does anyone have any stories of consequences of hot/neutral hot/ground neutral/ground reversals? motors? appliances? injuries?
not morbid, but seems like you learn things better from mistakes.
C

No morbidity in this, but I was present when a 10 Hp DC motor coupled to a generator for a lab experiment had its field removed. The DC motor immediately increased it RPM from about the 3,600 it was at to around 15,000 in around 2 seconds. The room shook quite bad. If it wasn't for the professor hitting the emergency kill switch to the supply, the motor would hav blown apart causing massiv injuries to the people in the room. Not to many people realize how dangerous DC motors are if not properly controlled.

On my very first job in the trade there was a 120/208V panel in a kitchen area that got energized with a phase conductor and neutral reversed. Luckily, the only casualty was a couple of sign transformers. Unfortunately I have seen the same thing a few more times since.

The guy that lives three doors down asked me about a tree limb hitting the service drop. I went over to look and the guy wire/neutral was pulled loose at the house. He said it had been that way for a week. I explained the dangers involved and put a temporary jumper on it until the power company could get out to fix the drop. He said every time they took a shower or washed their hands "the water tingled". It still makes me cringe.

[This message has been edited by wolfdog (edited 01-09-2002).]

Cindy,
Last months issue of EC&M magazines Forensic Casebook feature told an incredible story of a series of unfortunate co-incidences that resulted in the death of a mother of young children. Maybe Joe can help you acquire the article.

I remember hearing of a case here a few years ago in which an "electrician" had done some kitchen installation work -- I forget whether it was a washer, dryer, waste disposal or whatever. Somehow he managed to hook the stainless-steel sink up to the hot side of the supply (For crying out loud: How??!! ).

The owners reported tingles and mild shocks, he was called back twice and told them nothing was wrong. Third time was definitely not lucky, as someone touched it barefoot and was killed.

If I recall correctly he was charged with "causing death due to criminal negligence," or whatever the proper legal wording is.

***

Another accident which is sort-of polarity related was reported from a telecoms facility when I was with BT in about 1984. Like many big plants they had their own generators, and the control gear incorporated synchronization circuitry to allow parallel operation.

Apparently someone mis-wired a unit so that two gennies synched up 180 deg. out of phase. I understand they had to pull bits of engine out of the roof.

[This message has been edited by pauluk (edited 01-10-2002).]

most things in a house will run on reversed hot/neutral won't they? just wondering what would happen in a typical home. don't think i want to experiment to find out i mean besides energizing metal.

btw, tonight i was using a tanning bed at a salon and felt what i thot was a sharp edge on the bed frame, felt it on previous occasions too, but tonight realized it was a tingling sensation and not a sharp edge. the beds use 24, 105-watt fluorescent bulbs and it is wired by flex and controlled by a timer in the other room. any ideas on eliminating the tingling? maybe it's not grounded properly? C

If the metal frame isn't grounded, then you may well be getting a practical demonstration of capacitive coupling. (See? It's not just theory! )

Yes, a great many normal household appliances will work perfectly well with hot and neutral reversed. Over in Continental Europe many countries use a standard appliance plug which is reversible (even the grounding type).

Many old radios/TVs (both in the U.S. & U.K.) were "live chassis," meaning that one side of the cord went straight to the chassis. They were designed so that no part was exposed to touch, but it was still best to ensure that the chassis went to neutral. It's also why we use an isolating transformer when servcing this type of equipment. Although live chassis went out of favor, it has made a slight comeback in modern TV switch-mode power supplies.

With swapped connections, any single-pole switch will leave the bulb, element, motor or whatever hot when off. There's also the point that an in-line fuse (as used in mUch line-powered electronic equipment) will end up in the neutral, so the house breaker will be the only protection against ground faults.

how about computers, stereos, printers, monitors? and what would a garbage disposal or dishwasher motor or washer motor do when hot and neutral are reversed?

think i'll slip an amprobe into the tanning room next time and take some readings... not worried really, just curious

As we use non-polarized plugs here in Austria I can say that I never got problems with any kind of appliances. My printer is imported from the US (nice thing: The printer was designed to work on both 120 and 230V, but the power cord was rated for 10A 125V, the previous user just fitted a new plug). So in everyday use it makes no difference.
The only thing I ever saw that wouldn't work if polarized incorrectly was a hardwired gas heater.

As Tex said, they use non-polarized plugs in most of Europe, and even in countries like France where grounding-type plugs ARE polarized, there's still not much concern over which way hot & neutral are wired to a receptacle.

These days in this part of the world, everything from toasters to electric drills to computer printers are sold in basically the same model right across Europe, so they're designed so that polarity is unimportant. A lot of power tools are now fitted with a double-pole switch as well.

