One of my wall outlets seems to not be grounded?

[dentaku]

I got a new power strip from Canadian Tire this morning and plugged it into the outlet I have my analog oscilloscope usually plugged into.
The "Grounded/Mise a terre" LED doesn't light up. When I plug it into the other outlets in the same room the LED is on so they all seem fine.
I remember plugging my UPS into that outlet in the past and the Ground Fault warning light came on so I plugged it on the other wall.

What makes an outlet act like this? My oscilloscope seems to have worked fine even though it's always plugged into that outlet.

Is this a bad thing for my old BK Precision 1472C?

[IanB]

What makes an outlet act like this?

Usually when there is a break in the ground connection back to the distribution panel. It can happen, house wiring often has faults.

[Falcon69]

Anything is possible.

I hope you are able to fix it yourself.  My roommate had to pay to have an electrician come and fix his electrical before I had got there.  $700.00 for 4 hours of work, and still didn't completely fix the problem.  In his bedroom, somewhere inside the wall, the bare copper wire which is usually ground, was connected to hot! 

It was shorting his TV out every time he plugged his coax cable from his cable into it.  Fried two TV's before realizing what was going on. (Coax was arcing on the back of the chassis of the TV, NOT GOOD).

It's amazing what you find in homes that you don't build yourself.  Later, I remodeled his kitchen for him, I won't go into that, but I will say that it was worse than his bedroom.

Sometimes old houses, especially the one I live in, has such old cable, all you have running through it is a neutral and a hot wire.  No ground wire at all. 

[dentaku]

What makes an outlet act like this?

Usually when there is a break in the ground connection back to the distribution panel. It can happen, house wiring often has faults.

Considering my scope seems to work just fine on this outlet is there any reason I should avoid it?

[IanB]

Considering my scope seems to work just fine on this outlet is there any reason I should avoid it?

Yes, it is dangerous.

Of course your scope seems to work fine. A missing ground connection will not stop it displaying signals on the screen.

[dentaku]

Considering my scope seems to work just fine on this outlet is there any reason I should avoid it?

Yes, it is dangerous.

Of course your scope seems to work fine. A missing ground connection will not stop it displaying signals on the screen.

Well, I guess I'm going to have to figure out which breaker shuts off the power to that outlet and check it out.

[Falcon69]

if this is a ranch house, or on an upper floor, do you have room to crawl in your attack?  Running a new wire is fairly easy.  Just get up there, string a new cable, drill a hole in the header of the wall, feed the cable down, re-wire into a new grounded outlet, then string the cable in the attic over to the wall where your panel box is, fish it down the wall into your panel box, and wire it into a breaker.  It's not hard to do, should only take you about an hour.  Just keep in mind that you'll want a grommet where you bring it into the panel box.

I recently just did this to bring an updated outlet to each room in this old house....after the electrician installed a new 200amp panel box and meter. (i couldn't do that, city wouldn't have liked it).

[VK5RC]

Usually power circuits are wired in 'runs'  from a circuit breaker on the distribution panel,  it would be worthwhile finding out which power points are on that 'run'  (by switching off the circuit breaker),  the power points are usually wired with the physically closest to the distribution board often the 1st electrically as well,  it may be an interupted earth either for the whole run,  or just part of the 'run'.  It is definitely worth solving!
ps have you checked the active and neutral are correct as well?

[pickle9000]

You may have dropped the "box ground", switch the power off and pop the receptacle out. Do the easy stuff first.

It's also possible for the main panel or any box in between to be missing the ground. These things happen with "handyman" type repairs. New plate covers are an excellent place to start looking.

[chipwitch]

Since all your other outlets seem to be grounded, It's probably a simple fix.  If the ground in the outlet box is insulated, depending on your local codes and wiring methods, multifamily homes are almost always insulated here, it could be that a ground wasn't mechanically twisted together well before binding them with a wire nut.  I've seen that a lot.  Often times, insulated grounds will be stranded wire, which doesn't make a good "mechanical connection."  Unlike solid wire, which a good electrician will twist tight before binding with a wire nut, stranded wire wants to unravel. 

