[weatheredwood]

It looks like the conduit fill for 1/2 emt is nine 12 gauge, so I should be good. I still have a few questions:


Do I need to two separate grounds, or can the circuits share a ground?


Do I need to designate/mark or run a different color wire for the other circuit (red)?


Are plastic bushings required? If so, are the required at each fitting?


This is for a commercial application.

 

[rjniles]

Single ground or user the EMT as the ground.

Different colors not required but is helpful.

Plastic bushings not required.

 

[joed]

Circuits can share a ground. The ground has to be sized to the largest circuit.
Example: If you have 15, 20 and 30 amp circuits, the ground has to be sized for the 30 amp.

 

[Jim Port]

Commercial work should be done by licensed professionals.

 

[seharper]

Competently assembled EMT requires no ground WIRES. The EMT is the ground path. You're always welcome to "belt and suspenders" but it will cost you a tiny amount of conduit fill. (since you can use a bare Cu wire).

Since this wire is redundant, it does not need to meet minimum standards (#10 for 30-60A circuits).

 

[betelgeuse]

Since this wire is redundant, it does not need to meet minimum standards (#10 for 30-60A circuits).

Does the Code say this anywhere? If so, where?

 

[Jim Port]

Since this wire is redundant, it does not need to meet minimum standards (#10 for 30-60A circuits).

I would like you to cite that article.

I

 

[CodeMatters]

Competently assembled EMT requires no ground WIRES. The EMT is the ground path. You're always welcome to "belt and suspenders" but it will cost you a tiny amount of conduit fill. (since you can use a bare Cu wire).

Since this wire is redundant, it does not need to meet minimum standards (#10 for 30-60A circuits).

Doubtful that would meet code here. Even if it does, not very practical
as, around here at least, bare copper is not normally sold in sizes smaller
than #6.

 

[weatheredwood]

It will be two 20 amp circuits. I plan on running a 12 gauge ground.


I was planning on grounding the metal boxes and each receptacle. Is this over doing it?

 

[A Squared]

I would like you to cite that article.

I

Soooo, not an NEC expert and not necessarily claiming that he is or is not correct, but if the EMT is assembled such that it meets the requirement for a grounding conductor by itself, then an separate grounding conductor isn't required to be there, so if you do add a redundant grounding wire which is not required, what requirements must it meet?

 

[Jim Port]

I would say it needs to meet the same as if it wasn't using the conduit.

 

[betelgeuse]

I would say it needs to meet the same as if it wasn't using the conduit.

^^^^^THIS^^^^^
The exception can't be cited because it doesn't exist

 

[weatheredwood]

It looks like a supplemental ground is not necessary. Do you guys recommend installing a 10-32 screw at the junction box to run to the receptacle. The boxes will be surface mounted, so the receptacles will make direct contact with the junction. I've read that grounding to the box is only necessary if the ears of the receptacle are sitting on drywall.


Does the raceway need to be bonded at the panel, or is the nipple connection sufficient?

 

[seharper]

I would like you to cite that article.

NEC 250.118(4).

What you're *really* asking, though, is "If I have multiple, redundant ground paths, do they ALL need to be large enough for the largest conductor?" And that's easily understood with a thought exercise. Suppose you run PVC conduit to a laundry room. You provision a 30A dryer recep and the mandatory 20A/120V laundry room circuit. You choose the following conductors:

- 10 AWG, H-H-N-G
- 12 AWG, H-N-G

However, the boxes in the laundry room are metal with EMT between them, so they are a valid grounding path, 250.118(4). Your first box has 2 ground screws so you ground both wires there. Is the 12 AWG ground a codevio because it can't support the dryer? Of course not. Nothing wrong with it. The second ground is redundant, and the other ground is good enough for the dryer.

In this case, the EMT is the primary grounding path and the #14 is redundant.

It will be two 20 amp circuits. I plan on running a 12 gauge ground.


I was planning on grounding the metal boxes and each receptacle. Is this over doing it?

Grounding the boxes is required. Grounding the recep *may* be overdoing it, depending on how the recep mounts in the box.

I've read that grounding to the box is only necessary if the ears of the receptacle are sitting on drywall.

Thats a "web oversimplification" of a somewhat complex issue.

The deal is, here's what's not good enough for a receptacle: resting contact between mounting screw head and yoke. (that *is* good enough for a switch). So if your recep is proud of the metal box, and the only ground route is through the yoke and screw head, not good enough.

A "self-grounding recep" that has brushes which touch the mounting screw threads, that is good enough. NEC 250.146(B).

Otherwise, all these must be true on one attachment point:

- The yoke makes hard flush contact with the metal box.
- The metal box is bare, and is not spooged up with paint, rust, etc.
- Neither is the yoke.
- Those little paper squares that keep the screw captive, cannot be there.

Does the raceway need to be bonded at the panel, or is the nipple connection sufficient?

If the EMT conduit is properly assembled, then the EMT to the steel service panel case is a valid grounding path. Trust me, I've tested it lol.

Code can be funny about concentric knockouts (you knockout the 3/4" hole but around it is a 1" hole that could be knocked out) or stepdown adapters (you knockout a 1" hole by mistake and use a special washer to downsize it to 3/4"). But I can't find anything in Code that pertains to branch circuits or feeders.

 

[Jim Port]

250.118 only lists the allowable means for grounding. 250.122 tells you how to size a egc if one is used. Since one is being pulled it needs to be properly sized based on the ocp. There is no exception that allows lesser sizing since it would be redundant.

Once the 20 amp circuit left the common junction box from the 30 amp it would only not carry a ground based on the 20 amp ocp. The #12 would be adequate.

Since we are not talking about anything over 250 volts the discussion about concentric knockouts is not needed.

 

[surferdude2]

Emt installed properly is still accepted even though it isn't as safe as a copper conductor. The indoor type set-screw connectors and especially the couplings often used for EMT are made from pot metal and are easily broken.

I recommend using the compression type emt fitting and making them up good and tight. As for a good DIY standard MO, if you have any doubts or just want safer protection, then by all means pull in a ground conductor sized for the largest circuit... it won't hurt (pun intended).