Self grounding devices

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  #1  
Old 09-02-01, 01:35 AM
ZZZDonna
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I posted this question about a month ago, I think, but have lost the reply and can't find it in the site. I apologize for the repetition.

We have a dug well that requires a light-bulb to burn continuously during the winter to prevent the water from freezing. The light fixture is attached to the bottom of the well boards so that the light warms the well; the boards are covered by many layers of blankets as insulation to keep the heat from escaping.

The problem is that if the light bulb burns out, you have no way of knowing unless you lift the insulating layers and look down in there.

We'd like to rig a 'warning light' -- that will go on or off when this light bulb burns out. We tried series wiring -- like some Christmas tree light strings -- but that didn't work because of the wattage difference between the well light (about 200 w) and the warning light (about 15 w).

Someone on this site posted a reply suggesting putting a sensor in the well. But I thought he meant the type of sensor is set in a light bulb fixture, for a light to go on automatically when there is darkness. Recently someone told me that there are sensors that are separate from light fixtures.

Could someone please go through the idea again, if possible, or other ideas that might solve this problem?

Thank you for your patience and help.

Donna Walker
upstate New York
 
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  #2  
Old 09-30-01, 04:08 PM
Able Sashweight
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Not sure that "self grounding" is the proper term, but what I mean is the switch or receptavle that has the extra brass shim that the mounting screw fits through. I gather that these kinds of devices, when mounted on a metal box, provide a bond between the box and the device strap. And in that case, either the box or the device need to have a ground wire or pigtail screwed to them, *but not both*.

Assuming I've gather correctly, are these bonds reliable, or should I screw a ground wire/pigtail to both the metal box and the device just to be on the safe side?

Able
 
  #3  
Old 10-01-01, 07:00 AM
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Self grounding devices

Originally posted by Able Sashweight
Not sure that "self grounding" is the proper term, but what I mean is the switch or receptavle that has the extra brass shim that the mounting screw fits through. I gather that these kinds of devices, when mounted on a metal box, provide a bond between the box and the device strap. And in that case, either the box or the device need to have a ground wire or pigtail screwed to them, *but not both*.

Assuming I've gather correctly, are these bonds reliable, or should I screw a ground wire/pigtail to both the metal box and the device just to be on the safe side?

Able
These devices are fully reliable as long as they are used in accordance with their listing. If the device is not listed for corrosive locations do not install it in the docking area of a salt water boat house or the battery shed of a photo voltaic installation and you will do fine.
--
Tom
 
  #4  
Old 10-01-01, 02:49 PM
s1nuber
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All metal boxes must be properly grounded. A box is not allowed to be grounded through a receptacle, but a properly listed 'self grounding' receptacle is allowed to be grounded through a properly grounded metal box.

In english: put the ground wire (green or bare) under a ground screw or lug in the metal box, then install the listed self grounding receptacle (typically spec grade) without a ground wire. The other way around is incorrect.

Enjoy your day!
 
  #5  
Old 10-01-01, 05:12 PM
Able Sashweight
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Most helpful. Many thanks.

Someone I know lives within 200 yards of the beach in San Diego, in the salt spray zone. Aluminum windows rot, and her computers corroded from the inside out. Pretty impressive. Sounds like a place to use the ground screw.

Able
 
  #6  
Old 10-02-01, 01:05 PM
Wgoodrich
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S1nuber, what Code reference are you referring to that forbids the bonding of a metal box from the receptacle. As far as I read it the bonding jumper can be eliminated between the device and the metal box whether you connect the equipment grounding conductor to the receptacle and bond the box by way of the grounding clip of the self grounding receptacle or you connect the equipment grounding conductor to the metal box and bond the device by way of the self grounding clip. I didn't know of an article clarifying that you can't go either direction in using the spring clip on the yoke of a switch or receptacle to replace the bonding jumper between the box and the device.

Curious

Wg
 
  #7  
Old 10-02-01, 03:05 PM
s1nuber
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When I was younger, I was failed by an inspector who said the receptacle is listed to provide it's own grounding means, not to provide grounding means to the box. I never verified this, but it made sense to me. The white book would say for sure. If you have one handy, let me know what you find.

As for the code part:
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 (a) through (d).

(a), (b), and (c) would apply to your question, but I trust that you have them, and I don't feel like typing them.

This says that the main rule is that a jumper is required, unless:
a) the box is already grounded, and
b) one of the four methods is used to ground the receptacle

By requiring the box to be grounded, this prohibits the wiring from going to the receptacle and not the box. I would guess that this is to ensure the box stays grounded when the receptacle is removed.

If you don't buy that, and I can see that people might think that I'm splitting hairs, try the following...

250-148. Continuity and attachment of equipment grounding conductors to boxes. ... The arrangement of grounding connections shall be such that the disconnection or the removal of a receptacle, fixture, or other device fed from the box will not interfere with or interrupt the grounding continuity.
(a) Metal boxes. A connection shall be made between the one or more equipment grounding conductors and a metal box by means of a grounding screw that shall be used for no other purpose or a listed grounding device.

You have no choice but to run the EGC to the box anyway, so my vote is that the spec receptacle is only intended to ground the receptacle to the box.

Enjoy your day!

 
  #8  
Old 10-02-01, 04:36 PM
Able Sashweight
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My local inspector said he was prepared to flunk me on the spot for rough in because the ground wire to the dryer 240V receptacle box was not bonded to the steel box.

He softened a bit when i said I had planned to insert the ground wire into the lug of the device, and that the 4 device mounting screws would serve as a bond. He clearly didn't like it, because there was chance for error. He cautioned me to make sure the screw mounts were clean (I'd been plastering the gaps around the box, and yes that would have to be clean). He allowed that a bight could be made in the ground wire for screwing it to the box, and then the continuation would be inserted into the device's ground lug.

Methinks I'll find a way to ground the box even if the device isn't present. The goodwill could come in handy.

Able
 
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