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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: John Penkala on September 10, 2017, 04:49:40 PM
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I just came across a venue where every receptacle had the Hot and Neutral reversed according to my Extech circuit tester. And yes, I've verified that the tester is working correctly. I'm thinking the reversal is at the panel. I would think this could be extremely dangerous under certain circumstances. I'd like to hear the opinions of the pro's here.
-JP
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It is not automatically dangerous by itself. Line and neutral are both insulated inside properly designed equipment.
However it is WRONG and should be corrected. >:(
It can be dangerous in connection with other wiring faults. :o
JR
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It is not automatically dangerous by itself. Line and neutral are both insulated inside properly designed equipment.
Yes, in combination with a bootleg ground it becomes an RPBG which is REALLY dangerous. And if you're working inside of a piece of gear that's not unplugged from the outlet, everything that's connected to the incoming neutral will still be energized even if the switch is off. Never assume anything is off!!!
However, I just don't see how the hot and neutral could be reversed at the panel. And if this is a new building, how did it pass inspection?
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Yes, in combination with a bootleg ground it becomes an RPBG which is REALLY dangerous. And if you're working inside of a piece of gear that's not unplugged from the outlet, everything that's connected to the incoming neutral will still be energized even if the switch is off. Never assume anything is off!!!
However, I just don't see how the hot and neutral could be reversed at the panel. And if this is a new building,how did it pass inspection?
This guy?
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I just came across a venue where every receptacle had the Hot and Neutral reversed according to my Extech circuit tester. And yes, I've verified that the tester is working correctly. I'm thinking the reversal is at the panel. I would think this could be extremely dangerous under certain circumstances. I'd like to hear the opinions of the pro's here.
-JP
There really is no way to reverse this at a service panel. The NEC refers to the neutral as the grounded conductor (different from the grounding conductor). The neutral is bonded to the grounding conductor, making it the "neutral"-until that happens it is not really a neutral. If any of the 3 wires (on a typical split phase system) feeding a subpanel are mixed up, you might run into a hot/neutral reversed scenario on half of the receptacles-the other half would have 240 volts across them because they would have 2 hots connected.
Of course, I am assuming the service panel is properly bonded-lacking proper inspections that might be a dangerous assumption. Lacking proper bonding, the same could happen on the service panel as in the subpanel.
I would suggest shutting off the main breaker and having a qualified electrician inspect the system (or a qualified inpsector). That pretty much rules out the installer-as a qualified installer should have verified his own work.
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One of my RV readers told me about a new campground that had every one of the campsite pedestal receptacles wired with swapped hot and neutrals. This was a COE campground (US Army Corp of Engineers), so the wiring SOP document must have been incorrect, and the technician wiring the pedestals dutifully mis-wired some 50+ pedestals incorrectly.
Perhaps in your case someone drew a hookup diagram on a napkin from the front of the outlet perspective, and some non-electrician helper wired up all the outlets while looking at the back of the receptacles. That would do it.
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Also, some of my church DIY helpers have wired receptacles with swapped hot and neutral wiring because they assumed that the longer slot on the receptacle must be hot. Of course the shorter slot is hot and the longer slot is neutral. As Sister Mary Charles back in 5th grade at Saint Mary's School would tell us, ASSume makes an ASS out of YOU and ME. That always cracked up all the boys in the classroom.
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There really is no way to reverse this at a service panel. The NEC refers to the neutral as the grounded conductor (different from the grounding conductor). The neutral is bonded to the grounding conductor, making it the "neutral"-until that happens it is not really a neutral. If any of the 3 wires (on a typical split phase system) feeding a subpanel are mixed up, you might run into a hot/neutral reversed scenario on half of the receptacles-the other half would have 240 volts across them because they would have 2 hots connected.
Of course, I am assuming the service panel is properly bonded-lacking proper inspections that might be a dangerous assumption. Lacking proper bonding, the same could happen on the service panel as in the subpanel.
I would suggest shutting off the main breaker and having a qualified electrician inspect the system (or a qualified inpsector). That pretty much rules out the installer-as a qualified installer should have verified his own work.
