Metal box wiring question

When using a metal junction box, eg handybox for a switch, is it acceptable code to:
A - Just ground the metal box and rely on the switch getting grounded by being fastened to the box
B - Just ground the switch and rely on the box getting grounded by being fastened to the switch
C - Both must be grounded using wire?
Thanks all.
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On 10/5/2011 3:30 PM, snipped-for-privacy@optonline.net wrote:

Yes, this is explicitly permitted under Article 404.9(B)(1).

No, the equipment grounding conductor must be screwed to the box per Article 250.148(C). Ground the switch by attaching it to a grounded box with metal screws.

Acceptable but not necessary as long as the box is grounded.

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wrote:

C) is usually the correct answer; sometimes A) is as well but only if the switch is listed as self-grounding. Otherwise you have to run ground to both.
good luck
nate
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On 10/5/2011 4:59 PM, N8N wrote:

Once again Nate, you're thinking receptacles, not switches. Switches have different rules.
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On 10/05/2011 05:31 PM, RBM wrote:

I'll have to check my copy of the code later (it's at work) but I thought that the same rules applied for typical residential installations. That's not the part that I usually look at though, so I'm willing to allow that I may be mistaken.
nate
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I know this is the case in a lot of places but Im not sure it is a code requirement. Thats the way they were wired when I was a maintenance man at a hospital years ago and the way they are at work now. Its not true for the way my house is wired. In my house only the box is grounded. Of course assuming my house was wired to code could be a reckless assumption.
Jimmie
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On Tue, 11 Oct 2011 13:53:37 -0700 (PDT), JIMMIE

How old is your house? Grounding switches is only a few cycles old.
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On Wed, 5 Oct 2011 12:30:40 -0700 (PDT), " snipped-for-privacy@optonline.net"

With switches, the BOX must be grounded - the switch grounds to the box.
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On Oct 5, 7:25pm, snipped-for-privacy@snyder.on.ca wrote:

OK, so now we have the switch grounding question resolved. But there was mention of a difference for receptacles? So, what is the rule for a receptacle with a metal box? And why would one be different than the other?
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On 10/8/2011 7:03 AM, snipped-for-privacy@optonline.net wrote:

1. Surface metal box (handybox, ...) with 2 screws securing the receptacle strap to the box. Often the screws have a paper or similar disc on the screws to keep them attached to the loose receptacle - at least one disc has to be removed.
2- Receptacle attaches to metal cover on metal box - all I can think of are for 4" square boxes. Receptacle has to attach to the cover with 2 screws (a few other requirements). Old covers have the receptacle attached to the cover with one screw.
3. "Self grounding" receptacles with a clip from the yoke to the screws, metal box.
4. In almost all other cases, a ground wire to the receptacle.
(406.11, 250.146)

Grounding of switches is to ground any metal plates. It should be quite difficult to get high ground currents.
Grounding of receptacles is to make a good contact for ground return currents from devices attached to the receptacle through the receptacle ground pin.
--
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I just installed a Leviton receptacle and 2 Leviton switches, a STSP and a STDP.
All three devices had a paper disc on 1 screw and a metal bracket that was riveted to the strap for the other screw.
Here's a pic:
http://i.pgcdn.com/pi/75/87/77/758777524_260.jpg
No need to remove a disc as the devices are "self grounding" - assuming the box is grounded, of course.

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On 10/10/2011 10:17 AM, DerbyDad03 wrote:

That is #3 below. Many receptacles (particularly cheap ones) don't have the metal clip from yoke to screw and you have to remove at least 1 of the paper discs.

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I'm not arguing, just curious...
Why do you need to remove the paper disc?
If the device is tightened securely then there is a grounding path since the screw head contacts the device and the screw threads contact the threads of the box. If the box is not tightened securely, then even if the disc is removed, the connection would still be suspect.
Is removing the disc just so that there is a more contact than just the screw head and threads?
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In wrote:

No response from here caand be deemed correct as only your local code enforcemant offce knows whether they have requiremenrs over & above the NEC etc.. Check with them for the fnal word regardless of what anyone here tels you.
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HTH,

Twayne`
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On 10/14/2011 5:00 PM, Twayne wrote:

That's what I think. Previously the code said "direct metal-to-metal contact between the device yoke and the box". The change to remove at least one washer clarifies that.
I am not a big fan of self grounding receptacles. Seems like the contact area is not very large.

The usual useless information from Twayne. Congratulations on your consistent record.
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But his presentation was so elegant that it must be correct.
caand enforcemant offce requiremenrs over& fnal tels
How could a paragraph with an 18% error rate *not* be considered credible?
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Thanks for the explanation Bud. But unless I'm missing something, at the end of it, the rules for a switch or a receptacle in a metal box seem the same. Meaning the switch gets grounded to the metal box via the two screws that hold it to the box or metal cover too right?
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On 10/11/2011 9:47 AM, snipped-for-privacy@optonline.net wrote:

Yes on the switch. The requirements are much tighter for a receptacle.
The requirement for a switch was added fairly recently because with plastic boxes the switch (and metal plates) are not grounded. Receptacles in plastic boxes were always required to have a ground wire.
--
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