View Full Version : sort of OT - running electrical wires in conduit

11-14-2007, 03:06 PM
i guess this may be "on topic" as it will be used to power my machine tools.

i need to run some additional 110V and 220V lines in my shop. all of my wiring is in metal conduit, and i plan on running these in conduit as well. i need to run three additional 110V outlets, and three 220V outlets, and i can put them next to each other for convenience. i plan on using 10ga wire for both. is it acceptable to run four wires in a single conduit (say a black, a white, a blue and a red) and use the black and white for the 110V and the blue and red for the 220V?

andy b.

11-14-2007, 03:20 PM

Though I am not an electrician, I do my own electrical work, so I'll relate my opinion.

Last year, I bought my home from somebody who is an electrician. He had a 3-conductor, 12 gauge, wire connecting some lights together. Unknown to me, there were two circuits there with red to white making up one and black to white making up the other. While working on this, the first time, I almost got zapped because one circuit was turned off and the other was still live.

Given what you are suggesting, my first thought is what are you using for ground? Without a ground wire, this is not good. Also, if I were to look at the wires, I would be wondering if you have something rigged up with 3 phase (the blue wire).

So, given the above, my opinion would be no because I don't think it is a standard way of doing things (even with a ground, because the wire colors are wrong)....and if I forgot about how I wired it up, I could have an "enlightening experience" sometime in the future.

As far as the electrical codes are concerned (assuming that you add a ground wire)...I don't know what the correct answer is and I am sure that somebody will let us know. I will be interested in finding out myself.

Personally, I would run 2-conductor 12 (or 10..if it was available, free, etc.) gauge for the 110 volt outlets and 3-conductor 10 gauge for the 220 volt outlets.


11-14-2007, 04:09 PM
There is nothing wrong with running multiple wires in the same conduit if the conduit it properly sized. Of course, you want to use the standard THHN, not romex in conduit. The NEC states that the ground must always be either green or bare. The NEC further states that white is not to be used as an ungrounded conductor. There used to be an exception for putting a piece of colored tape on the white wire to say that it wasn't neutral but methinks this went away in a recent edition though I'm sure that it's still done regularly either way.

The 120 circuits should be run on black (hot) and white (neutral or the grounded conductor in codespeak) to simplify things for you or anyone who has to diagnose it later. Running the 220 on blue and black shouldn't violate anything although my understanding is that running it on an additional red and black pair might be more standard. Don't forget to run a green ground to each box.

I recently encountered a piece of advice from the local electrical supply which suggested I run Type MC, metal clad cable instead of bothering to run conduit and pull wire. It looks a touch less nice but may save some annoying wire pulling if you are lucky.

12 gauge is sufficient for 20 amp outlets either 120 or 220 although you can run 10 gage if you are a masochist, need to combat voltage drop etc. 10 is a lot bigger pain to get to go where you want it to than 12. It looks like the conduit fill calculation is good for about 9 current carrying number 12 conductors in 1/2 electrical metallic tubing so I think you should be alright with 4 current carrying conductors and ground.

So, in summary my personal advice would be to run black and white for the 120's , black and red for the 220's, don't use the white for anything other than what you're supposed to and don't forget to run a green ground wire. If you ask at the electrical supply they'll look crosseyed at you but tell you which size ground wire everybody else uses.

I am not an Electrician, but just took the Fundamentals of Engineering Exam for my engineering license. It's not professional misconduct (yet) if I have this wrong but I'd like to think I've got it right;) I'm sure somebody like David Cofer who is a real electrician will comment and verify if any of this has been botched somehow.

11-14-2007, 05:46 PM
I'm no electrician either, a friend of mine who does this stuff every day, is. So maybe I have no business offering this. Soon, I will need to replace my service cable, I wanted it conduit to protect it from the elements. I have about 100' of #2/0 copper that I would like to use for this purpose. From the wether haed to the breaker box is less than 30', so I think I have enough. He told me I was nuts, but anyhow, he told me that there are requirements on conduit size based upon the number/size and amperage carried in each conductor directly related to what size the conduit must be "by code".

He said this had someting to do with the build up of heat generated by current simply passing along the conductors. Too many conductors, too much heat in too small of a conduit, will lead to insulation degradation. Is what I was told.

