Does a GFCI require a polarized plug to work properly? For instance, if someone were to replace a damaged connector on an extension cord with the white lead on the brass screw and the black lead on the silver screw, would the GFCI trip if it attempted to power that extension cord?
Thanks in advance for all responses.
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Replies
Though having a properly polarized plug is a good idea, the GFCI does not depend on it, nor would having an improperly polarized cord be likely to cause a "false trip" of the GFCI.
"...extension cord with the white lead on the brass screw and the black lead on the silver screw, would the GFCI trip if it attempted to power that extension cord?"
How would it know? All the GFCI is doing is comparing current flow on the hot side of the circuit to current flow on the grounded side. It trips when it sees a difference above a pre-determined threshold.
The basic GFCI function is to just compare the electrical flow between the hot and neutral lines. Many of the newer household GFCI outlets are designed to shut off if they are not wired properly. I am not sure what conditions they test for, however, with modern electronics I would not bet against a GFCI extension cord testing for the hot/neutral reversal condition.
Newer GFCI's, as well as all "job site" GFCI's, do in fact require proper wiring to operate.
The white wire must go to the silver screw.
OP's question was not about mis-wiring the GFCI, it was about plugging in an extension cord that has its hot and neutral wires reversed (or by extension, an old one without polarized blades). I understand how a GFCI might identify hot and grounded wires connected to its line terminals, but how can it tell if you plug your load device in with the hot and grounded wires reversed?
BruceT
Bruce, you are correct. Yet, somehow I fail to see why this is a non-issue ... whether the GFI works, or not. Reversing the hot and neutral wires must be a bad idea. Otherwise, the screws would not be so plainly marked, plugs would not be 'polarized,' etc. Sure, one can always split hairs, and say 'it worked this time,' or 'things aren't done as they once were,' or even 'who knows what goes on withing electronics?' You're still back at square one: you are deliberately doing something wrong. I'm not about to say it's OK to do something wrong ... especially when such great lengths were taken to keep that 'something' from happening accidentally. Breaktime had a similar issue come up some time ago, where some folks thought that it was OK to fill propane tanks with compressed air. They seemed to think it made perfect sense to circumvent all the design features that were there to prevent just this from happening. In this case, as in that, I will say: Don't do it. Maybe you can get away with it THIS time. Yet, we cannot foresee every circumstance, or understand every implication. Do it right. If you goofed, go back and fix it. If nothing else, combine two "handyman electrical theory" maxims, and you have a recipe for disaster ... "electricity doesn't know the difference' and "you can't get shocked from a neutral." (Both statements are beyond ignorant). All you need is one thing to have the neutral bonded to the case - generators, anyone? - and you've set things up for a serious shock. Don't rely on the GFCI to protect you all the time. After all, things do fail. I guess what I'm really saying is "I don't know why, or understand why anyone would do something so silly in the first place."
Equipment is commonly designed with knowledge of which wire will PROBABLY be the neutral. For instance, with an ordinary table lamp fixture the supposed neutral will be connected to the threaded outer cylinder of the light socket (which one could, under certain rare circumstances, come in contact with), with the hot being connected to the center pin. In devices with a single-pole switch, the switch will be placed in the supposed hot line, so that nothing beyond the swithc is "live" with the switch off. In other cases where some large internal part must be connected to one side of the line or the other, it will be connected to the supposed neutral side.Additionally, electronic devices assume that the neutral side is closer to true ground and less apt to have transients, and some signals may be referenced to that side.This does not mean that a device connected improperly with regard to polarity is "unsafe", just somewhat less safe than it would otherwise be, plus (in the case of electronics) it's error-free/noise-free operation may be impaired.But, of course, that's not to say that this sort of thing should be done. It only takes a half a second to check that the right wire is on the right pin, and it's idiotic to not observe the polarity.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
This does not mean that a device connected improperly with regard to polarity is "unsafe",
It can mean exactly that, under the right circumstances.
