[PatentPending]

I'm installing new framing in my basement workshop. I'm using steel studs because I like them. All wiring is going to be in EMT because I'm originally from the Chicago area where wires live in tubes like God intended.

The size of conduit I need determines the width of the stud. The punchouts on the 2.5" studs will only accommodate up to 1/2" EMT, so if I need 3/4" I'll need to go up to 3.625" studs.

I plan on having outlets on two different circuits: one 20A 120V, and one 30A* 240V.

My understanding is that 20A requires 12G wire, and 30A requires 10G wire. I'm assuming THHN wire. The table at E3904.6 of the Virginia Residential code says that 1/2" EMT can hold 9 x 12G or 5 x 10G. If I go with 240V three conductor (i.e., hot, hot, ground -- no neutral), that's 3 (out of 5) 10G, so 60% fill, right? Add to that 3 (out of 9) 12G, or 33%, I figure I'm at 93% fill, right?

Is that how this works? Am I missing something?

(Just to be clear, I'm not doing this wiring myself, just the framing. I just need to figure out the correct conduit size because it needs to be run through the web holes as I put the studs up.)

*My understanding is that 30A is the largest 240V allowed to be installed in the house. Please correct me if I'm wrong. Currently my thirstiest indoor tool is my 3HP bandsaw (15A/240V), but if I were to put a large dust collector on the same circuit, 30A might be pushing it...

 

[longdrive]

You know you can drill larger holes in the studs, right?

 

[jbfan]

Your understanding about the 30 amp circuit is wrong.

You can have whatever size 240 volt circuit as needed anywhere in the house.

You do not need to run a ground wire as long as the conduit is continuous from point to point.

You can drill bigger holes if needed.

 

[Jim Port]

Tha is not the way conduit fill is calculated. You add up the conductor volumes and compare to the allowed amount of fill.

 

[PatentPending]

Your understanding about the 30 amp circuit is wrong.

You can have whatever size 240 volt circuit as needed anywhere in the house.

That's good to know, thanks. I'm not sure where I got that idea.

You do not need to run a ground wire as long as the conduit is continuous from point to point.

Okay, so that brings up an issue tangential to this. The room in question has the breaker box in it. There's exposed Romex all over the place, mostly in the joists, going to various parts of the house (no drywall in this room). I want all of that in conduit. I'm assuming an electrician can run THHN in conduit to the edge of the room in question, and then tie it in to the remaining existing Romex (i.e. the stuff still protected by drywall) in a box (I'm obviously not gutting and rewiring my entire house).


I did not know you could drill bigger holes in steel studs. That makes my life a lot easier.
I was under the impression that for at least load bearing steel studs you weren't allowed to mess with the web holes (but now I can't find the relevant code section). Code is silent as to non-load bearing steel studs, so I was just assuming the same rule applied.

 

[PatentPending]

Tha is not the way conduit fill is calculated. You add up the conductor volumes and compare to the allowed amount of fill.

That's not surprising. Given that I'm apparently allowed to drill bigger holes, and that I was wrong about being limited to a 30A 240V circuit, I'll probably go with the 3/4" conduit just to be safe.

 

[anyacolo]

I did not know you could drill bigger holes in steel studs. That makes my life a lot easier.
.

you can, but keep in mind a larger hole will weaken the stud/wall

 

[Oldmaster]

They make a punch for holes in steel studs.

 

[rjniles]

Use this to calculate conduit fill. You can use the conduit as the ground or use a single #10 to ground both circuits.

http://conduitfillcalculator.com/
2 #12 (hot and neutral)


3#10 ( hot, hot. ground)

is only 30% fill, you are allowed 40%

 

[Oldmaster]

In your situation de-rating of conductors may come into play.

 

[surferdude2]

I don't see any need for 3/4" EMT... 1/2" will be plenty loose with only 2 #10 and 2 #12 (thhn/thwn) in it. No need to butcher the studs.

Derating won't affect you since you get to use the 90° C. rating when required to derate.

 

[rjniles]

For #14,#12,#10 THHN conductors derating is not required with 9 or less current carrying conductors.



Sent from my RCT6A03W13E using Tapatalk

 

[surferdude2]

For #14,#12,#10 THHN conductors derating is not required with 9 or less current carrying conductors.



Sent from my RCT6A03W13E using Tapatalk

Yeah, that was always fun when a rookie inspector imposed derating on a conduit fill and found out that limiting the conductors to 80% of the 90° C. rating put them down to a little higher than the already derated limit for #14 thru #10 conductors. One of the times we get to win. :smile:

 

[jbfan]

That's good to know, thanks. I'm not sure where I got that idea.



Okay, so that brings up an issue tangential to this. The room in question has the breaker box in it. There's exposed Romex all over the place, mostly in the joists, going to various parts of the house (no drywall in this room). I want all of that in conduit. I'm assuming an electrician can run THHN in conduit to the edge of the room in question, and then tie it in to the remaining existing Romex (i.e. the stuff still protected by drywall) in a box (I'm obviously not gutting and rewiring my entire house).


