Wife plugged the vacuum cleaner into a GFCI outlet in the kitchen. When she turned on the vacuum, the lights went out and the clock on the stove went off. She swore like a sailor and then came out to tell me. No breakers were tripped. I got my outlet tester and the GFCI tested as ‘ground-neutral reverse’. I killed the circuit and removed the GFCI–it was installed end-run and NOT as a feed to the lights or the stove plug. That solved the problem, so I assume the GFCI failed (it was maybe 20 years old) and caused the lights and stove to go off. Sound plausible, or is there more (and maybe more sinister) going on?
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A GFI outlet will trip if ground and neutral are reversed. When it trips, it often will trip the breaker as well, since it uses a "crowbar" technique (throwing a dead short across the output to throw the breaker).
Had that outlet ever worked correctly?
Dan, I question your idea of a GFCI outlet opening the circuit by "throwing a dead short across the output to throw the breaker". They work by sensing the current on the hot and the current on the neutral, and opening the circuit if there is an imbalance. This is completely independent of the circuit breaker in the main or sub panel.
(However, I do wonder how your tester could tell that ground and neutral were reversed.)
Dan, I've got a couple of outlet testers, the yellow devices with the 3 leds--they plug into the outlet and light up various combinations of lights depending on what the wiring condition is (correct, open ground, open neutral, etc). One has a button for testing GFCIs. My question is whether or not a GFCI failing would cause the other devices on the same circuit to malfunction.
And I answered that one -- the GFCI outlet contains a "crowbar" that shorts the outputs when it trips. This can sometimes trip the breaker on the circuit before the breaker inside the GFCI trips.
First there is no BREAKER inside the GFCI.
A GFCI is not a current limited devices. As a test wire one up to a 30 amp breaker and plug in a couple of 1500 watt heaters.
The GFCI will not open. It might metal after a period of time, but it is not a current limiiting device.
The GFCI has a relay that opens when the current flows in the hot and neutral are unbalanced.
Secondly, if the pannel breaker did not trip and this was not a feed through GFCI then even if it did have a crowbar HOW WOULD THAT CAUSE THE LIGHTS TO GO OUT?
A GFCI outlet consists of some current sensing logic, a crude circuit breaker, and a "crowbar" -- an SCR or some such across the output terminals. When a current imbalance is sensed the SCR shorts out, and the crude circuit breaker (hopefully) opens. It's not intended to be a regular current-limiting breaker, but only to operate with reasonable reliability when triggered by the crowbar circuit.
No matter what, a GFCI unit MUST have either a crowbar circuit or a series-pass electronic breaker in order to meet the requirement to trip within a millisecond or so. Waiting for the mechanical contacts to open takes far too long. And a series-pass system is far too expensive for common use, plus it adds unacceptable voltage drop.
So, the crowbar shorts the outputs, and then it's a race to see if the GFCI breaker will open first or the panel breaker. Sometimes the panel breaker "wins".
That seems to solve my question as to why panal breaker kept tripping.
There is no "crowbar".
http://www.glencoe.com/ps/ee/articleFiles/GFCI.ppt
http://www.ecmweb.com/ar/electric_think_gfci/
There is no "instantous trip". UP TO SEVERAL SECONDS.
"When installing and testing GFCIs, you should know that they do not trip instantaneously. In fact, while they typically trip in 25 ms or so at fault currents exceeding 20 to 30mA, they are permitted by UL to take several seconds to trip at fault currents in the 6mA range. This is important to recognize when selecting GFCI testers, for some have timing circuits in them that may limit the test current to a time less than necessary to trip a GFCI. (We'll cover this in more detail in the testing recommendations, which follow.)"
Here is the spec sheet for one of the common devices used in GFCI's
http://www.national.com/pf/LM/LM1851.html
Download the the PDF and you will find an application schematic. NO CRAWBAR.
Here is generic schematic from Lawrence Livermore National Laboratory
p://www-training.llnl.gov/wbt/hc/Electrical/ES28.html
Again no crowbar.
They all show a relay.
All though it is called a circuit breaker in some places it is not a circuit breaker in the definition that is common used, ie, a current limiter. But rather just something that will break the circuit - which an switch or relay will do.
I vote for "yes, there is more going on", simply because I can think of no possible malfunction to a GFCI (or any other device, for that matter) causing the symptoms you describe: located at the end of the circuit (ie: feeding nothing else), and causing other devices to lose power WITHOUT blowing a breaker. If there were multiple cables in the box with wirenuts, I vote for a loose connection that got fixed when you installed the new GFCI. If you are saying there is only one Romex cable coming into the box with the GFCI in it, then I'm clueless.
