Question on grounding wire in EMT conduit

[MN BIANCHI]

I have run a 3/4" EMT conduit from my main service panel to the mezanine area of my shed. The run is approx 60 ft to a large juction box. At the juction box conduits will go in several directions.

I will be running 3 #10 STR, 1 ea black, red and green and most likely 8 #12 THHN conductors of various colors.

Do I also need a green #12 wire between the main panel and the juction box if I am already running the #10 green wire?

 

[wyliesdiesels]

I have run a 3/4" EMT conduit from my main service panel to the mezzanine area of my shed. The run is approx 60 ft to a large junction box. At the junction box conduits will go in several directions.

I will be running 3 #10 STR, 1 ea black, red and green and most likely 8 #12 THHN conductors of various colors.

Do I also need a green #12 wire between the main panel and the junction box if I am already running the #10 green wire?

Yes, u can use the #10 egc for all circuits! NEC 250.122(c) Also, u will have to derate the ampacity off all the wire because more than 9 current carrying conductors are being run in the same conduit! I believe its 50% deration for 12 but don't have my book in front of me!

What exactly are u feeding with all this wire? Have u considered using a small subpanel instead? U may also have to upsize to compensate for voltage drop depending on what you're feeding but I'm too tired for math to figure out for sure! I will figure it out in the morning if no one else responds by then!

 

[madosta]

Dang, 3 #10s and 8 #12s in 3/4!? Y u need so many #12s?

 

[Alchymist]

Good luck pulling all that through 60 feet of 3/4 inch conduit. Subpanel sounds more feasible.

 

[MN BIANCHI]

The number 10's are for a future water heater.
One pair of number 12's is for the well pump. That will be going in later this month.
One pair of number 12's is for a 240 outlet.

Any other number 12's I put in the conduit are spares for future use.

The pull has one 90 degree turn just above the panel, so the pull should be OK

 

[Zeke]

I don't see how that many wires is possible, let alone to code. I've got 3 #10 stranded in older 3/4 conduit with some bends and it was all I could do alone. I may have to re pull it because I don't have an equipment ground.

 

[wyliesdiesels]

The number 10's are for a future water heater.
One pair of number 12's is for the well pump. That will be going in later this month.
One pair of number 12's is for a 240 outlet.

Any other number 12's I put in the conduit are spares for future use.

The pull has one 90 degree turn just above the panel, so the pull should be OK

With those details, I HIGHLY recommend putting in a sub panel instead of pulling all that wire for individual circuits for the following reasons:

1) All of the wire will have to be derated because u are running more than 9 current carrying conductors in a conduit! Since u have 10 or more conductors, they ALL have to be derated by 50%, meaning your #10 THHN wire will be derated to an ampacity of 20a and the #12 THHN wire will be derated to 15a! This means that if you're feeding a 30a water heater you will have to use #6 THHN (75a/2=37.5a)! #8 THHN might work but I don't remember if a water heater is classified as a continuous load or not which would effect the allowable circuit loading!

2)Your #12 wire is @ the maximum distance recommended by the NEC to keep voltage drop @ 3%! This means that if you were planning on running any high amperage devices, you may have to upsize some of your #12 wire!

3) The upsizing of just the conductors for your water heater alone will mean that 3/4" EMT is too small for all the conductors, even when calculating conduit fill based on #8s for the water heater!

EDIT: What I would suggest is putting in a small subpanel, like a 4/8, 70 amp. Keep in mind that u can't have more than 6 disconnects without a main breaker, which shouldn't be a problem since u will have 2 double pole breakers! U could pull 4 #6 THHNs in the 3/4" EMT and be ok(with code, maybe not your hands and back!)...

Good luck!

I don't see how that many wires is possible, let alone to code. I've got 3 #10 stranded in older 3/4 conduit with some bends and it was all I could do alone. I may have to re pull it because I don't have an equipment ground.

Possible to pull, maybe not! But up to code, it is. I just did the calcs!

Did u try wire lube? U could fit 10 #10s in a 3/4 EMT conduit!