11-14-2007, 06:33 PM
Another roll yer own electrician here. I just run romex around the top corner of the shop where the walls meet the rafters. The romex goes into metal boxes with conduit drops down the wall as necessary. Easy to change/add to/etc.

I also stick with the spec wire gage for the circuit. It's been my experience that larger than called for is almost unworkable. On a 15A wall socket the plug in connector won't accept the next size larger wire for instance. Looping 10 ga around a screw terminal is a lesson in, "what made me think this would work?"

Just my .02.


11-14-2007, 07:03 PM
#10 is good for 30 amps.. 12 is a large 120 volt circuit 20 amps breaker.. 14, well I rarely use it anymore except in lighting circuits.

Rarely you will find a outlet capable of that much power (30 amps)

Derating wire, after the 4th conductor in a conduit they must be derated and oversized.

Now conduit size? 66% maximum fill rate with cross sectional of wire/insulation per conduit internal diameter.

I have sixty or so wires in some of my robotics conduits here, have wired Tva's systems with seven miles of wire in 30 foot jumpers on the last good job.

Color coding is a excellent way to keep circuits separate, I'd do all the colors I could buy, then take phasing tape and make "cables" out of bundles, then use cheat sheets to hook them up. Mucho faster than trying to number every single wire before you pull them, then label them afterwards after you cut them and form them into the machine. I used 200 500' reels of #14 in 120' pulls in one machine I remember in particular. Had two minor mistakes, niether of which brought smoke forth. They were on my apprentice's end. We'd take a old set of telephones recievers and actually talk through the wires as we hooked them up. To talk to a young man for 16 hours in one day you must have some interesting jokes to tell and listen to "their life story also".. That machine I mentioned using that much wire, I remember it cause the "materiel cost" was $280,000 for a three day job with nine people involved, materiels were marked up 15% by my employer and he went to the Bahamas and left all us saggy pants electricians in Georgia.
He also stole my airline miles.. Not that I hold a grudge.
I've trained a bunch of electricians in my 30+ years.. most hate my guts.

Ohh yeah,...
BROWN, ORange, Yellow, Purple is High voltage normally, 277, 480
Black, red, Blue is 220,240,120...
White/grey is Neutral (return load carrying)
GREEN or bare gets no power.. only a saftey wire.. oKAY? it shuts the circuit down.

There is a hundred other colors you can use..

While ya got me talking and typing 60wpm..

Notice the white screw on the receptacle? it gets the white wire.. the green screw gets the green/bare wire/ the gold screw gets the "hot wire".. and away you go.. You are on your way to wiring things up. THE little prong on the front is the HOT, the larger prong is the neutral, the round is the ground.. 120vac..
Most house fires, the plug slips out of the recepacle slightly making it no longer able to conduct full power *surface area reduced.. it heats up.. catches fire and burns the house down.. Someone said England and other places require a twist lock for this reason.. There is two ways to install a 120 outlet,, ground on top, ground on bottom.. both is right but either can be wrong.. depends on the inspector and the master electrician.

J Tiers
11-14-2007, 08:22 PM
Use the next larger size EMT (I KNOW you ain't using real threaded "conduit"), or you will not like pulling the oversized wires.

If the breakers are rated for 12 ga (they should be), there is nothing to stop you from pigtailing 12ga off the 10 ga for the outlets (instead of a piece of 10ga) if you think there would be any trouble getting the 10 ga on the screws.

Since the added wires in same raceway would need to be derated, you are probably better off to set more EMT and pull the 220 separately. It will make changes later a lot less of a hassle, and will make the present situation easier also, since pulling all those wires will take some tugging.

I'd also mention that with all those wires in one raceway, you could end up with a "box fill" problem also. Easier to separate them.

Oh, yeah..... use stranded wire....

11-14-2007, 09:17 PM

I am running the electrics for my shop with 3x 2/0 copper and a #6 ground for for a 200 Amp Feeder. In 2 inch Rigid Metallic Conduit, this is fine for running a 200 amp service on 2/0. I believe 3 2/0 and a #6 ground is also fine in 2 inch EMT. I don't believe that EMT is suitable for service masts, running in trenches etc. however so if you need to do any of those things, use rigid metallic conduit or intermediate metallic or perhaps one of the nonmetallic conduits.


