Connecting ground wires

55826 Views 18 Replies 15 Participants Last post by micromind, Mar 19, 2008

subelect

Discussion Starter · Mar 9, 2008

My question is regarding connecting ground wires from 2 separate circuits in the same plastic nail on box.
Yesterday, I was installing a small appliance branch circuit in a 2 gang plastic box and the boss ran a 14-2 into the same box for a can light. At the end of the day, I was trimming out and he specifically said to make sure that the grounds were not tied together. It was pretty hectic and I did not want to ask his reasoning until I had researched it a little better.
Usually, I tie all grounds in the same plastic box together and leave one ground stubbed out for each device that will be installed in the box.
What is the correct method: tie all together or leave the circuits apart?
What is the NEC reference for this?
Thanks

1 - 19 of 19 Posts

JohnJ0906

· #2 · Mar 9, 2008

250.148 and 250.148(D)

This is a debatable point. I used to separate them, but now I do tie them together. I'm not sure that either way is wrong.

In the situation you describe (fairly common), I tie the EGC of each gauge separately, and use a #12 jumper between the splices.

If you are using metal plates, the EGCs will be connected through the plate anyway.

Speedy Petey

· #3 · Mar 9, 2008

I am firmly on the side of tying them together, for exactly the code sections mentioned by John.

Ask your Boss for a code section prohibiting this.

480sparky

· #4 · Mar 9, 2008

What about 310.4?

Tiger

· #5 · Mar 9, 2008

I rarely run NM so I haven't thought of this aspect before, but if you consider the same branch circuit system in emt all the grounding is together with no code violation.

Dave

JohnJ0906

· #6 · Mar 9, 2008

480sparky said:
What about 310.4?

Doesn't apply to EGCs, IMO.

The first sentence talks about conductors compromising each " phase, polarity, neutral, or grounded circuit conductors" No mention of EGCs.

leland

· #7 · Mar 9, 2008

All together here. Makes a nice ground ring, redundance is good for a ground.

chenley

· #8 · Mar 10, 2008

Have tied them all together myself and have never heard of not doing so. Oddly enough just got back from installing pigtails in all the metal boxes that I had overlooked for inspection tomorrow.

gilbequick

· #9 · Mar 10, 2008

It's NM, the grounds are bare wires so it's next to impossible to truly separate them in the box without touching. Also like said above, if a metal plate is used all that separating went to poo and the last time I checked metal plates were ok to use.... Ground wires are also not current carrying conductors so it's not like you're going to overload it.

Now here's something you guys can debate about: If different gauge wires are run into the same box and all of the grounds are tied together, do all of the ground pigtails have to be the largest gauge used?

SparksNY

· #10 · Mar 10, 2008

subelect said:
My question is regarding connecting ground wires from 2 separate circuits in the same plastic nail on box.
Yesterday, I was installing a small appliance branch circuit in a 2 gang plastic box and the boss ran a 14-2 into the same box for a can light. At the end of the day, I was trimming out and he specifically said to make sure that the grounds were not tied together. It was pretty hectic and I did not want to ask his reasoning until I had researched it a little better.
Usually, I tie all grounds in the same plastic box together and leave one ground stubbed out for each device that will be installed in the box.
What is the correct method: tie all together or leave the circuits apart?
What is the NEC reference for this?
Thanks

Maybe he meant the neutrals, or grounded conductors. You should tie all the ground wires together, albeit in reality it really doesn't matter as long as none are disconnected.

cmec

· #11 · Mar 10, 2008

Try to have only 1 circuit in a gang box , If you cant Never tie all the neutrals together from differnt 2 wire circuits in a gang box the current will take the path of least resistance back and possibly overload 1 of the neutrals, Unless its a multi wire branch circuit, then tie em all together.

Speedy Petey

· #12 · Mar 10, 2008

cmec said:
Try to have only 1 circuit in a gang box , ......

Why would this be?

gilbequick

· #13 · Mar 10, 2008

cmec said:
Try to have only 1 circuit in a gang box

If you've wired anything up bigger than a shed, this can be tough to accomplish at times!

480sparky

· #14 · Mar 11, 2008

cmec said:
Try to have only 1 circuit in a gang box , If you cant Never tie all the neutrals together from differnt 2 wire circuits in a gang box the current will take the path of least resistance back and possibly overload 1 of the neutrals, Unless its a multi wire branch circuit, then tie em all together.

Hard to do when you put a 20-a kitchen circuit in a 2-gang box with a switch for the sink light. Or a 4-gang switch box that has one circuit from the living room lights and another from the hall lights.

brian john

· #15 · Mar 11, 2008

From a practical point YOU CANNOT separate grounds. Ground is ground as hard as the computer geeks try to isolate their equipment in the end most end up grounded to ground. (Ground being that entity that is a current carrying metallic structures). While a house has little metallic structures compared to a commercial building the fact is it makes little difference..But probably would be better to tie all grounds. In a rare circumstance under high fault conditions or lightning strikes their is a SLIM possibility of flash over.

guschash

· #16 · Mar 18, 2008 (Edited)

310.4B Conductor Characteristics might apply but reading the whole article I has to do with conductors 1/0 and larger. But 310 .4 E says something about conductors smaller than 1/0 but I am not sure what that is yet.
If you 250.122F, I would have to say no. But we all do it, does that make it right, I don't know.

BryanMD

· #17 · Mar 19, 2008

The only reason to NOT do them all up together is for later service reasons, right?

So... how about a practical compromise?
Twist the 12's and 14's as separate groups then put both groups in ONE wirenut.

nap

· #18 · Mar 19, 2008 (Edited)

all of the grounds must be connected unless it is an isolated ground.

as to the size;

there needs to be one ground heading home that is as large as required for the highest ampacity circuit in the group. You need no other ground technically. 250.122C

310.4 concerns parallel conductors for the same circuit. Not applicable here. Rarely have I seen the section used in resi wiring.

250.122F not applicable because it addresses situations in 310.4, which is not applicable.

250.148 says they must be connected together except for the isolated ground situation I mentioned previously. If metal boxes are used, tey must also be connected to the metal box.

btw; the reason an iso ground is not required to be interconnected at any point past the main service is; noise can be found on many EGCs due to non linear loads and this can affect the operation of a sensitive piece of electronics. The conection at the main will not cause those currents to be seen by the electronic equipment. If it is connected in the field, the noise can be present at any point between that connection and the main service and as such, could subject the electronic equipment to those interfering currents.

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micromind

· #19 · Mar 19, 2008

The few times I've worked with NM, I've always spliced all grounds together. Even if they're different sizes. I usually use the little crimp sleeves, sometimes a wirenut.

Rob

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