 

[Charles (in GA)]

I don't see how that many wires is possible, let alone to code. I've got 3 #10 stranded in older 3/4 conduit with some bends and it was all I could do alone. I may have to re pull it because I don't have an equipment ground.

Not sure what the OP meant by "STR" wire, cannot find it in the code book, and a Google search doesn't turn it up. I'll assume THHN for the calculations.

3/4 EMT has a 100% interior area of .533 in/sq and a 40% interior area of .213 in/sq and 40% is what is used for over 2 wires in a conduit.

12 AWG THHN has an area of .0133 in/sq per wire

times 8 wires is .1064 in/sq

10 AWG THHN has an area of .0211 in/sq

times 4 wires is .0844 in/sq

Thus all the wires add up to .1908 in/sq, which means the wire fill is legal, but will still be a real bear of a pull.

Due to the number of conductors in the conduit, an amperage adjustment factor of -50% will need to be calculated, thus 12AWG THHN which is 30 amps at not to exceed 86°F in conduit is reduced to 15 amps and 10 AWG THHN which is 40 amps at temp to not exceed 86°F will be reduced to 20 amps. If ambient temp is to exceed 86°F then the wire is further derated.

Norcal or Aceman please correct me if I have calculated this totally wrong or I'm somehow out in left field.

Charles

 

[wyliesdiesels]

Not sure what the OP meant by "STR" wire, cannot find it in the code book, and a Google search doesn't turn it up. I'll assume THHN for the calculations.

I think the OP means stranded!

3/4 EMT has a 100% interior area of .533 in/sq and a 40% interior area of .213 in/sq and 40% is what is used for over 2 wires in a conduit.

12 AWG THHN has an area of .0133 in/sq per wire

times 8 wires is .1064 in/sq

10 AWG THHN has an area of .0211 in/sq

times 4 wires is .0844 in/sq

Thus all the wires add up to .1908 in/sq, which means the wire fill is legal, but will still be a real bear of a pull.

My code book lists 3/4 EMT int. diameter as .824 NOT .533! All ur other calcs. and #s are correct and match mine!

The #10 is for a water heater, so it would be 3 wires NOT 4(no neutral)!

Due to the number of conductors in the conduit, an amperage adjustment factor of -50% will need to be calculated, thus 12AWG THHN which is 30 amps and not to exceed 86°F in conduit is reduced to 15 amps and 10 AWG THHN which is 40 amps at temp to not exceed 86°F will be reduced to 20 amps. If ambient temp is to exceed 86°F then the wire is further derated.

Woops, I forgot to mention ambient temperatures!

Norcal or Aceman please correct me if I have calculated this totally wrong or I'm somehow out in left field.

Charles

Charles, did u read my post? U pretty much matched what I said! I'm thinking a subpanel is better! What do u think?

 

[Charles (in GA)]

I think I was composing my post when you posted yours, as I did not see it when I started typing.

My code book lists 3/4 EMT int. diameter as .824 NOT .533! All ur other calcs. and #s are correct and match mine!

.533 is the AREA of the interior cross section, not diameter.

The #10 is for a water heater, so it would be 3 wires NOT 4(no neutral)!

I included the #10 ground conductor, thus two hots, neutral (if needed) and a ground. Yes you could reduce it by one #10.

Charles

 

[Aceman]

EDIT: What I would suggest is putting in a small subpanel, like a 4/8, 70 amp. Keep in mind that u can't have more than 6 disconnects without a main breaker, which shouldn't be a problem since u will have 2 double pole breakers! U could pull 4 #6 THHNs in the 3/4" EMT and be ok(with code, maybe not your hands and back!)...

Going along with what Wylie said, I'd haul three #6's out there Blk, Red, and White with a #10 green. Set a 100 amp main lug subpanel with at LEAST 12 spaces in it. Then go from there.

Or, run another 3/4 conduit out there to split the circuits up better and skip the subpanel.

 

[Alchymist]

Going along with what Wylie said, I'd haul three #6's out there Blk, Red, and White with a #10 green. Set a 100 amp main lug subpanel with at LEAST 12 spaces in it. Then go from there.

