Electrical problem: 120V between GND's (FIXED!)

[0dbfs]

It did not pop the breaker. The smoke came out of a tiny little ground connection on a ribbon cable between two pcb's (that breaker was not rated for 15 amps apparently). Probably damaged some other components as well.

I'll be following up with the electrician on Monday but I suspect the circuit/branch feeding a particular wall outlet is mis-wired with hot/neutral swapped and a loose ground at the panel termination point.

Maybe I can start tripping breakers to see which one turns that outlet off then test all outlets for current to ID all outlets on that branch. I might have an extension cord to help me meter it out too.

Sounds plausible.

Best,
J

 

[JohnRoberts]

I'm not sure we know which outlet/branch is wrong yet.

I guess you could troubleshoot by just turning off breakers one at a time and using VOM to measure between the two problem outlet grounds.

The one breaker that makes the 120V between grounds go away is the branch that is miswired hot to ground.

The outlet that still has power, is OK.

If both outlets go cold, they are on the same branch with the wiring flip between them. 

JR

 

[Speedskater]

I'm a day late and the electrician is coming tomorrow, but anyway my thoughts on troubleshooting this problem:
First don't assume anything!
Second measuring 240V can be very dangerous!

Almost always the power company's hot wires will be black.
With plastic covered Romex "NM" the silver colored plastic is not a ground.
Expect Hot to Neutral swaps.
Expect boot-leg ground connections. Ground pins jumper-ed to Neutral.

So we have six wires entering the home:
Two G/N
Two Hot (phase A)
Two Hot (phase B)

We need a reference for Mother Earth.  This is an old home, so if it still has an all metal incoming water pipe we can use that, if not maybe a temporary ground rod or the system ground rod.

Using a very long test lead (like an AC extension cord ground wire) connect one end to Mother Earth.
At each breaker box find the two 120V connections and the very near 0V connection.
Each breaker box should have 240V between the two hot wires.
Do all the incoming service wires appear correct?

With one lead still connected to M.E.
At the outlets in question the Hot pin should have 120V the N and G should have 0V.
Plug a space heater into the outlet. The H should be less than 120V. The N should be a few volts. The G should still be near 0V.

Older building sometimes used Neutrals from other circuits and often just jumped the ground to the N.

The little LED testers wont catch a N G swap or a N G jumper, but the space heater test will.

 

[PRR]

> Do all the incoming service wires appear correct?

AFAICT, they are all black. Black is black. How can that be wrong?

I'm 99% sure that two blacks are swapped.

However after seeing that horror-house junction-box, it is possible there are MULTIPLE "small" problems.

> measuring 240V can be very dangerous!

Yes.

Especially at the fusebox.

Remember that a short will NOT blow a breaker instantly. A reasonable #2 feeder can deliver nearly 10,000 Amperes. The available 2,400,000 Watts of energy, or even the 600,000 watts available to a screwdriver shank, can burn your face off.

Also the feeder -before- the 100A main fuse is NOT fuse-protected. If you manage to weld your screwdriver across the utility side of the main breaker, current won't stop flowing until the pole transformer overheats or the feeder wires burn and drop on the lawn.

The guys who install meters wear a mask and apron. 99.9% of jobs are just "click" but one "BWOOM!!" means serious injury. Poking around a fusebox is more ways to get in trouble.

And if you don't de-bug service and circuit connections for a living, have not seen the infinite variety of wrong-ways, you probably can't FOR-SURE diagnose the problem.

Now that I see that junction box, if the electrician is 3/4 competent and conciencious, I fear the landlord is going to be surprised by the report and work required. The only "good" part is that many boxes are open for inspection. Some circuit cross-wiring can be easily seen, fixed, and covered. But a situation like that, there are probably hidden (illegal) junction boxes and junctions without boxes that may never be found except after the fire. The cloth-covered cable is getting older and more short-prone, and IMHO should not be used with the box-clamp seen in that picture (there's an edge which is OK with good plastic cable, and may have been Approved when the cloth was new, but the cloth is now fragile).

