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#136956 - 05/16/03 03:31 AM Reverse Polarity in Europe  
sparky74  Offline
Junior Member
Joined: May 2003
Posts: 12
Naples, Italy
Here we go, reverse polarity does not seem to be much of an issue here in Italy. As we know, reverse polarity is prohibited in the U.S.--according to the NEC (National Electrical Code) and other national standards. Reverse polarity is created when the grounded conductor and the ungrounded conductors are reversed when wired to a 120v receptacle/outlet. In the U.S. appliance plugs are designed to connect to receptacles in only one direction. Here in Italy, the design of the receptacle, allows the plug to be installed in either direction which can result in polarity reversal. Reverse polarity can be dangerous. Lets take a normal household lamp for example,(just a standard 100w incandescent lightbulb). If we have reverse polarity at the receptacle, the srew shell on the lamp is now hot, even if the swith on the lamp is in the "off" position. [The srew shell is where the lightbulb srews in]. Anyway, as we replace a lightbulb, it is possible that our fingers can make contact with the screwshell of the lamp and we can get shocked. So, my question is: Why are receptacles and plugs in Europe designed in such manner?


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#136957 - 05/16/03 06:24 AM Re: Reverse Polarity in Europe  
Texas_Ranger  Offline
Member
Joined: Dec 2001
Posts: 2,392
Vienna, Austria
Because our code-makers think people are bright enough to pull the plug before changing a bulb on such a lamp. At least taht's the explanation I heard from several German electricians. Hardwired lights are usually polarized. Besides, most modern light sockets are designed that way the screw shell is entirely covered until it looses contact.
I've got an old US metal light socket here (maybe 1970ies Leviton) which has more than 1 mm of the screwshell exposed even when the bulb is screwed in all the way. This can't happen with modern European sockets.
And besides, we just don't worry as much as Americans do. We don't try that hard to make everything foolproof, and lawsuits, for example the one of the old lady who dried her poodle in the microwave would have no chance at all. Common sense is estimated very much. And at least the Austrians (and definitely the Italians) rarely take things real serious. We just say "wadda heck! it can't be that bad..."


#136958 - 05/16/03 09:53 AM Re: Reverse Polarity in Europe  
djk  Offline
Member
Joined: Dec 2002
Posts: 1,237
Ireland
It's strange that given the UK/Irish situation where everything is properly polarised that the standard BC bayonet style light fiting used here is totally uneffected by that problem. it has 2 terminals at the bottom of the bulb.. doesn't particularly matter which one is live.

I don't like Edison caps they're a very bad design concept.

1) the polarisation/shock issue.
2) if the bulb overheats the screw cap expands and gets wedged into the fitting. I've had endless problems with recessed EC spotlights getting jammed into their fittings. Not a very likely problem with BC

BC is also much easier to change. You just push and turn a 1/4 turn.. all that twisting of EC in the middle of a complicated chandelier fitting up a high ladder can be annoying!

It'd make you wonder why EC is he predominant standard!


#136959 - 05/16/03 10:40 AM Re: Reverse Polarity in Europe  
SvenNYC  Offline
Member
Joined: Aug 2002
Posts: 1,691
New York City
DJK:

Another benefit of Bayonet fittings is that the bulb doesn't work itself loose due to vibrations, so it's excellent for use in ceiling fans, trouble-lights, wall sconces etc. Why do you think that cars use bayonet fittings for some of their lightbulbs?

You don't get that flicker flicker and arcing inside the lampholder that eventually destroys the center contact of the socket!

Was sitting in a coffee shop in Chelsea last weekend and watching the bulbs in the oh-so-trendy goose-neck fixture flicker and dim...

Was half-tempted to climb onto the table and re-tighten the little suckers.... [Linked Image]

And any fool can get themselves electrocuted by sticking their finger into a double-contact bayonet socket also....

Why are Edison fittings the world standard? One word...EDISON. Guess he was the Bill Gates of his time.

Ragnar:

Regarding the exposed section of screw-base...you remember my story about my mom's co-worker (and amateur electrician) in Germany who got himself killed while on a ladder changing the lightbulb hanging from the ceiling in his room.

[This message has been edited by SvenNYC (edited 05-16-2003).]