Or, run another 3/4 conduit out there to split the circuits up better and skip the subpanel.

One other minor point - if you go with a sub panel, you won't need to chase all the way back to the main panel if you do pop a breaker.

 

[jbberns]

Just run another pipe.

 

[MN BIANCHI]

I went out to my shed today and ran just the wires I plan on using in the next year.
3 #10 XHHW stranded and 4 #12 THHN solid.

According to the Southwire Conduit Fill Calculator the fill is 21.26%.

The pull was very easy.

When and if I need more circuits in that part of the building I will run an additional conduit to the same junction box.

Thanks everyone for the input.

 

[wyliesdiesels]

I went out to my shed today and ran just the wires I plan on using in the next year.
3 #10 XHHW stranded and 4 #12 THHN solid.

According to the Southwire Conduit Fill Calculator the fill is 21.26%.

The pull was very easy.

When and if I need more circuits in that part of the building I will run an additional conduit to the same junction box.

Thanks everyone for the input.

EDIT: Ok, a number of things wrong here. First off, a conduit fill, when there is more than 2 wires, is 40%. But you're fine as far as how many wires u have! Second, the 90c deg. THHN wire must be derated to a 75c deg rating because of the 75c deg. rated xhhw al. When wire with different temp. grades are run together, the higher rated wire must be derated to the lower temp. grade ampacity! Third #10 al. is limited to 25a max, not 30a. Fourth, because u have 7 wires in a conduit, they must further be derated to 70% of ampacity. This means both the #10 and #12 are derated to 17.5a and can be protected with a 20a breaker max! So the #10 will not work for your water heater.

 

[Alchymist]

Ok, a number of things wrong here. First off, a conduit fill, when there is more than 2 wires, is 40%. But you're fine as far as how many wires u have! Second, the THHN wire must be derated to a 75C deg rating because of the al. Third xhhw is rated for 25a max, not 30a. Fourth, because u have 7 wires in a conduit, they must further be derated to 70% of ampacity. This means both the #10 and #12 are derated to 17.5a and can be protected with a 20a breaker max! So the #10 will not work for your water heater.

Depending on the water heater, the #10 on a 20 amp breaker "MAY" work. 4500 watt heaters draw right about 19 amps, depending on actual line voltage. Course that is over the 80% rule for individual circuits. Lotta gotcha's running running around, no?

 

[pattenp]

Ok, a number of things wrong here. First off, a conduit fill, when there is more than 2 wires, is 40%. But you're fine as far as how many wires u have! Second, the THHN wire must be derated to a 75C deg rating because of the al. Third xhhw is rated for 25a max, not 30a. Fourth, because u have 7 wires in a conduit, they must further be derated to 70% of ampacity. This means both the #10 and #12 are derated to 17.5a and can be protected with a 20a breaker max! So the #10 will not work for your water heater.

I may be looking at this out of context, but why is #10 Cu XHHW only rated 25A max? Am I missing something?

 

[Norcal]

If this shed is detached, we have a problem, only one circuit is permitted to a outbuilding.

 

[Aceman]

Ok, a number of things wrong here.

I was going to say the same thing about your post?

First off, a conduit fill, when there is more than 2 wires, is 40%. But you're fine as far as how many wires u have!

Ok.

Second, the THHN wire must be derated to a 75C deg rating because of the al.

What aluminum?

Third xhhw is rated for 25a max, not 30a.

#10 XHHW Cu is rated for 30 amps, or 35 amps under a few specific rules.

Fourth, because u have 7 wires in a conduit, they must further be derated to 70% of ampacity. This means both the #10 and #12 are derated to 17.5a and can be protected with a 20a breaker max! So the #10 will not work for your water heater.

These wires have 90C insulation, so derating starts in that column.
#10 XHHW Cu
40 amps x 70%=28 amps

#12 THHN Cu
30 amps x 70%=21 amps

He could put a typical 4500w water heater on the #10's with a 25 amp breaker and be just fine.

 

[wyliesdiesels]

I may be looking at this out of context, but why is #10 Cu XHHW only rated 25A max? Am I missing something?

