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Old 01-10-2009, 11:51 AM   #1
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Ground tester?


Good morning from the cold and snowy New Jersey!

I would like to test all of the ground wires/connections on receptacles.
A lot of the wiring is old MC, without ground or bonding wires; uses the sheath as ground.
I am getting concerned that, while I get a good test with the simple 3-light tester, but this thing doesn't draw any current, so I could still have a bad ground and not know it.

What devices are there that I could plug into the receptacle to get a true ground test?
I am looking for something in the $25 range, otherwise I would build my own.

Thanks

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Old 01-10-2009, 11:55 AM   #2
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Ground tester?


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Originally Posted by KE2KB View Post
Good morning from the cold and snowy New Jersey!

I would like to test all of the ground wires/connections on receptacles.
A lot of the wiring is old MC, without ground or bonding wires; uses the sheath as ground.
I am getting concerned that, while I get a good test with the simple 3-light tester, but this thing doesn't draw any current, so I could still have a bad ground and not know it.

What devices are there that I could plug into the receptacle to get a true ground test?
I am looking for something in the $25 range, otherwise I would build my own.

Thanks
If your old BX wiring does not contain a bonding wire then you cannot use the jacket as a grounding path to begin with and only two wire receptacles can be used, or the receptacles need to be gfci protected.

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Old 01-10-2009, 12:41 PM   #3
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Ground tester?


KE, I don't know of any low cost ground testers.

Commercial Testers are $$$$$$

But then again there is that "Free Shipping"

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Old 01-10-2009, 12:51 PM   #4
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Ground tester?


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Originally Posted by chris75 View Post
If your old BX wiring does not contain a bonding wire then you cannot use the jacket as a grounding path to begin with and only two wire receptacles can be used, or the receptacles need to be gfci protected.
Chris;
I am in the process of rewiring the house, but doing so at a very slow pace, pretty much doing the receptacles first.
Rather than spend the $$ for GFCI receptacles I won't need once the rewiring is complete, I would like to check the grounds, knowing that I am not up to code, but when I find a bad one, I will rewire it much sooner.

I thought I could put a load between hot and ground, and see what voltage I get between ground and neutral. Since neutral would not be carrying current for the test, that should be my 0V reference point. I would then be able to determine whether or not the "ground" is bad or not.
I'm not sure what I would consider a bad ground, but in relative terms, I could go about replacing the worst ones first.

What you are telling me about not allowed to use the MC cable sheath as a ground, I understand, so I really need to completely rewire all of the old MC and 60's BX, since a lot of the 60's BX does not have the bonding wire properly terminated, and when I attempt to do so, it just breaks off.
Sometimes I pull slightly on this bonding wire in the cable, only to have it pull out on me. It's really not much good, is it?

Thanks for your help.

FW
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Old 01-10-2009, 12:54 PM   #5
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Ground tester?


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Originally Posted by PaliBob View Post
KE, I don't know of any low cost ground testers.

Commercial Testers are $$$$$$

But then again there is that "Free Shipping"

.
Uh, I think that's just a little out of my ball park.
I am going to make up a tester. Perhaps a 100W light bulb wired between the hot and ground of a plug, then bring the neutral and ground out to measure voltage between them. I'll have to use relative measurements to know what is bad and needs immediate replacement, and what is "acceptable", for the time being.
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Old 01-10-2009, 02:48 PM   #6
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Ground tester?


The earth ground tester isn't the right tool for what you want to do, anyway. It's intended for measuring the resistance from a ground rod to the earth, but you want to measure the resistance of the Equipment Grounding Conductor from a receptacle to the ground bus in your panel. Ideal makes a couple of models of Suretest Circuit Analyzers that will measure ground impedance, among other tests. They're cheaper than the Fluke, but probably still out of your price range (they're around $250-$300).
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Old 01-10-2009, 02:50 PM   #7
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Originally Posted by KE2KB View Post

What you are telling me about not allowed to use the MC cable sheath as a ground, I understand, so I really need to completely rewire all of the old MC and 60's BX, since a lot of the 60's BX does not have the bonding wire properly terminated, and when I attempt to do so, it just breaks off.
Sometimes I pull slightly on this bonding wire in the cable, only to have it pull out on me. It's really not much good, is it?

