I would like to undestand exactly why, when you
interchange Live & Neutral, then the appliance can "blow up"?

I am situated in Belgium. Here all residential installations are TT systems.
Some are 3 x 230V and others are 230/400V. All fusing is on all poles.
In the 230/400V instalations, when we use 230V (ie. Live & Neutral), we can
interchange live & neutral in a plug of any domestic appliance and we do
not have any problems resulting from that (nothing "blows up").

One more thing I wanted to clarify. I have heard from somebody that in
England, it is not the neutral which is grounded at the supply, but that
it's the live which is grounded. See the attached picture. If this is true,
then I don't understand how it can be a TN system? Is this true?

Welcome!

It's nice to have another member from continental Europe besides me and Ranger here.


This can only happen in Britain. I'll explain why in a moment, but first:

Contrary to what many people believe neither North American nor European appliances rely on the polarity of the supply for their safety and only rarely for their function. There is however a notable exception to this: North American lampholders are apparently designed in such a way that there is a safety advantage in having the live on the center of the lampholder. For this reason, plugs are polarised. In Europe lampholders are designed in such a way that it is not possible to touch any metal parts of the light bulb, regardless of polarisation. Therefore, there is no need for polarisation.

Now for British appliances blowing up: The appliances meet the same requirements as those used in Belgium. (Laid out in various EN standards) The difference lies in the fusing of the mains cord to the appliance.

In all countries except those who have adopted the present British system, the mains cord, and in many cases the appliance, rely on the protection of the fuse or breaker in the panel (consumer unit) in case of a short-circuit in cord or appliance.

In the UK the fuse or breaker used in the panel has a too high rating to offer sufficient protection. Therefore, British 13A plugs contain a fuse on the live side of the plug. Should you reverse the polarity a British socket, you will find yourself with a fused neutral. Although this still offers protection for live-neutral short-circuits, there is no longer a protection for live-earth faults. Hence, in theory, the appliance can blow up.

(Feel free to correct me on this Paul or David!)


Cool! For the 3 x 230V system this makes perfect sense, since there are two lives feeding each socket outlet.


Nah, the Brits are nuts alright (sorry Paul and David!), but they can't defy the laws of physics. Whatever you connect to earth, it will no longer be live with respect to earth. The British 230/400V system identical to the other 230/400V wye systems used around the world. As far as I know, all of them have a grounded neutral.

Theoretically, if you have a three-phase system, you can earth one of the phase conductors. I'm not aware of anyone using such a system, but there are a couple of odd systems around, especially in North America.


[This message has been edited by C-H (edited 10-10-2002).]

Hi Belgian, and welcome to ECN!

I think C-H (he's in Sweden) has summed up the situation here in Britain fairly well.

The most widely used residential arrangement for receptacles is the ring circuit, fed from a 30 or 32A fuse or circuit-breaker. Our plugs then contain a cartridge fuse, the maximum rating of which is 13A. That's why polarity of wiring at the socket is considered so important here, because if you swapped the line and neutral then the fuse in the plug would be in the neutral line.

You'd be left with the 30 or 32A fuse at the main panel as the only protection against shorts to ground. For most appliances the actual polarity of supply on the cord is unimportant, and these days you'll find the same model sold right across Europe with just a different plug.

In TT systems there is a main RCD (GFI) which would obviously provide ground-fault protection in this situation. Although RCDs are becoming increasingly common in TN systems as well, they are not required, and therefore with reversed polarity you could end up with a 0.5 or 0.75 sq. mm cord having no better protection than a 30A fuse.

No, all public supplies in the U.K. have been required to have the neutral solidly grounded since at least 1930. Except for a few remote houses which are fed from a single-phase 240V xfmr, practically all LV distribution is 3-phase. Officially the levels are now 230/400V, but in practical terms we are still nominally 240/415V.

Residential service is normally just 2-wire single-phase tapped from one phase and neutral of the 4-wire network.

See the diagrams at this link to get a better idea.

I'm not quite sure I understand your terminology here. Do you mean a 230V delta system? Or maybe a 133/230V wye system without the neutral brought into the house?

By the way, I'm not sure how you tried to post the picture you referred to, but if have any problems feel free to e-mail me and I'll explain how to do it. Alternatively, e-mail the picture to me as an attachment and I'll post it for you.




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

You could, but going by the colloquially accepted definition of live then the earthed phase would no longer be live.

