how many wires in conduit allowed?

[Rick Moyer]

I know this is probably in this forum somewhere already. I want to run conduit and wiring in the new shop. I don't know yet how many circuits, how many 220's and 110's , etc; just looking for some general info before planning out the circuits. I know if I go beyond a certain number they get "derated", so I guess I want to know how many up to the point of derating. I believe the grounds don't count? Also can I run #10 with #12 in the same conduit for different circuits? Sorry for the general questions, but will get more specific when I know better what my options are. I have a 100a panel box, so far using one 30a (heater) and one 20a (220 outlet) and one 20a 110 (courtesy box). The rest of the panel is avalable but I don't want to run more conduit than necessary.

Also, I can run lighting wiring between the ceiling joists from above, but I need to get it three ft up the wall first. Can I run this in conduit to the ceiling to a j-box, then run romex out of the j-box above the ceiling along the joist above the ceiling to the lights, or is there a better way?

[Sam Layton]

Hi Rick,

Your question can not be answered without knowing the size of the conduit and the size of the wires is same. I wired my house and shop. I used romex every where I could, (requires no conduit). While going up the walls romex is OK (in Calif) as long as the walls are covered.

As I remember I ran most of my wiring in romex. A lot of the 30 amp 220 I pulled in conduit. I ran a lot of dedicated circuits which required homeruns.

Think about dedicated circuits. I have a 100 amp panel in the shop. I can run my 5hp saw, 3hp dust collector, and 5hp compressor at the same time without any problem. You never know when the compressor will kick in.

At Home Depot I picked up a chart called, "Code check Electrical". It is the same chart the inspector uses and he advised me to get one for myself. It came in handy.

Sam

[Sam Layton]

Hi Rick, it's me again,

Don't worry about how may circuits you have. My 100 amp panel has 40 spaces for circuits. I have 28 circuits in my 750 sq ft shop. all but about 2 are for the shop. The 220 take 2 spaces.

Your best bet is to talk to your local inspector prior to doing any wiring. What is legal in Calif may not be legal in other states. My inspector hepled me a lot when I did my shop.

Sam

[Chris Padilla]

The answer is:

4 if they're fat, 8 if they're skinny :D

We do need more info to properly answer your question. As you begin filling a conduit, you may need to start derating the ampacity of the wire. In other words, the #10 may no longer be considered to carry 30 A...it could be derated to 20 A. The main issue is heat build up amongst all the wires.

[Bill Houghton]

Also, I can run lighting wiring between the ceiling joists from above, but I need to get it three ft up the wall first. Can I run this in conduit to the ceiling to a j-box, then run romex out of the j-box above the ceiling along the joist above the ceiling to the lights, or is there a better way?

Yes, as long as the junction box is accessible after you've covered things up with drywall. I don't know what your local code requirements are, but in many areas, it's not permissible to run romex (technically "NM" - romex is a brand name) in conduit - the combination of the NM sheathing and the conduit can, in theory anyway, result in too much heat buildup.

Remember that NM needs to be properly supported every four feet, and needs to be stapled or otherwise held within 12" of the junction box.

Recommendation based on way too much weekend worrier experience: get a junction box larger than you think you'll need. It's very, very easy to overfill a junction box. Even if you are within code, it's easier to stuff the wires back in and close it up if you have plenty of room. "Larger" can be an oversize box or an extra-deep box or both.

[Chris Padilla]

I always recommend using the largest electrical boxes possible: the 4 11/16" x 4 11/16" suckers. A large variety of mudrings can be a tad hard to find for these boxes but any electrical store will have them.

[Rick Moyer]

I guess I wasn't very clear about some things in the OP. I will have a dedicated circuit for the cyclone, and possibly the table saw and maybe the jointer, too. ALL circuits will be run in SURFACE MOUNTED conduit, except the ceiling lighting. There won't be any drywall or wall covering to be dealt with. I was thinking I might be able to run several 20a 110 circuits in one conduit and split them at the receptacles, thereby having a cleaner conduit run and still having mutiple circuits/outlets available. I'd guess I'd probably homerun the 220's or most anyway. I was hoping someone could give some general info, such as "you can run up to eight current carrying wires in a 3/4 (or 1"?) conduit as long as they are the same amp rating" , etc. so let's assume I use 3/4 conduit and run 20a circuits(110v) with 12ga wire, how many then? what about mixing 110 and 220 circuits, how does that affect the limitations? If this is just too general I'll wait until I know how many circuits, outlets, etc, I want and where they will be, but it would be easier to make some decisions armed wiht a little info first.

As far as the ceiling lighting, my panel box is about 3-4' from the ceiling. I would run conduit from the panel box to a j-box, either at or above the ceiling (which?), and hoped I could then run NM from the j-box parallel with the ceiling joist (above the ceiling) over to where it would come down thru the ceiling into the light fixtures. There is drywall on the ceiling and insulation between and plywood on top of the ceiling joists. Clear as mud?

