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#147681 - 01/03/03 08:51 AM Bad Advice Here! Got to be Very Careful Dude?  
Joe Tedesco  Offline
Joined: Oct 2000
Posts: 2,749
Boston, Massachusetts USA
Question: Hi, I am moving a hanging ceiling fixture from one room to another. The power cord on the hanging lamp is one color, not black and white at the ends. I forgot to take note which cord went to black and which to white. One lead is ribbed and the other is smooth instead of being color coded. Is there a rule of thumbe as to which will go to white and which to black?

Answer: Lamp cords typically have these types of cords, and if you look at one of those, the ribbed is on the "large" conductor of the plug, which would be the negative (or white) side.

With an incandescent bulb, though, there shouldn't be any problem if they're reversed, since they work both ways. I wouldn't worry about it. Greg

FYI: [Linked Image]

Joe Tedesco, Bob Vila Moderator

The polarity is very important and must never be reversed!

Please disregard the last sentence in the previous message here!

Reference 2002 NEC

200.10(C) Screw Shells.

For devices with screw shells, the terminal for the grounded conductor shall be the one connected to the screw shell.

200.11 Polarity of Connections.

No grounded conductor shall be attached to any terminal or lead so as to reverse the designated polarity.

WOA is me!!!!

[This message has been edited by Joe Tedesco (edited 01-03-2003).]

Joe Tedesco, NEC Consultant

Arc Flash PPE Clothing, LOTO & Insulated Tools

#147682 - 01/04/03 01:23 AM Re: Bad Advice Here! Got to be Very Careful Dude?  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
Here is a sobering tale:

My mom was living in Germany during her college/nursing school years.

A co-worker at the hospital she was working was very much into do-it-yourself electric work.

One night after work he got back home and flicked the switch only to discover the light bulb in his room wouldn't turn on.

So he gets out the ladder and proceeds to fiddle with the pendant fixture (lampholder hanging from a short stump of flex). He got electrocuted and killed.

Apparently, according to my mom, the guy had somehow made contact with the screw-shell of the bulb thereby electrocuting him. She said that German lampholders aren't as deep as the American ones and a little bit of the screw base always shows. This was back in the 1970s...things may have changed now...I hope.

Obviously polarity was reversed and the hot wire was going to the screw-shell of the socket instead of the center contact.

[This message has been edited by SvenNYC (edited 01-04-2003).]

#147683 - 03/14/03 02:19 PM Re: Bad Advice Here! Got to be Very Careful Dude?  
Texas_Ranger  Offline
Joined: Dec 2001
Posts: 2,402
Vienna, Austria
Cheap ones of the old type used to expose part of the screw shell, but not remarkably mor than the Leviton metal one I've got here. Modern ones completely cover the thread.
Code on this topic is quite simple: Any permanently connected fixtures must be polarised, lamps connected via plug don't have to be polarised since you can unplug them prior to changing the bulb.
Exactly this issue always makes me a little nervous when I'm standing on a big ladder, maybe 8ft. above ground changing bulbs in the early-1900s chandelier in our stairway. Since the lights are off this isn't really dangerous, there's always the phase switched, but I don't really trust the polarity of the lamp sockets. So I don't really want to touch the screw shell while someone else presses the button 3 floors above.

#147684 - 03/15/03 09:03 PM Re: Bad Advice Here! Got to be Very Careful Dude?  
sparky  Offline
Joined: Oct 2000
Posts: 5,311
At one time the infamous 'Chicago 3 Way's"here switched the polarities at a lighting outlet

#147685 - 03/15/03 09:32 PM Re: Bad Advice Here! Got to be Very Careful Dude?  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Aren't all lamp cords now polarized for just this reason?

Bob Badger
Construction & Maintenance Electrician

#147686 - 03/16/03 08:58 AM Re: Bad Advice Here! Got to be Very Careful Dude?  
sparky  Offline
Joined: Oct 2000
Posts: 5,311
but there are still plenty of 2P male cord caps without a larger noodle that are integral to a variety of appliances.

I am unaware of how this is sanctioned, perhaps the integral x-formers are ambidextrous?

[This message has been edited by sparky (edited 03-16-2003).]

#147687 - 03/18/03 03:33 PM Re: Bad Advice Here! Got to be Very Careful Dude?  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
Also most replacement two-pin plugs I've seen in al the hardware stores and lighting stores I've visited are un-polarized.

I keep a mix of both types at home. Some radios need unpolarized plugs so you can invert the plug in the socket if you get too much hum in one position. Polarized plugs go on any lamps I fix for other people.

Guess the easiest and most fool-proof way to polarize an appliance would be to use a properly attached three-pin replacement plug on any Class-2 appliances that require polarization.

The Brits and the Australians do just that. That still doesn't guarantee anything....but it's a start.

#147688 - 03/19/03 07:10 PM Re: Bad Advice Here! Got to be Very Careful Dude?  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Another point here in Britain is that the double-contact bayonet-cap bulb is by far the most common type of fitting, at least in domestic applications. Polarity on such bulbholders is completely irrelevant, although on portable lamps which incorporate a switch there's still the problem of reversed wiring at the plug leaving the switch in the neutral.

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