"Hot chassis" TVs have the neutral tied to the chassis of the TV - so if they are plugged in backwards or the wiring is reversed, it can put AC on the exposed metal parts of the TV. I don't think those TVs have been manufactured in years, but there are still a surprising number still in use.
The old sets put AC on parts that COULD become exposed relatively easily (eg, by pulling off a knob), but not on parts that WERE exposed by default. And the standards for this were tightened 20-30 years ago, so it's unlikely that any significant number of the old TVs with hot shafts are still around.Keep in mind that 30-40 years ago electricians often didn't observe polarity when wiring a house, especially when working with old K&T. (I'm guessing a fair number still don't, when the inspector isn't looking, but the situation has at least improved.) Polarized plugs have never been a "first line of defense" but rather an "add on" for additional safety.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
The old sets put AC on parts that COULD become exposed relatively easily (eg, by pulling off a knob), but not on parts that WERE exposed by default. And the standards for this were tightened 20-30 years ago, so it's unlikely that any significant number of the old TVs with hot shafts are still around.
FWIW, I have a set manufactured in 1989 that has metal knobs and a hot chassis. It has a warning tag on the cord though, to the effect that the TV is unsafe if plugged in backwards. Industry estimates suggest that the percentage of hot chassis sets could be as high as 30%. When you consider that the average number of sets is something lik 3.4 now, that's a lot of potentially dangerous TVs out there.
There are other examples, usually due to faults (e.g. a power tool shorts the neutral to the case), but that was just the first example that came to mind.
It may have metal knobs, but I'll bet they're plastic shafts. The set probably causes cancer in California too.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
"Newer GFCI's, as well as all "job site" GFCI's, do in fact require proper wiring to operate.
The white wire must go to the silver screw."Now does a GFCI "know" if t he neutral or hot is connected to the silver terminal?Specially if it is wired without and EGC (which is allowed for retrofitting on old ungrounded circuits)..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I have no idea, Bill. Nonetheless, detection of miswiring, or open neutrals, was a condition of the UL standards. You may recall a year or two back, when all the GFCI receptacles were changed ... for example, Levitton began boasting of "smart lock" technology.
Smart Lock has been around a number of years. Since 2002 and possilbe 1999.The GFCI specs where updated in 2003. And again July 28, 2006.The lastest changes added two requirments.One that it have an end of life feature. One acceptable method is a unit that won't reset if the unit has failed. The Cooper (Smartlock tm) had had that feature since the 2003 version.The other require was if the GFCI is "reverse wired", that is when the power is connected the LOAD terminals rather than the line.I saw nothing in the announcements at the time that it would detect a hot neutral reversal.There is a thread that discusses the changes in GFCI specs.
http://forums.prospero.com/tp-breaktime/messages?msg=71065.8And another thread about that same time where was claimed that the GFCI's could detect reverse polarity. And I ran test on a GFCI showing that was not correct. But that was a pre July, 2006 unit.http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=71180.117&search=yAfter that thread I updated by profile..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
As I noted before, I am willing to concede, for the sake of argument, that even the newest GFCI's will only detect 'reversed' connections on the line side. And, as I stressed in my last post, the GFCI issue is a non-starter for the load side, because reversing the connections is a bad idea for a whole bunch of reasons. Whether these reasons are ALWAYS a factor, or if they require something else to go wrong as well, is not the issue. I say that any situation that results in a white wire being 'hot' is a bad situation- whether things 'work anyway' or not. If the OP is looking for a "go ahead, it's fine" answer, he won't get it from me. I don't care if it "works" - or not. Nor will I allow that the GFCI is the be-all and end-all in safety devices, one that allows for any amount of hillbilly engineering to be 'safe.' Nor will I 'test' a GFCI, not even for 'academic' reasons ... not until I can see a good reason why someone would want to reverse the wires. I suspect that the OP has some other problem, one that he thinks he found an "easy" fix for. If that is the case, it is very likely that the GFCI will not be relevant, as the problem will still exist.