I thought it might be reversed at the panel because literally every receptacle that I measured was reversed. Now I know better. I had to have checked at least 15 on the second floor where I was. I even went downstairs to see if it was the same there. It was. And, I was just in the conference center that is attached to an even bigger hotel with a restaurant. I did bring this to the owner's attention and they are taking it very seriously.
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I thought it might be reversed at the panel because literally every receptacle that I measured was reversed. Now I know better. I had to have checked at least 15 on the second floor where I was. I even went downstairs to see if it was the same there. It was. And, I was just in the conference center that is attached to an even bigger hotel with a restaurant. I did bring this to the owner's attention and they are taking it very seriously.
Just how did you confirm that your Extech tester was measuring correctly? Are you using the original short Euro cable that came with it? You need to try an alternate testing method just to confirm your readings, as in "who will guard the guards"? If you buy a $5 outlet tester with 3 lights, what does it indicate? Before I send up a balloon I would triple check my readings.
Also, a visual inspection would tell you a lot. If you're authorized and trained sufficiently to be safe, just pulling a receptacle out of the box and looking at the wiring colors would point the blame in the right direction.
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Just how did you confirm that your Extech tester was measuring correctly? Are you using the original short Euro cable that came with it. You need to try an alternate testing method just to confirm your reading, as in "who will guard the guards"? If you buy a $5 outlet tester with 3 lights, what does it indicate? Before I send up balloon I would triple check my readings.
Also, a visual inspection would tell you a lot. If you're authorized and trained sufficiently to be safe, just pulling a receptacle out of the box and looking at the wiring colors would point the blame in the right direction.
I was in disbelief. Therefore , I did verify the Extech CT80 tester at home after the show and 30 seconds ago on my current show. It works as it should. Also, on the show that day I use 12ga SJ cables with an outlet tester that's integrated into the Edison connector. They usually glow green when all is good and red when something is wrong. On this day the green and red LED's were on simultaneously on all 4 of them regardless of where I plugged them in. I have never seen that.
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I was in disbelief. Therefore , I did verify the Extech CT80 tester at home after the show and 30 seconds ago on my current show. It works as it should. Also, on the show that day I use 12ga SJ cables with an outlet tester that's integrated into the Edison connector. They usually glow green when all is good and red when something is wrong. On this day the green and red LED's were on simultaneously on all 4 of them regardless of where I plugged them in. I have never seen that.
I would also get a meter on it just to triple check. Here's what I send to my RV groups on how to measure a standard 120-volt outlet.
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I would also get a meter on it just to triple check. Here's what I send to my RV groups on how to measure a standard 120-volt outlet.
(http://forums.prosoundweb.com/index.php?action=dlattach;topic=164811.0;attach=20300;image)
While I have abandoned my outlet tester I explain why simple AC voltage measurements can be tricked. The rare but hazardous RPBG will measure exactly the same as a properly wired outlet using a simple AC meter. http://www.johnhroberts.com/OD1.htm (http://www.johnhroberts.com/OD1.htm)
The less hazardous, but still incorrect line-neutral reverse can be effectively metered with a simple AC meter since ground to neutral will not measure 0V.
I have shared this before a crude but simple way to identify if outlet pins are energized is to use a cheap Neon lamp probe. (http://i.ebayimg.com/00/s/NDAyWDEwMjQ=/$(KGrHqV,!iUE+Qn0NpCQBP9GB))sqg~~60_35.JPG?set_id=8800005007)
Holding one lead of the neon lamp probe in your bare hand, touch the other lead to the outlet pins. Any hot pins will cause the neon lamp to glow dimly. Current "should" be limited to well below dangerous levels, but don't do this while standing in your bathtub full of water.
I do a similar trick with a VOM but am reluctant to share details since you can get shocked using the wrong mode.
JR
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I do a similar trick with a VOM but am reluctant to share details since you can get shocked using the wrong mode.
JR
Or cheap VOM with low internal resistance ;)
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I do a similar trick with a VOM but am reluctant to share details since you can get shocked using the wrong mode.
JR
What about a NCVT? Wouldn't that give the same results, and be the correct tool for the job?
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What about a NCVT? Wouldn't that give the same results, and be the correct tool for the job?
Here's how to use a NCVT to test for swapped Hot and Neutral wiring as well as a RPBG. https://www.youtube.com/watch?v=XfAPkJVYUpY
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What about a NCVT? Wouldn't that give the same results, and be the correct tool for the job?
