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Paul Simmel
11-08-2006, 10:29 PM
I’m going to check with the Inspector, but for now how many #12 wires can I run in ½” pipe?



Thanks!

Matt Newton
11-08-2006, 11:03 PM
It depends what kind of pipe you are using. Is it EMT or PVC? Also what kind or wire are you using? Is it THHN? You shouldn't try to run romex through conduit somyou need to use individual wires. Appendix C of the NEC will give you the answers, but if the number is less than 7 you will be fine. Good luck I hope this helps.

Matt Newton

Paul Simmel
11-08-2006, 11:14 PM
Matt, thank you. It is EMT and THHN.

Rob Russell
11-08-2006, 11:16 PM
Paul,

If, by "pipe", you mean EMT, you can run (9) #12 THHN/THWN conductors. That's from Table C1 in Annex C of the NEC.


Rob

David Rose
11-09-2006, 1:31 AM
I think maybe you could get one wife in 1/2" conduit. But wouldn't that be a serious event? ...oh wait... you said "wires"... that is a different subject. Jury, please disreguard the previous statement.

David


I’m going to check with the Inspector, but for now how many #12 wires can I run in ½” pipe?



Thanks!

Russ Filtz
11-09-2006, 8:22 AM
Depending on your run, I would consider upsizing to 3/4 even if the code/inspector says it will fit. If you go through a couple of bends, you can get jamming of the wires. Happened to me running my subpanel.

EE friend of mine said there's a calc for jamming somewhere in the codes. Will tell you if there's a problem based on conduit/wire size and degrees of bend in each pull.

If it's a straight pull, then forget everything I said! :D

Mitchell Andrus
11-09-2006, 10:13 AM
Cheap insurance.... instead of bends, install 'pull boxes' to make adding a new circuit much easier. You'll thank me in a few years.

Mitch

Rob Russell
11-09-2006, 10:57 AM
Something I forgot to post last night and is sort of referred to in Russ' post - derating based on the number of conductors you pull.

When you have conductors "bundled" for more than 24", you need to derate the ampacity (current-carrying capacity) of the conductors based on table 310.15(B)(a). 4-6 conductors means derating to 80%, 7-9 conductors means derating to 70%.

If you're running 1/2" EMT and want to pull (3) 20-amp 120v or 240v-only circuits, you're OK. If you wanted to pull (2) 120/240v circuits where you ran a neutral with the 240v circuit so you could pull a 120v off - that'd be fine also.

If you ran (4) 20-amp 120v circuits and used the conduit as your equipment grounding conductor, you'd have a problem.

I also agree with the other posts about running 3/4" conduit. It doesn't cost that much more and will make the pulling a lot easier.

Rob

Dan Mages
11-09-2006, 12:41 PM
Conduit is cheap, so if you have the room, add an extra run or two. I ran three separate 1/2" conduits approximately 40 ft from the circuit panel to the basement. I was able to pull two pairs of 12aug THHN per pipe with a 1/4" snake with no problems.

Paul Simmel
11-10-2006, 12:15 AM
Thanks, guys,

I appreciate the info! (Another question at bottom)

I know the Topic/question is dumb… I had all of last night off to think about today’s work and the conduit-fill was an important consideration for planning today’s work… and the help was very well taken. (I just couldn’t remember how many wires for ½)

The shop/garage is the first phase of the electrical work I will be doing for new construction. Garage is a 100 amp sub-panel (neutral only back to main panel aside from 1" tightly connected EMT).

I have many pull boxes between rather short runs all over. Everything is ½ EMT thus far.

I was afraid of a bottle neck at the beginning of the run. But I think I’ll be ok.

Thus far, within two ½” 10’ runs before breaking up and distributing to their respective locations, I’d like to feed the following:

a)Ceiling lighting (1 circuit)
b)10 Wall outlets (2 circuits)
c)3 garage door openers, outside lamps (1 circuit)
d)Furnace (1 circuit)
e)Hard-wired compressor (3-wire 220, 1 circuit)

If I ran separate neutrals for each circuit, I’d have 13 total wires to split between the two ½ feed lines.

If I shared ceiling lighting/wall outlets, garage openers/wall outlets with common neutrals, then I’d have it down to 11 wires.

Two part question please?

Re the above, sharing neutrals should be every other circuit, right?

From my current sub-panel… (neutral back to main panel – no grounding outside the 1” EMT)… regarding approximately 4 yet to be run 20 amp, 220 circuits, is it safe/code to share every other (in my case) neutral (third wire)? In my last shop, all my 220 third wires were commonly grounded to the conduit – no neutrals.

Thanks fellas!

Paul

Russ Filtz
11-10-2006, 8:20 AM
Not sure about code, but if you share neutrals, you better be darn sure they are on opposite phases for 120v and still only do it for 2 circuits. Should be able to share a GROUND, but not neutrals without thinking about it.

