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-   -   Grounding basics in 4 gang box (http://www.diychatroom.com/f18/grounding-basics-4-gang-box-19496/)

scottmatt 04-04-2008 06:27 PM

Grounding basics in 4 gang box
 
Hello,

I have a 4-gang box that houses (3) - three way switches, and then a single switch (4 total switches). Is it mandatory that I pigtail the grounds coming into the box, and then feed out of the pigtail a ground cable to the screw on each switch? Or can I twist the grounds together and then cap them off?

Thanks in advance!

Speedy Petey 04-04-2008 06:43 PM

Quote:

Originally Posted by scottmatt (Post 113858)
Is it mandatory that I pigtail {ALL} the grounds coming into the box, and then feed out of the pigtail a ground cable to the screw on each switch?

Yes.
If the box is metal it MUST be grounded as well.

Silk 04-04-2008 09:38 PM

Geez Petey, I'm surprised you got that one through without any debate. And no I don't want to debate it either!

But I do feel it's one of those ambiguous sections again.

Speedy Petey 04-04-2008 10:31 PM

There was a LONG discussion on this somewhere recently....was it here? Maybe CT or ElectricianTalk? I can't remember.

I believe it was about 80%/20% in the "ALL grounds" or "related grounds" camps respectively.

scottmatt 04-04-2008 11:32 PM

So, do I twist all the grounds, and then bring 4 pigtails off that one large twist (gulp).....or can I break it into two and two?

Also, what is the downside to just leaving all four grounds twisted and not pigtailing to each grounding screw - just out of curiosity.

WoodworkerDave 04-05-2008 12:11 AM

Good question Scott. You have 4 ground wires coming into the box. Do you need an additional 5 wires to ground all the switches plus the box itself? That's 9 wires you would need to connect together. I don't think a large red twist-on connector will work for that (max of four 12 gauge wires). Perhaps a large crimp-style connector might work. This is where the experience of an electrician could really come in handy. Is it legit to use a single grounded wire and just daisy-chain the ground screws of the switches?

I'm sure things can get tight in that box pretty quickly, so a low volume solution would be nice.

You definitely need to connect all the switches and the box to the equipment grounding conductor (EGC - often referred to as the "ground" wire). The whole purpose of bonding (connecting) these things together is to provide a low resistance path back to the circuit breaker in case of a short. That way, a short will cause the breaker to trip. If you didn't have these grounded, then a short occurring at one of the switches could produce lethal voltage at the screws and any exposed metal of the switch. Your body does not allow enough current flow to trip the breaker as you are being electrocuted. These guys who wrote the NEC rules are pretty smart!

Side note: When I say grounded I actually mean bonded (connected) with the service panel. "Ground" is a misnomer since an actual earth return path also does not provide enough current flow to trip the breaker. It took me a while to figure this out. Why do they connect the service panel to earth then? That's to help dissipate lightning strikes and also to help stabilize the line voltage since the power company transformers are connected to earth.

Stubbie 04-05-2008 01:57 AM

Quote:

The whole purpose of bonding (connecting) these things together is to provide a low resistance path back to the circuit breaker in case of a short. That way, a short will cause the breaker to trip
Close but not quite correct.

We bond all metal to complete what the NEC calls the effective ground fault path. This is a low impedance path back to the source (center tap of the transformer) not back to the circuit breaker. This bonding brings all metal to the same potential and all metal that is likely to be energized will be part of the effective ground fault path. A short to ground produces an inrush of current thru the circuit breaker to the effective ground fault path and then to the transformer center tap. This inrush of current is great enough due to the low impedance of the effective ground fault path back to the source to exceed the the magnetic trip threshold of the circuit breaker and causes it to open deenergizing the branch circuit.

Stubbie 04-05-2008 02:04 AM

I'm going to cause an argument....:)

The NEC allows switches mounted to metal boxes with metal screws to not have to be connected to the egc with a bonding jumper (pigtail) so long as the metal box is connected to the egc. So as far as code you do not have to run pigtail bonding jumpers to each switch if your boxes are metal and bonded to the egc.

