Shared ground wire sizing

[bmxdad]

I'm going to be running several circuits through 3/4" Sch 40 conduit and want to use a shared ground.

Wire is individual THWN/THHN and my plan is to run 4 hot, 4 neutral and a single ground ... one 30 amp, two 20 amp and a single 15 amp circuit. So there will be 2x #10, 4x #12, and 2x #14 wires. Question is, do I use a #10 or go up one to a #8?

I'd like to have the 30 amp circuit be a 240v circuit, but don't think that is legal. Still looking in 2008 NEC to see if it is. If not then it will be omitted, so 7 wires instead of 9.

 

[wyliesdiesels]

Yes its legal to share a ground/EGC. U could even use the conduit if its metal. However, all your conductors need to be derated, which means u may need to upsize. 4 or more require derating....so your ground wire would have to be proportionately upsized as well....

 

[Eriehunter]

You size the ground according to the largest breaker.

After derating if necessary.

240v is OK in the same conduit.

 

[alfredeneuman]

7 thru 9 conductors require the circuits to be derated to 70%.
The #10's , thus will be derated to 28 Amps (40A on the 90°C rating, which is the one used for derating THHN/THWN). Those will need #8s, along with a #8 ground.
The #14s and #12s are OK even when the derating factors are applied.

You'd probably be better off running a 1" PVC for that.

If it's going to be run to a detached structure then it would be illegal, as only 1 circuit may be used to feed a detached structure.

 

[bmxdad]

Awesome .... this is a detached pole garage, and the 3/4" conduit is already run under the pad. So all good, just need to run #8 instead of #10. NEC References?

Conduit question ... This run is taking power to a wall opposite the sub-panel, so could I switch to metal after feeding under the pad with the schedule 40, and use the conduit as the ground from there? Might be a little cheaper and easier to wire everything up.

 

[CNGsaves]

You're running 4 wires to garage itself ?? Detached garage must be 4 wire and have it's own two grounding rods outside.

So these runs are AFTER the main subpanel to garage??

If so, how about Sub-Subpanel from the garage's Subpanel from house?? Doesn't make sense that you're wanting to run bunch of circuits through underground conduit (thus redundant long runs), rather than just put Sub-Subpanel in other location of garage and go from there.

 

[alfredeneuman]

NEC References?

Provided that the subpanel is in the same structure..........

Table 310.15(B)(3)(a) Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable
Number of Conductors Percent of Values
4–6 --------------- 80
7–9 --------------- 70

Table 310.15(B)(16) Allowable Ampacities of Insulated Conductors Rated Up to and Including 2000 Volts, 60°C Through 90°C (140°F Through 194°F), Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth

#10 ---- 30A @ 60°, 35A @ 75°, 40A @ 90°
#12 ---- 20A @ 60°, 25A @ 75°, 30A @ 90°
#14 ---- 15A @ 60°, 20A @ 75°, 25A @ 90°

250.122 Size of Equipment Grounding Conductors.
(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors

 

[Blk88GT]

Conduit is not suitable as a ground conductor anymore up here in Canuckistan, not sure about down there.

 

[bmxdad]

You're running 4 wires to garage itself ?? Detached garage must be 4 wire and have it's own two grounding rods outside.

So these runs are AFTER the main subpanel to garage??

If so, how about Sub-Subpanel from the garage's Subpanel from house?? Doesn't make sense that you're wanting to run bunch of circuits through underground conduit (thus redundant long runs), rather than just put Sub-Subpanel in other location of garage and go from there.

Yes, I have a 100 amp sub-panel in a detached pole garage ... too code as I already passed my final. I also have sch 40 conduit routed under the slab to the opposite walls, so I don't need to fish it up and over.

I'm looking to add some 20 amp outlets, a switched 15 amp outdoor light and a 30 amp, 240v compressor hook up on this wall.

Provided that the subpanel is in the same structure..........

