the cable not for that circuit through the boxes? Can they just pass through at the back of the box? If so, do they contribute to box fill calculations?

6. Would ½” PVC conduit be sufficient to run, say, three 12-2 cables?

7. I plan on using 12-2 for all the 120V circuits, as this simultaneously permits the circuit to use 20A breakers as well as creating the possibility of going to 240V at some subsequent point if required. However, a couple of the planned circuits will be 240V with a single dedicated duplex receptacle that will service a particular machine. I'm wondering if there'd be any value in using 10-2 for those, just in case I'd ever need/want to go have it be a 30A service after futurre upgrade to the tool at that spot?

8. I suspect the cable from the main panel to the subpanel needs to be 6-3 but am not 100% on that. Am I correct?

9. The usual ampacity-wire gauge correlations are what led to me concluding that #6 cable is required with a 60A breaker. However, information from a one person I consulted flies in the face of that conventional wisdom. The lingering doubt in my mind is that this is the only dissenting source, as everything else I’ve come across corroborates this usual correlation:

15 A...14 ga
20 A...12 ga
30 A...10 ga
40 A...8 ga
60 A...6 ga
80 A...4 ga and so on...

What this fellow said is that #6 copper is rated 55A at 60C and 65A at 75C , and NM cable (Romex) ampacity is limited to the 60C column. Many folks use the 'round up' rule and use #6 as 60A feeders. But, he cautioned that I’m likely as not to get gigged by the inspector, saying a subpanel is not a known load like a heating unit or motor load, where the cable is sized to the load, and a breaker can be rounded up to the next larger standard size if the requirement is between sizes - a panel is whatever load you put on it, so the round-up rule really doesn't apply. He cites info in the follwing link, which is similar to the NEC table:

http://www.armstrongssupply.com/wire_chart.htm

10. Is it possible to have a box in a run that’s present only for ‘future provision’ for that circuit? What I’m thinking here is just a loop of wire in the box, with a blank faceplate, in order to facilitate addition of an outlet later?

Are there any other questions you’d expect I should ask, but haven’t?

[James Waters]

Lets see if I can help you with some of these...I am famaliar with US codes and the canadian ones may be different. I did electrical work for several years for what thats worth also.

#1 - I assume that you are gong to set a 60 amp sub panel hence the #6 wire. It needs to be in 3/4" conduit at a minimum and possibly 1" depending on the run (bends, etc.) You will never get 4 wires of that size through 1/2" and it will be pushing it at 3/4" I would run that in 1" and save yourself alot of hassle.

#2 -If you are planning on making all of your runs in conduit then you do not need romex at all. I would use #12 THHN STRANDED....not solid...trust me...MUCH easier to work with. The downside of all conduit is that it is surface mounted which, if not properly planned out, will give you fits if you want to put things against the wall where the conduit is. If you run conduit between the studs (through the top plate and down the side of the studs) it is a ton of work with bends, etc.

#3-Tis kinda ties in to number 2 a little. If romex is used and ran in the garage like it is in the house ( center of the side of the stud and secured there) it does not need to be physically protected. Only if it is surface mounted or otherwise subject to damage. Almost all of my garage is ran with romex, 12/2 for all outlets, 14/2 for all lighting. I have a few areas with conduit but I plan on replacing them with romex as described because of the issues of the conduit getting in the way with storage but that is just me. Several people on here have all their power ran in surface moounted conduit and like it. The other advantage of conduit is that you can always usually pull more and/or bigger circuits through the pipe, you would have to run a whole new line to do this with romex. Either was has it's pros and cons it is a personal decision.

#4 - this can get complicated and there is math and charts that must be used based on the number and size of the wires in a given sized conduit. Unless you are running a ton of different circuits this should not be an issue for you but the numbers add up quickly with bigger size conductors. If in doubt I would run your welder and dust collector circuits in a second conduit run if needed. Not much money difference there at all since you have to buy the wire already, just a few more pieces of pipe and fittings.

#5-The extra circuits can pass through the back of the box just as you described but they are figured into the conduit calculation. You probably will bot have anywhere near enough wires in any particular outlet box to worry about overfilling the bob itself. This problem is usually when boxes are used as true junction boxes.

#6-Yes 1/2" would be fine for three circuits using #12 THHN....not for 12/2 romex. Hence why in my opinion the THHN route is a better way to go. I would also run the conduit as EMT and not PVC. A conduit bender is about $25 and it is not that difficult to learn. Also the wire is typically much easier to pull in EMT than PVC. The metal outlet covers and boxes will hold up alot better also. There is a reason why most industrial applications are ran in EMT and not in PVC. Again, just my personal opinion.

#7-Running your dedicated tools in #10 is not a bad option. A little more money up front but, as you mentioned, could facilitate a seamless upgrade to a larger tool in the future if desired.

#8 - Depends on the size of your subpanel. The codes here require there to be 4 wires to supply a sub panel. In that case the ground can typically be downsized one size while the other three are the same size. If you are running conduit between the two panels you can use individual lengths of wire. Again, if this is the case just be sure to tape each conductor on each end to identify it, (Hots, nuetral and ground). If you are using 6/3 romex this will already be done for you in the wire.

#9 - Your numbers in your chart are dead on. Go with those.

#10- You can do this but thr inspector may question it on the final inspection. Discuss this with them to get the final answer. If they have an issue just make it another regular outlet. You can always change it later if needed.