Same goes for 220v, if the equipment needs a NEUTRAL (like a lot of stoves), it better be a separate wire, not grounded to the conduit. If it's just truly a ground, then you might be alright. If it was me, I'd still run a separate ground wire to the box, and pigtail it to the outlet box.

Kent Fitzgerald
11-10-2006, 8:29 AM
Paul, my quick recommendation would be keep it simple, upsize the conduit as needed, and run a separate neutral for each circuit. If you're convinced, you can stop reading now. ;)

If you want the long version:



Re the above, sharing neutrals should be every other circuit, right?

Sharing a neutral between two 120V circuits (a "multiwire branch circuit" in NEC-speak) requires that the two circuits be fed from the opposite hot legs of the service (i.e., 240V will be present between the hots). If this is done correctly, the out-of-phase neutral currents will cancel, and the neutral wire will not be overloaded. Get it wrong, and the currents will summate, potentially putting 40A through a 12 ga wire. Very bad.

In most panels, adjacent breakers (not "every other" breaker) are on opposite legs. However, this may vary by manufacturer. You need to be 100% sure.

Having said that, my strong preference is to avoid multiwire branch circuits. The reasons I don't like them are:

1. As described above, it's easy to miswire this kind of circuit. This mistake could easily go undetected, as both circuits will appear to work properly, until an overloaded neutral melts or starts a fire.

2. Even if it's done right the first time, subsequent wiring changes could result in a dangerous condition.

3. A neutral fault in a multiwire branch circuit can be disastrous (i.e., 240V applied to a 120V load).

4. Multiwire branch circuits don't allow downstream GFCI protection.

In my non-professional opinion, there are just too many drawbacks to justify the small savings in materials.

Paul Simmel
11-10-2006, 1:27 PM
Russ, Kent,

I think you guys are absolutely correct. I’m going to keep it simple and not share neutrals. I am going to run the appropriate sized conduits as needed and sleep at night.

Now that I think about it, another reason for keeping everything separate is to avoid a hot (A) circuit when the breaker is off, if (B) circuit energizes (pulling through the common neutral)? The only safe way to work on either (A) or (B) would be to turn off both breakers. I might remember this, or I’d alternate red and black hots all the way down, but for someone down the line it could be dangerous.

(Please correct me if I am wrong on that.)

Also, and I forget this sometimes, a major factor in running EMT is to have the ability to pull additional lines in the future, so some larger conduit or extra runs t leaves room. I think I will run some empty chases to strategic locations as well.

Thanks very much for the conversation. It is of tremendous value to me.

Paul

Rob Russell
11-10-2006, 4:49 PM
Paul,

The NEC requires common disconnect for all hots on a single device [210.4(B)], but not on shared circuits. How's that for partially protecting things.

To explain further, I "split-wired on a multi-wire circuit" a large room in our addition. There is a huge wall that could be a place where you might want to put a big entertainment center. I ran 20 amp circuits and did a multi-wire circuit (shared neutral), using 12-3 Romex. There is nothing in the code that requires use of a 2-pole breaker for the multi-wire circuit. I also split-wired the receptacles, so each outlet on any given receptacle is fed from a different hot leg. That way you effectively have 40 amps worth of power available through each duplex receptacle. Because both circuits are tied to a single yoke, I had to use a 2-pole breaker (or handle ties) so shutting off 1 circuit would shut off both.

For shop wiring in conduit, I'd definitely run separate neutrals.

In terms of running extra large conduit so you can pull lots of extra conductors - that's not going to help. You will run into the derating issue. For example, let's say you ran 3/4" EMT because it would allow you to pull up to (16) #12 conductors. You decide to run (5) 120v circuits through it. That means you'd have (10) current-carrying conductors - (5) hot and (5) neutrals, plus 1 equipment grounding conductor. Sounds good - right? Based on the derating table 310.15.B(2)(a), you'd have to derate the ampacity of your conductors by 50%. That means, to run 20 amp circuits, you'd need to pull #8 conductors for your 20 amp circuit - you couldn't pull #12 anymore.

If you're running 20 amp circuits, you can fit a max of (3) 20-amp circuits with separate neutrals running on #12 THHN/THWN in a single conduit before you have to upsize your conductors to #10.

Rob

Kent Fitzgerald
11-10-2006, 6:09 PM
Now that I think about it, another reason for keeping everything separate is to avoid a hot (A) circuit when the breaker is off, if (B) circuit energizes (pulling through the common neutral)? The only safe way to work on either (A) or (B) would be to turn off both breakers.

Paul, your instincts are correct. If the neutral is carrying current, it can become a hazard. The NEC sort-of addresses this by requiring that shared neutrals be pigtailed.