Are there any 240V appliances (stove, dryer, hot-water, large fixed heater) which appear to run 1/4 power? Any "120V" outlets showing 240V? Any outlets dead for no reason?

If there is a NEW NEAT main box, and you feel competent (and like splinters and cuts), you could re-wire the whole building RIGHT. On a rental, in most jurisdictions, this is not allowed: a Master Electrician must supervise you. I as homeowner can do my wiring, but if I rent-out I must have an Electrician be in-charge and sign-off on the job, so a sleazy landlord does not put tenants at risk.

> you said there are two services coming into the house. That sounds a little odd.

It is. NEC strongly urges a SINGLE service per property. There are situations like barn-light and house where two entrances are justified, but here he has both in one place. Two entrances could be justified for rental space.... but he has both feeds in one room, so it's not about billing the tenant. The only way I see his hookup as 'OK' is if it is very temporary to install a full new service and abandon the old service.

 

[Speedskater]

> Do all the incoming service wires appear correct?

AFAICT, they are all black. Black is black. How can that be wrong?

I'm 99% sure that two blacks are swapped.

However after seeing that horror-house junction-box, it is possible there are MULTIPLE "small" problems. >

By appear correct, I meant:
Is the Neutral in each breaker box connected to Mother Earth?
Is each incoming black wire, about 120V from it's N/G ?
Is there about 240V between the two black wires in a box?

Now about the "two blacks are swapped" part:
Do you mean that my above measurement is incorrect?
Or do you mean that Phase "A" is on the Left in one box and on the Right in the other box?

I agree 100 % with your well written Safety Warning.

 

[0dbfs]

> measuring 240V can be very dangerous!

Yes.

Especially at the fusebox.

Remember that a short will NOT blow a breaker instantly. A reasonable #2 feeder can deliver nearly 10,000 Amperes. The available 2,400,000 Watts of energy, or even the 600,000 watts available to a screwdriver shank, can burn your face off.

Also the feeder -before- the 100A main fuse is NOT fuse-protected. If you manage to weld your screwdriver across the utility side of the main breaker, current won't stop flowing until the pole transformer overheats or the feeder wires burn and drop on the lawn.

The guys who install meters wear a mask and apron. 99.9% of jobs are just "click" but one "BWOOM!!" means serious injury. Poking around a fusebox is more ways to get in trouble.

And if you don't de-bug service and circuit connections for a living, have not seen the infinite variety of wrong-ways, you probably can't FOR-SURE diagnose the problem.

We'll see what the electrician comes back with. Still no appointment scheduled. If I don't hear from them today I'll be calling up someone to diagnose this and going from there.

BTW, A decade or so ago I thought it would be cool to poke around in my 50W Marshall combo with a screwdriver and this exact thing happened. Just about melted the end of the tool. Severely pitted for sure accompanied by nice pretty big blue flame and that BWOOM!! you mentioned.

I'll leave this work for the sparkies.

Best,
j

A couple more photo's just for fun:

GND CONNECTION FROM MAIN DISTRO-BOX:


GND TO BLDG-COPPER:


PLENTY OF CONNECTIONS:


INSPECTED 1987:

 

[kazper]

Wowsers 

I'd say the best thing is to move...

It honestly looks like years, years and years of DIY home electrical on the whim.

Best guess is someone will be paying allot of money to fix a few things at that place.

 

[kato]

Oh yes, that looks like the wiring job in the last house I owned. A 1938 bungalow that had clearly been rewired and "upgraded" several times, never once by a licensed electrician.

Luckily, professional electricians secretly love dudes like us to follow them around and ask questions during their inspection while they point out how wrong and dangerous everything is. It's a great learning experience; worth every penny. Enjoy!

