Anotheer NEC question (OH NO!)

[Marty Gulseth]

Hi All,

I've been pouring through the online version of the Nat'l Electric Code, perhaps I've forgotten my way around the book. I'll post my query here in case I'm "mis-remembering" something.

Regarding conductors in conduit (PVC, but for my question, I don't think that matters.) I recall, and I found, the requirements for percentage fill by cross-section area. But I think I'm also remembering something about a maximum number of circuits in the same conduit. Or has my imagination gotten the better of me?

Also - can 220V and 110V circuits run in the same conduit?

Thanks, all!

Marty

[Charlie Velasquez]

Hi All,

I've been pouring through the online version of the Nat'l Electric Code, perhaps I've forgotten my way around the book. I'll post my query here in case I'm "mis-remembering" something.

Regarding conductors in conduit (PVC, but for my question, I don't think that matters.) I recall, and I found, the requirements for percentage fill by cross-section area.
Southwire makes a nice calculator https://www.southwire.com/calculator-conduit


But I think I'm also remembering something about a maximum number of circuits in the same conduit
. Or has my imagination gotten the better of me?
No limit, but your conduit fill will limit you.
You may be thinking of having to derate ampacity as the number of current carrying conductors increases. So running two 120 volt circuits in the same conduit means four ccc, = 80% ampacity. But you get to use the 90°C column to start. NEC 310.15 discusses adjustments.
Edit: This derating usually limits you before the conduit fill. In my shed I ran two 120v 20amp circuits, one 120v 30 amp circuit and one 240v 30 amp circuit along one wall in 3/4” emt. I ran all the conductors in one conduit to the first box 20” away as the derating doesn’t go into effect till the conduit is 24” or longer. But after that first box I needed two runs of conduit or upsize my conductors which would have affected my conduit fill.

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Also - can 220V and 110V circuits run in the same conduit?

Thanks, all!

Marty

It should be noted that conductor counting for conduit fill is different than conductor counting for ampacity derating.

[roger wiegand]

I can answer your second question, yes 240 and 120 can (and for 240 with a neutral have to) run in the same conduit. I'm a big fan of the flexibility that running MWBCs provide for giving you both 120 and 240 at every general purpose access point. (big machines that might run simultaneously got dedicated lines) Yes it's a bit more wire; probably cost me an extra $50 when I wired my shop 8 years ago, half the price of the latest lathe tool I absolutely must have. I've already had 3-4 occasions to swap or add an outlet with changing shop configuration to get more 120 or 240 capability (most recently, for example, I got a deal on a 240 v vacuum pump for the vacuum chuck on my lathe), a trivial task when the wires are already there.

My memory of pulling wires in conduit is that the code allows way more wire than an old guy has the strength to pull. Conduit is so cheap I always upsize it to make it easier to fish the wires through.

[Marty Gulseth]

It should be noted that conductor counting for conduit fill is different than conductor counting for ampacity derating.

I haven’t had occasion to even look at the NEC since I retired over 2 years ago. I had forgotten about the ampacity reduction - thanks for that reminder! Also, the Southwire table is a great add and helpful. Appreciated!

[Marty Gulseth]

I can answer your second question, yes 240 and 120 can (and for 240 with a neutral have to) run in the same conduit. I'm a big fan of the flexibility that running MWBCs provide for giving you both 120 and 240 at every general purpose access point. (big machines that might run simultaneously got dedicated lines) Yes it's a bit more wire; probably cost me an extra $50 when I wired my shop 8 years ago, half the price of the latest lathe tool I absolutely must have. I've already had 3-4 occasions to swap or add an outlet with changing shop configuration to get more 120 or 240 capability (most recently, for example, I got a deal on a 240 v vacuum pump for the vacuum chuck on my lathe), a trivial task when the wires are already there.

My memory of pulling wires in conduit is that the code allows way more wire than an old guy has the strength to pull. Conduit is so cheap I always upsize it to make it easier to fish the wires through.

Thanks for the confirmation, good suggestions! My plan is indeed to oversized the conduit. And about pulling the wire - I’m right there with ya’!

[Bill Dufour]

Remember regardless of what the NEC says the inspector has the final say as to interpretation of the code. So if you are close to being at capacity it is a good idea to upsize the conduit before he fails it. I agree that most people can not pull the wires to fill a conduit to max allowed fill. How many use wire lube indoors? I see it used only for underground main supply lines.
How big do wires have to be before you can use a winch? I would think a single #14 pair would be torn apart if it snagged.
Bil lD

[Bill Dufour]

Are ground wires counted for conductor fill?

[Charlie Velasquez]

Are ground wires counted for conductor fill?

Yes. But the nice thing about that is you only need one equipment grounding conductor per conduit run. So if you’re running four circuits in one run, as I did, you only need to pull one egc. Just make sure to size it to handle the max amp rating of any circuit in the run. In my case I had 20 amp and 30 amp, so I had to pull a 10awg egc. Then pig tail all my other devices from that. (technically, if you’re in a pinch for fill and using a metallic conduit (and metallic boxes or jumpers) you can ground the raceway at the panel and use the conduit itself as a egc, foregoing any additional conductor. I always pull a separate ground anyway.)

They are not counted for derating purposes. Nor are the neutrals on a 240v circuit or a multi-wire branch circuit. Or one of the travelers on a 3-way switch, a few other exotics..

[Rollie Meyers]

Remember regardless of what the NEC says the inspector has the final say as to interpretation of the code. So if you are close to being at capacity it is a good idea to upsize the conduit before he fails it. I agree that most people can not pull the wires to fill a conduit to max allowed fill. How many use wire lube indoors? I see it used only for underground main supply lines.
How big do wires have to be before you can use a winch? I would think a single #14 pair would be torn apart if it snagged.
Bil lD

The AHJ, Authority Having Jurisdiction, has the final say, the inspector is not the AHJ.

[ray grundhoefer]

I have been an electrician in central minnesota for 40 years and the electrical inspector IS the authority having jurisdiction. If you want you can climb the ladder and go above him and speak to regional inspector but you had better be damn sure you are right . And also expect that in any future dealings he will go through everything you do with a fine tooth comb. No, I personally have never done this because whatever you may get away with now you will pay for many times over in the future.
Sometimes the NEC can be very hard to interpret even for people who have followed it for years. If you have anything you are not sure of most inspectors are more than willing to answer questions because they would rather it be done right the first time also