Hi, you stated that your tester displayed neutral-ground reversed! When you pulled the old GFCI out of the wall was it in fact wired incorrectly? Were the wires landed on the wrong terminals? are the grounds and the neutrals ALL terminated on the same bus bar at the service? Is the neutral bonded at the service? Your tester worked on a circuit that was de- energized? Grounds and Neutrals are NOT interchangable, they are NOT the same conductor. Is this house wired in Romex? or EMT ? do not trust your three wire tester unless you have proven it is reliable on a "good" circuit ! The capacitance of any circuit can cause false readings with those things. What I mean is ....on a new circuit that has no load on it the tester can show the the wiring is reversed, but, add a load to that same circuit and the problem will go away . this is caued by the built in capacitance of the wires in that circuit merely passing thru the resistors inside of the tester,also the raceway can significantly impact the testers ability to "read " the condition of the wiring this condition is further aggravated by mixing grounds and neutrals at the service or any other junction in the house or premises ..... confusing enough?
I mis-spoke when I typed the original post--the tester said 'HOT-GROUND REVERSE'. Please disregard the contrary info above. I had put the tester back in my truck before posting and gave y'all incorrect information. Sorry, 11 hour day, my bad.
In addition to the wiring tester I also have one of the pencil-shaped testers that senses current at a device or wire. When I approached the GFCI with that, there was current. The circuit was not de-energized and the breaker was ON. The outlet tested correctly a year ago with a different tester--a home inspector checked every outlet with his and listed them all as properly wired and working. My tester gets infrequent use but I've used that one before and have to assume it works.
I removed the GFCI from the wall and threw it out. It was wired correctly. It had its own wires coming out of it and they were connected black-black, white-white, ground-ground. No load was connected and those leads were individually wire nutted to keep them safe. It was all done right, and I have not found any wiring problems at all when working on this house. It was rewired in 1981 with Romex and 20 amp breakers, and done by a pro (who used cheap receptacles because the previous owner was renting it out). I did not install a new GFCI.
The electrical service was replaced 6 months ago and done correctly. It's a 200 amp panel with left and right breakers. Grounds and neutrals are bonded in the panel. I am not an electrician and didn't wire the panel but the state inspector looked through it and gave it the green tag.
Presumably hot-neutral reverse means that there's current on the bare copper ground wire. If you touched the chassis of a device plugged into such a circuit, and were standing in a puddle of water, you could get a helluva shock. If that's what GFCIs do when they fail, it's dangerous.
now we are making progress. When your tester said "hot-ground reversed", it meant "open neutral". (no, I can't tell you why those testers do that, but they do). If you answer my question from my previous post about how many cables enter that box, we'll make more progress.
And one more, possibly important, question: did the vacuum cleaner run for a while when your wife plugged it in, or did the lights go out immediately ?
Edited 4/8/2004 10:53 am ET by r
Edited 4/8/2004 11:06 am ET by r
"Presumably hot-neutral reverse means that there's current on the bare copper ground wire. If you touched the chassis of a device plugged into such a circuit, and were standing in a puddle of water, you could get a helluva shock. If that's what GFCIs do when they fail, it's dangerous."
Here is what the common tester (Ampprobe PY-2) will show.
"Detects correct wiring or following faults: open ground, reversed polarity, open hot, open neutral, hot & ground wires reversed, hot on neutral with hot open"
"In addition to the wiring tester I also have one of the pencil-shaped testers that senses current at a device or wire. When I approached the GFCI with that, there was current. The circuit was not de-energized and the breaker was ON."
The "tick tester" works by measuring electrical fields. IT DOES NOT TEST FOR CURRENT FLOWING. They typically have a range of a couple of inches. So even if the receptacle is "dead" because the GFCI had tripped there would still be power in the wires to it and close enough for the tick tester. Also they are know for false positives (and sometime false negatives).
"She swore like a sailor and then came out to tell me."
Just because the lights went out and the vacuum did not run or was there a "pop", "flash", or other starteling event?
Where there other wires other than the feed cable and the pigtails to the GFCI?
What all is on this circuit?
It is a strange circuit in that it has a GFCI on it along with lights and the stove. Those are not suppose to be on a kitchen small applinace circuit. And normally there would not be a GFCI except on those receptacles that servived the counter top.
OK david, I am an electrician, the tester read hot -ground reversed ? if the panel is wired correctly the breaker should have tripped? you stated the circuit checked out ok last year with an inspector, and now the wiring is reversed, how did that happen? hopefully the grounds all land on their own bus bar and similarly do the neutrals but not together !!!! the Neutral must be bonded to ground only ONCE. the Grounds must be connected the the incoming ground, period. These are just questions, I AM NOT TRYING TO PUT YOU ON THE SPOT ! please please never assume a tester is in working order . I want more than a blinking light between me and the hereafter. ALWAYS check your gear on a known circuit before proceeding with your troubleshooting. two more? if this was wired correctly why did you throw it out, granted things go bad all the time but I think the problem lies elsewhere in that circuit . does this vaccum have a polarized plug on it ?