 

[PRR]

> I thought it would be cool to poke around in my 50W Marshall combo with a screwdriver and this exact thing happened. Just about melted the end of the tool. Severely pitted for sure accompanied by nice pretty big blue flame and that BWOOM!! you mentioned.

Uh, no. Not "the same".

A Marshal power supply has a steady output like a string-trimmer (Weed-Whacker) engine; you can get an instant output like a lawn-tractor. Clobber a screwdriver, tear off off a few toes.

A short across a #2 feeder is more like a railroad locomotive or a DC-3 or a supercharged cammed large V-8 hot-rodded for drag racing. Perhaps most like the drag-race engine: *HUGE* power available for several/many seconds before something lets-go. Personally you may not care that it burns-clear in a few seconds: the MEGAWATT of power available can burn lots of flesh quicker than that.

Marshall: toy Easy-Bake oven (100 Watt lamp)
Typical small kitchen stove-top burner: 1,000 Watts
Feeder short: A THOUSAND 1,000 Watt burners in a small area a foot from your face

If I sound concerned: I was thinking of replacing my feeder. When I learned about what might go wrong, I decided to have a Master Electrician liaison with the utility company. It will cost more to hire the skills and experience; its cheaper than a short hospital stay, far cheaper than a funeral, far-far cheaper than a month in intensive burns care.


> Still no appointment scheduled.

OK, and I'd suspected that from the current condition. This guy does not understand the risk.

Call him again.

Tell him this is a life-safety issue, and you don't want to find your wife child or dog laying dead and crispy between two appliances.

Then call an electrician YOURSELF. Tell him you measure 120V between GROUND holes on nearby outlets. (Clients who know voltmeters get some respect, and this sure sounds wrong.) "Who pays?" will be a question.... I think you should pay for an hour's look-around, and if it leads to real work then take it off your rent.

Is that a gas-line or oil-line next to the wire-maze?

Seriously: think about moving. I know it's tough when you are already settled, but the condition and apparent unconcern are frightening.

 

[JohnRoberts]

I agree with PRR  this is serious stuff...

But I am also a fan of self help, at least in diagnosing what is amiss..  If the panel has breakers and is wired competently you shouldn't have the wrath of THOR, hanging off the ground pin of that outlet, but still enough power to kill pets or people (15a).

#1  with one or several long extension cords, or a long pice of wire, you should be able to grab a good earth ground from somewhere (cold water pipes in old houses are usually good).

#2 Determine "which" outlet of the two has hot connected to it's ground pin.

#3 Turn off the breaker that makes that rogue outlet go cold. If you can't find a breaker that makes that ground go cold. Slowly back away from the outlet, and wait for a real electrician. If the branch isn't fused you could see PRRs worst case scenario.

#4 Identify other outlets or appliances connected to that same branch that go cold when the bad outlet goes cold. .

#5 re-energize the breaker, and test their grounds too. Tape over all bad outlets...

#6 look for a pattern. If multiple outlets in a row have hot grounds the branch may have a flip in it upstream of the rogue outlet. You can usually guess the path that the wiring takes from the service to the end of the branch. I the one outlet is the only one backwards, the problem could be local inside it or very close. If several in row, the flip likely occurred elsewhere. You want to fix this at the root of the problem.

At this point it is up to your sense of adventure. If just the one outlet that is bad, it might be as simple as, swapping around a couple wires inside that outlet box, while with your experience I'd be tempted to replace with a GFI protected outlet, even though that horse is already out of the barn.

If not ready to get close and personal with your house wiring, start withholding rent and maybe get a quotes from an electrician with some sense for the scale of the problem from your tests.

I am not a big fan of just moving away from the problem, because it can still hurt some future tenant. If a building inspector learns of this, you may be moving out anyhow, because the house is dangerous and would be condemned immediately. 

Perhaps use that a leverage with your landlord... You don't want to move out or stay and put your family at risk. He doesn't want a condemned property that he can't rent. The win-win for both of you is to get this fixed.