11-14-2007, 10:12 PM
okay, thanks for all the replies and i'll hopefully clear up any questions.

the conduit i currently have (and was planning on using more of) is 1/2" metal with the ends that are held together with fittings that are held on with a setscrew. the condut itself is not threaded. i guess this is EMT conduit.

right now there are no green or ground wires in any existing conduits. i am guessing the ground is the conduit itself since it is all metal, the boxes are metal, and the fuse panel is metal, and they are all screwed together. this is an older garage, so maybe it was up to code 50 years ago when it was built.

the vast majority of the wiring is single conductor, solid copper. no romex or multi-conductor cables (except a romex run to my phase converter).

the 220 has to power a 6HP Craftsman air compressor (i know, that is 6 chinese HP), and a 2HP bandsaw that is rated at a nominal 18A draw. i think the existing wiring is 10 ga.

i have a dust collector with a 110V 2HP motor that is listed as nominal 14A and max of 20A. sometimes it takes a couple of seconds for the motor to spin up if i don't have all the dust ports open, and i have on occasion blew out the 20A fuse for the circuit. i was thinking of going with the 10 ga wire and a 25A fuse. although i have no idea if this is allowed, or a good idea.

these wiring runs (both the 110V and 220V will be at least 40'. that is one of my reasons for wanting to go with 10 ga. i thought if you get over 50' you need to go up one size in wire.

yes, i am aware of the issue concerning number of conductors in a conduit and heat build-up.

i am open to any suggestions or warnings. :) i won't be buying supplies until the weekend, so nothing is set in stone. i do like the conduit arrangement for the extra protection it offers the wiring in a shop setting, but the outlet for my phase converter is a run of 4 ga romex with a conduit drop to the outlet. if that is acceptable and recommended, i have no problem doing that instead.

andy b.

Rich Carlstedt
11-14-2007, 11:13 PM
Several things here..
Been wiring all my life, but am not a certified electrician like David
I think your requirements are fine with using a 30 amp 120 volt circut, and the 220 in the same EMT is Ok.
Code says only 2 # 8 wires, or 5 #10 wires are allowed in a 1/2" Conduit.
Code says more than 3 wires in a conduit requires a 80 % reduction in capacity...you still are OK with your loads as I see it, but you choose.
Code says that metal ( continous bonded !) conduit is "ground" so no wire is needed
Code says 220 volt appliances MUST not use a neutral (!)
Therefore you only need 4 wires, not 5.
use a 'RV" 120 volt outlet, they are made for 30 amp service. Do Not use a duplex receptical, or as David pointed out, you may get undesirable effects.
Local codes vary , so you may want to check that.
For what its worth, you cannot have a 120 AND A 240 Outlet in the same Outlet box according to code as well.

11-14-2007, 11:17 PM
MOre EMT help?

Cut the conduit with a hacksaw, not a tubing cutter. tubing cutters leave a sharp knife like edge.. ream it out well. Klein makes a nice screwdrive attachment to do this or you can use a tube reamer.

They also make compression fittings, they have a ring in them like a copper fitting, they are considered drip-tite.

You didn't say anything about straps? one hole? two holes? unistrut channel with straps? support normally in a small area every 6 feet or 6" from a box or termination.

Solid wire, well it is okay but it seems to come loose more often than stranded. After each connection is made, tug on the wire to see if it comes out.. sometimes you get surprised. I can remember a apprentice making up 500mcm (big as a nickel conductor) and I asked him if he beat on the split bolts.. he said nope.. I jerked them out. Fell out so easy it made the apprentice mad at me for a week for embarrassing him. With them split bolts you have to shake them and beat on them to overcome any galling.

When you WIre nut wires together, the ideal nuts are more common, but the wing nuts I like best they seem to tighten well and take up less room. ALSO pull on the wires to see if they caught good. You can twist them with a pair of sidecutters to get them started, then screw the wirenut on them.

Not a real worry about voltage drop till the length goes further than the voltage, then it is time to upsize the wire... #10 should be fine for a "real" 2-3 hp compressor. NOW THAT 7 1/2 I have has to have #6's... and a real 50 amps.