Why?

I did not know you could drill bigger holes in steel studs. That makes my life a lot easier.
I was under the impression that for at least load bearing steel studs you weren't allowed to mess with the web holes (but now I can't find the relevant code section). Code is silent as to non-load bearing steel studs, so I was just assuming the same rule applied.

I have to ask why do you want to go through the trouble and expense of basically rewiring the basement of you house.
Are you putting up sheetrock when this project is finished? Are you putting in a ceiling?

Where will you be using steel studs for a load bearing wall?

 

[seharper]

I'm installing new framing in my basement workshop. I'm using steel studs because I like them. All wiring is going to be in EMT because I'm originally from the Chicago area where wires live in tubes like God intended.

My hero!

My understanding is that 20A requires 12G wire, and 30A requires 10G wire. I'm assuming THHN wire. The table at E3904.6 of the Virginia Residential code says that 1/2" EMT can hold 9 x 12G or 5 x 10G. If I go with 240V three conductor (i.e., hot, hot, ground -- no neutral), that's 3 (out of 5) 10G, so 60% fill, right? Add to that 3 (out of 9) 12G, or 33%, I figure I'm at 93% fill, right?

I see where you're going with that, but don't waste the brain cells. Just use any conduit fill calculator.

Oh, and aside from conduit fill, you are confined by derating to 4 circuits per pipe. There's a lot of gory details in there, but the crux is, 4 circuits of any kind per pipe that are 15-30A. (because those are under control of NEC 240.4, which *already* applies a 30%-ish derate, so the 30% derate in NEC 310.15B3a is redundant). Once you are #8 and larger, you are outside the protection of 240.4, and the derate starts to be a problem.

*My understanding is that 30A is the largest 240V allowed to be installed in the house. Please correct me if I'm wrong. Currently my thirstiest indoor tool is my 3HP bandsaw (15A/240V), but if I were to put a large dust collector on the same circuit, 30A might be pushing it...

You can have any amperage of 240V circuit that you can get a breaker for. But you still have to follow the same rules as 120V.

- You can put 15A receps on a 15A circuit.
- You can put 15 or 20A receptacles on a 20A circuit.
- You cannot put 15A or 20A receps on a 30A circuit, only 30A receps.

And on your tools the plugs must reasonably match the power draw. A 15A/240V appliance takes a NEMA 6-20 plug if you're doing 125% derate (which you probably should), most others will take NEMA 6-15.

If you want to bring 30A of 240V to your workshop and divvy it out to multiple 15-20A plug appliances, you must fit a subpanel. I advise using /3 cable and running a neutral also; it will reduce the chance of future idiots installing 120V on bootlegged neutral.

Okay, so that brings up an issue tangential to this. The room in question has the breaker box in it. There's exposed Romex all over the place, mostly in the joists, going to various parts of the house (no drywall in this room). I want all of that in conduit.

And that is why I mentioned the conduit fill derate above. 4 circuits per conduit max, 3 if any circuits are 40A or larger.

Also, when calculating conduit fill for Romex, you must treat it as a single wire whose diameter is the wide dimension (because it twists).

Any splicing from THHN to Romex must be in a junction box that remains accessible. I use 4-11/16" square deep boxes for 4 cables at a time, or 6" x 6" x 10" junction boxes (360 cubic inches) giving physical room to splice 39 cables.

 

[PatentPending]

I have to ask why do you want to go through the trouble and expense of basically rewiring the basement of you house.
Are you putting up sheetrock when this project is finished? Are you putting in a ceiling?

Where will you be using steel studs for a load bearing wall?

I know this is old as Methuselah at this point, but I'd like to answer those questions. For some reason I didn't get (or missed) the email notifying me of this reply (and I haven't logged in in forever).

It's just one room (for now, at least) in the basement hat I use as my "workshop" that I'm completely redoing. I had removed all the sheetrock (including the ceiling -- I like to be able to hang things in the joists), insulation (all soiled because the previous owners had a huge mouse problem they ignored), and framing. I also had the uneven concrete floor completely replaced and topped with self-leveling slurry, which I then put epoxy on.

After all that, I Drylok'd the foundation walls, and put up R10 XPS insulation, per code. The new framing is 2.5" 20G "equivalent" light steel, because I find steel studs to be a pleasure to work with. I will be putting drywall back up, if only because the exposed XPS is a huge fire hazard. I do not plan on putting drywall back on the ceiling at this time.

Anyway, because I still needed power in that room during all this, the original Romex was just kinda hanging out flapping in the breeze. It also had spots that mice had chewed on it, so it needed to go (I think I've also explained that I don't like Romex in general, too). My plan was all EMT, but my electrician explained that EMT usually isn't used behind walls like this even in commercial applications. He convinced me to use MC (the real stuff, not the "lite" aluminum crap).

The load bearing steel studs are part of a completely different project. I've got a thread about it in "Project Showcase" that I need to update.