Paul Simmel
11-10-2006, 9:34 PM
Thanks, Kent.

Rob,

That’s pretty confusing. One part of the code says you can run (9) #12 in ½” EMT. But after (3) 20-amp circuits (6 conductors), I’d have to pull #10 conductors for any additional circuits due to the ampacity derating table.

Assuming all is #12 so I don’t get further confused… On this one particular run, I would like to pull at least (3) circuits through (1) section of ½” conduit.

a) shop lights
b) garage door openers
c) furnace

That’s (6) conductors initially. However, one of the circuits will be switched (shop lights) into two zones… so there is going to be an extra hot making it (7) conductors. So, according to the code I’d have to pull that 7th hot as a #10?

Now in reality, the furnace and the door opener circuits will be #14, 15-amp, so I will probably be alright, but I want to stick to your 20-amp example so I can better understand this. After the shop/garage is wired, I will have the rest of the house to do. Because I’m the guy bending and installing conduit, it would obviously be of great benefit to know how to plan additional runs.

Thanks to you, and all others, for your expertise!

Paul

Rob Russell
11-10-2006, 11:29 PM
Paul,

It can be confusing.

The maximum number of conductors in a raceway (conduit) is so there is adequate air space to allow for heat dissipation.
The derating for bundled conductors is similar. If you have a lot of current carrying conductors next to each other, you need to make sure the conductors don't heat up.

The first calculation for sizing your conduit is simply saying how many conductors of a given type and size you can fit in the available raceway cross-section. If 1/2" EMT can take (9) THHN/THWN conductors, that's simply saying that you can fit those conductors in the pipe.

Next, you have to look at the circuits that you want to run and ensure that your conductors have adequate ampacity (current-carrying capacity) for the circuits that you want to run. There are a lot of rules that can affect the amount of current a conductor is allowed to carry. These factors include:

conductor size (gauge), i.e. #12 vs. #14
conductor material, i.e. copper vs. aluminum
conductor type, i.e. insulation and single conductor vs. cable
temperature ratings of the terminals the conductors attach to
etc.When you bundle current-carrying conductors, you make them run hotter. Put too many conductors together and you need to find a way to cool them off. You do that by using a larger conductor which has a higher ampacity and will run cooler. There is a table that specifies how much you have to derate (reduce the ampacity of) conductors when you bundle them for more than 24". Remember that the neutral is a current-carrying conductor. The derating factors in Table 310.15(B)(2)(a) Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable are as follows:

4 - 6 current-carrying conductors - 80%
7 - 9 current-carrying conductors - 70%
10 - 20 current-carrying conductors - 50%
21 - 30 current-carrying conductors - 45%
31 - 40 current-carrying conductors - 40%
41+ current-carrying conductors - 35%

#12 THHN/THWN conductors have a normally rated ampacity for the devices we'd use (switches, receptacles, etc.) of 25 amps. That's using the 75°C column in Table 310.16 Allowable Ampacities of Insulated Conductors Rated 0 Through 2000 Volts, 60°C Through 90°C (140°F Through 194°F), Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30°C (86°F). When you determine the ampacity of a conductor for your specific application, one of the criteria is the temperature rating of the terminals on the devices or equipment you're connecting the conductors to. There are (3) temperature ratings - 60°C, 75°C and 90°C. Take a circuit breaker and look at the teeny print on it - it'll say that it's rated for 60°C/75°C connections. I've never seen anything with a temperature rating higher than 75°C other than the wire itself.

I know that we always think of #12 as being good for a 20 amp circuit. That's because Nonmetallic Cable (aka "Romex"), which is what most of us use for wiring, is restricted to the 60°C column in the conductor ampacity table (310.16) and it's therefore limited to 20 amps for #12 Romex. That restriction is in section 334.80, which is the article that's specific to the installation and use of NM Cable.

The bottom line is that you use the 60°C column in table 310.16 for Romex but can use the 75°C column for THHN/THWN, which yields higher ampacities for the individual conductors in our applications.

So - #12 THHN/THWN has an ampacity of 25 amps using 75°C rated connections. If you bundle (3) 120v circuits in a raceway, that means (6) current-carrying conductors. Again - remember that the neutral is a current-carrying conductor when you're figuring out how many current-carrying conductors you have. From the derating table above, (6) current-carrying conductors means a derating factor of 80%. 25 amps * 80% = 20 amps. In other words, you can bundle (3) 120v 20-amp circuits run through THHN/THWN in raceway because the derated ampacity of the conductors is 20 amps.