I don't disagree about not reversing the polarity on any connection.But I wonder where the question came from orginally?What could have happened was that it was reversed and some one said that is was "OK because the GFCI was not tripping".That is why it is import to make it clear that a GFCI receptacle does not detect either it'self having reverse polarity nor that of something plugged into it (unless it has other problems).Now load end GFCI's are a not just GFCI receptacles mounted in a box at the end of a cord. They have a different spec.And it MIGHT BE that they are polarity sensitive. But they whould also require a ground connection to work. And all of that (GFCI and verified ground) might be part of an OSHA requirement. But I really don't know..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Gee guys, you've made this a very interesting discussion. I'm the original poster and I asked the question simply because I had temporarily attempted to power a circuit using an extension cord that was attached to a GFCI that would instantly trip as soon as I connected the cord. A quick check of the circuit revealed no shorts. Then I noticed that the extension cord had been previously repaired on one end with a new connector. It was the end of the day, so I wrapped things up and called it quits. Later that evening, I was mulling over the possibilites and got to wondering if someone might have reversed the leads when repairing the cord, and further wondering if that might be enough to "trigger" the GFCI. So, I simply posed the question to our excellent panel of experts here on the forum...and I thank you for enlighting dialogue.
I got an opportunity to recheck the problem this morning and found an intermittent short (56k ohms between the black and bare) in a brand new piece of 12/3 cable (completely disconnected with no visible damage).
Ironically, I found the problem before I ever got around to checking the polarity on the extension cord, so I still don't know if it's wired correctly...or if it even matters to the GFCI. However, polarity always matters to me, so I wire everything with as much consistency as possible...whether it matters or not.
Thanks again.New knowledge is priceless.
Used knowledge is even more valuable.
I once stripped down about a 5' length of romex for the individual wires and found inside that the black wire had been spliced with a crimp connector. The black was exposed for a total distance of 8 inches or so, with only the paper separating it from the ground wire.(I suspect that the splice was supposed to be automatically cut out as the cable was spooled, but someone screwed up.)
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
I once stripped down about a 5' length of romex for the individual wires and found inside that the black wire had been spliced with a crimp connector.
I assume you mean the cable was manufactured that way? And I gather there was not a visible bulge or other sign external to the NM-B of the splice?
That is kind of scary.
Yep, it was a factory splice, presumably used because the black spool ran out. I suspect something should have sprayed a big black (or maybe orange) splotch on the cable at that point to identify the bad spot, but there was noting visible on the jacket. Or it may be that they depended on a magnetic detector to detect the crimp splice, but it didn't trigger.Yep, it's scary. That was basically in the middle of a 50-foot roll I'd used in various areas throughout the house, and it was the merest of accidents that I stripped down that particular part of it.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
intermittent short (56k ohms between the black and bare)
So you think this was the problem? Interesting. 56,000 into 120 = 0.002 , or 2 mA.
Edited 5/1/2007 1:19 pm ET by edlee
Cmon, edlee. GFCI's are supposed to be accurate to within about 5 milliamps. So I was off a few thousandths.
You should see my framing.New knowledge is priceless.
Used knowledge is even more valuable.
M-dubya,
I wasn't complaining. It's simply interesting to me that your read shows it tripping around 2 mA. I keep track of details like this.
As for accuracy, well, I definitely notice a couple of milliamps on a circuit, but when I rough wire a house I use a basic 8' electrician's tape measure, which is marked off in 1/2" increments I don't know why anyone needs anything more detailed than that it's not like we're building churches or anything know what I mean? BTW anyone got work for me? I can't understand why I don't get more repeat business........Ed
Does a GFCI require a polarized plug to work properly?
The short answer is no, assuming the GFCI is wired correctly, it will still protect you from a "ground fault" even if you plug a non-polarized plug into it.. and it will power the appliance you're plugging into it.
That being said, wiring a polarized plug in reverse is not a safe practice and should be avoided.....but that would not trip the GFCI.
Geoff
Hey, since when did we start allowing short answers around here????
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
LMAO, I had to see a man about a horse! :)
G