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Topic Title: Regulation 314.4
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Created On: 12 March 2019 04:11 pm
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 12 March 2019 04:11 pm
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robertchilds

Posts: 19
Joined: 16 July 2014

It has been reported on a fixed wiring report that a circuit connected to the live side of a DB should be protected by its own circuit protective device in accordance with regulation 314.4 of BS7671. Is this correct?

Essentially it is two distribution boards in parallel, one cable to the first board and then a 1 meter cable to the second board. All supply conductors are the same CSA and are suitably protected. Each board has its own isolation.
 12 March 2019 04:23 pm
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wallywombat

Posts: 96
Joined: 19 October 2018

well 314.4 is about final rather than distribution circuits, so I can't see how it's relevant.
 12 March 2019 04:31 pm
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AJJewsbury

Posts: 17795
Joined: 13 August 2003

I think the report writer is mistaken - on several counts.

Firstly 314.4 applies to final circuits - any circuit supplying a DB cannot, by definition, be a final circuit.

Secondly, looping into the supply terminals of one DB (or any other accessory for that matter) doesn't constitute the creation of an new circuit - it's simply a continuation of the first circuit that feeds the first DB.

What you describe isn't that uncommon - in effect you have one submain feeding one large DB - the parts just so happen to be in two distinct enclosures rather than a single one. Electrically it makes little to no difference.

The only point that would worry me would be the capacity of the first incomer's terminals to accept an extra full sized cable - snipping of strands is commonly seen in this situation - and that would certainly warrant an adverse comment on an EICR. Even if all the strands fit it's not always the case that the terminal holds them properly - e.g. a 50mm2 terminal might well hold one 50mm2 conductor perfectly well, but won't necessarily cope as well with two 25mm2 conductors. Not strictly following manufacutrer's instructions in that respect would also technically be a departure from the regulations.

Needing a second DB might also suggest that the original design was inadequate and there have been a large number of additions that were not originally catered for - which in turn might raise questions about whether the original submain is overloaded and provides adequate voltage drop and so on - but really those are separate considerations.

- Andy.
 12 March 2019 04:48 pm
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lyledunn

Posts: 1228
Joined: 13 August 2003

I wonder how much has been spent on unnecessary repairs arising out of ill-considered recommendations on EICRs.

-------------------------
Regards,

Lyle Dunn
 12 March 2019 04:55 pm
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robertchilds

Posts: 19
Joined: 16 July 2014

Many thanks for the quick and comprehensive replies, they all concur with my own interpretation.

Totally agree Lyle and main reason for requiring the clarification.

Robert
 13 March 2019 05:12 pm
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gkenyon

Posts: 5354
Joined: 06 May 2002

Originally posted by: AJJewsbury

any circuit supplying a DB cannot, by definition, be a final circuit.
Sorry to be pedantic Andy, but there are exceptions (as there are to any rule).

For example, a final circuit on a Caravan Site may supply a Caravan which has a DBO in it !

But of course this post is a little "roger irrelevant" to this thread

-------------------------
EUR ING Graham Kenyon CEng MIET TechIOSH
G Kenyon Technology Ltd

Web-Site: www.gkenyontech.com
 13 March 2019 05:21 pm
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AJJewsbury

Posts: 17795
Joined: 13 August 2003

Sorry to be pedantic Andy, but there are exceptions (as there are to any rule).

For example, a final circuit on a Caravan Site may supply a Caravan which has a DBO in it !

OK, fair point. Perhaps I should have phrased it as "any circuit directly supplying only a DB (or two) cannot, by definition, be a final circuit."

Hopefully the original was clear enough in context though.

- Andy.
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