If you ran another 120v circuit through that same raceway you now have (8) current-carrying conductors. Based on the derating table above, the derating factor will now be 70%. That derating factor is applied to ALL current-carrying conductors in that raceway, not just the extra one(s) you added to push yourself to the next derating level in the table. If you run #12 THHN/THWN, which has a normal ampacity of 25 amps, with the 70% derating those conductors will be rated for 17.5 (18) amps. You can't run 20 amp circuits through conductors rated for 18 amps (well, there are times you can, but let's not go there now) - so you have to use a larger conductor. #10 THHN/THWN has a normal ampacity of 35 amps using the 75°C column. 35 amps * 70% = 24.5 amps which is plenty of ampacity for your 20 amp circuit.

Does the above make sense to you?

One other thought I'd add is that I wouldn't run #12 conductors, derated such that you can only run 15-amp circuits. You may understand the derating thing now, but a following homeowner may not. I know it's not your responsibility, but I wouldn't want to put in an installation that could be easily overloaded because a future homeowner sees the #12 and thinks it's safe to put in 20-amp breakers, not knowing about what we're discussing here.

Rob

Paul Simmel
11-13-2006, 3:57 AM
Rob,

Thanks for the time you have put into this for me.

Does it make sense? Yes and no.

>>> One other thought I'd add is that I wouldn't run #12 conductors, derated such that you can only run 15-amp circuits. You may understand the derating thing now, but a following homeowner may not. I know it's not your responsibility, but I wouldn't want to put in an installation that could be easily overloaded because a future homeowner sees the #12 and thinks it's safe to put in 20-amp breakers, not knowing about what we're discussing here.

Pulling # 10’s to derate for (4) 20-amp circuits in one raceway (1/2” EMT) would also prompt a future HO think 30-amp breakers are ok for the #10.

So why are (9) conductors allowed in ½” EMT per the same code? The only so-called non-current carrying conductor would be a ground (still a potentially current carrying conductor).

Conductors (wires) are in-and-in-themselves current carrying…. Yet the code says (9) of them are allowed in ½” EMT and (17) in ¾”. I could understand derating conductors in order to exceed the tables limit… but there are only (6) #10 allowed in ½” EMT.

The only raceway where ALL conductors could potentially be active at the same time would be my 220 v. run for shop machinery. Dust collection + at least one other machine and likely the compressor running from time to time during a machining session. I was planning to run either two ½” conduits or one ¾” (4 dedicated circuits) to a junction/distribution box. ½” EMT with one circuit from there to each respective need.

Here’s one chart: http://www.westernextralite.com/resources.asp?key=47

Initially I hired an electrician to install the main panel and the meter hook-up. I’ve asked him twice about how many #12’s I can run in ½” EMT, and twice he told me (9).

I am now fairly confused…

… but will call the Inspector Monday for a definitive answer and will go with his instruction. I have no problem pulling three circuits (6 wires) per raceway, even if the NEC table says I can pull more.

Thanks again.

Paul

Bill Lewis
11-13-2006, 7:41 AM
4. Multiwire branch circuits don't allow downstream GFCI protection.

In my non-professional opinion, there are just too many drawbacks to justify the small savings in materials.

To do GFI properly for these circuits you have to have a 2 pole GFI which are expensive. I wired my last kitchen using a multibranch circuit as described so that each socket in each outlet would be on separate circuits. It was overkill, and probably unnecessary but after living with a kitchen that was on a single 15A circuit for everything... well it made sense at the time.

Rob Russell
11-13-2006, 8:34 AM
Paul,

An example of where you'd have (9) #12 conductors in 1/2" EMT is specifically what you mentioned - (3) 120v branch circuits but where each had an equipment grounding conductor. An example of where that would be used is a hospital or patient care environment and the EGC is isolated and not bonded to the device yoke. In some cases, you could have (4) wires going to a receptacle, where only (2) are considered current-carrying. If you were wiring a space that required isolated EGCs and used plastic because of rust or corrosion, you'd need (2) grounding conductors - (1) for the grounding pin on the outlets and a (1) for the device yoke.

While any conductor can carry current, a "current-carrying" conductor is one that is normally carrying current vs. something like an equipment grounding conductor. The derating calculations pertain to those conductors that are normally carrying current and would therefore be normally subject to heating up. Conceptually, you could overstuff a raceway with nothing but EGCs and nothing would happen because those conductors only carry current in the event of a problem, which wouldn't normally happen. The NEC doesn't allow that, of course.

Derating conductors isn't so you can exceed the conduit fill tables. Derating conductors has to do with preventing heat build up based on bundling. You can run into the very same derating limitations just by running too many "Romex" cables in a parallel bundle.

I didn't post it, but I wouldn't run circuits in my house where I had to use #10 for 20-amp circuits either and for a couple of reasons, but we don't need go into those details.

