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Topic Title: 314.1
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Created On: 25 March 2013 09:25 AM
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 25 March 2013 09:25 AM
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GB

Posts: 359
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314.1 > Every installation shall be devided into circuits as necessary to:

Definition of a Circuit > An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s)

How did we end up with split DBs c/w dual RCDs

 25 March 2013 09:38 AM
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impvan

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What's the problem? For decades there's been circuits with different protective devices for shorts and earth faults. Admittedly it's taken a while to reach the domestic end of the industry...
 25 March 2013 09:45 AM
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tomgunn

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This is a question that has been bothering a lot of people, me included, on this forum - the simple answer doesnt exist - but the conclusion is somewhat quite simple - its because 'they' havent got a clue what 'they' are doing - although, to be fair, it does make sense... if you think about it... one fault on a circuit will shut the whole side of that CCU down and probably plunge people into darkness - this is an alternative to having, say, a 3036 Wylex board - but they are boring because they wont fail, unlike the RCDs which have a failure rate of, something like 6%? Also you don't have to turn off the Wylex board every six months to make sure that the isolating switch is working properly - BUT - how many homes actually do turn off their beautifully installed RCDs every six months - so that they would then have to go around each timer on their DVDs / clocks / digital appliances etc.. etc... and reset them? Now we have one RCD for newly installed CCUs I believe, ( I think I'm correct - but I feel assured that someone will up-date me on this!! ). I have a 6 way 3036 Wylex CCU and my son keeps asking me to let him change it for a new RCD protected CCU... but theres no way I would change it... why? Because I dont get any bother from it and my firdge keeps working away very nicely thank you!

regards... Tom

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 25 March 2013 10:24 AM
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AJJewsbury

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I agree - it's a muddle. It would make a lot more sense to me if the definition of a circuit left out the word "overcurrent" as from just about every practical point of view the opening of an RCD will have identical consequences to the opening of a fuse or MCB.

I suspect it's historical - when RCDs (ELCBs) were very expensive it wasn't practical to give every circuit (or even reasonably small groups of circuits) individual RCD protection - so we ended up with front-end RCDs, but the powers that be didn't want to dilute the regulations to the point where 'one fuse for everything' (slight exaggeration) could be seen as acceptable.

Personally, I see a dual-RCD CU as a main switch feeding two submains (of only a couple of inches length), feeding two distribution boards, with overcurrent protection omitted at one tier and RCD omitted at the next.

- Andy.
 25 March 2013 11:10 AM
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tomgunn

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Why not use RCBO's? I know that they cost a bit more.. but - I feel it would be safer and better all round.

Tom

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Tom .... ( The TERMINATOR ).

handyTRADESMAN ... haha

Castle Builders

Why did Nick Clegg cross the road? Because he said he wouldn't!

I can resist anything..... except temptation! ( Karl Gunn ).
 25 March 2013 12:43 PM
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AJJewsbury

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Why not use RCBO's?

I'm sure that's where we'll end up (for domestic at least) - we just need to go around the more demand -> lower prices -> more demand loop a few more times. DP RCBOs with a DP bus-bar CU makes a very neat arrangement.
- Andy.
 25 March 2013 04:54 PM
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dbullard

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Originally posted by: AJJewsbury

Why not use RCBO's?


I'm sure that's where we'll end up (for domestic at least) - we just need to go around the more demand -> lower prices -> more demand loop a few more times. DP RCBOs with a DP bus-bar CU makes a very neat arrangement.

- Andy.


Good thread,

My last 3 jobs where I have changed DB's CCU's etc, I have installed whole RCBO boards.
1. Mainly due to the cost coming down
2. For client ease (elderly or infirm)
3. Easier for me.

Just started a new build, which will be totally RCBO protected with the exception of the main switch, expensive yes, smaller DB and easier for the customer.
It will be a "Green home" with lots of pumps etc for rain water harvesting etc etc etc, the last thing I want is a call at 3 am with the client moaning he has half a house off because one of his "pumps" is faulty.

314.1 > Every installation shall be devided into circuits as necessary to:
Definition of a Circuit > An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s)
How did we end up with split DBs c/w dual RCDs


Maybe it would be time for the powers that be to re word the definition slightly.

Regards

D

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 25 March 2013 09:14 PM
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ebee

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I usually fit a few RCBOs I must admit (shower, cooker, boiler are favourite) then power and lighting across two RCDs.

I feel I`m approaching the the plainswitch and all RCBOs way without all of the expense, but as you say price coming down might make this feasable.

Gosh it`s only ten minutes since we started to install with one RCD as a front-ender


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Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
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