JR

PS: I recall when I was a kid we used to have these little neon bulbs with probes. They would light if more than 90v or so across them. Handy for troubleshooting wiring.

 

 

[0dbfs]

Electrician was here for two hours today. Nothing conclusive except that something is wrong. Needs to reschedule to localize the fault. I'll add more notes but current was still available on GND even after the breaker feeding those outlets was OFF.

Best,
j

 

[Gus]

Google "arc flash"

 

[0dbfs]

Ok. This is quite interesting. Here's what I know:

- At least two circuits feed upstairs from the basement/crawl-space distro box to this attic-renovation. Those are for ceiling lamps and wall outlets. May be more circuits.
- There is a dedicated AC unit up there too so that probably receives a dedicated circuit.
- Electrician first tried to explain that everything was fine and I was measuring at my IEC power-cords wrong or that they were wired wrong. I convinced him to get his own extension cord and compare grounds. Did that between several outlets and he started scratching his head.
- I brought him outside and explained the two service points and then showed him the fuse boxes. He very carefully measured between all the neutral bars, the hot-lines, and the gnds in the boxes, on the chassis, etc until he was convinced they were all good.
- He did try to pop a breaker by shorting an outlet (good one JR!) and it would not pop. (this seems to contradict previous statement or even suggest that maybe there is no breaker in series here)..
- Stopped using the DMM fairly quickly and started using the inductive signal probe to confirm that there was signal on all prongs on all outlets, also on lamp fixtures, etc...
- He held a ground in one hand and the inductive probe in the other to make it beep. But he didn't light up.
- I can tell he like this problem. Probably a good diversion from the run of the mill work load.

I used his inductive probe to confirm that the downstairs outlets are ok while he tested additional outlets upstairs. One downstairs outlet is also corrupted so I'll tape over that one for now. Useful device. Use the audio fox/hound thing for installs and some telco stuff. I've got to get one of these for the kit (since my 3-LED tester failed to identify the fault).

Ran out of time for the day so he's scheduled back for Thursday morning. I know the landlord was hoping this to be a quick fix but it appears that finding the fault may take some time.

Upstairs is off limits for everyone in the house until this is sorted out. Any funky business with the landlord and I'll get a county inspector to come out and see where we stand.

I can't thank you guys enough for your continued input here on this. You all may have helped keep the smoke in some people on this one. Thanks.

Best,
j

 

[JohnRoberts]

The breakers, current limit each branch to 15A (or they are supposed too).

The fact that he couldn't pop the breaker with a short may only mean there is so much wire loss in the path that it doesn't draw enough to pop the breaker, but that is also dangerous, since the wire will heat up dangerously.  Either way bad juju.

Without that branch breaker protection, your ground short could pull up to the 100A or whatever service breakers limit. Some red hot wires inside your walls are never a good thing.

I'd leave this one to the experts.  I'm glad you have one working on the case.

JR

PS: I knew he would go for the smoke test, because that's what I'd do if I was him...  ;D  

 

[PRR]

> Turn off the breaker that makes that rogue outlet go cold. If you can't find a breaker that makes that ground go cold.

Found that once. Radio in the kitchen, turned off every breaker one-by-one, radio never stopped. Magic? Zero-point energy?? Turned off ALL breakers, radio stopped (no magic). Turned on one-by-one, TWO breakers fed the radio.

My father had a different "no fuse" issue. Could not de-power the dryer. It had been tapped ON THE FEEDER, no fuse/breaker. Dryers DO short-out. That gets back to a thousand 1,000W burner-plates but now inside the wall.

> couldn't pop the breaker with a short may only mean there is so much wire loss in the path that it doesn't draw enough

Line-drop at circuit rated load "should" be under 2%. This is often ignored, but 5% is annoying and 10% usually gets attention.

You are suggesting that line-drop could be 100% at rated load. That would be Very Bad Practice.