In my code book, xhhw wire is listed as 75c deg al. wire. Is that wrong? It also says that #10 al. is suppose to be max 25a breaker!

...What aluminum?

Read what i said above. And when wire with different insulation grades are run together, the higher rated wire must be derated to the lower temp. grade. So i should've said "because of the 75c deg. rated xhhw al." I edited and added to my previous comment!

10 XHHW Cu is rated for 30 amps, or 35 amps under a few specific rules.

Those are the ampacity values for 75c deg. al and 90c deg. al.

These wires have 90C insulation, so derating starts in that column.
#10 XHHW Cu
40 amps x 70%=28 amps

#12 THHN Cu
30 amps x 70%=21 amps

He could put a typical 4500w water heater on the #10's with a 25 amp breaker and be just fine.

xhhw wire is 75c deg. wire not 90c deg. xhhw-2 wire is 90c deg.

 

[pattenp]

wylie, I'm still lost on where you're saying the #10 XHHW is 25A. Where in code are you seeing this? I think we're talking about copper with the XHHW rating, not aluminum. Also my understanding is XHHW is 90c in dry areas and 75c in wet. XHHW-2 is 90c in both dry and wet. See 310.104

 

[wyliesdiesels]

pattenp- my 'code check electrical' lists xhhw as al. Of course, this is the fourth edition based on 2005 NEC. Maybe xhhw cu. wire didnt exist back then. Ive never seen xhhw cu. wire so i didnt know it existed. I was gonna get a 2011 NEC the other day but was shocked @ the $90 price tag! Maybe the OP should specify what type of wire it is. Also, that book lists #10 al. wire max OCPD 25a and refers to NEC 240.4(d) for that limit. I didnt know xhhw had a dual rating either but since its in conduit outside wouldnt that be considered a wet location? I guess i need to do some studying in 310.104....

 

[Aceman]

Wylie, you are mistaken if you think XHHW is only aluminum AND only 75 degree wire.

You need a real code book, not some NEC quick guide or whatever you're using. Everything I posted was straight out of the current code book.

I didnt know xhhw had a dual rating either but since its in conduit outside wouldnt that be considered a wet location?

He never said anything about outside?

 

[wyliesdiesels]

He said shed, so i took that as being outside. I guess im wrong and as i said, i need a new code book....

 

[pattenp]

Wylie, you can get the paperback 2011 NEC for $75 on Amazon.

 

[alfredeneuman]

If you are using EMT, you already have a ground.
EMT when properly installed, is a grounding conductor in itself, & provides less impedance than even a #10 Cu EGC.

You don't need to run a separate ground in EMT (or rigid steel, or intermediate metal conduit either)

 

[pattenp]

If you are using EMT, you already have a ground.
EMT when properly installed, is a grounding conductor in itself, & provides less impedance than even a #10 Cu EGC.

You don't need to run a separate ground in EMT (or rigid steel, or intermediate metal conduit either)

Very true, but properly installed is key. Personally I feel more warm and fuzzy with a ground wire being run as part of the system.

 

[wyliesdiesels]

Wylie, you can get the paperback 2011 NEC for $75 on Amazon.

Ok thx. I'll check it out! Obviously, my 'code check electrical' book and 2011 'Uglys' book no longer cuts it!

 

[Charles (in GA)]

If you are using EMT, you already have a ground.
EMT when properly installed, is a grounding conductor in itself, & provides less impedance than even a #10 Cu EGC.

You don't need to run a separate ground in EMT (or rigid steel, or intermediate metal conduit either)

Very true, but properly installed is key. Personally I feel more warm and fuzzy with a ground wire being run as part of the system.

I agree. Way too easy for conduit connections, especially EMT, to come loose, sustain damage, or in the future be modified by someone, possibly by insertion of some PVC and you lose the ground, or compromise it in some way. Pull the ground, and no question if it is there or not.

Charles

 

[alfredeneuman]

If one tightens the setscrews or glandnuts on the fittings, and tightens the locknuts up as they should be, the EMT won't just fall apart on its own.