Rob

Paul Simmel
11-14-2006, 1:46 AM
Thanks Rob,

It is getting a little clearer. For #12 I’ll stick to 6 conductors and run a parallel conduit as needed for addition wires. (6) 12’s is pretty tight anyway.

Do you feel it would be safe to run (4) 110v # 14 circuits, 15 amp, through ½’ EMT? A lot of my lighting is going to be on 15 amp circuits because they will be relatively small. Each circuit should yield 1650 watts… more than enough for our kitchen and dining area, with 10 100 watt cans, for example. Everything else in the kitchen will have separate 20 amp (outlets, deposer, fridge/freezer, hood, etc.

Do you think I’d need to run #12 for three garage door openers all on same circuit? Or would #14 be alright? I don’t know what typically three garage doors would draw. With the way the conduit is installed, it would be no problem to pull #12 to be safe, and once the door openers arrive, check the amperage on each motor. If a 15 amp breaker can handle it, I’ll us a 15 amp breaker and keep the #12 where it is.

So how many current carry conductor can I stuff in 3/4” or 1” raceway? Ideally I’d like to use a once installed raceway as a means to move voluminous conductors from one portion of the house to another … maybe in two places… then split off to a bedroom or a bathroom, etc. I do NOT want to run single 1/2” EMT from the main panel to each respective location/s. I’d like to get the bulk of the conductors up and over to where they can be branched off up into their respective 12” EMT runs. If I could pull 4 or 5 circuits from the main panel to the upstairs, in ¾” or even 1” EMT, this would save me from having to bend and install 2, or 3. ½” side by side EMT runs.

On my shop machinery I will have a minimum of 4 220 v circuits (3 conductors per machine… hence only two machines per ½” EMT run. I can handle this easily enough. I will also have a 220 volt compressor, but I will probably just run a line over there from the sub panel

I think I can easily achieve my needs by sticking to the (6) #12 conductors in EMT for the shop.

Thanks for the help!

Paul

Rob Russell
11-14-2006, 2:12 PM
Paul,



It is getting a little clearer. For #12 I’ll stick to 6 conductors and run a parallel conduit as needed for addition wires. (6) 12’s is pretty tight anyway.

If (6) #12's is a bit tight, remember that you might also have an Equipment Grounding Conductor (EGC) for a total of (7) conductors. The EGC is optional - EMT is acceptable itself as the EGC per 358.60, although I would still run a EGC if I could. That way a loose conduit connection doesn't jeopardize your EGC. Running (7) #12's is well within code for 1/2" EMT but - if that's "pretty tight" - consider going to 3/4" EMT just to make the pulling easier. Upsizing the conduit also gives you the ability to rip out the #12 conductors and pull #10's if you ever, in the future, decided that you needed to run an additional circuit and didn't want to tear the walls open to run new conduit.



Do you feel it would be safe to run (4) 110v # 14 circuits, 15 amp, through ½’ EMT?

Nope.

Unless you're running multiwire circuits and therefore using a shared neutral (which I wouldn't do) - (4) 120v, 15-amp circuits can't run on bundled #14. If you're running separate neutrals for each circuit, which is what I'd do, you're limited to (3) 15-amp circuits running on bundled #14.

The reason is that the ampacity for #14 THHN/THWN is 20 amps using the 75°C column in table 310.16. The derating factor for 4-6 bundled current-carrying conductors is 80%. 20 amps * 80% = 16 amps, which is fine for your 15 amp circuit.

If you try to run (4) circuits with #14, that would mean (8) current-carrying conductors. The derating factor for 7-9 bundled current-carrying conductors is 70%. 20 amps * 70% = 14 amps, which isn't sufficient to run your 15 amp circuits.



Do you think I’d need to run #12 for three garage door openers all on same circuit? Or would #14 be alright? I don’t know what typically three garage doors would draw. With the way the conduit is installed, it would be no problem to pull #12 to be safe, and once the door openers arrive, check the amperage on each motor. If a 15 amp breaker can handle it, I’ll us a 15 amp breaker and keep the #12 where it is.

I would run a 20-amp circuit. That way, if you install (3) heavy-duty door openers that draw 5 amps each and you open all (3) doors at the same time, you won't pop the breaker. In reality, you wouldn't necessarily pop the breaker even if you did have (3) 5-amp loads running off of a 15-amp circuit, but I'd rather have the extra capacity. If you're going to run the #12, you might as well put in a 20-amp breaker.



So how many current carry conductor can I stuff in 3/4” or 1” raceway? Ideally I’d like to use a once installed raceway as a means to move voluminous conductors from one portion of the house to another … maybe in two places… then split off to a bedroom or a bathroom, etc. I do NOT want to run single 1/2” EMT from the main panel to each respective location/s. I’d like to get the bulk of the conductors up and over to where they can be branched off up into their respective 12” EMT runs. If I could pull 4 or 5 circuits from the main panel to the upstairs, in ¾” or even 1” EMT, this would save me from having to bend and install 2, or 3. ½” side by side EMT runs.