I appreciate the other details and suggestions given as well. I'll look for that chart, Sam. I wonder if Lowe's has it? Inspectors? we don't need no....:rolleyes:

[David Christopher]

Rick, the answer is chapter 9 ( tables ) in the NEC. it all depends on what size conductor that you are using

[Chris Friesen]

As others have said, the proper answer is to read the NEC, which is available for free (after registration) online at:

https://www.nfpa.org/catalog/services/Login/login2.asp?npg=http%3A%2F%2Fwww.nfpa.org%2Ffreecod es%2Ffree_access_agreement.asp%3Fcookie%255Ftest%3 D1%26id%3D7008SB

[Rob Russell]

Rick,

I will post answers to your questions in a bit. I'm typing this 1-handed because our cat is occupying the other hand.

[Mark Norman]

I didn't read all the replies, but I did read most of em. some good advise posted, I'll chime in with my experience since it is close to what you have going Rick..

I have a 20' X 24' shop I built out of concrete masonry block. with a 100 amp sub panel. Ten 4 bulb 4' fluorescent fixtures and outlets at all four corners of the shop. I could run romex in the rafters but once ya go to conduit you can't run romex, you have to use thhn wire. To run conduit on the surface of the cmu to the outlets I had to add large j-boxes above the ceiling height and transition all the wires to thhn. PITA!! a lot of work considering I wanted to have multiple switches controlling the lighting.

from the sub panel outside there is an 1-1/4" conduit leading up into the attic space carrying all seven circuits, one 220, four home runs for 110 and two lighting IIRC. No,,,correction, eight, one more for the propane cieling mounted heater..

I have a few pics but can get more for ya..

http://i158.photobucket.com/albums/t116/triangle5/random/DSCN1565.jpg

You can just make out the romex in the rafters and the rmc going down the walls and the gas line for the heater. If you look above the overhead door you can make out the wires for the 220 dedicated circuit:

http://i158.photobucket.com/albums/t116/triangle5/random/DSCN1563.jpg

http://i158.photobucket.com/albums/t116/triangle5/random/DSCN1564.jpg

http://i158.photobucket.com/albums/t116/triangle5/random/DSCN1566.jpg

[Sam Layton]

I am sure Lowe's has them. They are really handy and easy to read. They don't have everything in them, but they are handy.

Sam

[Darrin Vanden Bosch]

I believe that whatever size conduit and wire you use
you need to have at least 40% air space in the pipe.
I think this is NEC correct.
Either way this is something you'll need to check with
your local inspector.

Darrin

[Rollie Meyers]

I didn't read all the replies, but I did read most of em. some good advise posted, I'll chime in with my experience since it is close to what you have going Rick..

I have a 20' X 24' shop I built out of concrete masonry block. with a 100 amp sub panel. Ten 4 bulb 4' fluorescent fixtures and outlets at all four corners of the shop. I could run romex in the rafters but once ya go to conduit you can't run romex, you have to use thhn wire. To run conduit on the surface of the cmu to the outlets I had to add large j-boxes above the ceiling height and transition all the wires to thhn. PITA!! a lot of work considering I wanted to have multiple switches controlling the lighting.

from the sub panel outside there is an 1-1/4" conduit leading up into the attic space carrying all seven circuits, one 220, four home runs for 110 and two lighting IIRC. No,,,correction, eight, one more for the propane cieling mounted heater..

I have a few pics but can get more for ya..

http://i158.photobucket.com/albums/t116/triangle5/random/DSCN1565.jpg

You can just make out the romex in the rafters and the rmc going down the walls and the gas line for the heater. If you look above the overhead door you can make out the wires for the 220 dedicated circuit:

http://i158.photobucket.com/albums/t116/triangle5/random/DSCN1563.jpg

http://i158.photobucket.com/albums/t116/triangle5/random/DSCN1564.jpg

http://i158.photobucket.com/albums/t116/triangle5/random/DSCN1566.jpg


This picture shows a good example of what is called "bundling".

http://i158.photobucket.com/albums/t116/triangle5/random/DSCN1563.jpg

Whenever a cable is bundled together for more the 24" it is supposed to be derated, the reality is how bad it is depends on the load(s) being served, but a NEC violation anyway.In the pic the majority of the load is the lights so would be not a major problem..

[Mark Norman]

This picture shows a good example of what is called "bundling".

http://i158.photobucket.com/albums/t116/triangle5/random/DSCN1563.jpg

Whenever a cable is bundled together for more the 24" it is supposed to be derated, the reality is how bad it is depends on the load(s) being served, but a NEC violation anyway.In the pic the majority of the load is the lights so would be not a major problem..
It passed inspecion:D
I also went with 12 guage for all except the one outlet dedicated to the propane heater which is 14. A lil overkill realy for the lighting circuit.