The cheap NCVT I own will sound in the same time zone as an outlet. Perhaps a more expensive one will have lower sensitivity.
But yes if a grounded metal chassis, triggers an NCVT alarm approach with caution.
JR
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The cheap NCVT I own will sound in the same time zone as an outlet. Perhaps a more expensive one will have lower sensitivity.
But yes if a grounded metal chassis, triggers an NCVT alarm approach with caution.
JR
This is the one I have Fluke 1AC II A1 (http://en-us.fluke.com/products/electrical-testers/fluke-1ac-ii-a1-electrical-tester.html) and I have to insert the tip into the receptacle slot to sense the voltage. I've only had it alert once while approaching the receptacle and the Line had broken insulation and was energizing the metal box behind the wall board.
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This is the one I have Fluke 1AC II A1 (http://en-us.fluke.com/products/electrical-testers/fluke-1ac-ii-a1-electrical-tester.html) and I have to insert the tip into the receptacle slot to sense the voltage. I've only had it alert once while approaching the receptacle and the Line had broken insulation and was energizing the metal box behind the wall board.
That's also the one I use in all my videos and seminars, and it works perfectly all the time. They only cost around $25 or so, and like any Fluke it should last forever.
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That's also the one I use in all my videos and seminars, and it works perfectly all the time. They only cost around $25 or so, and like any Fluke it should last forever.
Mine cost a small fraction of $25 and will detect live wiring behind walls... :o Perhaps useful would be a sensitivity switch or adjustment.
Professionals should probably buy something other than the cheapest NCVT. 8)
JR
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I use to see a lot that when I worked as a commercial electrician. There are a lot of guys working as electricians that are not qualified to even put on a receptacle cover plate. I was sent to help a foreman on the tail end of a job. I saw a few receptacles that were crooked and decided to check them with my tester after I straightened them. My plug tester lit up weird and iirc my meter read about 200 volts on the hot and neutral. I went to the new breaker panel and the neutral was pumping out about 118 volts. I turned off the transformer disconnect and pulled the cover and the XO was not grounded. There was a ground rod next to the xformer and the ground wire was lugged to the case but there was no jumper to the XO lug. The foreman told me the owner sent out his best electrician to wire it up and that he did not need to check it. Well his best electrician didnt have a clue and the foreman should have never been made a foreman cause he didnt know how to wire a xformer. I saw a lot of crap like this. Also the electrical certification is BS. All a guy has to do is take the class and learn the answers and pass the test and they get their journeyman card and they dont know crap. Every guy that I interviewed that had a card could name most of the basic electrical tools on my 100 question "fill in the blank" test. I dont do multiple choice where a complete idiot could win the lottery.
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I was in disbelief. Therefore , I did verify the Extech CT80 tester at home after the show and 30 seconds ago on my current show. It works as it should. Also, on the show that day I use 12ga SJ cables with an outlet tester that's integrated into the Edison connector. They usually glow green when all is good and red when something is wrong. On this day the green and red LED's were on simultaneously on all 4 of them regardless of where I plugged them in. I have never seen that.
Are you using the Legrand/Pass and Seymour GCM plug/cord-receptacle devices? https://www.legrand.us/search.aspx?q=GCM (https://www.legrand.us/search.aspx?q=GCM)
I have them on all my cords, which provides a "canary in the coal mine test" of anything I plug into. Not that those devices should be used exclusively, but if the Extech reads fail and all the GCM devices are either blank or showing a red indicator, you have a pretty reliable indication something is definitely wrong. The NCVT test as a third test should remove any and all doubt something is amiss.
Is it safe (enough)?
After confirming a confirmation of an indication that there is a problem, but no RPBG, should the show go on? Would that be a reason to load the gear back on the truck? Does anyone have a contract clause that defines actions should the power prove unsuitable or unsafe?
Temporary fix to make it safer (or not)
If one had an "adapter" that reverses neutral and ground, would the stage be safer? If there were any RPBG on any of the downstream wall receptacles, would that not cause a direct short and pop the breaker? Arc flash an issue?
Edited due to mind-finger malfunction and general stupidity...
When do we stop when electric tests good?