Thanks for your help.
What makes you think that bonding wire gets terminated? What that bonding wire does it bond the outer jacket together, and thats it.

Last edited by chris75; 01-10-2009 at 02:53 PM.
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Old 01-10-2009, 03:07 PM   #8
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Ground tester?


That little bonding wire is to reduce the back EMF within the twisted steel jacket of the cable. Nothing more. We normally use it to hold the red head in place, but that is just a practice.
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Old 01-10-2009, 03:13 PM   #9
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Originally Posted by chris75 View Post
What makes you think that bonding wire gets terminated? What that bonding wire does it bond the outer jacket together, and thats it.
I usually see it wrapped around the BX outside the clamp. I guess I should not have used the term "terminated".
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Old 01-10-2009, 03:15 PM   #10
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Ground tester?


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Originally Posted by Bob Mariani View Post
That little bonding wire is to reduce the back EMF within the twisted steel jacket of the cable. Nothing more. We normally use it to hold the red head in place, but that is just a practice.
OK, I've seen that too. With the old MC, there is no bond wire, so I've got to depend on the clamp to hold the red bushing (I think you're talking about the anti-short bushing).
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Old 01-10-2009, 03:16 PM   #11
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I usually see it wrapped around the BX outside the clamp. I guess I should not have used the term "terminated".
You dont even have to do that, I just cut it off.
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Old 01-10-2009, 03:19 PM   #12
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Quote:
Originally Posted by Bob Mariani View Post
That little bonding wire is to reduce the back EMF within the twisted steel jacket of the cable.

The bare wire in Type AC cables is a bonding wire to enhance the ground fault capability of the interlocked outer metal armor.
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Old 01-10-2009, 03:21 PM   #13
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Ground tester?


One other thing, I wish you guys would get your terminology correct....

Type AC cable uses the interior bond wire in combination with the exterior interlocked metal armor as the equipment grounding means of the cable, Also known as BX type cable.


Type MC cable is manufactured with a green insulated grounding conductor, and this conductor, in combination with the metallic armor, comprises the equipment ground

Last edited by chris75; 01-10-2009 at 03:28 PM.
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Old 01-10-2009, 03:48 PM   #14
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Ground tester?


Quote:
Originally Posted by chris75 View Post
One other thing, I wish you guys would get your terminology correct....

Type AC cable uses the interior bond wire in combination with the exterior interlocked metal armor as the equipment grounding means of the cable, Also known as BX type cable.


Type MC cable is manufactured with a green insulated grounding conductor, and this conductor, in combination with the metallic armor, comprises the equipment ground
Thanks for the correction.
I had thought MC a general term used for metallic sheath cable.

What about the very old metallic sheath cable. It looks like BX outside, but it has no bonding wire inside, and has conductors covered in rubber/cloth.
Sometimes there is a woven waxed cloth covering the conductors, which are waxy rubber.
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Old 01-10-2009, 03:53 PM   #15
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Ground tester?


Turns out, my little "ground" test was inconclusive.
I used a 100W lamp wired between hot and ground of a plug, ran an additional wire out from the ground terminal, and one from the neutral terminal and connected the meter between those.

I did use my little 3-light tester to make sure that the receptacle was wired correctly before plugging in the test lamp, in case the neutral coming out would be hot!

Sometimes the voltage reading was higher with the light off than with it on.
Voltage readings were between 2mV and 575mV between neutral and ground with the light on.

I guess that a real ground tester will put a known voltage between neutral and ground, and measure the current.
I could do that with a 12V power supply that can deliver 10A.
But, I don't think I'm going to bother. I'll just rewire them all ASAP.

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