I'm going to start to sound like a broken record ... :rolleyes:

Remember that - as you "stuff" more and more conductors into a single raceway(conduit) - you have to derate the ampacity of the conductors more and more. That really starts to take away the reason to run lots of conductors in a raceway.

If you have a lot of circuits that you want to run for the upstairs in your house, it might be practical to install a subpanel "upstairs". You could run a single 1" conduit to feed a 100 amp subpanel. From that subpanel you'd run your branch circuits. Assuming I did the math correctly using Tables 4 [Dimensions and Percent Area of Conduit and Tubing] and 5 [Dimensions of Insulated Conductors and Fixture Wires],1" EMT can take (3) #3 THHN/THWN conductors + (1) #6 THHN/THWN conductor (for your EGC). #3 THHN/THWN is rated for 100 amps, using the 75°C column in table 310.16, and per Table 250.122 Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment, a #8 THHN/THWN is all you need as an EGC for the subpanel, but you can fit the #6 if that's what you wanted to run.



On my shop machinery I will have a minimum of 4 220 v circuits (3 conductors per machine… hence only two machines per ½” EMT run. I can handle this easily enough. I will also have a 220 volt compressor, but I will probably just run a line over there from the sub panel

I think I can easily achieve my needs by sticking to the (6) #12 conductors in EMT for the shop.

Unless you're planning to run 120v loads off of those 240v circuts, you don't need a neutral conductor. That means you only have (2) current-carrying conductors per 240v circuit. You'd still need (2) 1/2" EMT runs for the (4) 240v circuits if they are being wired as 20-amp/240v circuits using #12 THHN/THWN.

Your profile doesn show it - but do you live in Chicago? That's one of the areas where local codes prohibit "Romex".

FYI, I am not a licensed electrician. Your local AHJ (Authority Having Jurisdiction) is the final word in terms of what you can and can't do according to code in your area.

Rob

Paul Simmel
11-15-2006, 3:54 AM
Rob,
I ran (4) #14 curcuits 1l2” emt… so I will have to pull one of them out of there and reroute. Other than that I’m ok… Little work to get it straight.

So the rules for BOTH #14 and #12, is (3) circuits plus a green ground. (6 hot) (1) not. If (4) circuits must run in that line, all must be changed to #12 during the hot spot, for 15 amp ciruicts ITMT, I'm sticking with (3) #14 and #12 cicuits per conduit.


Got it.

Thanks again.

Paul

EDIT: My subpanel doe not hav (EGC)... just the two hot #4's and a # 4 neutral running back to the main panel. The 1" EMT is the ground. For my 220 hookups, I was istructed to run the thrid wire (normally grounded) to the subpanel's neutral. So in my case, I've have three cuncucting wires per 220v circuit. Ithought I'd keep each 220v circuit within its own 1/2" emt, unless (6) 20 amp #12's coukld safely fit.

>>> Unless you're planning to run 120v loads off of those 240v circuts, you don't need a neutral conductor. That means you only have (2) current-carrying conductors per 240v circuit. You'd still need (2) 1/2" EMT runs for the (4) 240v circuits if they are being wired as 20-amp/240v circuits using #12 THHN/THWN.

What am I missing here?

Rob Russell
11-15-2006, 7:55 AM
Rob,
I ran (4) #14 curcuits 1l2” emt… so I will have to pull one of them out of there and reroute. Other than that I’m ok… Little work to get it straight.

So the rules for BOTH #14 and #12, is (3) circuits plus a green ground. (6 hot) (1) not.


This is correct, with a clarification. It's not so much that the "rules" are that you can only run (3) circuits plus [green] Equipment Grounding Conductor in 1/2" EMT - but that's what you get when you do apply the conduit fill and conductor ampacity derating rules.



If (4) circuits must run in that line, all must be changed to #12 during the hot spot, for 15 amp ciruicts ITMT, I'm sticking with (3) #14 and #12 cicuits per conduit.


I take it you mean if you have a section of 1/2" EMT where you must run (4) 15-amp circuits - then, yes, you'd need to upsize the conductors in that section of raceway to #12.



EDIT: My subpanel doe not hav (EGC)... just the two hot #4's and a # 4 neutral running back to the main panel. The 1" EMT is the ground. For my 220 hookups, I was istructed to run the thrid wire (normally grounded) to the subpanel's neutral. So in my case, I've have three cuncucting wires per 220v circuit. Ithought I'd keep each 220v circuit within its own 1/2" emt, unless (6) 20 amp #12's coukld safely fit.

