Conduit, etc. as Ground?

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  #1  
Old 05-26-05, 12:56 PM
jakeami
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Conduit, etc. as Ground?

This is my 2nd attempt...

I live in the Chicago area, Cook County, and metal conduit, boxes, etc. are required. The conduit etc. serves as the grounding system. When I check for ground, it is there. The house is from around 1960 and has no ground wires. Most outlets are already 3 pronged.

Do I need to run a separate ground wire?

I've searched and browsed here for a couple hours and haven't found what I would consider to be a definitive answer. I've had electrical work done by electricians over the years and they have NOT added any ground wires. I've received conflicting advice on this issue from people that should know what they are talking about.

Any feedback would be appreciated!
 
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Old 05-26-05, 01:15 PM
jakeami
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Add-on To Original Message

The service panel was upgraded. At the time I asked the electrician about the house ground. After I asked, he ran a number 6 wire from the service panel to the service entrance for water (about 25 feet away). Is this ok? I've heard that maybe I should still have some ground rods installed outside. Also heard somewhere that the house ground should be as close as possible to the service panel and so skip the cold water pipe ground and have ground rods installed outside near where the electrical service enters the house?
 
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Old 05-26-05, 01:37 PM
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The Neutral Conductor of the Service Condutors that supply power to the interior system from the utilty co. is required to be connected to a "Primary" Grounding Electrode, and if the water-service line to the premises is an under-ground metallic pipe or tubing, the NEC requires that such a water-line be utilized as the "Primary" Grounding Electrode; the location of the water-service is irrelevant.

Ground-Rods are "supplemental" , or "secondary" Grounding Electrodes and are a relativlely recent NEC requirement for new or re-placement Service Installations.

The NEC permitts using metallic raceways ( conduit/ tubing) and the metal of Armored Cable as Equiptment Grounding Conductors.

Good Luck and Enjoy the Experience!!!!!!!!!!!
 
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Old 05-26-05, 01:37 PM
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Conduit is allowed to be used as the ground. Some people prefer to also use a separate ground wire, as conduit can and does sometimes fail.

As for your house ground, you are somewhat misinformed. If your water pipes are metal, they must be bonded to the electrical system ground. This is for safety within the house. If the pipes are metal and extend outside the house and into the ground at least ten feet, then they are the primary means of grounding the electrical panel. This connection is to be made as close as possible to where the pipes enter the house. However, a secondary ground is also required, which is usually done via a ground rod.
 
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Old 05-26-05, 01:46 PM
jakeami
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Ok - the above answers are real clear and I appreciate it!!

Next question--

Then if I install a fixture or outlet that has a ground wire or a ground screw - can I assume the metal of the box makes a grounding connection to the fixture or outlet? Or should I attach the wire to the box (and in the case of an outlet run a pigtail from the ground screw to the box?)
 
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Old 05-26-05, 05:34 PM
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If it has a ground wire attach it to the box.
 
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Old 05-26-05, 10:09 PM
jakeami
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more specific question(s)

Recessed can light fixture has ground wire soldered to the box that's part of the fixture. This wire is to be attached to the ground wire which I don't have. But the box is atttached to the grounded conduit. Clip wire or ???

3 pronged outlets are installed in metal boxes attached to metal conduit, with the outlet ground screw not attached to anything. Is this ok, or should I run a pigtail from the outlet to the box?

thanks again!
 
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Old 05-27-05, 05:08 AM
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Modern metal boxes have a threaded hole in the back specifically for attaching ground wires. You can by ground screws or ground screws with 6" lengths of wire pre-attached. For the fixture with the ground lead, you can just run the grounding lead to the grounding screw.

If you don't have the grounding screw hole, then just use the ground clips that attach to the side of the box.

Don't use a screw that is holding something else (eg a cable clamp).

For your receptacles, they are grounded through their mounting yoke, which _may_ be okay. If you have looked are a new receptacle, you will see that the screws come pre-attached, and are generally held on by little plastic washers. Some receptacles are known as 'self grounding', where one of these clips will actually be a _metal_ clip that is permanently attached to the yoke. When the receptacle is screwed in, this clip makes contact with the box and provides a suitable ground fault path.

If you use a regular receptacle with a metal box, one that is _not_ listed as 'self grounding', then you will get a ground connection through the metal screws; enough to fool the outlet tester, but not enough to be a safe ground fault path. For these receptacles you should add a grounding pigtail or replace them with self grounding receptacles.

-Jon
 
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