Point is, it's very likely a simple issue, but it could be just about anything.  And it could also be the ground was dropped in a nearby box as well.  Look to outlets and switches nearest to the one not working (assuming everything looks good in the outlet in question).  Also check any boxes on the other side of the wall that may be on the same circuit (sometimes multiple circuits can also be in the same box, so be careful with that too.)  A loose ground under a wire nut isn't uncommon.

More I think about it... Local codes vary greatly.  You wouldn't happen to live in a multifamily would you?  If the wire is in conduit and the building is a little older, they used to allow the metal conduit to carry the ground.  Stopped that about 35 years ago, I believe.  Take some pictures of the outlet if you need more help.  There are so many wiring methods, it'll make your head spin.  It would help if I could see what yours is like.

[nanofrog]

+1 on checking the easy stuff first. 

I had the same issue once, cut the power, opened the outlet, and discovered the screw had come loose on the ground connection over time. Very quick and simple fix in that instance, and you might have something similarly simple.

[Mr. Coffee]

Someone probably replaced the receptacle at some point and left the grounding conductor off.

[dentaku]

Well, I guess I know what I'm doing when I get back form work this afternoon.
If it's not something simple like the ground wire not being screwed down I can always ask my friend down the road who has done electrical work before.

[dentaku]

You may have dropped the "box ground", switch the power off and pop the receptacle out. Do the easy stuff first.

It's also possible for the main panel or any box in between to be missing the ground. These things happen with "handyman" type repairs. New plate covers are an excellent place to start looking.

The quote Adam Savage
"Now THERE'S your problem"

That outlet is a mess.
It has a big four conductor wire running into the box and only the black and white are used. No ground wire at all.
I'm guessing my father did this back in the 80's.

[w2aew]

Looks like there is enough romex in that box to strip back the sheathing and wire-nut on two pigtails - one for the receptacle, and one to connect to the box.  Then you should be good to go.

[nanofrog]

That outlet is a mess.
It has a big four conductor wire running into the box and only the black and white are used. No ground wire at all.
I'm guessing my father did this back in the 80's.

I see a bare wire and barely a 4th with red insulation in the pic. What's the other wire color on the stripped/bare copper?
And can you trace it back to where it's connected to (i.e. breaker panel hopefully)?

[chipwitch]

Looks like your standard 3 conductor romex with ground.  Dead end circuit.  Easy fix.  Use a voltage tester first.  Ensure that you have 120v between the bare wire and the black one.
0v between bare and white
Wouldn't hurt to check the voltage between white and red too.  That red may or may not be connected to anything.  But, I'll bet there's a switch in the room that controls that red wire.  Someone wanted both receptacles (top and bottom) hot all the time and just cut the red wire flush and replaced the outlet.

Be careful with the red wire.... it's possible (though not likely) there is 120v on it from the other leg which means it could be live, AND 240vac to the black one.  My money is on a switch somewhere.

[chipwitch]

Looks like there is enough romex in that box to strip back the sheathing and wire-nut on two pigtails - one for the receptacle, and one to connect to the box.  Then you should be good to go.

+1

This is an easy fix, perfectly legal, safe and rather ordinary.  You just want to make sure the ground goes back to the panel.  Confirm with a meter.

[Excavatoree]

I didn't know my father in law ever went to Canada and wired any receptacles - looks like his work.

Fortunately, as someone said earlier, it's an easy fix.   Don't forget to put a wire nut on that red wire.

[chipwitch]

... and lest you be tempted.... NO SOLDER!   

[IanB]

Don't forget to put a wire nut on that red wire.

Seconded. That red wire could easily have 120 V on it. Leaving it chopped off and exposed like that is a very bad idea. When you put the outlet back into the box the wires get bent and squeezed together. If the bare end of the red wire was live and it touched a metal part of the (un-grounded in this case) outlet, you have a hazard just waiting for a victim.

Strip back half an inch of the red insulation, put a wire nut on it, and wrap it in electrical tape for good measure.

[dentaku]

Looks like your standard 3 conductor romex with ground.  Dead end circuit.  Easy fix.  Use a voltage tester first.  Ensure that you have 120v between the bare wire and the black one.
0v between bare and white
Wouldn't hurt to check the voltage between white and red too.  That red may or may not be connected to anything.  But, I'll bet there's a switch in the room that controls that red wire.  Someone wanted both receptacles (top and bottom) hot all the time and just cut the red wire flush and replaced the outlet.