Table 310.15(B)(3)(a) Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable
Number of Conductors Percent of Values
4–6 --------------- 80
7–9 --------------- 70

Table 310.15(B)(16) Allowable Ampacities of Insulated Conductors Rated Up to and Including 2000 Volts, 60°C Through 90°C (140°F Through 194°F), Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth

#10 ---- 30A @ 60°, 35A @ 75°, 40A @ 90°
#12 ---- 20A @ 60°, 25A @ 75°, 30A @ 90°
#14 ---- 15A @ 60°, 20A @ 75°, 25A @ 90°

Perfect, thanks alfredeneuman. If I can read it myself it sticks in my head better, and I have an idea on where to look next time

Conduit is not suitable as a ground conductor anymore up here in Canuckistan, not sure about down there.

Any info on this? Must be a reason to change.

 

[Eriehunter]

Awesome .... this is a detached pole garage, and the 3/4" conduit is already run under the pad. So all good, just need to run #8 instead of #10. NEC References?

Conduit question ... This run is taking power to a wall opposite the sub-panel, so could I switch to metal after feeding under the pad with the schedule 40, and use the conduit as the ground from there? Might be a little cheaper and easier to wire everything up.

the conduit question.

You can do that if you have a ground wire in the pvc to the first metal box and pigtail to the metal box, I don't like to do it that way and I don't recommend it. I recommend a ground wire in the conduit the entire way and pigtailed in each box and pigtailed to the device in each box.

 

[bmxdad]

the conduit question.

You can do that if you have a ground wire in the pvc to the first metal box and pigtail to the metal box, I don't like to do it that way and I don't recommend it. I recommend a ground wire in the conduit the entire way and pigtailed in each box and pigtailed to the device in each box.

Just talked to an electrician ... no more using EMT as a ground. Since around 2004/5 you cannot use EMT as a ground. You must have a wire for ground in all conduit.

So ... thats that. Might just branch the 30 amp/240v circuit to its own EMT. If I did that, would I then be allowed to run a #12 ground to the other circuits, and just tie it into the #8 where they branch out. Basically having a 20amp ground tie into the 30 amp ... make sense?

 

[CNGsaves]

You trying to use strange wire with no ground??

Why not just put up another SubPanel on that side of garage (fed with your underslab conduit), and branch out with legitimate circuits on a breaker??

 

[alfredeneuman]

J
Might just branch the 30 amp/240v circuit to its own EMT. If I did that, would I then be allowed to run a #12 ground to the other circuits, and just tie it into the #8 where they branch out. Basically having a 20amp ground tie into the 30 amp ... make sense?

Yes it is perfectly acceptable. In addition if you separate the 30A circuit from the others you'd be able to use #10 with a #10 ground, and just splice them to the #8s.

 

[bmxdad]

Sweet ... even better. Now to learn the art of bending EMT

 

[Cmreschke]

What is your compressors fla? (Current draw)
You say an electrician told you emt no longer allowed as a ground path, is that a local amendment, because it is not an NEC rule.
Note if you run your compressor in a second conduit by itself it only needs a #10 size wire for each conductor as you don't have to derate it for more current carrying conductors(you would have 2)

 

[bmxdad]

Compressor will be 20 amp/3.1 hp. Craftsman Professional 60-gallon air compressor

 

[pattenp]

Compressor will be 20 amp/3.1 hp. Craftsman Professional 60-gallon air compressor

I'd buy a different compressor if I were you.

Something like this...
http://www.northerntool.com/shop/to...i_sku=305175&gclid=CLX-iZv3ysECFVNk7AodvDwAzQ

or even the Kobalt 60 from Lowes.

 

[bmxdad]

I'd buy a different compressor if I were you.

Something like this...
http://www.northerntool.com/shop/to...i_sku=305175&gclid=CLX-iZv3ysECFVNk7AodvDwAzQ

or even the Kobalt 60 from Lowes.

I haven't bought it yet, but why the warning? There is a Puma for sale on CL.


Edit: $250 for shipping??

 

[Eriehunter]

Just talked to an electrician ... no more using EMT as a ground. Since around 2004/5 you cannot use EMT as a ground. You must have a wire for ground in all conduit.