On a tangent, If the Extech says all is OK, is it safe? How about with a solid green only indication on the GCM device in addition to the Extech? Is that safe? Should one's test always use a three-tester test?
Granted, neither the Extech nor the GCM devices will actually identify a RPBG condition, apart or together. if you used the Extech, and all/any of the cords one has made up has an GCM device, there is an automatic second-level test. Can there be a possibility of a RPBG if there is no indicated reverse polarity, and the ground shows voltage within expected ranges on the Extech? Would that preclude the actual test with the NCVT?
I will grant the NCVT is so quick, easy, and positive this question is more a technicality than a practical matter.
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A
Temporary fix to make it safer (or not)
If one had an "adapter" that reverses neutral and ground, would the stage be safer? If there were any RPBG on any of the downstream wall receptacles, would that not cause a direct short and pop the breaker? Arc flash an issue?
For me RPBG is a deal breaker-and no way I am gonna have an adapter laying around to fix that-that's a hazard in itself.
Reversed polarity? Depending on gear and setup. Obviously, first look for an alternative-however in most modern gear polarity is not an issue-nor really is voltage if something is happy from 90-240 volts.
IMO, polarity is really more of an issue for the electrician's-once they leave leve they have no control over what is plugged in there and if someone plugs in an Eico tube amp like the one I used to run on a metal bookshelf in my room as a teen that has it's chassis tied to one side of the line that can get ugly. If you know and are aware and can control what is plugged in, honestly you are probably OK. Again, really don't like the idea of an adapter unless it is kept under lock and key for teaching purposes only!
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Are you using the Legrand/Pass and Seymour GCM plug/cord-receptacle devices? https://www.legrand.us/search.aspx?q=GCM (https://www.legrand.us/search.aspx?q=GCM)
I have them on all my cords, which provides a "canary in the coal mine test" of anything I plug into.
If these use similar technology to 3 lamp testers, they may have similar vulnerabilities.
Not that those devices should be used exclusively, but if the Extech reads fail and all the GCM devices are either blank or showing a red indicator, you have a pretty reliable indication something is definitely wrong.
probably
The NCVT test as a third test should remove any and all doubt something is amiss.
NCVT is the holy grail for hazardous voltages, at least more professional NCVT than mine. If the chassis ground is hot, DO NOT TOUCH. Back away slowly.
Is it safe (enough)?
After confirming a confirmation of an indication that there is a problem,
I am probably repeating myself but swapped line-neutral with a good safety ground is wrong, but not a safety hazard for users. Whomever is in charge of the venue needs to be informed so he can jack up his electricians but the show can go on.
but no RPBG, should the show go on?
yes
Would that be a reason to load the gear back on the truck? Does anyone have a contract clause that defines actions should the power prove unsuitable or unsafe?
RPBG is a show stopper, swapped line-neutral not so much.
Temporary fix to make it safer (or not)
If one had an "adapter" that reverses neutral and ground, would the stage be safer?
no and that adapter sounds like an accident waiting to happen.
If there were any RPBG on any of the downstream wall receptacles, would that not cause a direct short and pop the breaker? Arc flash an issue?
swapped line and neutral is the RP of RPBG, so a bootleg ground in combination with the reversed polarity is the grim reapers parley.
When do we stop when electric tests good?
um when the tests are good?
On a tangent, If the Extech says all is OK, is it safe? How about with a solid green only indication on the GCM device in addition to the Extech? Is that safe? Should one's test always use a three-tester test?
sorry I am not familiar with those... A NCVT can tell you a bunch, a neon lamp probe even more...
Granted, neither the Extech nor the GCM devices will actually identify a RPBG condition, apart or together. if you used the Extech, and all/any of the cords one has made up has an GCM device, there is an automatic second-level test. Can there be a possibility of a RPBG if there is no indicated reverse polarity, and the ground shows voltage within expected ranges on the Extech? Would that preclude the actual test with the NCVT?
?
I will grant the NCVT is so quick, easy, and positive this question is more a technicality than a practical matter.
If only there was a better way... 8)
JR
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For me RPBG is a deal breaker-and no way I am gonna have an adapter laying around to fix that-that's a hazard in itself.
Reversed polarity? Depending on gear and setup. Obviously, first look for an alternative-however in most modern gear polarity is not an issue-nor really is voltage if something is happy from 90-240 volts.