These are just my two cents. Talk with your inspector if you have any doubts as they have the final say. They can be pricks sometimes but mostly they are helpful. If it is anything like here alot of times when they see homeowners pulling their own permits and doing the work themselves they tend to go over your work with a fine tooth comb. Just make sure everyting is done right and keep it as neat as possible. That will make the inspector happy!!!!

Also, make sure that 60 amps is enough power for everything that you think you may need. I would recommend that you set a 100 amp sub panel if possible with at least 24 spaces. I have a 100 amp 12 circuit panel and while I have pleanty of power I am maxed on spaces. I am good not but one more dedicated power supply to a tool and I will have to install a bigger panel. I am not a big fan of the piggyback breakers because they can cause alot of problems dependng on how the circuits are pulled if you do not know what you are doing and hook them up wrong. You can really ofset the balance in the panel if you are not careful.

Make sure you check all my advice against your local codes also before you decide to do any of my suggestions. Again, I am not famaliar with canadian codes. Also check and see if all of your 110 volt outlets are required to be GFCI protected there.

Hope this helps. Feel free to contact me if I can help you more.

[Chris Friesen]

1) Almost certainly not. It's just a short run of conduit, so just use whatever size of conduit will easily pass the cable.

2) loomex/romex/nm is the same thing. nmw/nmwu is similar, but rated for underground burial where it can get wet. thhn and thwn are two different kinds of sheathing used for individual conductors that will be within a conduit. If you were putting wire through the studs behind the drywall the "normal" way you'd want loomex....however, since you're doing conduit it will be much easier to use thhn. For the feeder line, you want 6-3 NMD90.

2) You had two questions labelled #2, this is the second one. Your plans here sound fine. The conduit is just for mechanical protection going through the wall. Take a look at the section in Knight on doing a main panel service...it would be similar.

3) PVC should be fine.

4) Yes you can share cables, but you need to derate the ampacity appropriately due to the bundling. Note that for this purpose the ampacity of a THHN #12 cable is 30A, even though it's never allowed to carry more than 20A.

5) Just pass them through the back, and don't include them in box fill.

6) 1/2" conduit is good enough for 10 conductors of #12 THHN (aka T90). That will give three circuits and a ground. However, it will be a TIGHT fit and you might want to upsize at least one size to allow for easier pulling. If you use NMD90 jacketed cables, then you will need much bigger conduit.

7) If you think it's likely that you'll run 5HP motors, then go ahead with the #10. However, since it's going to be in conduit you can easily upgrade later if you don't do it up front.

8) Yes.

9) It all depends on the insulation type. #6 is rated for 65A at 90 and 75 degrees, and 55A at 60 degrees. However, there is an exception that it is acceptable to rate it at 60A for services and subservices.

10) Yes.

[Dave MacArthur]

You have two great answers up above, which I concur with. Your proposed layout matches mine almost exactly, including all your proposed conduit loading, wires thru boxes, 12-2 etc...

200A main panel outside, #6 wires feeding a subpanel surface mounted inside garage( you said 6-3, but really #6 will be individual cable, and you'll need 4: black, red, white, green). 60A feeder breaker in the main panel, 100A subpanel with a 100A main breaker in it--not functional as a breaker since the main panel 60A breaker functions first, but useful as a master on/off. 1 1/4" conduit used to make that run.

12-2 is a good idea for your plug circuits, and 20A (110 OR 240) circuits. 14-2 only for lighting usually. Many folks do run a 10-2 circuit for future 30A (5hp) potential use--I'd say that it might be wise to make at least one long "difficult" run to the far side of the shop from the subpanel using 10-2. This way, you can use it with 20A breaker for 20A circuit, but can upgrade it to 30A later if needed.

I would run inside conduit using THNN. You can certainly run multiple circuits inside the same conduit, when doing this I'd use 3/4", and use 1/2" EMT for runs between boxes when you drop down to just one circuit. When multiple circuits come into a box, just run the unused circuit right through the back of the box. There is a derating for thnn in contact inside conduit, but as noted above you can use the max amperage for the derating calc--effectively, if you use 20A for 12-2 you're fine. I had great concern with this based on this rule and the temperature derating rule (I live in Phoenix, and my garage attic where most runs are can get to 130 F or more). The inspector said the derating for that was already fully built into "20A for 12-2, 30A for 10ga, etc.".

I specifically asked the inspector before installation on the PVC vs. EMT conduit. I had all the code parts with me after extensive study. He said that the code only required "protection", and that while EMT was more common, PVC was fully allowable, and in fact that I could mix them on the same circuit runs so long as the proper termination/joints were used; just be sure you're running a ground and not using the EMT as a ground. HOWEVER, I agree with poster above--EMT is just as easy to run as PVC, bender is $25 at home depot and easy to use, and a 10' length of EMT costs $1.26 or so. In Phoenix, the EMT vs. PVC for an entire shop, 10 circuits, 8 trougher lights etc., was only $15 different. I ran EMT for all except one multi-bent run.

Below in my signature is a decent link for wiring a home garage shop (US NEC, but similar to CN I'd think and good info) with references directly to the NEC for each area. Also, there is good information on GFCI and dedicated plug for 220 information, which is VERY often mis-read in an overly stringent application in the US.
Good luck!

[Roland Coppens]

Thanks for the very helpful replies, guys!