OK david, I am an electrician, the tester read hot -ground reversed ?
That is correct.
if the panel is wired correctly the breaker should have tripped?
The breaker did not trip.
you stated the circuit checked out ok last year with an inspector, and now the wiring is reversed, how did that happen?
The circuit checked out OK last year. There is no reverse wiring as far as I know. All I am saying is that the tester showed 'hot-ground reverse' when plugged into that GFCI after it failed--I presume it failed because it would not reset.
hopefully the grounds all land on their own bus bar and similarly do the neutrals but not together !!!! the Neutral must be bonded to ground only ONCE. the Grounds must be connected the the incoming ground, period.
I am not looking in the panel right now, but my recollection is that there is a large buss bar on each side of the panel (a Square D panel). Grounds and neutrals are both bonded to the bar on the right side. There are not separate bars for ground and neutral. The electrician who put the panel together did not put anything on the left side buss bar because he didn't need to. The two bars appear to be connected by a large aluminum strap that runs up behind where the incoming service conductors terminate. I cannot actually see that the bar is continuous because of where those terminals are.
These are just questions, I AM NOT TRYING TO PUT YOU ON THE SPOT ! please please never assume a tester is in working order . I want more than a blinking light between me and the hereafter. ALWAYS check your gear on a known circuit before proceeding with your troubleshooting.
The circuit tester seems to work, but I've plugged it into outlets I'm pretty sure are right, namely stuff I did myself. The 'proximity' tester (for lack of a better term) is very reliable and I never touch anything if that tester beeps when near a wire or device. It seems to work perfectly and I'm happy I have it.
two more? if this was wired correctly why did you throw it out, granted things go bad all the time but I think the problem lies elsewhere in that circuit . does this vaccum have a polarized plug on it ?
I tossed the old GFCI because I think it's failed and I'd rather buy a new one. This house was rewired in 1981 and the former owner had lousy devices used. A lot of the plugs are too loose to hold a cord in reliably and I've been changing those out. He used lousy switches too.
The vacuum is a new Miele and has a polarized plug but no ground.
As far as I can see, the circuit in question went to a plug first (non GFCI) then to a switch box where it fed two lights, and then to the GFCI that I removed. A newer Kenmore propane range with an electronic brain is the only thing plugged into the first outlet. The vacuum did not run before the failure happened--it was immediate and wife reports no sound of a GFCI popping.
Thanks to everyone for their input. If I need to get an electrician over here to take a look I can do that in a matter of an hour or so. Circuit is off at this point, also.
EDIT: photo of the inside of the panel here:
http://www.bailerhill.com/panel.jpg
You can see the buss bars on the left and right. There are two bars on each side, but they are all tied together. The wires on the right were mostly put there by the electrician, a few by me, and he put grounds and neutrals on both bars, as did I. The wires on the left bar were put there by me. The aluminum strap at the top of the bars goes behind the big terminals and appears to tie all of them to the incoming neutral from the utility. The 6 ga. braided copper going to the ground rods and hot/cold/gas are tied to the same bars are the other neutrals and grounds, and are in the back row on the right bar. The 2-2-4 conductors loose on the right are for a future shop building and are just sitting there in the way.
Edited 4/8/2004 12:35 pm ET by davidmeiland
OK, everyone is ignoring me, so I'll just guess without the data:
You are using a Sperry GFCI tester which, when it says "hot-ground reversed" indicates an open neutral. I don't know why, it just does. Hot-ground reversed is a complete impossibility without blown breakers, so stop wasting your time there.
If the vacuum ran for a while, somewhere the neutral may have heated up/vibrated loose. If it was a wire nut connection in the box with the GFCI you replaced, you may have fixed the problem already. If there are no other cables coming into that box, as you may or may not have said, then the problem is a connection in the neutral upstream. Open all the boxes on the circuit and tighten wire nuts and screws on devices. The problem is in the neutral of that branch circuit.
r,
Sorry, not trying to ignore anyone here, just trying to lay out the info.
The tester has a separate indication for open neutral, which is not what I got. The tester is a Radio Shack version made in Taiwan. It gives a possible 6 results including correct, open neutral, open hot, open ground, hot/gd rev, hot/nt rev.
The vacuum did not run.
There are no other cables coming into the box where the GFCI was. The power to that is either coming from another box in the room or from a J-box under the house, not sure which yet. I can easily open the boxes in the house and see what's happening in there, going underneath is less fun but I'll probably have to go see just for the helluvit.
