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?

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..."

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!

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....

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).]

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.


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

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

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!!



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).]

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.

Re Bill Gates:

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

None! They'd just standardise on darkness.

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.

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.

For those unfamiliar with the modern style of European ES holder here is an example:



As has been said above, the screw shell doesn't make contact with the circuit until it's screwed right down into the holder.

As in Ireland, however, the BC lamp is by far the most common in most domestic fittings, and with a symmetrical double-contact fitting polarity is of no importance.

One point that used to be of concern though is the bedside or tablelamp which incorporated a switch at the holder. These days, they're fitted with the standard BS1363 plug and color-coded cordage making it easy to connect the hot side to the switch.

Back in the "old days" though, such lamps were commonly wired with twisted twin flex with no polarity identification. Even if coded cords were used, many were fitted with the reversible 2-pin 5A plug, making it impossible to guarantee placement of the switch in the hot conductor.

Obviously it would always be advisable to pull the plug before fiddling with the lampholder, but there would always be someone who would assume that because the switch on the holder was off that they could touch the contacts in safety.

[This message has been edited by pauluk (edited 05-18-2003).]

I know one of our friends from the British Isles mentioned BC lampholders where you couldn't even get hurt by putting your finger in the lampholder. That is, all live parts are shrouded in some way.

Perhaps it is time for all of Europe to switch to this style? Sure, you can make substandard bayonet cap lampholders too, but if they are properly made they are significantly better than the Edison design.

We Europeans can't make things as cheap as the Americans, so let's make them better instead. The BC lampholder is a British, thus European design...

Let's outlaw BC bulbs with more than 100W and require all holders to withstand a 100W bulb. More powerful bulbs should not fit a standard lampholder. Far less risk of fire, at a very low cost.

The simple rule:

Pull the plug before you stick your fingers into anything that is potentially live!

Relying on switches which should be on the hotwire only is just dangerous.

I always take precautions when changing light bulbs and if I need to work on a light fitting I would never rely on switching. Always trip the breaker or remove the fuse at the consumer unit and test all the conductors at the fitting just to be 100% sure!

As someone mentioned before a guy working on a central heating boiler here was electrocuted when he switched off the power at the socket (it was connected via a BS1363 plug). The socket, however, was wired in reverse so remained live and the guy got 230V up the arm.

Generally, regardless of polarity, even if the switch is on the neutral an applience can be switched off safely.. i.e. it will stop and no longer be pose any risk but anyone working on an applience should ALWAYS pull the plug.

On another point, I know someone who got a shock from from a live neutral cable in Spain. Old 127 - 127 system.

Off topic point:
How are central heating systems usually connected elsewhere?

Here it's normal to do one of the following:

Old installations usually had a fused spur feeding a timer feeding 2/3 a sockets (BS1363 or 5amp BS546) connecting into the pumps and burner/boiler.

Newer installations have a double-pole switch (fused at 5 amps usually) feeding through to the boiler and pumps hardwired using waterproof glands.

[This message has been edited by djk (edited 05-18-2003).]

>Pull the plug before you stick your >fingers into anything that is potentially >live!

I ALWAYS carry a voltstick & a socket tester (cheapo plugtop with LEDs) after our Electric Board (best quote) put in a new disconnect and wired one phase upside down.

Chris

djk said...

"How are central heating systems usually connected elsewhere?"

This May, I discovered that my parents' system [Lancastrian (UK) central heating/hot water on demand (gas)] was on the kitchen lighting circuit - the very last breaker that I threw!

Hardwired on a simple 10A circuit, probably the one for bathroom lights and receptacles. Either NYM or flex conduit sticking out of the wall (if an electrician did it) or simple round flex (yep you guessed it, plumber was here) sticking out of the wall. I've also seen them on the dedicated 16A circuit for the washing machine. In larger new houses or where all the wiring is redone they'd probably be on a dedicated 10A circuit.
Did I already mention I hate plumbers doing electrical wiring?

Over here in Ireland if it's a gas-fired heating system the gas company lays down very rigid rules regarding installation.

Gas fired system will always be wired to a 10amp dedicated breaker and have a local 2-pole isolating switch that isolates absolutely everything including any remote timers/thermostats/controls.

If it's an oil pressure jet system, soild fuel or "Calor Gas" (LPG) things tend to get done differently.

I was talking the typical 15 or 18kW natural gas combi boiler. Unless it's a complete remodel the plumbers who remove the old gas water heater to install the new boiler will just tap into the next available power line, sometimes they get into a receptacle, but sometimes if you're less lucky they also cut a line, splice it in the middle of nowhere and plaster it over. From their splice they'll usually just nail 3x1.5mm2 flex onto the walls. Another plumber I heard of ran the wire horizontally froma receptacle at 80cm from the floor and then up to the boiler, along with the water pipes. When my uncle installed new pipework he hit the flat cable phase to ground and everything went dark.
As paranoid as the gas guys are concerning the gas lines, the boiler and the chimney, they don't care for the electrical part at all. Many plumbers even have an electrical license for side jobs, but I doubt their wiring is any better (I've seen some examples of plumber sparky wiring, for example Schuko receptacles without a box, just in a hole in the wall, no ground anywhere. Or the washing machine cord sneaking through a hole into the adjacent room (Had some pics in the violations forum some time ago). Or the 1mm2 wiring fused with 16A slow Diazed.)

In England, the electrical feed for oil/gas furnaces varies.

New properties in which the central-heating has been installed during construction may well have a separate dedicated circuit.

