Calculating Conduit Fill

Leo G

When you are calculating conduit fill by cross sectional area, is it the c.s.a. of the wire ga or the actual cable size.

Or more direct I need to run five 8ga and one 12ga (THHW) in a conduit. Can I put that in a 3/4" conduit. It is going to be in EMT and run about 100' with 4 bends.

I would rather know both answers so I can figure things out for myself later on. Thanks

Leo

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mdshunk

The total cross sectional area of 3/4" EMT is .5330 square inches. You're only permitted to fill a conduit that contains more than two wires to 40%. In your case, the conductors (along with the insulation) may only fill the pipe to .2132 square inches.

Yes, the insulation does count. For instance, 8 gauge THWN has a cross sectional area of .1830 but 8 gauge RHH has a cross sectional area of .2780.

In your case, the five #8's and the one #12 THWN have a total cross sectional are of .1963 square inches, which is less than the .2132 you have to work with. With such a long run and the max number of 4 quarter bends in this run, upsizing to 1" would make your pull so much easier.

You can find the cross sectional areas of the various conduit types and wire/insulation types in the tables in chapter 9 of the NEC.

mdshunk

If this is for your exhaust, I'm a little puzzled about the conductor choices. Three #12's for the motor, a #12 for the ground, and two #12's for the thermostat would be my choices.

Leo G

The thermostat wires on the 3HP motor were labeled P not T (2 white wires, all others were (9) yellow wires with numbers on them), I am assuming that there is no need for me to worry about the different letters.

Believe me, that's what I would have run also. Maybe 10ga because of the length. But the listing that came with the motor stated 3HP 50ft run needed 10ga and a 100ft run needed 8ga . The name plate on the motor states that the current draw is a little more than 8 amps 3 PH. The SFA (?) was 9.7 but I haven't a clue what that rating is for. Going by memory on those abbreviations so the letters could be wrong. The run I need is about 90 ft. Are they oversizing the conductors because it is a hazardous location motor?

While I have you here , When I run the 3 PH I also need to power the 120 system in the room. I am assuming that I can have 3 conductors for the 3PH hots (L1,2,3) a neutral and a ground. I assume I should still run the 2 seperate hots (two breakers) for my 120vac. So I would have (according to my motor manual) Three 8ga (L1,2,3) for the motor circuit, and three (or 4) 12ga ((1 or 2)120 hot, neutral, ground). Is that still going to make it in my 3/4" EMT? I couldn't find anything on NEC Chapter 9 through the internet, so I was hoping you could give me some of the THHN, THWN c.s.area (w/insulation) 8, 10, 12ga should cover it.

Here is a drawing of what I think I need to do for the conduit run. Do you think I should ignore the motor manual gauge ratings and just go with the 12ga for all of my runs (I do).

Sorry to be such a PITA. So far you've been a great help, thanks a bunch:Thumbs: .

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mdshunk

Those gauge sizes that came in the paperwork reccomendations make more sense for single phase 3 horse motors. For a 3 phase motor, they're way big. Twelve gauge is upsized already, since #14 would do. With #12 doing 100 feet with a 9 amp load, you're only looking at a very miniscule 1.3% voltage drop at the motor.

Run your general power circuits in another conduit. If you don't, you'll get into a issue called derating for when you have more than 3 current carrying conductors in the pipe. That makes things messier yet.

mdshunk

I havn't sprung on you yet about the special wiring methods involved with wiring a motor in a hazardous location yet.

Leo G

So if I run my power in two seperate conduits I should be able to go with 1/2" conduit, correct? Four 12ga (L1,2,3+gnd) in 1 conduit and Four 12ga (2 hot, neutral+gnd) in the other.

I see you posted again, well, you might as well SPRING it on me before I get started.

The motor is mounted on top of the tubeaxial fan, the motor will be exterior to the spray area seperated by fire rated sheetrock with a sealed metal access plate for maintenance. The spray room is really a building within a building, so I have a 2 foot space between the interior spray room wall and the exterior outside wall which is where the motor will reside. The box on the motor has a threaded inlet. I was planning on using a threaded steel conduit which would be going to the sealed control box which is also exterior to the spray area. The motor contactor will be activated by an RF remote control to keep any sparking exterior to the spray room. The only real issue I am going to have is my 120vac outlets in the room which are going to have sealed covers, but not explosion rated . So lay the dreaded news on me. And I really appreciate the fact that you didn't immediately come down on me right away about the hazardous nature of this project. And I am glad that you can help me along with this so that I can keep everything a safe as possible. I am trying to keep this as close to code as I can and when my budget won't let me I will upgrade in the future when it does allow. I've sunk about $6K into this so far (and more $ to come, err.. go) so I want to make it as safe as I can.

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mdshunk

Any conduit that is actually in the hazardous area has to be threaded IMC or Rigid. When the conduit exits the hazardous area, you have to transition in a seal off fitting (looks like a plumbers wye, with a cap that you pour in the sealing stuff), then you can change to whatever raceway system pleases you. I guess you already know that you can't use regular receptacles in a hazardous area. There are special receptacles and associated plugs that you use in a hazardous area. There's tons of special tools like drills, hand lamps, etc. rated for use in such an area. The receptacle boxes are to be what's called "FS Boxes", which are cast iron with a cast threaded hub for the rigid conduit to screw into.

Most of the time spray booths have all the conduit on the outside of the box, then you just nipple through into the fixture or box so that you have little conduit inside.