I think you'll find some older radio/audio equipment made in the U.S. (perhaps 1960s or earlier) which had an ungrounded cord and used a high-value resistor (1 meg up) or a small capacitor direct from neutral to casing. Swapping H&N on one of those could result in some tingles, especially if the cap has gone leaky with age.

Redsy: I checked and found the following article in the November issue of EC&M. You mentioned that I might be able locate it -- here it is: Look under Forensic Case Book

Mother Electrocuted By Pressure Washer

By Kenneth E. Buske, P.E., Buske Engineering

Electrical Construction & Maintenance, Nov 1, 2001


http://industryclick.com/magazine.asp?magazineid=31&siteid=13&releaseid=9603


[This message has been edited by Joe Tedesco (edited 01-12-2002).]

Oops, I did something wrong. http://industryclick.com/magazinearticle.asp?magazineid=314164&siteid=13


[This message has been edited by electure (edited 01-12-2002).]

Cindy,
While an amprobe may be valuable, especially if you can take some voltage readings, it may be as useful to take one of those "pen type" voltage detectors with you. This would be a bit more surreptitious, and they are quite a bit more concealable. My guess is the owners of this salon would not like you experimenting on their equipment, especially if you're going to expose a hazard.

thanks for all the information again.
guess a gfci would have saved that woman, if plugged into the garage or outside.. wonder if the afci would have done anything, guess it wasnt really an arcing fault so probably not.
on the tan bed frame, the amprobe bounced around 2 volts from one side of the bed to the other. stings and still makes you nervous, but guess i'll live.. maybe die of skin cancer first

The incident in the article had a number of factors, either of which if not present, would likely have prevented an electrocution. The pressure washer had a puncture in the insulation on the neutral then came in contact with the frame. The ground prong on the cord was cut off, but it was also a non-polarized plug, either safety feature individually could have prevented her from inserting it into the receptacle backwards. Finally, she plugged it into an indoor receptacle which was not GFCI protected. Hard to believe this sequence of events played out the way it did.
Proper polarity is indeed a critical safety, if not functional, consideration.



[This message has been edited by Redsy (edited 01-12-2002).]

A story about hot/ground reversed came to my mind. It happened a few years ago here in Austria, and I can't remember the exact details. However it was about the following: A guy repaired or built his own pool. When working at the pump he reversed hot/ground. Then he jumped into the pool. His wife saw him, thought he fainted and jumped in too. Their som saw them, but was bright enough to switch off the power. I think they survived, but I'm not sure.

Eek! Nasty...

Was that due to some sort of confusion with the old "red = ground" color coding there?

I have no idea about that. All i know is from a very short newspaper article about 6 years or so ago.
However what about that power washer story?
It says that using a polarized plug would have saved that woman. In this special case it's true, but in any other the insulation of the hot wire could have been faulty too, in that case it'd have actually saved that woman. I thought this is something to think about.
I agree that the missing ground prong was really dangerous.

There may be a good reason to prepare a new proposal to be sent in for consideration in the 2005 NEC. I found the following related to "reverse polarity" and offer it here for discussion.

See NFPA 302 Fire Protection Standard for Pleasure and Commercial Motor Craft 1998 Edition

Section 8-7 Shore Power Polarity Devices.
8-7.1*

Reverse-polarity indicating devices having a continuously visible or audible signal shall be installed in 120 VAC shore power systems, provided the following applies:
(a) The polarity of the system is maintained for the proper operation of electrical devices in the system
(b) A branch circuit is provided with overcurrent protection in the ungrounded current-carrying conductors only
Exception: Systems with polarization or isolation transformers that establish the polarity of the onboard system.

A-8-7.1
Reverse-polarity indicating devices should respond only to reversal of the ungrounded conductors and the grounded (white) conductor where there is continuity of the grounding (green) conductor to shore.
Reverse-polarity indicating devices should not be required to respond to reversals of the ungrounded conductors and the grounding (green) conductor, the grounded (white) conductor and the grounding (green) conductor, or to reversal of three-phase conductors.

Yes, on the pressure washer story you can say that had it been the black wire shorting to the frame then reversed polarity would have saved the unfortunate victim. It's the missing ground connection that was, to my mind, the primary reason.

I write for a monthly "Motorcaravan" journal (RVs to you) here, and the reverse-polarity question is one which seems to cause a lot of queries, especially among people visiting the Continent due to the reversible plugs etc. mentioned above.

As the 240V systems of all recent RVs here have a GFCI on the hook-up, swapped H & N really isn't such a problem as many of the readers have been led to believe.