In retro-fit heating (and some new) it will quite likely be fed through a fused spur unit from the nearest ring circuit. Sometimes the cord from the back of the unit is just connected to a normal BS1363 plug and plugged into a single outlet, fitted nearby and wired into the ring or as a spur.

I've seen some where the installer ran the flexible cord up through the back of adjoining kitchen units and to the nearest existing receptacle!

As Hutch said above, you sometimes even find the unit tapped off a lighting circuit.

Plumbers doing electrical work? Don't want to think about it. I've sorted out too many screw-ups with the thermostat, control wiring.

We had a guy manage to wire the live terminal to the case of a timer!!!!

Hutch said:

Hutch, I ran across this little beauty on Clipsal's on-line catalog.

A couple of years I also bought two of them from Clipsal (expensive little suckers - cost me like US$5) because I was intrigued and wanted to see if they really were American configuration non-polarized plugs. Behold it was....

[img]http://alfred.clipsal.com/scripts/apeweb.dll?GetImage&CatNo=492Y&Large=1[/img]
[img]http://alfred.clipsal.com/scripts/apeweb.dll?GetImage&CatNo=492&Large=1[/img]

What would an Australian electrical system use this for?

There is also a mating socket. Looks just like an American socket (two flat parallel pins).

It's rated for 250 volts, 10 amps. The plug is Catalogue #492. Unpolarized. And it had the Australian certification marks on the bag it came in...

Something else to add to my electric plug collection. Not kidding. I collect the little suckers.

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

Lets not forget the \ / system is also used in China (Along with the UK system to a lesser extent (in Hong Kong)... possibily the worlds largest single electricity market (at least potentially). Fully polarised.

We have over here in NZ and Oz, the isolated type batten-holder there should be a picture of it below.
This type of batten-holder uses a system of spring operated base in the thing, so that you cannot contact live terminals at all.
The only time that the outside contacts are live, is when the lamp is fitted.



[This message has been edited by Webmaster (edited 05-24-2003).]

Those "safety" lampholders where the pins aren't energized until the bulb is locked in place are available in the U.K. as well, although not that common.

The Australian plugs are non-reversible, but I remember reading in Electronics Australia some years ago that originally there was no standard as to which pin was "active" (their terminology) and which neutral. The query had arisen when someone found an old 2-way adapter which had hot & neutral connected the opposite way round on each of its two receptacles. I have no idea when the positions were specified in a standard.

This does seem to match up with the fact that in some other places where the Aussie/Kiwi plug is used they have the pins the opposite way round to the current Australian standard (Argentina, if I recall correctly).

Sven,

I would hazard to guess that the plugs you pictured were not for the Australian market but maybe the Chinese market. As DJK points out the Chinese also use the Oz/NZ with inclined blades but only on grounded circuits. For inexplicable reasons, ungrounded two pin circuits use standard NEMA 1-15 making the two systems incompatible and completely missing the chance to polarize all of their systems. If anyone knows the history behind this I would be interested to know – didn’t we have a correspondent from Hong Kong some time ago?

All the Oz/NZ plugs in my travelling collection look like this:-



The top right one looks like the same manufacturer as yours Sven, and are a devil to wire and reassemble.



[This message has been edited by Hutch (edited 05-25-2003).]

As far as I know the Oz/Nz style plugs are the new standard for all installations in china replacing the old ungrounded systems hence the incompatability. Similar to the transition from BS546 to 13 amp plugs in the UK

DJK,

The words "China" and "electrical standards" put together make me laugh out loud.

I wonder if the American style two-pin plug is now technically obsolete in China whether all Class II appliances will be fitted with three-pin Australian plugs with a dummy earth pin.

Of course this will lead to even more kludges and use of shoddy adapters as people buy new Class II devices like radios, TV sets, record players, etc.

Here is a picture of a combination socket that accepts either American or European style two-pin plugs and Australian-style earthed plugs:



I also have a light-duty two-pin plug from China whose prongs can be rotated in order to fit American or Australian sockets. It's designed to be used with things like lamps.

The pins are fitted on rotating blade-holders on the plug face that allow them to be pivoted to adapt the thing to the proper configuration. Of course they can rotate either way so the plug is not technically polarized. You can pivot it either
[| |] [/ \] or [\ /]


[This message has been edited by SvenNYC (edited 05-29-2003).]

Sven,
the question is if it is the 10A or 15/16A version?

Sven, the great thing about keeping polarity on the Oz/NZ system is that it doesn't need a dummy earth on class II appliances. The phase and neutral can only mate one way round.

On you picture above, I see at least the grounded socket is the right way up!

That's because as far as Trumpy and his friends are concerned, we're all standing on our heads up here in the northern hemisphere!

I've seen travel adapters which have the rotating pins as well, although if I recall correctly the pins would only rotate from vertical in one direction, so they would be polarized on an Aussie/Kiwi outlet.

Sven,
Them two pin plugs that look like the US plugs, are used for Extra-low voltage AC systems, Emergency lighting, 12, 24 and 48V systems where they are rarely unplugged and reversal of the pins won't matter.
And of course, where no earth is required!.
They are just used as an alternative to our normal 230V plugs, to ensure that they can't be inter-changed.
Paul,
Standing on your heads?.
Well in that case we must be all hanging on for dear life, down here!.

A slight aside, but in the U.K. we have a small two-pin connector with angled blades which has become quite common for 12V DC outlets in "caravans" (travel trailers).

The plugs look like a much-scaled down version of a two-pin Australian type.