latest nec on yoke grounding clips?

fixizinMarch 4, 2011

For decades, the two 6-32 screws tying a device to a metal j-box was considered adequate Equipment Ground Bonding for that device (and if the device was a receptacle, by extension, anything plugged into that device).

Sometime later, it was deemed that a small brass clip must be affixed to at least one end of the device yoke, the clip wrapping around both sides of the yoke strap, and the 6-32 screw passing through both sides of clip, securing it in place, with the screw head bearing down on the outer side of the brass clip. Given setbacks, plaster interference, etc., it was probably rare that the backside of these clips ever contacted any useful metal, with any useful level of bearing force.

It seems to me that the weakness of both these earlier schemes is that they rely on the 2 to 4 screws securing the mud-ring (or exposed-work cover) to transfer the ground-fault amperage to the larger metal conduit system... and apparently some combo of real world post-mortems and engineering analysis in the lab eventually reached this conclusion...?

ANYWAY, I still find higher quality receps that come with a one-sided version of these clips, crimped/riveted to the outer surface of one of the two yoke straps, and the retail packaging claims this makes the device "self-grounding"... which implies NEC compliance...?

OTOH, while I can still find GND clips that fit over the edge of a j-box, the smaller ones which fit on device yokes seem to have faded from the scene, even at hardcore elec wholesalers... or am I just shopping at the wrong places?

What say ye, RKIs?

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Ron Natalie

There are only a few cases where the yoke can be used to provide the equipment ground in the current (2011) code (and I don't think this has changed in the past few revisions):

1. Surface mounted boxes, can use the ears if you pull off the little retention washer so the ear mounts metal-to-metal with the box. Depending on the cover, there still may need to be a jumper (if the receptacle gets mounted to the cover rather than to the box.

2. Receptacles listed as self grounding may be mounted to flush boxes. To me the wording of the code lends me to believe you have to go direct to the box. No mudrings or extensions are mentioned so it's unclear you can use them. Of course, they're probably attached with machine screws which might provide adequate ground.

3. Floor boxes designed to mount receptacles with adequate contact.

The use of listed means (those clips) is allowed by the code.
Some AHJ's do not permit them.

    Bookmark   March 5, 2011 at 9:41AM
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brickeyee

"For decades, the two 6-32 screws tying a device to a metal j-box was considered adequate Equipment Ground Bonding for that device (and if the device was a receptacle, by extension, anything plugged into that device). "

The yoke mounting screws have never been adequate for grounding.
The exceptions are for when the yoke itself makes solid contact with a grounded metal box.

The 'self grounding' receptacles have a metal clip that ensures ground contact, not just the screw.

    Bookmark   March 6, 2011 at 9:27AM
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