Be careful with the red wire.... it's possible (though not likely) there is 120v on it from the other leg which means it could be live, AND 240vac to the black one.  My money is on a switch somewhere.

Yup, 120V between black and the bare wire, 0V between white and the bare one, nothing between white and red.

I found a better, more modern receptacle downstairs so I guess tomorrow I'll switch off the breaker that leads to it and replace the whole thing.

The receptacle seems to lead to a junction box that branches off to a bunch of other places including the water pump and the furnace. I then traced the wire going INTO this box and it leads to the circuit breaker section that's labeled pump and furnace.
Lots of the outlets in the house are connected to breakers named PLUGS including the other two outlets in this room but this one seems to have just been added later so it shares with other stuff.

By the way, why would you connect the ground wire to the box anyway?
The junction box this wire goes to has the bare ground wire screwed into the box though.

[IvoS]

Looks like your standard 3 conductor romex with ground.  Dead end circuit.  Easy fix.  Use a voltage tester first.  Ensure that you have 120v between the bare wire and the black one.
0v between bare and white
Wouldn't hurt to check the voltage between white and red too.  That red may or may not be connected to anything.  But, I'll bet there's a switch in the room that controls that red wire.  Someone wanted both receptacles (top and bottom) hot all the time and just cut the red wire flush and replaced the outlet.

Be careful with the red wire.... it's possible (though not likely) there is 120v on it from the other leg which means it could be live, AND 240vac to the black one.  My money is on a switch somewhere.

Yup, 120V between black and the bare wire, 0V between white and the bare one, nothing between white and red.

I found a better, more modern receptacle downstairs so I guess tomorrow I'll switch off the breaker that leads to it and replace the whole thing.

The receptacle seems to lead to a junction box that branches off to a bunch of other places including the water pump and the furnace. I then traced the wire going INTO this box and it leads to the circuit breaker section that's labeled pump and furnace.
Lots of the outlets in the house are connected to breakers named PLUGS including the other two outlets in this room but this one seems to have just been added later so it shares with other stuff.

By the way, why would you connect the ground wire to the box anyway?

The junction box this wire goes to has the bare ground wire screwed into the box though.

Because it's a code.

[chipwitch]

Looks like your standard 3 conductor romex with ground.  Dead end circuit.  Easy fix.  Use a voltage tester first.  Ensure that you have 120v between the bare wire and the black one.
0v between bare and white
Wouldn't hurt to check the voltage between white and red too.  That red may or may not be connected to anything.  But, I'll bet there's a switch in the room that controls that red wire.  Someone wanted both receptacles (top and bottom) hot all the time and just cut the red wire flush and replaced the outlet.

Be careful with the red wire.... it's possible (though not likely) there is 120v on it from the other leg which means it could be live, AND 240vac to the black one.  My money is on a switch somewhere.

Yup, 120V between black and the bare wire, 0V between white and the bare one, nothing between white and red.

I found a better, more modern receptacle downstairs so I guess tomorrow I'll switch off the breaker that leads to it and replace the whole thing.

The receptacle seems to lead to a junction box that branches off to a bunch of other places including the water pump and the furnace. I then traced the wire going INTO this box and it leads to the circuit breaker section that's labeled pump and furnace.
Lots of the outlets in the house are connected to breakers named PLUGS including the other two outlets in this room but this one seems to have just been added later so it shares with other stuff.

By the way, why would you connect the ground wire to the box anyway?
The junction box this wire goes to has the bare ground wire screwed into the box though.

Yes, grounding the box is code, but it's really just customary on anything to ground anything metal that isn't directly electrified.  The reason is because a chafed wire, broken down insulation, a gum wrapper in the wrong place or anything could inadvertently make contact with a hot wire (see that screw on the receptacle where the black wire goes?  Pretty close to the box, eh?) and the metal box. Then you'd have a box that's exposed for anyone to touch and "zap".  A lot of people don't know this, but the frame of the receptacle is in electrical contact with the box.  And the trim screw that holds on the plate screws into the frame.  If the box gets electrified and it's not grounded, anyone who touches that screw with bare feet on tile could conceivably be killed.

