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#96813 - 12/29/05 12:22 AM Grounding Question  
kyelectric  Offline
Member
Joined: Aug 2005
Posts: 64
When bolting 4" metal boxes to I beams that are part of a metal building that is grounded are the 4" boxes still required to have a ground attached to the box and to the receptacle? I have all of the ground wires connected to the receptacles but It seems redundant to have to add a pigtail to ground the box to the receptacles when the box is bolted to the I beam and the receptacles are bolted to the 4" box with the mounting screws. If anyone has any input it would be greatly appreciated.


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#96814 - 12/29/05 02:02 AM Re: Grounding Question  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,123
Estero,Fl,usa
250.136(A) ... The structural metal frame of a building shall not be used as the required equipment grounding conductor for ac equipment.


Greg Fretwell

#96815 - 12/29/05 09:08 AM Re: Grounding Question  
kyelectric  Offline
Member
Joined: Aug 2005
Posts: 64
Thanks for the information!


#96816 - 12/29/05 12:59 PM Re: Grounding Question  
macmikeman  Offline
Member
Joined: Jul 2002
Posts: 717
Honolulu, Hawaii
It sounds like you have "surface" mounted boxes. Also are you running metal conduit for this installation? The answer to your question may change depending on the conditions.


#96817 - 12/29/05 01:42 PM Re: Grounding Question  
hbiss  Offline
Member
Joined: Dec 2003
Posts: 886
Hawthorne, NY USA
It's immaterial what the box is mounted to. If you are running NM, MC or EMT with a ground conductor it must be bonded to the box. Depending on the receptacle and the cover you may not have to connect the ground screw on the receptacle to the box with a pigtail.

-Hal


#96818 - 12/30/05 10:41 AM Re: Grounding Question  
kyelectric  Offline
Member
Joined: Aug 2005
Posts: 64
The boxes are being mounted to I beams with 1/4" bolts. All of the wiring is being run in MC. I am connecting all the wiring grounds but I was just wondering about the pigtail from the box to the receptacle grounds because the receptacles is mounted to the metal cover which in turn is mounted to the metal box with the mounting screws. Another problem I was having is the ground holes in the boxes are in the back. To put the ground screws in those holes I would have to pull all the boxes back off and drill the I beams behind them so that the grounding screw doesn't hit the I beam before it bottoms out. I drilled new holes in the boxes and tapped them with 6/32 tap and installed the grounding pigtail there. Is there a clip made for grounding purposes for metal boxes that I can use the next time instead of drilling new holes? Thanks for the replies, I love this site!


#96819 - 12/30/05 11:12 AM Re: Grounding Question  
electricman2  Offline
Member
Joined: Nov 2003
Posts: 269
Thomasville, NC USA
This is why I like the newer handi-boxes and 4S's that have the raised area for the ground screw. Saves having to provide clearance behind it. [Linked Image]


John

#96820 - 12/30/05 12:19 PM Re: Grounding Question  
macmikeman  Offline
Member
Joined: Jul 2002
Posts: 717
Honolulu, Hawaii
There is a clip, but it is so junk that I wont tell you about it. Like electricman2 says, get the boxes with raised tapped holes for your bonding screws to fit into. If your boxes are metal on the surface and you use RS covers and self grounding receptacle outlets you do not need to use the jumper to the box from the receptacle outlet, but I still do it anyway even if it isn't required.


#96821 - 12/30/05 04:41 PM Re: Grounding Question  
tdhorne  Offline
Member
Joined: Mar 2001
Posts: 345
Maryland, USA
Quote
If your boxes are metal on the surface and you use RS covers and self grounding receptacle outlets you do not need to use the jumper to the box from the receptacle outlet, but I still do it anyway even if it isn't required.
I was unaware that there were RS covers and boxes that were listed for grounding.

It may sound like a quibble but 250.46 B only applies to flush boxes. I can understand the position that the self grounding receptacles would be sufficient to ground the RS cover if the receptacles grounding terminal is bonded to the Equipment Grounding Conductor (EGC) but to say that pathway is adequate for the box via the cover is not within the language of the code.

250.146 Connecting Receptacle Grounding Terminal to Box.
An equipment bonding jumper shall be used to connect the grounding terminal of a grounding-type receptacle to a grounded box unless grounded as in 250.146(A) through (D).
(A) Surface Mounted Box. Where the box is mounted on the surface, direct metal-to-metal contact between the device yoke and the box shall be permitted to ground the receptacle to the box. This provision shall not apply to cover-mounted receptacles unless the box and cover combination are listed as providing satisfactory ground continuity between the box and the receptacle.
(B) Contact Devices or Yokes. Contact devices or yokes designed and listed for the purpose shall be permitted in conjunction with the supporting screws to establish the grounding circuit between the device yoke and flush-type boxes.


Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison

#96822 - 12/30/05 06:11 PM Re: Grounding Question  
jwhite  Offline
Member
Joined: Dec 2005
Posts: 64
Trenton, NC, USA
I am anxious to see the application of a switch cover (RS = Raised Switch) for a rec.

RR covers seem more appropriate.


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