"or in the future be modified by someone, possibly by insertion of some PVC and you lose the ground,"

Charles

How can you insert some PVC into the conduit system without first pulling the wire out?

 

[pattenp]

If one tightens the setscrews or glandnuts on the fittings, and tightens the locknuts up as they should be, the EMT won't just fall apart on its own.



How can you insert some PVC into the conduit system without first pulling the wire out?

I didn't see where Charles implied you could insert a piece of PVC without removing the wires. That would be a neat trick.

 

[Charles (in GA)]

If one tightens the setscrews or glandnuts on the fittings, and tightens the locknuts up as they should be, the EMT won't just fall apart on its own.

How can you insert some PVC into the conduit system without first pulling the wire out?

You cannot, but I've seen people extend conduit with splices in it, I've seen it half ripped off the wall and poorly put back, all kinds of stuff that would either eliminate or compromise the ground. If the wire is there, they would extend it to the "new" box if needed, but if it isn't there, they don't give a fleeting thought to the fact, there is not ground.

People hang stuff from EMT, do all kinds of stuff that will loosen the connections, and whose to say that every connection is put together exactly as it should be. A ground wire just doesn't hurt and really doesn't add significantly to the cost.

Charles

 

[walrus]

You cannot, but I've seen people extend conduit with splices in it, I've seen it half ripped off the wall and poorly put back, all kinds of stuff that would either eliminate or compromise the ground. If the wire is there, they would extend it to the "new" box if needed, but if it isn't there, they don't give a fleeting thought to the fact, there is not ground.

People hang stuff from EMT, do all kinds of stuff that will loosen the connections, and whose to say that every connection is put together exactly as it should be. A ground wire just doesn't hurt and really doesn't add significantly to the cost.

Charles

How are you going to prevent someone from hacking a conduit system? Who knows whether they would extend the ground, or need another conductor and use it(the green wire) as a hot which I've seen many times. Emt done right is a perfectly proper ground. Pull in a green or don't, one can't be responsible for someone down the road

 

[wyliesdiesels]

Wylie, you can get the paperback 2011 NEC for $75 on Amazon.

A few posts back I mentioned 240.4(d). How does that apply? Both my books(code check and Ugly's 2011) list it. The book says that #10al is limited to 25a and #12al 20a and for cu- #10 30a, #12 20a, and #14 15a. Does this only apply in certain situations? Thx!

 

[pattenp]

A few posts back I mentioned 240.4(d). How does that apply? Both my books(code check and Ugly's 2011) list it. The book says that #10al is limited to 25a and #12al 20a and for cu- #10 30a, #12 20a, and #14 15a. Does this only apply in certain situations? Thx!

Well hells bells... I see what you're saying. I've read the section a couple of times and there must be a catch, but I don't see one. I've never used Al smaller than #2 for anything so I never had to deal with the amp limits of 240.4(D), so I was unaware of it. You taught me something.

 

[wyliesdiesels]

So Aceman corrected me but I guess maybe I'm right. How does it apply in the OP's situation. Should it all be breakered @ 20a each what with 240.4(d) and 70% ampacity correction for multiple wires?

 

[pattenp]

So Aceman corrected me but I guess maybe I'm right. How does it apply in the OP's situation. Should it all be breakered @ 20a each what with 240.4(d) and 70% ampacity correction for multiple wires?

I had to go back and see where all this started. I'm only going to speak to the wire amp for the #10. I see you were saying 25A for the #10 and agree with what you're saying if it's aluminum. But I assumed the OP is using #10 Copper XHHW and that's what Aceman was thinking when he corrected you.

XHHW does come in copper, but it is XHHW-2....
http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet385

 

[Aceman]

I'm lost at this point......?

 

[pattenp]

I'm lost at this point......?

Actually I didn't want to admit it, but so am I.

 

[alfredeneuman]

#10 & #12 Aluminum wire are not commercially available these days, so it really doesn't matter what their ampacity is.
The smallest wire now available in Al is #8

http://www.southwire.com/commercial/ALBuildingWire30YrsOfReliability.htm