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A majority of the electrical outlets in a house I checked out yesterday showed positive for grounding, however there weren't any wires connected to the green screws.

How is this possible? Even if the junction boxes were grounded--and there was no evidence of that in the crawlspace--shouldn't the tester display "open ground?"

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If this is an old two wire system, the only possible grounding would be "bootleg", where the neutrals are jumpered to the ground screw, in the back of the j box. Then grounding for the pin is achieved thru the two screws holding the receptacle. Because neutral is grounded in the panel, you get a false ground at the receptacle.

You didn't say if the supply cables have the ground wire, but assuming the ground wire is there, 3 wire system, it is likely wrapped around the ground screw in the back of the box. I think those are metal j boxes, but even the plastic boxes will often have a ground strap to one of the mounting screws.

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Is that a metal box? Maybe the box is grounded and the screw carries the ground to the outlet.

Marc

EDIT: John K beat me to it.

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They WERE metal boxes, so I think you nailed it. I just wasn't clear on how the tester could be fooled if there was no direct connection to the ground-prong slot.

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The tab for the ground screw is the same piece of metal stamped for the mounting screws.

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Ahhhh, that's so simple, I'm embarrassed I wasn't aware of it. Thank you.

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The tab for the ground screw is the same piece of metal stamped for the mounting screws.

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Ahhhh, that's so simple, I'm embarrassed I wasn't aware of it. Thank you.

Thanks for asking. Some of the rest of us just learned too.

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This particular detail is one of the reasons I like hard pipe installations.

There are outlets manufactured just for my market that have an extra wire wound around the screw and attached to the chassis; it's for a redundant ground path.

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Is that a metal box? Maybe the box is grounded and the screw carries the ground to the outlet.

Marc

EDIT: John K beat me to it.

My house is circa 1962. This is the way its wired. I think the requirement for grounded boxes came slightly before the 3 prong receptacle requirement.

A house in the neighborhood across the street I inspected has grounded boxes like I do but all 2 prong receptacles. I told the client all they had to do was swap out the 2 prongers for 3 prongers to get the receps grounded.

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Many times the ground conductors are wrapped around the cable and secured under the clamp. The following pictures are from my basement. One is at a wall receptacle and the other is at the entrance to the main panel.

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Many times the ground conductors are wrapped around the cable and secured under the clamp. The following pictures are from my basement. One is at a wall receptacle and the other is at the entrance to the main panel.

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I've never seen that down here. Is it legit? The closest thing I've seen is that aluminum bare conductor in AC cable (commercial) wrapped in a similiar manner.

Marc

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It's 'sub-optimal' to use a little Inspectorspeak, but it is what it is. There's a boatload of houses in New England wired that way.

Remember, at the time, it weren't no thang, but you & I never once rode in a car seat. Seen through the modern prism, our parents would be barbarians. But were they?

In the pantheon of safety, I think it's pretty safe enough.

I'm guessing, but I think that any ground path that a 3 light outlet checker can pick up is probably sufficent for most residential emergencies. Anybody know different?

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I'm guessing, but I think that any ground path that a 3 light outlet checker can pick up is probably sufficent for most residential emergencies. Anybody know different?

I don't agree. There are defects in appliances that can generate fault currents at least a few orders of magnitude greater than those generated by GFCI testers.

That little GFCI tester determines (within it's design limitations)whether or not a ground path exists, not whether that ground connection is able to pass an adequate fault current.

Marc

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Many times the ground conductors are wrapped around the cable and secured under the clamp. The following pictures are from my basement. One is at a wall receptacle and the other is at the entrance to the main panel.

I believe that when the cable manufacturers started including grounding conductors in their cables, the electricians simply didn't know what to do with the extra wire. However, they were all familiar with AC cable and the bonding wire that was *required* to stay outside of the boxes. I suspect that when the new grounded cables came out, the electricians just did what they were already accustomed to do with the *extra* wire.

- Jim Katen, Oregon

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Heck, they still don't. The other day, I had some electrician keep insisting to me that the little aluminum strip in AC cable was the "ground wire".

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Heck, they still don't. The other day, I had some electrician keep insisting to me that the little aluminum strip in AC cable was the "ground wire".

It is. It just stays outside the box and directly grounds only that box. Right?

Marc

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In my opinion, on the grounded boxes of the late 50's early 60's, it's most often sufficient and certainly better than no ground at all.

From the receptacle side, many times you can look into the back of the box and see the wrapped and clamped ground conductor. The picture is one of mine and typical of what one might see.

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Heck, they still don't. The other day, I had some electrician keep insisting to me that the little aluminum strip in AC cable was the "ground wire".

It is. It just stays outside the box and directly grounds only that box. Right?

Marc

No, it's for maintaining continuity in the sheath if the sheath is compromised or damaged in some manner.

Do you really want to count on that teeny little piece of aluminum nothingness as a ground path?

It's really easy and supportable to simply let the code decide this stuff. Why does anyone really want to apply their own "logic" to the question?

Because the local electrician will look at you funny? Because the realtor has someone that says we're wrong?

Just curious.

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Do you mean the electrical continuity of the sheath? Why is it important if it isn't for grounding purposes?

Marc

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Do you mean the electrical continuity of the sheath? Why is it important if it isn't for grounding purposes?

Marc

In old AC (BX) cable that had the little aluminum wire, the grounding conductor was the metal tape, which formed the outside of the cable assembly. The little aluminum wire was the bonding wire. Its purpose was to touch the spiral metal tape and maintain a direct path if the spiral metal tape were to become damaged and pulled apart like a slinky.

If the tape were to be pulled apart into a slinky shape, it might act as a choke coil if you were to pass current over it.

We had a good discussion about AC cable here:

https://www.inspectorsjournal.com/forum ... C_ID=10144

- Jim Katen, Oregon

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Do you mean the electrical continuity of the sheath? Why is it important if it isn't for grounding purposes?

Marc

In old AC (BX) cable that had the little aluminum wire, the grounding conductor was the metal tape, which formed the outside of the cable assembly. The little aluminum wire was the bonding wire. Its purpose was to touch the spiral metal tape and maintain a direct path if the spiral metal tape were to become damaged and pulled apart like a slinky.

If the tape were to be pulled apart into a slinky shape, it might act as a choke coil if you were to pass current over it.

We had a good discussion about AC cable here:

https://www.inspectorsjournal.com/forum ... C_ID=10144

- Jim Katen, Oregon

Thanks. So...in MC cable, the role of the green insulated conductor is equipment grounding conductor, but in AC cable, the role of that flimsy aluminum wire is bonding conductor?

Marc

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