IMO, polarity is really more of an issue for the electrician's-once they leave leve they have no control over what is plugged in there and if someone plugs in an Eico tube amp like the one I used to run on a metal bookshelf in my room as a teen that has it's chassis tied to one side of the line that can get ugly. If you know and are aware and can control what is plugged in, honestly you are probably OK. Again, really don't like the idea of an adapter unless it is kept under lock and key for teaching purposes only!
It never ceases to amaze me the translation that occurs between my mind and fingers. (BIG sigh)
The reversal adapter that crossed my mind was a HOT neutral swap, not a GROUND neutral swap as my fingers mistakenly tapped out.
Again, really don't like the idea of an adapter unless it is kept under lock and key for teaching purposes only!
Agreed. Even if I wrote what I meant, your last statement covers that, too.
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If these use similar technology to 3 lamp testers, they may have similar vulnerabilities.
JR
D'oh! Never thought of that comparison, but after you pointed out that possibility (probability), I'm just left shaking my head for missing that obvious question. Damn.
Oh well, they seem to be well made connectors, better than most I've seen and used. The 20a version easily and securely clamps on to 10/3 SEOOW cable. And Ooooo, the pretty colors, the colors!
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Here's my take, based on 35 years of not dying or killing anyone with electrical power....
If this *entire* facility is wired in this manner it will likely function in a manner that does not present direct and immediate hazards to the staff or patrons.
The likelihood of fire, injury or death increases significantly if only part of the facility is wired this way and multiple extension cords are run from various places for use in a single location. It's also a future problem when maintenance, replacement or expansion occurs and this charming little deviation from Code gets "corrected" in the new work, but the old work does not get changed.
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I would agree-unless someone plugs in a vintage amp with a chassis tied to one side of the line. Chances of that happening? You might know better than me-my point of view is as an electrician and anything can happen. I'm only really OK with this if I'm in control.
Even a DVM suffers the same limitations as the 3 light tester-the lack of a known independent ground reference. That's where an NCVT or neon lamp testers shine.
FWIW, Klein makes several meters with a built in NCVT. I also see the current Fluke 117 has a NCVT as well as being low impedance to avoid "ghost" voltages. Looks like a really good tool for quick testing of power-lacking load testing of course.
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I would agree-unless someone plugs in a vintage amp with a chassis tied to one side of the line. Chances of that happening? You might know better than me-my point of view is as an electrician and anything can happen. I'm only really OK with this if I'm in control.
Even a DVM suffers the same limitations as the 3 light tester-the lack of a known independent grouond reference. That's where an NCVT or neon lamp testers shine.
Here is another fun way reversed neutral ground can get you. I had a plasma TV that must have had neutral tied to the chassis. Somehow the outlet on the wall was wired backwards. I had a genny running the house when the power was off. The generator was feeding my office upstairs and a small portable air conditioner in the master. This was during Sandy, the power was off for days, I had everything moved to the garage fridge that was also on the genny.
So the Sandy part is important as we were bored and I said we can watch a movie off my laptop on the big TV. I ran an extension cord from the UPS in my office (a 2200w unit) as I didn't want to run the TV right off the generator. The laptop was plugged directly into the generator. The fault path was through the laptop and it was sitting on top of one of the speakers and it exploded. I knew exactly what happened, wife and dog were less than impressed.
Point being is that TV was wired backwards for years and connected to the receiver, startedwith component video then HDMI and this was never an issue (the stereo rack was not backwards).
FWIW, Klein makes several meters with a built in NCVT. I also see the current Fluke 117 has a NCVT as well as being low impedance to avoid "ghost" voltages. Looks like a really good tool for quick testing of power-lacking load testing of course.
Greenlee makes a screwdriver with one in the handle. Don't buy it, it's a poor design, you hit the button operating the screwdriver and it beeps incessantly. If you take it out of the handle it no longer feels right in your hand.
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I would agree-unless someone plugs in a vintage amp with a chassis tied to one side of the line. Chances of that happening? You might know better than me-my point of view is as an electrician and anything can happen. I'm only really OK with this if I'm in control.
Even a DVM suffers the same limitations as the 3 light tester-the lack of a known independent grouond reference. That's where an NCVT or neon lamp testers shine.
