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250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes #100837 01/10/07 02:40 PM
Joined: Oct 2004
Posts: 53
I
InspectorE Offline OP
Member
This section deals with connecting the EGC to a metal box. It specifies that the EGC may be connnected


"to the box with devices suitable for the use..."


This does not appear to define an acceptable technique for connecting the "devices suitable" to the box or to the other EGC in the box.


As an example, let the box have an EGC entering, an EGC leaving, and an EGC connected to the device mounted to the box. Most folks simply use a twist lock to connect the three EGCs together along with a fourth EGC that goes from the twist lock to the single green grounding screw on the box. Speed wise, this is probably the quickest way to make the EGC connections.


Is it code compliant to use a mix of "devices suitable" for making the EGC connections?


Can we simply connect each of the three EGCs to the box using a separate green grounding screw for each? Are you even permitted to drill and tap additional 10-32 holes in the box for additional grounding screws?


Could the entering/leaving EGCs be connected to a single green grounding screw while the device EGC is connected to the box with a green grounding clip? I don't believe that I've seen anything on the box for the grounding screws that limits each grounding screw to a single conductor. If you use crimp connectors on the entering/leaving EGCs, it would seem to be a secure connection, whereas just putting the wires under the screw might not hold.


Thanks!

2017 / 2014 NEC & Related Books and Study Guides
Re: 250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes #100838 01/10/07 03:24 PM
Joined: Jan 2001
Posts: 1,044
Tom Offline
Member
I believe that the answer to all your questions is yes.

Personally, I would trust a screw connection with solid wire over a crimp cap.


Few things are harder to put up with than the annoyance of a good example.
Re: 250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes #100839 01/11/07 04:52 PM
Joined: Jan 2003
Posts: 4,391
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iwire Offline
Moderator
I will also say yes.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: 250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes #100840 01/12/07 01:56 PM
Joined: Jul 2004
Posts: 9,569
G
gfretwell Offline
Member
The only thing specifically prohibited is using a sheet metal screw.


Greg Fretwell
Re: 250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes #100841 01/12/07 04:13 PM
Joined: Apr 2002
Posts: 7,233
HotLine1 Offline
Member
E:
"Could the entering/leaving EGCs be connected to a single green grounding screw"

Does this sentence indicate two (2) conductors under one (1) screw??

That would get a "No"

John


John
Re: 250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes #100842 01/13/07 10:17 AM
Joined: Oct 2004
Posts: 53
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InspectorE Offline OP
Member
HotLine1, is that true if the EGCs are terminated in a crimp connector? I realize that you can't put two separate wires under a single screw, one wire would tend to push the other out as you tightened the screw. Tom, I agree that a single wire under a screw is more secure than a crimped ring connector for solid, but this is stranded wire (didn't mention that).

Re: 250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes #100843 01/13/07 11:44 AM
Joined: Jul 2004
Posts: 9,569
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gfretwell Offline
Member
I read this to say that there were several EGCs spliced together in the box and one of them was bonded to the box under a screw. That is legal. Usually what I see in this case is one of the wires is looped under the bonding screw. If the splicing method is listed I see no problem. Back in the olden days it was common to simply twist solid EGCs together and if there was a significant amount of wire twisted (a couple inches) that worked OK too but it wasn't code compliant. The norm is a crimp ring or a wirenut these days. I am not thrilled with the crimp rings because it is too easy to get a bad crimp. I'm sure there are plenty of people who love them.


Greg Fretwell

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