It's brave (and arguably foolish) to deliberately short any wall-outlet. If properly connected, you still have the 99.9% reliability of breaker and 99.9% reliability of electrician screwing. When you KNOW there's "issues", deliberate shorts are probably a Bad Idea.

> I'd leave this one to the experts.

Yes. When I thought of the several ways J's observations could be explained, most led to things which "shouldn't happen", and the most-likely seemed to be Very Dangerous.

> he like this problem. Probably a good diversion

Good for him, and fun for kibitzers like us, but NOT a good thing. A key concept of Good Wiring is that most problems may be found by inspection, not rely on fallible brains.

 

[MagnetoSound]

He did try to pop a breaker by shorting an outlet (good one JR!) and it would not pop.

Shocking!


(Had to get that one in, surprised no-one else said it yet. No laughing matter, i know.)

 

[0dbfs]

You have at least two wiring faults; a reversed hot/neutral and a broken ground.

Your 3 light tester has a list of the faults it detects, and the fault you have is not detectable by measuring at a single outlet. Since AC has no absolute polarity, the tester can't tell that the N+G are reversed from the L. "locally" everything looks fine.

Michael, Good call!

It looks like we had a 2-wire (silver/alu woven romex) feeding the upstairs "attic-renovation". No dedicated ground back to the panel. Just white and black. A portion of the "new" 3-wire system in the attic was tied into this circuit/branch and the ground was left floating at this point. White/black on that 2-wire were swapped (white=hot, black=neutral).

Swapping it back fixed everything as far as the original symptoms were concerned, as well as tying the attic gnd into the 2-wire neutral.

Now I don't measure 120V between my two grounds in the different outlets anymore.

Thanks,
jonathan

 

[Speedskater]

The attic ground wire should follow the same path back to the panel as the Hot and Neutral.  If not you have a antenna for RFI and a big ground loop.  Plus things can get nasty if you have a nearby lightning strike or a big power co. surge.

 

[0dbfs]

At this point the attic ground connects up to neutral in the junction box where the 2-wire terminates in the attic.
That 2-wire neutral(/gnd) terminates back into the circuit breaker. Both breakers are also now bonded to building copper (one of them was floating).

There are two circuits/branches up into the attic. One was correct and the other was not. The incorrect one had reversed H/N and the disconnected ground. This caused HOT to be present on all GND/NEUTRAL's but only in the attic. Now, with the H/N corrected and GND connected to N everything measures correct.

I still feel like something is not adding up. Why did all N/G's in the attic measure H? Even the ones on the second branch/breaker AND not trip any breakers (second branch is 3-wire and correct all the way back to the distro-panel)? Nothing else in the house measured incorrect (except the one outlet downstairs which is a dedicated 2-wire and has no GND anyway. It measures as expected now but also had H on it's N previously)

Best,
jonathan

 

[JohnRoberts]

Good that you got the hot and neutral flipped back around. No more hot chassis or exposed metal. Your landlord still owes you an equipment repair, but he may not be in a giving mood after two days of electrician house calls.

The backward outlet downstairs should not be a killer since it is two circuit outlet, and all two circuit products are double insulated so not a human shock hazard.

I am still a little uncomfortable that the breaker didn't pop when the electrician shorted it out. Sometimes breakers can get tired, but surely they are designed with a secondary fuse or some failsafe.

While I wouldn't recommend plugging in a dead short to see what happens. maybe pick up a 20A or 30A fuse/breaker if you can find one, and try plugging that into the outlet (carefully). Hopefully the 15A branch breaker will open before the 20/30A fuse. Either way you shouldn't burn the house down but if the branch doesn't break at 15A you still have a bit of a safety issue.

But congrats on getting it squared away.

=======

To make this a little bit about audio, the fact that so many outlet grounds are apparently neutral instead of a clean ground, that is just another reason to make sure all your gear is pin 1 compliant so it can ignore and reject all that crapo ground noise.


JR