>>> Unless you're planning to run 120v loads off of those 240v circuts, you don't need a neutral conductor. That means you only have (2) current-carrying conductors per 240v circuit. You'd still need (2) 1/2" EMT runs for the (4) 240v circuits if they are being wired as 20-amp/240v circuits using #12 THHN/THWN.

What am I missing here?

First, connecting your Equipment Grounding Conductor to the neutral bus in your subpanel could kill you.

Seriously - all it would take is a high draw, 120v device on that subpanel and there is voltage potential on whatever is connected to the EGC. If you touched a machine and made a path to ground that was lower resistance than your house wiring, you'd become the current return path. That would be a bad thing.:eek:

The EMT is fine as the Equipment Grounding Conductor for your subpanel. However, the neutral has to be isolated in the subpanel. All EGCs connect to the EGC bus in your subpanel. All neutrals connect to the isolated neutral bus in the subpanel. If you are running a 240v-only circuit, you have (2) hots and an EGC - not (2) hots and a neutral.

I'm curious, what size breaker is protecting the #4 conductors - IOW, what is the amperage rating of your subpanel?

Rob

Paul Simmel
11-15-2006, 10:13 PM
Rob,

I have a Square-D, 100 amp sub panel.

I do not have a separate, independent grounding bus. I have two neutral busses, one on each side (right/left of breakers).

I am confused…

The same electrician who installed the main panel, also installed the sub. I asked him twice about my 220 hookups… I told him specifically that the hookups were to be for shop machinery. Two hots and a ground. He told me to use the neutral for the third wire… twice.

I’m not saying you are wrong… I’m saying that maybe, the electrician was thinking DRIER. I don’t know. Driers have two hots, one neutral, and one ground. I frankly at this point do not know what the difference is between 220v driers, and 220v shop machinery… I thought they were the same but apparently not.

In any event, in my last shop all my 220v hookups were (2) hots and a green ground connected to the conduit runs. That past sub panel also did not have an independent grounding bus.

I’d appreciate your opinion on how you would proceed to run your 220v shop machinery given the above.

I obviously do not understand what the difference is… in this case… between running a (green) ground from my 220v outlets back to the sub panel’s metal box, grounding to the metal conduit which runs back to the sub panel’s metal box, or a neutral (white) back to the sub panel’s metal box… all of which runs back via metal conduit and a #4 neutral to the main panel which is in turn all grounded (neutral busses and grounding rod all tied together… not separate or independent from one another.

I put in a call to the Inspector today but haven’t heard back from him.

Please explain why there is a neutral on drier hookups and not for 220v shop hookups. Sorry, I really need to know this for my own sanity.

Thanks for your input!

Paul

Rob Russell
11-16-2006, 12:06 AM
Paul,

I generally won't quote specific NEC articles in this post to keep things briefer. The local codes in your area may be markedly different than the base NEC, but from your last post it sounds to me as if your subpanel is incorrectly installed. Everything I'm posting is based on the unmodified NEC.

First, there is an entire chapter in the NEC devoted to the rules on Grounding and Bonding. The gist of the rules that you need to know about right now are:

The neutral conductor (properly called the "groundED", as in intentionally grounded conductor) and EGC (also called the "groundING" conductor) are tied together at one and only one point. This is called Bonding and is done at the "Service Equipment", which is the point where you have a disconnect from the power company's supply lines. For most of us, this is our main service panel.
As noted above, there is only one Bonding point in our residential services. That means that there can be no connections between the neutral/grounded and EGC/grounding conductors/busses at any other point in the wiring system.
A subpanel has to have an "isolated" neutral/grounded buss. In your main panel, there will be a screw that bonds the neutral buss to the metal panel box. You would also notice that the neutrals and EGCs can land on the same busses. In the subpanel, the neutrals and EGCs need to be separated. This means that a 240v, single-phase subpanel has a 4-wire supply (or 3 current-carrying conductors and something like EMT that acts as the EGC).
If your subpanel is wired such that the neutral busses are electrically connected to the EGC, then it's installed incorrectly.
If your subpanel was wired with EMT and the EMT has good continuity between the main and sub panels, then you can correct the neutral problem fairly easily. You would need to make sure that the neutral busses are isolated - in other words insulated from the metal subpanel box. The 2 neutral busses need to be tied together and connected to the neutral feed from the main panel. You would need to add separate EGC busses and move all of the EGCs to those busses. The EGC busses would mount directly to the subpanel box.
Dryers used to run with the (2) hot conductors and a neutral because so many dryers had a light in the drum. The neutral also was connected to the dryer chassis, in theory to ground the dryer chassis. Anyway - the 3-wire feed is no longer allowed - as you noted, current code requires a full 4-wire feed for new dryer circuits (and ranges - similar situation).
Your 240v machinery should be run with (2) hots and an EGC that ties to the EGC/groundING buss, not the neutral/groundED buss.
FYI, #4 THHN/THWN is really only good for 85 amps. There is a table [310.15(B)(6)] that allows for smaller conductors for services and feeders, but the conductors that run between your main panel and the subpanel are not feeders. This is actually a fairly common mistake. Here's a link to a "Code Question of the Day" archive question that is specific to this topic - CQD Link (http://www.neca-neis.org/cqd/index.cfm?fuseaction=showArchiveQuestion&id=2168).Have I explained this clearly enough, or just managed to confuse you more?