#136960 - 05/16/03 11:43 AM Re: Reverse Polarity in Europe  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
Quote

Reverse polarity can be dangerous. Lets take a normal household lamp for example,(just a standard 100w incandescent lightbulb). If we have reverse polarity at the receptacle, the srew shell on the lamp is now hot, even if the swith on the lamp is in the "off" position.


Then you should return the lampholder, as it is clearly unsafe and illegal. It should not be possible to touch the screw shell when the bulb is fully inserted. And the screw shell should not make contact with the live parts of the lampholder until almost fully screwed in, making it very difficult to touch the screw shell when it is screwed in.

Quote

So, my question is: Why are receptacles and plugs in Europe designed in such manner?


Please explain to me how a US 240V socket is polarized.

[This message has been edited by C-H (edited 05-16-2003).]


#136961 - 05/16/03 11:52 AM Re: Reverse Polarity in Europe  
SvenNYC  Offline
Member
Joined: Aug 2002
Posts: 1,691
New York City
C-H:
I think he means normal 110-volt NEMA plugs which correspond to the European 220-volt single-phase plugs (one live, one neutral, one earth) are polarized.

And a lot of those replacement two-pin 110 volt American plugs aren't polarized either!!

[Linked Image]

American 240-volt sockets like those used for air conditioners (placed across two live 110 volt conductors) are not polarized, although the plugs equipped with earthing pins only let you connect the plug in one way.

[This message has been edited by SvenNYC (edited 05-23-2003).]


#136962 - 05/16/03 02:42 PM Re: Reverse Polarity in Europe  
djk  Offline
Member
Joined: Dec 2002
Posts: 1,237
Ireland
actually if you screw in a bulb there's always a possibility that the bulb cap itself may be exposed not just the screw receptical.

Relatively few Edison fittings here other than on imported lamps (from other European countries) most aimed at this market have BC fittings.. including most of the fancy ones as screw-in bulbs can be hard to get.. You'll get BC in any shape in a typical supermarket where as EC tends to be hardware store / lighting shops only.. particularly for standard shape bulbs.. Very hard to get! Candle shapes are easier to come by.

Was practically impossible to locate a EC CFL bulb here! Only by special order.


#136963 - 05/16/03 02:44 PM Re: Reverse Polarity in Europe  
djk  Offline
Member
Joined: Dec 2002
Posts: 1,237
Ireland
Re Bill Gates:

How many Microsoft engineers does it take to change a light bulb?

None! They'd just standardise on darkness.


#136964 - 05/16/03 11:06 PM Re: Reverse Polarity in Europe  
Hutch  Offline
Member
Joined: May 2002
Posts: 381
South Oxfordshire, UK
Sparky74,

C-H said "Please explain to me how a US 240V socket is polarized".

As we've discussed before, this is quite the crux of the matter. US 240V is the product of a twin phase center tapped system and is not polarised. Early European systems used three phase 127 V phase to gound systems with 220V phase to phase. Historically, therefore, continental Europeans have been used to double live systems and this is why the Schucko or Italian standards are not polarised.

It would also explain why European ES fittings differ from US ones in that the shell is only energised by a seperate contact rather than the whole shell.

Most systems are now 220V phase to ground but the legacies live on. UK ac systems have always been >220V phase to ground and with grounded systems, polarised.

I'll take the opportunity once again to laud the Oz/NZ system where non-polarised plugs (even two pin, Sven) do not exist.


#136965 - 05/17/03 03:54 PM Re: Reverse Polarity in Europe  
Texas_Ranger  Offline
Member
Joined: Dec 2001
Posts: 2,392
Vienna, Austria
Quote
Regarding the exposed section of screw-base...you remember my story about my mom's co-worker (and amateur electrician) in Germany who got himself killed while on a ladder changing the lightbulb hanging from the ceiling in his room.


Yes I do. I was talking of modern light sockets. Some of the older type with a porcelaine ring had a too small ring that exposed parts of the screw shell. They were indeed dangerous. Modern ones aren't.
Or the socket was partially damaged. plastic ones aren't too solid, especially old ones, and thinking of what he did it wouldn't surprise me if he used 100W bulbs and the socket simply crackled away.


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