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#133945 - 10/10/02 06:43 AM English System?  
Belgian  Offline
Member
Joined: Oct 2002
Posts: 177
antwerp
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?


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#133946 - 10/10/02 11:45 AM Re: English System?  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
Welcome!

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

Quote

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


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!)

Quote

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.


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

Quote

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?


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).]


#133947 - 10/10/02 01:55 PM Re: English System?  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
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.

Quote
I have heard from somebody that in
England, it is not the neutral which is grounded at the supply

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.

Quote
Some are 3 x 230V

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).]


#133948 - 10/10/02 02:12 PM Re: English System?  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Quote
Theoretically, if you have a three-phase system, you can earth one of the lives.

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).

Quote
I'm not aware of anyone using such a system, but there are a couple of odd systems around, especially in North America.

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.

Quote
Nah, the Brits are nuts alright

Definitely! We vary from mildy eccentric to completely crazy! [Linked Image]

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.


#133949 - 10/10/02 02:24 PM Re: English System?  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
>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 [Linked Image]


#133950 - 10/10/02 07:55 PM Re: English System?  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,308
.....appliances that explode? [Linked Image]
your <ahem>...talking about a fuse right? ? [Linked Image]


#133951 - 10/11/02 05:24 AM Re: English System?  
Belgian  Offline
Member
Joined: Oct 2002
Posts: 177
antwerp
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.


#133952 - 10/11/02 06:30 AM Re: English System?  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,308
Quote
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...
[Linked Image]

i can always tell, every third breaker location is not used......
[Linked Image]


#133953 - 10/11/02 08:42 AM Re: English System?  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
Quote

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?


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)

Quote

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.


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 [Linked Image]
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.


#133954 - 10/11/02 03:55 PM Re: English System?  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Quote
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.

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! [Linked Image]


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