Non grounded outlet says it’s grounded?

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demoso

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We had two cream outlets in our living room and my wife painted and wanted all white ones. They are the three pronged 15amp outlets. So I bought two and switched them out. The first outlet is controlled from a light switch so you can plug a lamp into it and shut it off and on with a switch. The second outlet is always on. Both outlets were wired exactly the same. One wire going to the left side and the other wire going to the right side. There is no ground wire on either of these outlets. When I tested the outlets with a tester that you plug into the outlet the outlet that is on the switch says there’s an open ground. Which I expect. The other outlet that is not on the switch says it’s wired correctly even though I know there is no ground wire going to the outlet. How is that possible? I do plan on correcting this if I can or have an electrician do it but I’m just curious how it’s possible and should I check the rest of my outlets in the house for this even though they all test out correctly? Just bought the house a few months ago.
 

Snoonyb

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You'll need to do some more investigation to determine if there could be a grnd.

Was the switched receptionist. tested with the switch on or off?

Are the boxes metal and/or are the elec. conductors run in metallic flex or conduit?

Some old Rome had an 18ga. copper conductor that was bonded to the box with a spring clamp.
 

demoso

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Yes the switched outlet was tested when switched off and the tester didn’t light up at all. No power to the outlet either. The boxes are metal but I’m not sure about the conduit.
 

bud16415

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The one box has to be grounded then. The outlet is picking up the ground where the screw connection is holding the outlet to the box. To test it pull the outlet again and carefully do your tester where the outlet is just held away from the box by the wires. Look in the back of the box and see if there is a ground screwed to the box.
 

WyrTwister

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The one box has to be grounded then. The outlet is picking up the ground where the screw connection is holding the outlet to the box. To test it pull the outlet again and carefully do your tester where the outlet is just held away from the box by the wires. Look in the back of the box and see if there is a ground screwed to the box.
Exactly what I was going to suggest .

If you put a 3 prong receptacle on a 2 wire circuit , it must be GFCI protected ( maybe , Arc Flash , now , if it is not grandfathered ) . Either by a GFCI receptacle or circuit breaker .

With the receptacle hanging out of the wall by the wires , test hot to neutral , with a Volt Ohm Meter . Should read 120 VAC .

If you have a metal wall box , now test from it to the hot . If it reads 120 VAC , the box is grounded . This will work for what you are doing .

https://www.harborfreight.com/7-function-digital-multimeter-63604.html
Wyr
God bless
 

demoso

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Exactly what I was going to suggest .

If you put a 3 prong receptacle on a 2 wire circuit , it must be GFCI protected ( maybe , Arc Flash , now , if it is not grandfathered ) . Either by a GFCI receptacle or circuit breaker .

With the receptacle hanging out of the wall by the wires , test hot to neutral , with a Volt Ohm Meter . Should read 120 VAC .

If you have a metal wall box , now test from it to the hot . If it reads 120 VAC , the box is grounded . This will work for what you are doing .

https://www.harborfreight.com/7-function-digital-multimeter-63604.html
Wyri
God bless

I won’t get a chance to check the outlet out for a little while but when I do if I determine the box is grounded then do I still need a GFCI outlet or is the outlet fine being grounded through the box?

Thanks again!
 

demoso

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I won’t get a chance to check the outlet for a little while but when I do if I determine the box is grounded then do I still need a GFCI outlet or is the outlet fine being grounded through the box?
 

Snoonyb

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If when Using a VOM, with the red lead on the hot side of the receptacle, and the black lead on the box, you read 12ov, the box is grounded.

To ground the recep. you attach a 12ga. bare copper lead from the recep. ground screw to the box using a green ground screw.
 

raymond-

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I'm just smart enough to be stupid and just beginning to learn how to use basic electrical tools. I have a 70 yr old house with KnT wiring.

I happened to come across a 3 prong outlet in the unfinished basement. The 3 light outlet tester showed that it had a reversed hot/neutral, so I figured it would be a good first step to reverse the wiring and replace the outlet with a GFCI unit. I should mention that the outlet was served by a BX cable (2 wire, cloth, rubber clad) so I figured it was something the previous owner added...ergo the mix up.

Upon wrapping up the chore, I plugged in the GFCI and it lit up properly off-ON-ON. Cool. The next thing caught me by surprise: I pressed the tester's GFCI button for giggle, not expecting the outlet to trip. CLICK...and the tester light all extinguished. Huh?

