Calling all NEC grounding guru's...

[DonTx]

I've been told that it is wrong to double different sizes of ground wires up under single set screws at the ground bus. I often find #14 and #12's paired up as well as #10 and #14's. As I was told, only grounds of the same size and material can be doubled/tripled up under single set screws at the ground bus.

Can someone give me the NEC code for this?

[Richard Moore]

It's not NEC code. It's whatever the grounding bar is listed for by the manufacturer. Should be on the label inside the panel. Most list as accepting two xx AWG to zz AWG grounding conductors (I believe CH lists 3). You could read that as they have to be the same...or not (?) The issue with one large and one smaller conductor is that the screw may only be applying pressure to the larger.

Having said that, you have to keep in mind that a "perfect" connection for a ground is not as important as for current carrying coductors (hots and neutrals). Any current on a grounding conductor from a ground fault should only be momentary before the breaker trips. I believe that's why more than one is allowed at all.

I'm sure I've had 12s and 14s mixed lots of times and not called them as long as nothing was obviously loose. A 14 with a 6 I'll get excited about.

[Jim Katen]

Originally posted by Donald Lawson

I've been told that it is wrong to double different sizes of ground wires up under single set screws at the ground bus. I often find #14 and #12's paired up as well as #10 and #14's. As I was told, only grounds of the same size and material can be doubled/tripled up under single set screws at the ground bus.

Can someone give me the NEC code for this?

The NEC section would be 110.3(b), the one that says you have to follow the equipment instructions.

Like Richard said, RTFM.

The attached picture is from my ITE panel.

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As I read it, you can put a #10 a #12 and a #14 under the same lug.

- Jim Katen, Oregon

[Brian G]

I think you can read that either way. It looks very ambiguous to me. It doesn't indicate that they have to be the same, or that they can't be different. Lousy directions.

On a common sense level putting two different size wires under the same screw is bad practice. It would be easy to get good contact on one but not the other. Maybe if they were twisted together tightly first...

Brian G.

What We Got Here, Is a Failure to Communicate (clearly)

[DonTx]

Now I know where I saw it.....

....the last sentence

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[PAbernathy]

This may help you understand....

Basically the main reason we do not like to see Different size EGC's terminated together is because it is hard to figure good contact among all conductors to the terminal bar...Lets say (1) 10 AWG is put in a terminal with a # 14 AWG......( Equipment Grounding Conductors mind you...) and you tightened it down....would it make the SAME important contact on the # 14 AWG as it would on the # 10 AWG...not hardly.....

So while most manufactures will allow multiple taps ( if you want to use that word ) onto the Grounding Buss for EGC's that is fine....However, make sure they terminate accordingly otherwise in a fault condition it may ARC...and we know ARC's jump away from the point of ARC because of the Magnetic fields and laws of opposition....so it could leave a situation where the OCPD may not trip...YEP..it is possible.

It's important for people to NOT get into a everyday routine and forget some important safety factors....Hope this was helpful...

Notice- It has been a violation to put " Grounded" conductors under the same termination on a grounded/grounding buss bar for years..per UL Standard 67 and the intent of the manufactures markings of their equipment.

The ABOVE info is refering to the EGC ( Equipment Grounding Conductor ), If you wish to know the hazards of a double tapped Grounded( Neutral) on a buss bar.....just ask me...