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Topic Title: double pole MCBs?
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Created On: 23 January 2013 07:35 PM
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 23 January 2013 07:35 PM
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jcm256

Posts: 1792
Joined: 01 April 2006

What would be the advantage of supplying all circuits from a consumer unit with double pole MCBs?

Can only think off: (convenient to megger circuits).

Advantages to the consumer, who could switch off individual breakers to find circuit which may have a neutral fault.

Safety? (Not sure about that otherwise it would be specified in BS7671)

Is it a European standard but not a BS7671 standard?

Why type C MCBs in a domestic consumer unit.

Why type C 10 amp MCBs for lighting circuits (apart from lighting with an overhead combined large air-circulating fan)

This photo has nothing to do with questions but just to give small idea of the setup involved:

http://tonysparksinspain.blogs...lectricity-supply.html
 23 January 2013 07:57 PM
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peteTLM

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Its common place in france, italy and greece to have 2 pole mcb's, not seen a lot of them over here though.
Them seem to love type C's in europe, they are everywhere. Probably a 'de facto' standard more than anything else. Their circuits are maybe shorter as no rings, and smaller sizes generally allowing more leeway.

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Every man has to know his limitations- Dirty Harry
 23 January 2013 08:02 PM
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sparkiedave

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I suppose it would be an advantage for any place where there's a possibility of someone running a centre tapped generator, they're supposed to be used in marine applications for that reason, but rarely are in my experience
 23 January 2013 08:48 PM
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AJJewsbury

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Some continental countries traditionally didn't have a guaranteed earthed N in their supply - especially so in France and associated areas. Some even had 220V supplied from between two phases (each around 127V to earth). Hence DP breakers and non-polarised sockets. BS 7671 does have a requirement for DP MCBs - in caravans (which could be expected to be driven abroad and plugged into foreign supply systems).

We (many many years ago) used to have electricity for power & lighting metered separately (and charged at different rates) - hence different (round pin) plugs/sockets for lighting and power and strict segregation of lighting and power circuits. While the two meters have long since gone, the tradition of separate lighting and power hangs on (until relatively recently all our lighting accessories were 5A rated, so couldn't be used on a combined lighting/power circuit). Not so elsewhere, where one circuit per room, serving both lighting and sockets was the tradition - usually rated at around 10A.

Why type C? Why not? A lot less nuisance tripping (especially when you have relatively low rated (e.g. 10A and 16A) final circuits (a 16A C type would withstand a similar inrush to a 32A B type). Why don't we? 'cos we use reduced c.s.a. c.p.c. that probably wouldn't cope with the energy let-though nor supply a sufficiently low Zs (especially for our higher rated circuits). Most of the rest of the world think we're mad to have smaller c.p.c.s than line conductors.

- Andy.
 23 January 2013 09:02 PM
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Martynduerden

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I used to do a good amount of work for BT Facilities in the exchanges, some areas were 110v only the installations in those areas or passing through them was 110V, they had several DB's and all of them had DP MCB's for obvious reasons.

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 23 January 2013 09:36 PM
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jcm256

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The Technical know how in answer to curious questions is very much appreciated.

Thanks

jcm
 23 January 2013 11:24 PM
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DOUGIE1000

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Double pole will be 18th edition, I'll put £ on it

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Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 23 January 2013 11:25 PM
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Martynduerden

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Originally posted by: DOUGIE1000

Double pole will be 18th edition, I'll put £ on it


And under stairs cupboard will become under stairs rooms!

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Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com
 24 January 2013 03:16 PM
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OMS

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Safety? (Not sure about that otherwise it would be specified in BS7671)


Safety is a consideration - in some circumstances there can be considerable neutral currents flowing that are not subject to overload protection when using single pole devices (or double pole devices without neutral pole overcurrent protection). This can lead to all sorts of elevated temperatures etc.

Is it a European standard but not a BS7671 standard?


In part, both - but you can get other references to things like JSP 482, DSEAR etc

Regards

OMS

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 24 January 2013 03:38 PM
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AJJewsbury

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This photo has nothing to do with questions but just to give small idea of the setup involved:



http://tonysparksinspain.blogs...lectricity-supply.html


The talk of "ICP"s is interesting.... Perhaps we have something to to be grateful for after all. (I can see some caravan site owners talking an interest though!)

- Andy.
 24 January 2013 06:12 PM
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unshockable

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What would be the advantage of supplying all circuits from a consumer unit with double pole MCBs?



Have you ever had your main 20A fuse blow in Spain? The switch gear is locked and sealed. The man comes and takes €150 cash to change it for you. You'll be glad your incomer blew instead.

I believe it to be a form of rationing.

Simon
 27 January 2013 12:39 AM
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MrOther

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You them extenstively for the secondary side of 400/110v TXs protecting the secondary "double phase" 110v side.
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