code requirements for romex leaving subpanel

[Bob Cooper]

i have a question about what's required at the shop subpanel relative to clamping at the entrance to the panel -- i.e. where the knockouts are. I have a 100Amp service coming from the house the shop sub-panel. Here's my questions

1. does the 100Amp service need to be seperated from all other circuits ... where it enters the panel? I'm sure i'm not wording this super well but does the service need to go through a knock-out all by itself or can it share that with any of the circuits?
2. does everything have to pass through a "clamp-able" connector? Or do i just need to insert something (like a male threaded pvc nipple w/a screw on fitting to hold it in place) that keeps the romex from touching the box where the knockout has been removed.
3. if everything does need to be clamped, how does one know how many circuits/clamp are permitted -- is it based on current (and thus temperature).

Any guidance you can give me would be appreciated.

[Mike Cutler]

Bob

It's really going to be up to the building inspector. While the NEC is a "national" code, the state and local codes may implement the NEC a little differently based on location and adherence to local building codes.
In a nutshell though. Yes, each circuit must pass through the knockouts and be clamped. There will also "probably" be a minimum distance from the point of entry that the individual circuits will be stapled to the panel mount.
"Generally" each circuit will pass through it's own clamp and knockout, but there are special clamps that facilitate passing two circuits through one knockout. Each side of the split clamp will restrain an individual circuit by itself. It is "generally" not acceptable to clamp two circuits under a single clamp.
You sub panel box has a manufacturers rating for the total amount of circuits allowed. It "should" have a diagram for the placement of different breaker types that can be used in the panel, and where they can be located.

There are a lot of " generally"s and "should"s in my post. As I stated earlier though, what may be allowable in one state, or even a town within a state, may not be allowed somewhere else. It's a very good idea to touch base with your local inspector and ask what she/he wants to see for a final inspection and closeout.

[Scot wolf]

1. No

2. NO, You can use a nipple or nipple and stub of pipe. The NEC requires it to be "sealed" (I don't get too concerned about that as long as it has a pipe on the nipple)

3. Doesn't need to be clamped at the panelboard. You have to watch for bundling/derating at some point.

[Steve Meliza]

Your 100A service is so big you'll want it to come through its own 1" (or larger) knockout(KO) and all the branch circuits can run through 1/2" or 3/4" KO's. All NM cables must be clamped and you can only put one cable in each clamp unless it is listed as allowing two cables as mentioned above.
Wire connection.jpg

[Scot wolf]

Your 100A service is so big you'll want it to come through its own 1" (or larger) knockout(KO) and all the branch circuits can run through 1/2" or 3/4" KO's. All NM cables must be clamped and you can only put one cable in each clamp unless it is listed as allowing two cables as mentioned above.
Wire connection.jpg

What section of the NEC requires that? You might want to read the exception under 312.5 (C)

[Steve Meliza]

What section of the NEC requires that? You might want to read the exception under 312.5 (C)

Trick question? 312.5(C) says each cable shall be secured to the cabinet/box. Oh, right, I mislead Bob by not mentioning that if he is using a surface mounted panel (I doubt it) that instead of buying a 5-pack of 3/8" NM clamps for $1.49 that he could instead use a length of nonflexible conduit 18 inches to 10 feet long, fastening the cable within 12" of the outer end, the conduit only extends directly up and not into the ceiling, has abrasion fittings, is sealed at the outer end, the cable sheath extends at least 1/4" into the box, the conduit is properly supported as defined elsewhere in the NEC, and the cable doesn't violate fill requirements.

I hope Bob can forgive me for oversimplifying the NEC and only mentioning the normal, cheap, and accepted way of doing things for the task at hand.

[Bob Cooper]

OK...i think i'm on the right path. I pulled out everything i'd done and ran all the circuits through individual cable clamps. These are the small ones -- something like 5/8" (memory?)...5 to a bag for very cheap. So now everything -- feeder and branch circuit are clamped and stapled near where they enter the box.