I'd put in another drop or two for the "next machines" you plan on buying.

How are you pulling the wire in? got a fishtape? pushing a pull wire? got lube? polywater or yellow 77? DOn't use handsoap, it has too much alkali and will corrode the jacket and break down insulation early.. usually wire is good for 20 years..

I haven't burnt anything down in years. Ha..

Paul Alciatore
11-15-2007, 02:47 AM
The NEC does limit the number of conductors that can be run in a given size of conduit. And this probably differs with different types of conduit: EMT, plastic, etc. I would suggest purchasing a copy of the latest edition as they are not that expensive and they contain much valuable info.

Oh, one more thing, there are different limits depending on weather the installation is original construction or a later rewiring. At least it was that way the last time I checked. But frankly, it gets rather hard to pull more wires than the new installation limit so this is of limited value.

I am relatively certain that four 10 gauge wires would be OK in almost any size or type of conduit.

11-15-2007, 08:35 AM
HA! Must be a little shop. I used 500MCM in 4" ridge pipe for 400 amp service! Never going to need to upgrade service again! So far the interest on the security deposit pays about half the monthly bill!


I am running the electrics for my shop with 3x 2/0 copper and a #6 ground for for a 200 Amp Feeder. In 2 inch Rigid Metallic Conduit, this is fine for running a 200 amp service on 2/0.

11-17-2007, 11:36 PM
If you're using the type of boxes and covers where the device screws to the cover, (rather than a handy box where the device attaches to the box), don't forget to run a grounding pigtail from the device to the box. The ground connection is not sufficient otherwise. If the device screws directly to the box, you don't have to bother.

I seem to recall that the compression fittings require running a separate ground, but the screw type don't. Check the code or your local inspector for that one. I used all screw type when I wired my shop. I also sed a tubing cutter and then followed with a step drill which removed the burr very effectively. Much quicker and straighter than a hacksaw.

11-18-2007, 12:16 AM
when cutting emt with a tubing cutter if you stop before the cut is complete and snap the tubing apart across your knee it won't leave a burr or sharpe ridge like David Cofer described, kinda takes a little while to develop the feel for when to stop but then its a slick method to cut emt.

11-18-2007, 01:42 AM

I'd have a apprentice caught doing that picking up cigarette butts for a week.
One way to cut it, with a saw. NOW them neat lil battery cut saws with the zip blade.. them work too.

I'm pretty set in my ways of right and wrong thou. My way is right on my jobs. Your way is right on your job.

Another thing a swab rag on the pull fishtape to clean the pipe out. You'd be surprised at the dirt dauber nests I have pulled out of them conduits stored outside at the supply house.

J Tiers
11-18-2007, 10:03 AM
IMO, you SHOULD go ahead and run a ground wire regardless of whether you are "required" to or not.

It is a useful safety feature. Pigtail it to every box if you do.

I've lost count of the number of EMT runs I've seen that were actually loose or disconnected at the machine

Note also that large EMT etc may require a grounding bushing where it enters a box, i.e. a bushing with pigtail connection etc for positive ground.

Paul Alciatore
11-18-2007, 02:49 PM
IMO, you SHOULD go ahead and run a ground wire regardless of whether you are "required" to or not.

It is a useful safety feature. Pigtail it to every box if you do.

I've lost count of the number of EMT runs I've seen that were actually loose or disconnected at the machine

Note also that large EMT etc may require a grounding bushing where it enters a box, i.e. a bushing with pigtail connection etc for positive ground.

I was going to say the same thing. And the EMT is not safe at other locations: anywhere that man, animal, or machine can get to it, it can become dislodged and there goes your safety ground. I also have seen countless conduits like that and many of them were in out of the way locatins where you would never look, even if checking. I NEVER allow an electrician to get away with not running an actual ground wire to every box and device.

I suspect that the electricians must have a powerful lobby with the folks who write the code and the exceptions.

To be safe always run ground wires. EVERYWHERE!

11-18-2007, 03:34 PM

actually it is the fire inspectors that get things that "don't work" changed.

Some electricians smoke and fire follow them around. I cringe everytime I see one old beat up van around town.

We are responsible for the quality of the things we do. Sometimes it means life or death to others.