Rob

Paul Simmel
11-16-2006, 11:13 PM
Rob,

Thank you for your time and effort.

No, I understand completely.

My neutral busses on the sub panel are not bonded, so I’m isolated there. Rather than bond them, my solution is going to be to pull a #6 green from the main panel and install an isolated grounding buss and run my machinery greens to that.

Thanks for the info on the # 4’s. The sub panel is fed by a 60-amp breaker at the main panel. All is safe now and clear to me.

Thanks,

Paul

Rob Russell
11-17-2006, 12:23 AM
No, I understand completely.

My neutral busses on the sub panel are not bonded, so I’m isolated there. Rather than bond them, my solution is going to be to pull a #6 green from the main panel and install an isolated grounding buss and run my machinery greens to that.


Paul,

You wouldn't bond the neutral busses in the subpanel - only the main panel.

The subpanel housing needs to be connected to your EGC busses. You do not use isolated/insulated busses for the EGCs. You can use the EMT as the EGC, provided there is continuity from your main panel to the subpanel along that EMT path. You can certainly pull a #6, but for a 60-amp subpanel you only need a #10 EGC (per table 250.122). If you do pull a #6 EGC, you could upsize 60-amp breaker if you chose to do so (see below).

Bottom line, running an new conductor as your EGC is redundant to the EMT - which is fine and guarantees that you'll have contunuity on your EGC - but all of the panel casing, EGC busses and EGCs need to tie in together.



Thanks for the info on the # 4’s. The sub panel is fed by a 60-amp breaker at the main panel. All is safe now and clear to me.


For a 60 amp subanel, the electrician could actually have run #6 THHN/THWN. The #4 is actually upsized, which means you'll have lower voltage drop and motor loads will have more amperage available to them on startup (sort of like having a bigger straw to suck a thick milkshake through).

FYI, #4 THHN/THWN is good for 85 amps. If you run a #6 EGC, you could actually increase the size of the breaker feeding your subpanel if you wanted to, up to a 75 or 80 amp breaker.

Rob

Dan Mages
11-17-2006, 9:36 AM
All of this electrical technobabel... I think I am going crosseyed!!!

:rolleyes:

Al Willits
11-17-2006, 10:44 AM
Just a thought, your running one circuit for lights I see, kinda depends on how many lights you have, but you might want to think of running at least two circuits.

That way if you have to work on your lighting you can still keep one circuit on for light.
Also in my case I'll have about 10-12 fixtures when done, and would like the ability to run just what lighting I need, so I have three seperate circuits and at least 5 switches controlling them.
Bit overkill for most I bet, but it works for me.


Al

Paul Simmel
11-17-2006, 4:24 PM
Rob,

>>> For a 60 amp subanel, the electrician could actually have run #6 THHN/THWN.

I’m the guy who chose the #4, and the 60-amp breaker. The #4 for future upgrades from the sub panel, (it’s closer to the middle of the house) but 60-amps for what I figure my needs will be. Including the shop, I should be able to service the two bedrooms and bath upstairs as well.

If I need to add an 80-amp breaker in the main panel, I will. That’s also why I want to pull a #6 green (EGC) to the sub panel. I agree with you that pulling and additional green is redundant, and in my opinion the 1” EMT will likely never come loose… but, for the very same reason I will be pulling #12 greens from each machine location to the sub panel Grounding buss.

Al,

>>> Just a thought, your running one circuit for lights I see, kinda depends on how many lights you have, but you might want to think of running at least two circuits.

Thanks for the suggestion.

In a 24’ x 35’ “garage”, I now have (6) 64-watt overheads, and will have (8). On the same 15-amp circuit, I will run (5) outside lights (60-watts each).

That’s 812-watts total, roughly half of the 1650-watts a 15-amp circuit will supply. For a lighting circuit, this should be more than sufficient… with room to spare.

The overheads are switched into two zones, and each is plugged into their respective overhead receptacle. If I ever need to service the lighting circuit (cut the breaker) I can plug lights in to a different outlet as needed. (I have (9) 20-amp receptacles on (2) circuits.)

The garage and house is a shell at this point, and I have to wire the entire thing. I’m sure there will be changes along the way.

Paul