[Rollie Meyers]

It passed inspecion:D

It IMO is not a big deal there, but it is "bundling" I doubt that there will be any problems with it & would not lose a wink of sleep over it, BUT just because something "passes" inspection does not make it correct,there is a thread here where the "inspector" passed SER aluminum cable in a underground conduit and the bare aluminum equipment grounding conductor will fail in time creating a safety hazard.

[Tom Klass]

there is a little yellow book named ugley's it will give you the info you are looking for. it will also give you the formulas for figuring the ratings of the heat the wire bundles will build in the conduit. the book is indispensable in industry. there is also a little red one called pals that is more indepth to electrical also indispensable in industry.

[Rob Russell]

Sorry about the delay in my responding to this post after my “cat” comment. I had a big, long response typed in but I had exceeded the time limit and lost the post.

Derating of conductors starts at 4 conductors in a raceway (conduit) or bundled as Sonny noted in his post. The derating factor from table 310.15(B)(2)(a) for 4 – 6 conductors is 80%. THHN/THWN (the individual conductor that we’d typically pull through conduit) carries an ampacity rating at 75 degrees of 20A for #14 and 25A for #12. Derating that by 80% yields 16A for #14 and 20A for #12. That means we can run up to 6 current-carrying conductors (CCC) in a raceway for 15A/20A circuits and still use the “normal” size conductor that we’d expect to use.

A CCC would be both the “hot” and neutral conductors in a 120v circuit and the “hot” conductors in a 240v circuit. The equipment grounding conductors (EGCs) do not count when we count the number of conductors in a raceway for derating purposes.

= = = = = =

In terms of conduit fill, you can run up to (9) #12 conductors through ½” EMT, although that is the max fill for #12 in ½”. Personally, I’d run ¾” because it will be easier to pull the conductors.

= = = = = =

It is absolutely UNTRUE that it is “prohibited” to run NM cable in conduit. In fact, it is required to protect NM in some cases. The quote from the NEC [334.15(B)] is “The cable shall be protected from physical damage where necessary by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC rigid nonmetallic conduit, or other approved means.”

FYI, even if running NM cable across the tops of attic/roof framing members, the cable needs to be stapled down at least every 4 ½ feet. If the NM cable is being run in an "accessible" attic/roof space (like our garage attic where there is an access hole in the garage ceiling), you need guard strips where the NM cable crosses the joists. That way the cable can't get stepped on or squashed by people or stuff in the attic space.

= = = = = =



To summarize:

If you're using THHN/THWN individual conductors, you can run up to (3) 15A or 20A, 120V or 240V single-phase circuits in 1 run of conduit before derating starts to become a problem.
Use 3/4" to make the pulling easier if you're running more than 1 circuit.

[Rick Moyer]

Thanks Rob. That's the kind of info I was looking for. Three circuits should do me for what I want, if not I'll run another conduit.
The NM run will be stapled and parallel with the joist and where I would need to go perpendicular I can drill thru the middle of the joist. This will be all sandwiched between the ceiling drywall and the attic floor plywood. Now I just need to decide where and how many outlets, etc!

[Rob Russell]

Rick,



A couple of things to note on installing NM cable.

Don't over-hammer the staples. Many homeowners hammer the staples in too hard and crimp the cable. That's really bad because the crimp in the conductors becomes a hot spot. Ideally, the staple should be driven tight enough to hold the cable securely but so that you can still move the cable if you have to pull on it.
Make sure that your cables are at least 1 1/4" in from the edge of the joists. When installing cable in a wall, the 1 1/4" setback requirement is (I think) so drywall screws won't penetrate the cable assuming 1/2" sheetrock. I like to do the same thing when running parallel on a joist.
Based on the amount of electrical work you're doing, I'd pull a permit and have it inspected. It's better for you in the long run. Remember that, if this is a garage or unfinished basement, all 120v receptacles must be GFCI-protected.

I went back and reread some of your posts. You're planning to come up from your panelboard to the ceiling and then run from there. If it's ALL surface-mount, then you're OK. If you are planning to run anything inside the walls, just be aware of the need to "firestop" any penetrations between floors. That means if you drill through the plate that's on top of the studs, you need to caulk that hole with a "fire stop" caulk to prevent fires from spreading up through the holes. The firestop caulk is not regular caulk, but any of the big box stores sell it.

Best of luck on your installation.

[Chris Padilla]

Put those metal "nailers" or "nail plates" on the front of the studs where wires/pipes/etc. penetrate the stud. Just some extra insurance against nicking a hidden item in the wall some day in the future.

I ran some 12/3 NM--yellow jacket on it. Man, is the insulation on these wires thin! Heed Rob's advice about the staples. I "did something" to one of the hots in my circuit run and I'm sure it was from the staple so be careful. My "edison wired" or "multi-drop" wiring ended up NOT SO from there on.