FWIW, Klein makes several meters with a built in NCVT. I also see the current Fluke 117 has a NCVT as well as being low impedance to avoid "ghost" voltages. Looks like a really good tool for quick testing of power-lacking load testing of course.
The guitar amp issue is the same, it only takes the flip of a "polarity" switch on the amp to make it dangerous regardless of how the outlet is wired, but the building wiring issue certainly adds another variable.
One of my concerns is what happens when someone runs an extension cord to a device that has Scott's TV issue or the cord is mis-wired... The way most local bands and small PA operators must work involves finding multiple circuits from around the venue. Until something changes in the venue or there is a defective product or AC cable, the dangerous nature of this installation will not be apparent.
The OP asked what should be done, and after thinking this over I believe it needs to be reported to the head of the local AHJ.
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Here is another fun way reversed neutral ground can get you. I had a plasma TV that must have had neutral tied to the chassis.
2-wire consumer gear will sometimes wire a capacitor between chassis ground and neutral. The cap should be voltage rated to survive reverse polarity.
Somehow the outlet on the wall was wired backwards.
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I had a genny running the house when the power was off. The generator was feeding my office upstairs and a small portable air conditioner in the master. This was during Sandy, the power was off for days, I had everything moved to the garage fridge that was also on the genny.
So the Sandy part is important as we were bored and I said we can watch a movie off my laptop on the big TV. I ran an extension cord from the UPS in my office (a 2200w unit) as I didn't want to run the TV right off the generator. The laptop was plugged directly into the generator. The fault path was through the laptop and it was sitting on top of one of the speakers and it exploded. I knew exactly what happened, wife and dog were less than impressed.
I still don't..
Point being is that TV was wired backwards for years and connected to the receiver, startedwith component video then HDMI and this was never an issue (the stereo rack was not backwards).
might be worth more investigation of house wiring.
JR
Greenlee makes a screwdriver with one in the handle. Don't buy it, it's a poor design, you hit the button operating the screwdriver and it beeps incessantly. If you take it out of the handle it no longer feels right in your hand.
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I still don't..
JR
I am going to make a Visio 1 line and post it to further explain.
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I am going to make a Visio 1 line and post it to further explain.
Here is the drawing (https://uploads.tapatalk-cdn.com/20170921/834ee6bdcd8dd0cc84bc9a21d706937d.jpg)
Sent from my VS995 using Tapatalk
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Here is the drawing (https://uploads.tapatalk-cdn.com/20170921/834ee6bdcd8dd0cc84bc9a21d706937d.jpg)
Sent from my VS995 using Tapatalk
I hope you didn't spend much time on that because it tells me squat...
JR
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I hope you didn't spend much time on that because it tells me squat...
JR
No about 10 minutes but they say a picture is 1000 words. What part is confusing?
I ran a dedicated outlet from the breaker panel (load center) to my home office for the UPS. It was wired backwards. It was not picked up for years until I ran an extension cord down to power the plasma during a power outage and the laptop plugged into the non-reversed outlet was destroyed.
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Did the outlet have an RPBG-did you bootleg the ground? I assume not-but honestly, that is the only way I see this going "boom"? Unless the UPS bonds things-but that shouldn't happen either.
How did the chassis of the plasma become energized? Just looking for the path? Perhaps a cap from "neutral" to ground-either in the plasma or UPS?
Not attacking-just trying to learn and understand what happened.
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Did the outlet have an RPBG-did you bootleg the ground? I assume not-but honestly, that is the only way I see this going "boom"? Unless the UPS bonds things-but that shouldn't happen either.
How did the chassis of the plasma become energized? Just looking for the path? Perhaps a cap from "neutral" to ground-either in the plasma or UPS?
Not attacking-just trying to learn and understand what happened.
No attack at all, I was surprised myself. The only symptom prior to this issue was I had about 40v between the shield of the cable entering the house and the cable modem in my office, it had no current and did not arc when connecting so I did not think much of it at the time.
The TV had a 3 wire IEC C14 inlet.
I plugged in the laptop to an outlet on the wall and the signal cable to the TV. I didn't want to connect the plasma to the generator direct so I ran an extension cord (3 wire) to the UPS. As soon as I plugged it in the laptop popped. The laptop was connect direct to the generator via the normal house wiring (the generator was feeding the main panel).
