Metal Boxes and grounding

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Old 10-30-07, 08:32 PM
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Arrow Metal Boxes and grounding

Hi everyone:
A couple on grounding with metal boxes:

1) If I'm using a metal box (which is grounded, of course) do I need to explicitly attach a wire to an outlet's or switch's grounding screw or is the contact with the box good enough by code?

2) If a have a multi-gang box with several grounding screws, can I just attach each of the ground wires from cables to a different screw (and thus connect them) or do I need to wire-nut them all together and pigtail to one of the screws?

Obviously doing what I proposed "works" so I'm just asking if code has anything to say which forbids either of these situations.
 
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Old 10-30-07, 08:37 PM
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1. Only "self grounding" devices may be installed without explicitly connecting to the ground screw.

2. The only legal connection to the box is to the ground screw in the back of the box. Connecting to any screw is NOT up to code. All ground wires must be connected together, connected to the metal box and each device must be properly grounded.
 
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Old 10-30-07, 09:30 PM
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Arrow Clarification

You didn't quite get the question. The box has two green GROUNDING SCREWS because it's an adjustable depth box which Carlon pre-assembles out of two piece, each of which has a grounding screw. The parts are all metal.

Originally Posted by racraft View Post

2. The only legal connection to the box is to the ground screw in the back of the box. Connecting to any screw is NOT up to code. All ground wires must be connected together, connected to the metal box and each device must be properly grounded.
 
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Old 10-31-07, 04:58 AM
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You need to ground the box first and foremost.
After that you need to ground the devices.

You CAN hit the box at one grounding screw, then hit the devices from the other grounding screw. This is fine. As long as all the ground wires in the box are attached together and to the box.

Most receptacles do need a ground tail. Self-grounding receptacles do not, but it is still a good idea. There are other exceptions but it's not worth going into just yet.

Switches do not require a ground tail if mounted in a metal box, but again, it's a good idea.
 
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Old 10-31-07, 06:29 AM
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Clarify something for me. Do the ground wires from for example two cables need to connect together or can you connect one to each ground screw in the box and not to each other.
I Canada we do not need to connect them together.
 
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Old 10-31-07, 08:29 AM
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joed,

All grounding can be done through the box given the right situations -- the ground wires must have continuity with each other via the box, but do not need to be directly spliced to each other.

250.148 Continuity and Attachment of Equipment Grounding Conductors To Boxes. Where circuit conductors are spliced within a box, or terminated on equipment within or supported by a box, any equipment grounding conductor(s) associated with those circuit conductors shall be spliced or joined within the box or to the box with devices suitable for the use...
 
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Old 10-31-07, 10:34 AM
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Arrow More on grounding

Okay,
So you're saying I can connect all the ground wires to any ground screw directly or through a pigtail.
Now, I don't get the restriction on grounding the devices. If I look at my standard switches and receptacles it is plainly obvious the their grounding screws attach to the same metal which forms the tabs which will contact the box when I screw down the switch/receptacle.
So it there some situation where I need to pigtail to the grounding screws?

Thanks, Mitch
 
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Old 10-31-07, 10:44 AM
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Originally Posted by mopo999 View Post
So it there some situation where I need to pigtail to the grounding screws?
Yes, for "regular" receptacles.
Self grounding receptacles do not need a tail. These will have an obvious "clip" at one of the mounting screws.
 
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Old 10-31-07, 10:47 AM
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Clip?

Originally Posted by Speedy Petey View Post
These will have an obvious "clip" at one of the mounting screws.
Thanks. But what do you mean by this "obvious clip"?
 

Last edited by mopo999; 10-31-07 at 10:47 AM. Reason: typo
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Old 10-31-07, 10:52 AM
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I'd have to find a pic for you online. You would know what I mean of you saw it.


I found one. Here, look at the bottom mounting screw:

 
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Old 10-31-07, 11:46 AM
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Arrow Still okay?

It's more like this:


See how there's no clip, but the ground screw is obviously connected to the metal tabs?
This is still okay right? (I.e. I don't need a wire to the green screw if I'm using a (grounded) metal box?)
 
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Old 10-31-07, 11:49 AM
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Originally Posted by mopo999 View Post
It's more like this:


See how there's no clip, but the ground screw is obviously connected to the metal tabs?
This is still okay right? (I.e. I don't need a wire to the green screw if I'm using a (grounded) metal box?)
This device is NOT self grounding.
 
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Old 10-31-07, 12:02 PM
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Arrow Umm... are you sure?

Originally Posted by racraft View Post
This device is NOT self grounding.
Umm, are you sure, given that I got the picture from here:
http://www.levitonproducts.com/catal...A2748&pid=1208

Notice the features and title state "grounding"....
So are you wrong or is there some subtlety I don't understand?
 
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Old 10-31-07, 12:07 PM
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Originally Posted by mopo999 View Post
Notice the features and title state "grounding"....
To me that would mean that it contains the grounding screw. None of my switches in this very old house have grounding screws, so of course one needs a term to differentiate the two.
 
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Old 10-31-07, 12:18 PM
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The switch you posted requires a ground wire -- it cannot be grounded to the box via the mounting screws. The "grounding" in the description means that it has a screw for attaching a ground wire. Devices which may be grounded via the mounting screws are marked "self-grounding" and have a copper plate holding the mounting screw as pictured in Speedy's link.
 
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Old 10-31-07, 01:14 PM
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Thing is switches mounted in metallic boxes do not require an additional ground tail. You can if you want but it is not required.
The ground screw is there for this purpose and for use in non-metallic boxes.

404.9 Provisions for General-Use Snap Switches
(A) Faceplates
Faceplates provided for snap switches mounted in boxes and other enclosures shall be installed so as to completely cover the opening and, where the switch is flush mounted, seat against the finished surface.
(B) Grounding Snap switches, including dimmer and similar control switches, shall be effectively grounded and shall provide a means to ground metal faceplates, whether or not a metal faceplate is installed. Snap switches shall be considered effectively grounded if either of the following conditions is met:
(1) The switch is mounted with metal screws to a metal box or to a nonmetallic box with integral means for grounding devices.
(2) An equipment grounding conductor or equipment bonding jumper is connected to an equipment grounding termination of the snap switch.
 
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Old 10-31-07, 02:02 PM
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Arrow

Okay, this is too complicated w.r.t switches/receptacles. I guess I will just connect to all the device ground screws to be safe.
 
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Old 10-31-07, 06:48 PM
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Originally Posted by joed View Post
Clarify something for me. Do the ground wires from for example two cables need to connect together or can you connect one to each ground screw in the box and not to each other.
I Canada we do not need to connect them together.
Not to be overly picky , but the CEC says we dont need to connect them all together,but the local authority can have stricter rules, and in the case of our electrical inspection authority, (Nova Scotia Power), they do require us to twist our ground conductors together. In fact , they are now starting to push the use of those green wirenuts with the hole in the top so that one of the ground conductors can be continuos to extend to the device. A little bit of overkill, IMHO.
 
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