There's also a less nefarious reason... If the neutral wire touches the box, or even if the box is mounted to a metal conduit that goes under ground, there may be a potential difference (voltage) between the box and the ground you're standing on.  I've gotten mild shocks that way.  Seen the same thing with a metal kitchen sink before too.

If you can't ground the box easily, if you have a "self-grounding" receptacle, it will act as a ground for the box.  It's no longer legal, by code, but it was legal up to about 15 maybe 20 years ago.  Ground it if you can. 

Listen to the warnings about the red wire.  They are valid.  Though, stripping the wire and taping are overkill.  The wire nut is sufficient.  Whatever you do, don't cut it flush with the sheathing.  Code says a minimum of 6" needs to stick out of the box.  That "rule" is nearly ALWAYS violated by electricians because it isn't always practical.  Just leave as close to that as you can and you're good.

One more thing... that receptacle you're going to replace it with... if it's used, make sure you get the black and white on the right screw black is on the right, white is on the left as you're facing it with the ground jack down.   Also, you will see two screws for the black and two for the white.  Look closely, there is a small jumper that juts out a bit that electrically ties together those two screws.  They're intended to be broken off to isolate the top and bottom receptacles in case you want to feed them with separate circuits or have one on a switch.  Make sure the jumpers are there or else one receptacle will be dead.  Of course, you can jump it with a piece of copper wire.  14awg for 15A circuit.  12awg for 20A.

I hope I'm not being too presumptuous by volunteering so much info?

[IanB]

Yes, grounding the box is code, but it's really just customary on anything to ground anything metal that isn't directly electrified.  The reason is because a chafed wire, broken down insulation, a gum wrapper in the wrong place or anything could inadvertently make contact with a hot wire (see that screw on the receptacle where the black wire goes?  Pretty close to the box, eh?) and the metal box. Then you'd have a box that's exposed for anyone to touch and "zap".  A lot of people don't know this, but the frame of the receptacle is in electrical contact with the box.  And the trim screw that holds on the plate screws into the frame.  If the box gets electrified and it's not grounded, anyone who touches that screw with bare feet on tile could conceivably be killed.

...

If you can't ground the box easily, if you have a "self-grounding" receptacle, it will act as a ground for the box.  It's no longer legal, by code, but it was legal up to about 15 maybe 20 years ago.  Ground it if you can. 

But the frame of the receptacle is also directly connected to the ground wire (if the ground wire is attached to ground screw on the receptacle). So ultimately all metal parts are connected and grounded. I know it may not be to code, but I don't feel too bad about grounding the receptacle and letting the box share the same ground. Sometimes it's fiddly to make lots of pigtails.

Listen to the warnings about the red wire.  They are valid.  Though, stripping the wire and taping are overkill.  The wire nut is sufficient.  Whatever you do, don't cut it flush with the sheathing.  Code says a minimum of 6" needs to stick out of the box.  That "rule" is nearly ALWAYS violated by electricians because it isn't always practical.  Just leave as close to that as you can and you're good.

Especially if there are two or three cables entering the box    A useful trick is to form the cables into a spring like spiral inside the box before you connect them to the receptacle. Then they go back in much more easily than if you just try to squash them in randomly.

One more thing... that receptacle you're going to replace it with... if it's used, make sure you get the black and white on the right screw black is on the right, white is on the left as you're facing it with the ground jack down.   Also, you will see two screws for the black and two for the white.  Look closely, there is a small jumper that juts out a bit that electrically ties together those two screws.  They're intended to be broken off to isolate the top and bottom receptacles in case you want to feed them with separate circuits or have one on a switch.  Make sure the jumpers are there or else one receptacle will be dead.  Of course, you can jump it with a piece of copper wire.  14awg for 15A circuit.  12awg for 20A.

I also noticed in the photo that the black wire is hooked the wrong way round on the screw. The screw tightens clockwise, so the wire should go the same way. That way, when the screw is tightened it winds the wire tighter into the screw instead of winding it off. There's also a fair bit too much bare copper hanging off in my opinion