Consolidating grounds in a J box?

[The mean fish]

I've got a steel 12 x 14 enclosure which I'm using as a J box in my shop space, I've got 2 PVC 1 1/4" conduits running from this J box to my breaker panel about 30' away and I'm running EMT all over the shop back to this J box. I'm going to end up with about 9 outlet circuits and 2 lighting circuits running through this box. Everything is running over #12 THHN and I'm thinking about installing a ground bar in this J box then running some larger THHN ground wire back to the ground bar in my breaker panel.

I've got some green #4 THHN I could use for this and I had planned on grounding this enclosure anyway. As long as I'm using big enough wire is there an issue if I combine the grounds on these 20amp circuits inside this J box?

You can see the J box in this photo, right now I have my lighting circuits running through it but I haven't installed the ground bar in the box yet.

 

[C96]

In this case you’re talking about an equipment ground.

Your equipment ground needs to be sized according to the largest circuit running through each of the conduits. In other words, if the largest circuit is 20 amps, then 12 AWG would be all that is required. 60 amps would be 10 AWG, 100 amps 8 AWG and so on.


Remember, you must have an equipment ground wire pulled through both conduits if both are being used even though they both go to the same place.

Using a ground bar is a good idea, it will keep the wiring nice and neat and yes, you can use your 4 AWG for this, but talk about overkill….

 

[The mean fish]

In this case you’re talking about an equipment ground.

Your equipment ground needs to be sized according to the largest circuit running through each of the conduits. In other words, if the largest circuit is 20 amps, then 12 AWG would be all that is required. 60 amps would be 10 AWG, 100 amps 8 AWG and so on.


Remember, you must have an equipment ground wire pulled through both conduits if both are being used even though they both go to the same place.

Using a ground bar is a good idea, it will keep the wiring nice and neat and yes, you can use your 4 AWG for this, but talk about overkill….

I've got some #6 and #8, plenty to run down both PVC conduits. Thanks for the info.

 

[Charles (in GA)]

What are the most current carrying wires you will have in a conduit? With 1¼ conduit, it sounds like you might have a fair number of them. If you exceed 9 current carrying wires, you are going to need to be careful and properly derate the conductors.

Charles

 

[The mean fish]

What are the most current carrying wires you will have in a conduit? With 1¼ conduit, it sounds like you might have a fair number of them. If you exceed 9 current carrying wires, you are going to need to be careful and properly derate the conductors.

Charles

I'm not 100% sure yet but it looks like I'll have 1 20amp lighting circuit on #12 THHN (drawing 7.5 amp currently), 6 20amp standard outlet circuits on #12 THHN and 4 30amp 240V circuits on #10 THHN. I can always add another PVC run if I need it, it's just a PITA.

Keep in mind I have 2 separate 1 1/4" PVC runs between the boxes now, not 1.

 

[The mean fish]

What I envision running through this J box. I'v got a few more things running from the breaker panel but it doesn't run through this box.

1 20 amp lighting circuit
1 20 amp lighting circuit (future)
6 20 amp 120V outlet circuits
1 20 amp 240V lift circuit
1 30 amp 240V compressor circuit
3 30 amp 240V welder/plasma cutter circuits

I run L14-30 twist locks on my welder and plasma cutter and a few other 240V items so I'm just going to put in some 30amp twist lock outlets in certain areas.

 

[Aceman]

You have too many current carrying conductors, you either need to factor in derating by upsizing ALL the conductors, or lower the breaker ratings, or run at least one more conduit. I would run two myself.

 

[The mean fish]

You have too many current carrying conductors, you either need to factor in derating by upsizing ALL the conductors, or lower the breaker ratings, or run at least one more conduit. I would run two myself.

How many of what size could the 2 1 1/4" conduits support? I I believe I could get a third conduit in, I'm not sure if 4 would work but I could also increase the 2 existing to 1 1/2" fairly easy.

 

[alfredeneuman]

Unless the 2 conduits between the 2 boxes are more than 24" long, no derating is required.

 

[Charles (in GA)]

Oddly, that I can see, code doesn't address size when it gets to de-rating. You could have a 2½ conduit with 26 current carrying wires in it, and while there is loads of room, you still have to de-rate the circuits.

I count 29 current carrying wires if you include neutrals on every 240v run. Once you get past 9 you start derating, but due to the fact that a 12 gauge THHN wire is good for 30 amps (for the purposes of derating) you gotta exceed about 13 before it becomes an issue

 

[The mean fish]

Unless the 2 conduits between the 2 boxes are more than 24" long, no derating is required.

The J box is 24' away from the main breaker panel.

 

[The mean fish]

Oddly, that I can see, code doesn't address size when it gets to de-rating. You could have a 2½ conduit with 26 current carrying wires in it, and while there is loads of room, you still have to de-rate the circuits.

I count 29 current carrying wires if you include neutrals on every 240v run. Once you get past 9 you start derating, but due to the fact that a 12 gauge THHN wire is good for 30 amps (for the purposes of derating) you gotta exceed about 13 before it becomes an issue

I am running neutrals on the L14-30 twist lock outlets, not on the lift or the compressor circuits.

 

[C96]

If the run is only 24’ I would just install the extra 3rd conduit. Then split the circuits accordingly amongst the 3 conduits. This will allow you to maintain what you envision without having to upsize the wiring for derating purposes provided you use the THHN wire as stated.

Remember, the neutral conductor that carries only the unbalanced current from other conductors of the same circuit are not required to be counted as part of the current carrying conductors for derating purposes. Therefore, if you run multiwire branch circuits for the receptacle and lighting loads you can omit having to include the neutral wire as a current carrying conductor, but you must then install these circuits on 2 pole breakers.

 

[The mean fish]

If the run is only 24’ I would just install the extra 3rd conduit. Then split the circuits accordingly amongst the 3 conduits. This will allow you to maintain what you envision without having to upsize the wiring for derating purposes provided you use the THHN wire as stated.

Remember, the neutral conductor that carries only the unbalanced current from other conductors of the same circuit are not required to be counted as part of the current carrying conductors for derating purposes. Therefore, if you run multiwire branch circuits for the receptacle and lighting loads you can omit having to include the neutral wire as a current carrying conductor, but you must then install these circuits on 2 pole breakers.

Gotcha, I've already got all the #12 and #10 so I'd really hate to start upsizing wire to something I don't have. I'll just add the 3rd conduit or it may be easier to just run a couple conduit runs straight to the breaker panel and bypass this box completely. I need to do some more looking...