We're getting quite a few international members now, so let's recap for their benefit: The British use of live corresponds to the similar colloquial term hot in North America, and active in Australia/New Zealand. The official British IEE definition of a live conductor is somewhat different and means any conductor which carries current during normal operation (i.e. it includes the neutral).

There's the corner-grounded delta arrangement, with one phase grounded.

The other "odd" American system (from a European perspective) is the 4-wire delta where the ground is at the mid-point of one side of the delta. Always 240V between any two phases, but two phases measure 120V to ground and the third is 208V to ground. I'm not aware of any such system ever being used on this side of the Atlantic.

Definitely! We vary from mildy eccentric to completely crazy!

Seriously though, although many people people here do tend to look at Continental Europe and laugh at the "funny foreigners" and the way they do things, there are many cases where in fact it is we in Britain who are the odd ones out.

>You could, but going by the colloquially
>accepted definition of live then the
>earthed phase would no longer be live.

Ooops! Sorry! Of course. I'm too careless when I write. Error now corrected.


>Definitely! We vary from mildy eccentric
>to completely crazy!

I better move to Britain, then. I just might blend in

.....appliances that explode?
your <ahem>...talking about a fuse right? ?

Thank you all for your feedback!

"The most widely used residential arrangement for receptacles is the ring circuit, fed from a 30 or 32A fuse or circuit-breaker. Our plugs then contain a cartridge fuse, the maximum rating of which is 13A. That's why polarity of wiring at the socket is considered so important here, because if you swapped the line and neutral then the fuse in the plug would be in the neutral line.

You'd be left with the 30 or 32A fuse at the main panel as the only protection against shorts to ground. For most appliances the actual polarity of supply on the cord is unimportant, and these days you'll find the same model sold right across Europe with just a different plug.

In TT systems there is a main RCD (GFI) which would obviously provide ground-fault protection in this situation. Although RCDs are becoming increasingly common in TN systems as well, they are not required, and therefore with reversed polarity you could end up with a 0.5 or 0.75 sq. mm cord having no better protection than a 30A fuse."

Now I understand why the UK uses fused plugs! So, in the panel board you have only one fuse for all circuits? what about the lighting?

Regarding your TN system:
If I understand correctly, the only protection you have is from the fuse (where no gfi is installed). Then most probably you use only B curve fuses? And the ground cables must be very big diameter for adequate protection.

Here TN systems are used only in industrial systems, where there is a HV distribution next to the installation.

"I'm not quite sure I understand your terminology here. Do you mean a 230V delta system? Or maybe a 133/230V wye system without the neutral brought into the house? "

I meant a 133/230V wye system without the neutral brought into the house. These are older installations, where at the time used to be 110V.

" By the way, I'm not sure how you tried to post the picture you referred to, but if have any problems feel free to e-mail me and I'll explain how to do it. Alternatively, e-mail the picture to me as an attachment and I'll post it for you."

Yes, please explain how to do it.

The other "odd" American system (from a European perspective) is the 4-wire delta where the ground is at the mid-point of one side of the delta. Always 240V between any two phases, but two phases measure 120V to ground and the third is 208V to ground. I'm not aware of any such system ever being used on this side of the Atlantic.""

Very interesting, this 4-wire system! Never heard of it.

actually, they can be a pain-in-the A** for other than industrial ( all 3-phase) applications. Look Here , courtesy tech ref area...


i can always tell, every third breaker location is not used......

A ring main is still only one circuit. If there are more circuits, you obviously need more fuses.

Lights in the UK are on separate circuits )between 6 and 16 Amps). How are lights wired in Belgium? I've read that France has separate circuits, but I know a lot of countries that don't. (E.g. Sweden)


The TN system is standard in a number of countries, including the US, Germany, Denmark, Sweden etc. It's really France and Belgium who are the odd ones out here
There is no need for the ground wire to be larger than the other wires. (The Brits make it smaller! This is not a practice shared by neither Americans nor other Europeans as far as I know.) It is sufficent that the fuse blows or breaker trips within a few seconds.

Was it actually 110V, or were these systems at one time the nominal 127/220V systems as were used in some parts of France?

On the ring circuits, you'll find many smaller houses wired back in the 1950s or 1960s which do indeed have only a single 30A ring feeding all the receptacles. These days it's more usual to have two rings in the average house, or even three. Our rules state that each ring can serve a floor areas of up to 100 sq. meters.