I followed the BX cable about 10' where it terminated inside a ceiling screw in light socket. Exiting the junction were the knob and tube wires.... snaking through the floor joists and presumably, back to the service panel. I was stumped but figured I'd just spend time googling as I couldn't be the first on the planet to have come across such an anomaly.

After dinner, I ventured back down to the basement with a bright light just to follow the trail again. I found the answer behind some hot water pipe insulation:

basement grounded outlet.jpg

Thought you might find it amusing. I knew there had to be a simple explanation somewhere. I can't wait to see what other electrical hacks the previous owner created. Now I know what to look for if I see other BX clad wiring.
 

BuzzLOL

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If the neutral wire is connected to both neutral terminal and ground terminal it will fool most simple testers into saying it's separately grounded...
 

raymond-

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yes, I experienced that when using my Southwire outlet tester especially if someone installed a 3 prong outlet on a two wire outlet circuit: off, ON ON.

But what I didn't expect the actual GFCI outlet itself to be tripped on a 2 wire/KnT circuit when I pressed the GFCI test button on the Southwire tester. I interpreted that to mean that the ground hole detected a ground.
gfci tester.JPG
 

BuzzLOL

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But what I didn't expect the actual GFCI outlet itself to be tripped on a 2 wire/KnT circuit when I pressed the GFCI test button on the Southwire tester.
I thought the TEST buttons always trip the GFCI to show that it's in working condition?
 

raymond-

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Not that I'm aware of (pros welcome to pipe in). The TEST button of the GFCI OUTLET will test the outlet. It will work whether it's grounded or not.

The TEST button on the GFCI tester will only trip the GFCI circuit on the outlet if the outlet is properly grounded. If the outlet was installed on an ungrounded 2 wire knob-and-tube circuit, the plug in tester will be unable to test the outlet as it is shorting the HOT-GRD lugs on the tester which is 'upstream' of GFCI sensing circuitry.

That has been my experience and when I plugged in the Fluke DVM. But as I said earlier, I'm new at home electrics and may have used the wrong words so any experienced/pro folks can jump in.
 

Eddie_T

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I don't know how a GFCI tester works but a GFCI receptacle compares the currents in the hot and the neutral, if they are not equal the GFCI trips.
 

afjes_2016

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.

If the neutral wire is connected to both neutral terminal and ground terminal it will fool most simple testers into saying it's separately grounded...
This method of fooling a tester or in most cases an inspector into thinking a receptacle is grounded when in fact it is not is not only against code but extremely dangerous to do and it is called out in the field a "boot-leg ground".

No one, and I mean no one should ever attempt a boot-leg ground like this!

BuzzLOL - I believe you are only making a statement and not suggesting that anyone do this. I just wanted to make it clear to any one reading this in the future not to do it.

Note: Using a GFCI receptacle on an ungrounded circuit is absolutely OK to do and is utilized when changing out a 2 prong to a 3 prong receptacle on an ungrounded circuit. Unfortunately even some inspectors do not know this but if a GFCI receptacle is installed where there is no ground the plug-in tester will not trip the GFCI. The only way to test if the GFCI is functioning correctly in this case is to use the Test button on the GFCI itself.

Yes, the theory of a GFCI is that it takes the current going into it on the hot and compares it to the neutral going out and if there is a difference higher than 4-5 mA (milli-amps) it will trip for safety.

OUPS!! Sorry moderators we are riding on a two year old thread here. Did not realize it. Meantime, I just did not want anyone reading this in the future to attempt this method.
.
 
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raymond-

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question:
so though my post was related to the older thread, forum protocol dictates a NEW POST instead of latching on to a preexisting thread? is this what the 'hijacking' phrase means?
 

afjes_2016

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No No Raymond. Not a big deal - :cool: and you did not hijack ;)

We just try to avoid doing this to prevent confusion in a thread from the OP (Original Poster) to another person maybe such as yourself from asking a question that may not be totally related to the original thread starter. This will hopefully prevent us from addressing the wrong person or confusing either you or the OP with our replies.

It is just better to start your own thread. You can make reference to this thread in your new thread you start though. Little differences in an issue with the OP and your issue may not be as obvious to you and in turn may cause you to misinterpret or us to incorrectly advise you.
 

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