I am an Electrician.

2008 NEC 358.60 EMT shall be permitted as an equipment grounding conductor.

We are on the 2008 NEC here in Erie Pa. Either the code has changed since 2008, your electrician friend is wrong or there is a local code that applies.

However I still recommend pulling a ground in EMT especially if you are using compression fittings.

 

[pattenp]

I haven't bought it yet, but why the warning? There is a Puma for sale on CL.


Edit: $250 for shipping??

I just don't think the quality is there with Craftsman compressors and I personally don't like the aluminum pump with steel cylinder sleeves. Plus with the way Sears is going these days with more store closures I'm not too sure about their future. I just think you can do better for the same price.

 

[bmxdad]

Fair enough ...

New question ... when running individual wire, does the ground need to be coated? For instance, I was given 250' of 8/2 with ground ... for free. It's cable/Romax, which is not usable in conduit. So what if I just stripped it to individual wire? I'd have a black, white and bare ground. Can this be run in conduit? It would start with schedule 40, and then into 1/2" EMT.

Doable?? If not ... how come??

 

[Eriehunter]

The ground wire is permitted to be bare.

 

[TheEquineFencer]

Fair enough ...

New question ... when running individual wire, does the ground need to be coated? For instance, I was given 250' of 8/2 with ground ... for free. It's cable/Romax, which is not usable in conduit. So what if I just stripped it to individual wire? I'd have a black, white and bare ground. Can this be run in conduit? It would start with schedule 40, and then into 1/2" EMT.

Doable?? If not ... how come??

You cannot legally use stripped Romex inside conduit, it's not marked or rated for that use.

 

[bmxdad]

Dang ... NEC ref?

 

[Cmreschke]

If your compressor is only drawing 20 amps why pull # 8s? Just pull your tens you will be fine.

 

[Stuart in MN]

Dang ... NEC ref?

If you look at the Romex, there is stamped identification on the exterior sheath to show what it is, what size, what it's rated for, etc. However, if you strip off the exterior sheath to expose the individual wires you'll note they are not marked. As a result, they are not listed for individual use. It may be a technicality, but that's the way it is.

In any case, #8 wires will be too big to fit in a 1/2" conduit.

As has been discussed here many times, Romex can in fact be installed in a conduit, as long as the conduit is sized properly.

 

[alfredeneuman]

In any case, #8 wires will be too big to fit in a 1/2" conduit.

As many as 3 - #8 THHN/THWN conductors can be installed in in 1/2" EMT by Code.

 

[Stuart in MN]

As many as 3 - #8 THHN/THWN conductors can be installed in in 1/2" EMT by Code.

Depending on which calculator you use, it will come up with 1/2" or 3/4" minimum size - with three #8's, there a potential jamming issue in 1/2" conduit.

 

[Cmreschke]

Depending on which calculator you use, it will come up with 1/2" or 3/4" minimum size - with three #8's, there a potential jamming issue in 1/2" conduit.

No calculator, it's in a table. Use a 3/4 in bender to bend 1/2 and you will be ok.
Also the cost diff between 1/2 and 3/4 is minimal personally I would run 3/4.

 

[bmxdad]

If you look at the Romex, there is stamped identification on the exterior sheath to show what it is, what size, what it's rated for, etc. However, if you strip off the exterior sheath to expose the individual wires you'll note they are not marked. As a result, they are not listed for individual use. It may be a technicality, but that's the way it is ...

OK, that makes sense ...

The #8 is for a Welder outlet. I have #10 for the compressor. I learn'n ... slowly, but getting there.

 

[alfredeneuman]

Depending on which calculator you use, it will come up with 1/2" or 3/4" minimum size - with three #8's, there a potential jamming issue in 1/2" conduit.

It's right there in writing in the actual NEC book.

Annex C.1 — Electrical Metallic Tubing (EMT)

No calculator needed.

I've run 3 - #8s in 1/2" EMT numerous times. It will PUSH through 1/2" EMT in lengths of about 30' with no fishtape required.