User SpeedyPetey can straighten you out more on hazardous location wiring. He's the expert on that.

mdshunk

Oh, yeah. If you're running two conduits, 1/2" will be fine. Plus, that's easier to work with if you havn't worked with conduit before.

Leo G

I've played with enough conduit to get by. Thanks for all your help tonight. If you every have any questions about woodworking, cabinet making and such, I'm your man. Have a good one, and I'm sure I'll be back with some more simple (for you) questions. Thanks Again:Thumbs: .

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mdshunk

You've got that right. I took a look at your website, and I had my socks knocked off. That kitchen with the slant front uppers was super nice. Your style appeals to me. Some of those mantle surrounds and paneled rooms look like many of the historic homes in my area. Almost everything around here was burned by the confederate army, so most of the historic construction happened right after the civil war, which is the period you seem to specialize in.

Leo G

Just to prove to you I'm not totally nuts MD, here is a copy of the motor manual I got with my 3HP 3PH motor. It shows the wire sizes it recommends.

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Leo G

Ran my 2 conduits, a 3/4" and a 1/2". 4 wires in the 1/2", 3 hots, one ground. In the 3/4" I ran 5 wires, 3 hots, a neutral and a ground. I may add another circuit later on. It took me two nights to run everything. The first night I spent doing all the complicated (for me) bends and mounting the large box to hold my contactor and wireless remote, a fused 3 PH shutoff switch box, the rigid conduit to the motor and the wiring to the contactor box to the motor itself. About 6 hours. The second night I ran the conduit from the Main box to the conduits attached to my system boxes. Pushed the wires through the 2 conduits. Had trouble with both pushes, got stuck at 40' at a small bend to go over another existing conduit on both the 1/2" & the 3/4". So I pulled the conduit apart and threaded a fish tape from the other end and it was smooth pulling from there. Wired up the contactor and the fusible shutoff. Now I am waiting for my circuit breakers to come by UPS, most of the electrical distributor outlets in my area only carry Square D stuff and my box is Siemens, I needed the QP style. Got the singles for $4.75 and got the 3 PH breaker for $48. Total time on the second night was 7 hours, which included a trip to HD for some missing stuff. Total of 13 hours which included a self taught lesson in bending conduit and being at both ends of the pull (not to easy to pull off by ones self, LOL). I think I did pretty well and the job looks very professional, I think you would be proud of me. So that's my story (and I'm stickin' to it). Thanks for the info MD. Did that check come in the mail yet???

Leo

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mdshunk

Good job, Leo.

There's a little trick to pulling I'll pass on. If you take a piece of sandwitch baggie or plastic grocery store bag and loosely wad it up and stuff it in the end of the pipe with a lightweight string attached, you can shop vac the string through the pipe. Duct tape the shop vac onto the other and and feed the string in. In just a few seconds, you'll have a pull string installed. There is specialized equipment designed for this purpose that basically does the same thing, but almost everyone owns a shop vac and can round up some mason line and a wad of plastic or even a hunk of sea sponge.

Did you use the sealoff fitting where started the rigid conduit run to the hazardous area?

Leo G

I ran the rigid all the way from the motor to the box. The box is a 10" x 10" metal rainproof box, so that's not hazardous rated, but it is not near the hazardous area. I went from the motor box, which has a hazardous threaded box, using 3/4" IMC to a hazardous round box (definitely out of the hazardous area now) for a 90º turn to a rigid 90ºfitting, into a sealed rigid to box fitting. So I guess the answer is no. What is the sealant that needs to be used? Is it an epoxy or will silicon caulk do the same thing for me. The motor is not even in the hazardous area to begin with. It is separated from the area by fire rated Sheetrock and the Tubeaxial motor isolates the motor from the air stream. My spray room is a room within a building, the motor resides in a space (2' wide hallway between room and building) between the walls of the spray room and the building.

How do you think I did time wise. I had to run the conduit 10' 6" off the floor for 40' to get by some obstacles and move a lot of stuff out of the way to do it. The rest was still at the same level but I had to climb on (by ladder) the back hallway 2nd story section so it was really only 2.5' while I was on the 2nd story.

Leo

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Leo G

Hey MD,
Got my breakers in today, yippee:Thumbs: . Wired things up in the main box and hooked up the remote control to the contactor coil, went into the room and hit the remote, dang, backwards. Killed the power, opened the motor box and reversed the black and red and then turned the power back on and holy crap.. 3 HP on a 36" fan can really pull some air, and make some noise. So everything is spinning well, thanks for all your help.

Leo

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Teetorbilt

md, In a similar situation, my electrician installed a separate breaker from my main panel to a disconnect outside to a subpanel in my detached shed/garage. He's licensed and has worked for me for many years. Your opinion?

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mdshunk

Sounds like he did a good job. The outdoor disconnect would be a nice extra and is not required by the NEC, but it might be a local code modification. In any event, it sounds like a good job.

747

All new construction residental in Chicago has to have conduit by code. Meaning not just skyscrappers but also residental. I Think if you rehab you have to change over to conduit. Ya thats correct because when bob vila came to chicago did a rehab the electric. guy had to conduit everything.

MD you could pad your bill good in chicago :Thumbs:

Teetorbilt

Thanks for the input md. I like keeping track of my guys.
The disconnect may be required locally, I don't know. That is why I hire the best pros. Nobody can keep track of every detail nowdays, the details keep changing.
Working in old wood keeps me sane, it's always the same, unpredictable.

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