2008 NEC 404.9(B)(1)

Having said the above I also now that Speedy is aware of that article and so is Silk. Point being the NEC is a book of articles that will meet the minimum safety standards of our electrical industry. Speedy advocates in this case to wire above code minimums and I will not argue with the merit to that thought process.

Silk 04-05-2008 05:29 PM

Quote:

Originally Posted by Stubbie (Post 113941)
I'm going to cause an argument....:)

The NEC allows switches mounted to metal boxes with metal screws to not have to be connected to the egc with a bonding jumper (pigtail) so long as the metal box is connected to the egc. So as far as code you do not have to run pigtail bonding jumpers to each switch if your boxes are metal and bonded to the egc.

2008 NEC 404.9(B)(1)

Having said the above I also now that Speedy is aware of that article and so is Silk. Point being the NEC is a book of articles that will meet the minimum safety standards of our electrical industry. Speedy advocates in this case to wire above code minimums and I will not argue with the merit to that thought process.

Actually I was thinking of 250.148, and the word "associated".

And that's all I got to say about that:whistling2:

Stubbie 04-06-2008 12:45 AM

Yes thats a related article however it says nothing about whats allowed in ways to ground switches mounted to metal boxes. The box if metal must be connected to the egc and continuity must be maintained with other egc's and their associated branch circuit conductors.

scottmatt 04-07-2008 04:09 PM

Quote:

Originally Posted by WoodworkerDave (Post 113932)
Good question Scott. You have 4 ground wires coming into the box. Do you need an additional 5 wires to ground all the switches plus the box itself? That's 9 wires you would need to connect together. I don't think a large red twist-on connector will work for that (max of four 12 gauge wires). Perhaps a large crimp-style connector might work. This is where the experience of an electrician could really come in handy. Is it legit to use a single grounded wire and just daisy-chain the ground screws of the switches?

I'm sure things can get tight in that box pretty quickly, so a low volume solution would be nice.

You definitely need to connect all the switches and the box to the equipment grounding conductor (EGC - often referred to as the "ground" wire). The whole purpose of bonding (connecting) these things together is to provide a low resistance path back to the circuit breaker in case of a short. That way, a short will cause the breaker to trip. If you didn't have these grounded, then a short occurring at one of the switches could produce lethal voltage at the screws and any exposed metal of the switch. Your body does not allow enough current flow to trip the breaker as you are being electrocuted. These guys who wrote the NEC rules are pretty smart!

Side note: When I say grounded I actually mean bonded (connected) with the service panel. "Ground" is a misnomer since an actual earth return path also does not provide enough current flow to trip the breaker. It took me a while to figure this out. Why do they connect the service panel to earth then? That's to help dissipate lightning strikes and also to help stabilize the line voltage since the power company transformers are connected to earth.

So, if the box is NOT metal, what is the best way to ground each switch?
Do I carry each ground to the respective switch that the hot is on? The box has (3) three-way switches, so it's a little confusing - but if I use the ground wire from the same cable run as the hot I would think that would make the most sense? Is this correct?

220/221 04-07-2008 06:31 PM

Pigtail all your grounds together in some fashion.

If you feel that there are too many wires to get into a wirenut, just split them up and jumper between them. That is RARELY the case though.

Plan ahead and fold the wiring in NEATLY like you are packing a suitcase.

Fold the wires into position and cut them to EXACTLY the same length before attempting to nut them.

HandyPete 04-08-2008 07:06 AM

If the box is metal, cut all those green bonding wires! Take all the remaining bare ground wires and wire-nut them together. (and if you turn hard they'll pigtail automatically) You also want to have a small jumper from that group that goes to the grounding screw in the box.

- pete

Sometimes I just take one of the ground wires and run it around the screw before meeting the group, that way you save the hassle of making a small jumper.

comments?:whistling2:


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