Standard lampholders are allowed to be wired on any circuit up to a maximum of 16A, but in residential wiring 5 or 6A lighting circuits are the norm. Again, in many old properties with just a few lights one 5A lighting circuit was common, but two or more are the norm these days. We have separate circuits for electric range (cooker), water heaters, etc.

Many European countries seem to use 16A circuits feeding a mixture of receptacles and lights, but in France they seem to favor separate 10A lighting circuits.

Yes, in TN systems with no main RCD/GFI, then the fuses provide both overcurrent and ground-fault protection. There are still plenty of old (and not so old!) installations which use rewireable fuses. Why these remained so popular in the U.K. for so long, I don't know. Their characteristics are such that for many years the IEE current-rating tables specified ampacity based on these fuses with a footnote to the effect that ratings could be increased by 33% if cartridge fuses were used instead.

On the main ground lead, in the average residential system here we have 25 sq. mm phase and neutral on the service with a 16 sq. mm ground.

Re the American 4-wire delta, Sparky's provided the link I was about to search for in the Tech. Reference area. Thanks Steve!

Exploding appliances? Certainly reversed wiring at a recept. could result in some glowing cords given a fault and only a 30A OCPD!

I find the idea that an appliance could "blow up" on a UK power supply if you reverse the "live" (phase) & neutral in the plug top a little over dramatic!
During the course of my work I have encountered plugs with reverse polarity on many occasions, & all the appliances work normally. This does not mean to say they are safe, as any single pole control devices; switches, thermostats etc. would be in the neutral conductor. This could be a shock hazard, if for example you were changing a bulb & accidentally touched the pins, thinking it was safe with the switch off.
British regs. prohibit a single pole switch in the neutral, if the neutral is switched all associated phases must be switched simultaneously.

The purpose of the fuse in a 13A BS1363 plug is to protect the appliance cord only from short circuit. If the appliance requires additional protection it has to built in to the appliance, I believe this is an IEC standard.

Reverse polarity in the actual fixed installation wiring could be very dangerous, depending where it occurs.
The worst case would be TNC-S (PME) reversed
on the incoming supply before the cut-out (I know of this happening). All bonded metalwork would be live at 240V, along with every earthed point & appliance in the installation.
This is the 1 downside to TNC-S earthing system.

These are just a couple of reasons that us Brits are obsessed with maintaining polarity throughout our "eccentric" electrical installations.

As other members have stated the neutral is always permanently & solidly earthed in UK public supply systems.
Most systems are TNC-S or TN-S, with TT systems only used for rural supplies (though TNC-S is the norm in my area), building sites & petrol service stations (TNC-S not permitted) or any other location where PME (TNC-S) system is not allowed.

About appliances "blowing up". Well, I must have gotten it wrong. (misinformation)

The only thing that still bothers me is: why in a british PLUG (not in the socket) do you HAVE to put the brown to the Live (which is fused) and the blue to the Neutral. It would be as safe the other way round.

[This message has been edited by Belgian (edited 10-20-2002).]

Belgian,
I agree that in many cases reversing the brown and blue at the plug would have little or no effect on safety. You see the stickers attached to British cords about how essential it is that the wires are correctly connected though.

Many of the appliances sold in the U.K. these days are sold as the same model right across Europe. The two-prong "Euro" plug is non-polarized, as is the widely used Schuko plug (and a few others, e.g. in Italy). Even in France where grounding plugs are polarized, nobody seems too bothered about which way phase & neutral are connected at sockets.

The IEE is always quite adamant that all single-pole switches, even those inside equipment, should be in the "correct" side of the circuit.

There would be a case for some old electric heaters where the element terminations can be touched through the grill. If the switch were in the neutral, then somebody could touch an energized terminal believing the heater to be safe. But they don't allow those to be manfactured these days anyway.

The only other case I can think of is where a primary fuse is included on the supply input (typical of some radios, TVs etc.) and reversal could remove the protection by having that fuse end up in the neutral. It would still provide overcurrent protection, but not protect against ground faults.

Perhaps with the prevelance of TN-S and TN-C-S systems in Britain this was a major concern, whereas so much of residential service in Europe is TT where the main GFI/RCD would provide ground-fault protection. (As would also apply increasingly in this country.)