I have just a few more questions

1. i'm running 14, 12, 10 guage all through the same size cable clamp. They all seem to fit. Any issues? Does the 10 guage need anything bigger?
2. i have some knockouts that are knocked-out...some small 1/2" onces but also a larger 1.5" one. Do i need to plug these with an approved plug of some type?
3. i've run a piece of 1.5" electric pvc between the top of the box (terminating into a 1.5" nipple) and up through the double plate at the top of the wall. i'd liek to do this so that i can run a wire in the future if needed once the wall is covered. Any issues here. The distance is about 29".

Thanks for all of your help and advice

[Scot wolf]

1. What you are probably using are called 3/8" NM cable connectors (fit in a 1/2" knock-out). Although they have listings that tell you max # and size they are listed for, if allthe cables fit nicely you are good to go.

2. They make plugs for the unused knock-outs in all sizes you need. They should have them at the BORG.

3. That would be fine IF I was inspecting it. But, As Mike stated.....check with your Inspector. Leave yourself a Pull string in the empty 1 1/2" conduit.

[Bob Cooper]

ok great...thanks all. I'm sure more questions are to follow over the coming months.

[Matt Marsh]

i've run a piece of 1.5" electric pvc between the top of the box (terminating into a 1.5" nipple) and up through the double plate at the top of the wall. i'd liek to do this so that i can run a wire in the future if needed once the wall is covered. Any issues here. The distance is about 29".

Bob, you might be able to get by with this where you're located in SC, but if you heat the shop, and the temperature difference between the interior of the shop and the attic is great enough for condensate to form, I would advise against it. It is a well-known problem in colder climates, and worsens proportionate to the difference between indoor and outdoor temperatures. The inspectors here in my part of the country will generally not allow it. At the very least you will want to seal both ends of the conduit with an approved material (duxseal) to prevent moisture from entering the enclosure. as per 2011 NEC article 300.7(A)

[Joseph Tarantino]

ok great...thanks all. I'm sure more questions are to follow over the coming months.

bob....you're asking some pretty fundamental wiring questions here. is there any chance you can get a sparky to advise you for a fee to save on having to redo wiring that you might do incorrectly? and, with no intention of insulting anyone, have you at least perused the wiring books @ either lowes or home depot? electricity can be dangerous and the idea of someone bringing wire into a box with no connectors speaks to someone who needs to do some basic research on safe wiring procedures before they pick up their scewdriver and linesman's pliers. it's not rocket science but it's got to be done safely.

[Bob Cooper]

So Matt if one does not run a piece of conduit for future use how would you ever add a circuit in the future (w/o ripping out the wallboard)? What is common practice?

Thanks btw for mentioning why the end needed to be sealed. I'd read the section in the code that mentioned this exception but condensation had not occurred to me.

[Matt Marsh]

So Matt if one does not run a piece of conduit for future use how would you ever add a circuit in the future (w/o ripping out the wallboard)? What is common practice?

Thanks btw for mentioning why the end needed to be sealed. I'd read the section in the code that mentioned this exception but condensation had not occurred to me.

Bob,

What I like to do is have a removable piece of sheeting on the wall above the panel enclosure. That way you can access the top wall plate. Even more preferable is to surface mount the panel and build a vertical chase with a removable front over the top of the panel extending to the ceiling to enclose the cables. That way you get a full wall of insulation behind it.

[Scot wolf]

So Matt if one does not run a piece of conduit for future use how would you ever add a circuit in the future (w/o ripping out the wallboard)? What is common practice?

Thanks btw for mentioning why the end needed to be sealed. I'd read the section in the code that mentioned this exception but condensation had not occurred to me.

Running a piece of oversized conduit is common practice AND code compliant. Sealing of the end is also required.

[Matt Marsh]

Running a piece of oversized conduit is common practice AND code compliant. Sealing of the end is also required.

Its not common pratice around here. And I didn't say it was a violation in every case. But it would indeed be a violation to not secure the cable to the enclosure if the enclosure is flush mounted, and/or the conduit penetrates the structural ceiling 312.5(C)(b).