The UPS is connected to an outlet with BX home run to the main panel. I found the input to that outlet in the work box had the hot and neutral reversed.
That's the whole story.
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I plugged in the laptop to an outlet on the wall and the signal cable to the TV. I didn't want to connect the plasma to the generator direct so I ran an extension cord (3 wire) to the UPS. As soon as I plugged it in the laptop popped. The laptop was connect direct to the generator via the normal house wiring (the generator was feeding the main panel).
I guess it's synchronicity or irony or some other type of happy coincidence, but there's a similar discussion going on at http://forums.prosoundweb.com/index.php/topic,164891.0.html. One of my RV readers claims that his Tripp-Lite RV 12-volt inverter/converter can be damaged by a reversed hot/neutral. Say's there some sort of protection diodes on the 120-volt line input that will blow up, and this cost him $1,000 for find out. I'm not sure I believe this and I haven't had time to talk to Tripp-Lite directly for a conversation and a schematic, but sure sounds similar, doesn't it.
I do have another RV reader who blew up an LED/Television doing something similar to what you did with a hot-neutral swap. He's at least at electronics tech level and detailed what he discovered about the fail. I'll find his contact info and see if I can loop him into this discussion.
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No attack at all, I was surprised myself. The only symptom prior to this issue was I had about 40v between the shield of the cable entering the house and the cable modem in my office, it had no current and did not arc when connecting so I did not think much of it at the time.
The TV had a 3 wire IEC C14 inlet.
I plugged in the laptop to an outlet on the wall and the signal cable to the TV. I didn't want to connect the plasma to the generator direct so I ran an extension cord (3 wire) to the UPS. As soon as I plugged it in the laptop popped. The laptop was connect direct to the generator via the normal house wiring (the generator was feeding the main panel).
Is the generator wiring solid? Extension cord, UPS?
The UPS is connected to an outlet with BX home run to the main panel. I found the input to that outlet in the work box had the hot and neutral reversed.
Line and neutral reversed should not cause any drama from properly designed equipment. Line and neutral are single insulated from safety grounded (3 wire plug) chassis, and double insulated from 2 wire plug chassis.
That's the whole story.
Perhaps a ground got energized. Easy enough to find with NCVT. You say the TV is 3 wire line cord, so should not have a stinger cap to fail.
JR
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Is the generator wiring solid? Extension cord, UPS? Line and neutral reversed should not cause any drama from properly designed equipment. Line and neutral are single insulated from safety grounded (3 wire plug) chassis, and double insulated from 2 wire plug chassis. Perhaps a ground got energized. Easy enough to find with NCVT. You say the TV is 3 wire line cord, so should not have a stinger cap to fail.
JR
Generator wiring is 10/4 SOOW to an inlet connector and xfer switch. The junk generator is long gone now too and replaced with an Onan that can run the whole house.
The rest of this was 11 years ago. Was just sharing a story about the consequences of reversed NG in proximity to normal.
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And the reverse polarity receptacle?
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And the reverse polarity receptacle?
Stephen, are you asking if it was fixed. Yes, the day after it happened. I also noted the UPS connection is a BX home run to the load center. It is downstream of the transfer switch.
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I would also get a meter on it just to triple check. Here's what I send to my RV groups on how to measure a standard 120-volt outlet.
Just an update on the original post: I've just learned that the owner had an electrician in at 5am the following morning that confirmed the whole place was in fact wired with the Hots and Neutrals reversed!
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Just an update on the original post: I've just learned that the owner had an electrician in at 5am the following morning that confirmed the whole place was in fact wired with the Hots and Neutrals reversed!
One question, is how the HECK does this happen??
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One question, is how the HECK does this happen??
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How it happens is easy-how it gets "delivered" to the customer is another matter-especially if there was an AHJ inspector involved.
Consider that making up receptacles is a tedious job in an uncomfortable position-and in theory the jouneyman/experienced crew member should be able to show the newbie once and keep him busy for some time-so the newbie (first day as an electrician?) gets the task while the experienced guy makes up switches, etc.
We all know we need to check up on the newbie-but how many of us get busy and forget follow up? I'm not excusing it-it should have been checked.