As I posted, the circuit works now without the old GFCI plug in it. To me that means that the neutral is working.... but whadda I know?
OK, there are no other cables in that box, yet you mentioned wire nut connections. I guess you are saying the old GFCI had manufacturer installed 6" or so lengths of conductors coming out of the GFCI that were wirenutted to the incoming Romex cable. (The GFCI's I've used just had pressure-plate screw terminals).
So, I'm sticking with an intermittent open neutral upstream of this box (yes, it's not open right now if everything on the circuit works). When the problem occurred the open neutral caused the stove clock and lights to go out (no complete circuit), and the tester incorrectly reported the open neutral as hot-ground reversed at the GFCI. Since the vacuum didn't run for a while, it seems to be vibration related, not heat related. Maybe plug your tester back in to the GFCI (where it now reads 2 yellow lights lit indicating "correct", yes ?), and have your wife watch it while you bang on the receptacles, switches, or junction boxes of that circuit and see if it switches to "hot-neutral reversed". If so, open that box and tighten the loose neutral connection. I am assuming that not EVERYTHING on that circuit went out with stove clock and lights, but if it did, check the neutral for that circuit in the panel, also.
I'm also pretty sure the GFCI you replaced was good and had nothing to with the problem, but intermittent opens like this are a true pain to locate, and indeed, it may never malfunction again.
Good luck
PS: if you have time, turn off the breaker to this circuit, take the white wire off the GFCI, plug in your tester, turn breaker on, and confirm that your tester reads "hot-ground reversed". I have a high degree of confidence it will, but will be happy to publicly eat crow if I am wrong.
Edited 4/8/2004 3:05 pm ET by r
I agree with you r , however I don't like all of the grounds and neutrals tied together in the panel, this is cause for many nuisance problems as well as providing many paths for fault currents to travel along. The Neutral bus bar is just that ....A neutral bar, not someplace that everything that is not hot lands! but such is life with Romex! This problem is elsewhere on that circuit as you have suggested. Good Luck Dave
I'm not sure what you mean: if it's a sub-panel the grounds and neutrals must be electrically isolated from one another. In the service entrance panel they MUST be electrically tied together, and bonded to the panel box itself. Do you mean you prefer that all the grounds go to one bar and all the neutrals tie into another, and then you bond them together ? This ads visual clarity, although some electricians think troubleshooting is easier if the ground and neutral of each cable are next to one another.
But I thought he was talking about his main panel, no ?
yes I think he is talking about the Main but,what I mean to say is that the neutral is bonded at the point of service to the Grounding Electrode and the grounds are solidly attached to the grounding electrode, but not on the same bus this includes the Main! if all the grounds and neutrals are landed next to each other then the neutral could very well be grounded in more than one place ! since I do not play with Romex , I am having a tough time understanding why they all get to land on the same bus, in my neck of the woods these two conductors are not landed in this fashion, but then,everything I do is in pipe
" How stupid you sound always depends on what part of the country you are standing in "
Hmmmm... are you saying this panel is not what I want, or is it the way everything is with romex and so be it? If the electrician I hired could have used a better panel I'd like to know that.
Regarding r's suggestion of an intermittent neutral open, I pounded on the walls and floors where the switches, plugs, and likely J box are and the lights did not flicker. Certainly not conclusive but at least a start. I'll open stuff up and double check.
No Dave, I am trying to understand why grounds and neutrals are on the same bus, according to the NEC the neutral can only be grounded ONCE ! And if I installed a service around here in that fashion the inspector would not let it pass , but that is here, and the interpretation of codes is ALWAYS at the discretion of the authority having jurisdiction! so now I will shut up about technique and say once again that the problem is in that circuit .As "r" pointed out, there has to be a loose connection somewhere that is intermittent ,and good luck finding it, if that is what it turns out to be.
I was talking with my folks yesterday and they had the same thing happen, There is a GFIC outside that is feed from the kitchen circuit. The breaker that serves the kitchen was tripped and they could not get it to reset. They called an electrician who scratched his head and scratched his head then called another guy and some how they arrived at the outside outlet. They removed the GFCI and bingo, everything works again. The GFIC is downstream of the kitchen and is feed from one romex coming out of the house. It feeds some exterior lights. They live an hour away from me so I have not seen it but it seems to be a pretty similar situation. I don't know how long the GFCI has been installed, as I have not lived there for 20 years or so.
Here's a stupid thought; my DW kept tripping a GFCI outlet with the vac, and I couldn't figure out what was going on until I saw her plug it in; it has a large grounded plug, and the way DW plugged it in (not gently) the very bottom of the plug was actually pressing the "test" button and tripping the outlet.