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Topic Title: Domestic consumer unit capacity
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Created On: 07 November 2012 05:26 PM
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 07 November 2012 05:26 PM
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mrlondon

Posts: 241
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Some one told me that domestic consumer units should be fitted to allow 25% or 2 spare way capacity, had a look the the big green book but couldnt find anything, could anyone help?

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Mr_London

 07 November 2012 05:31 PM
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AJJewsbury

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I think that might be a good tradition, but it's not regulation.

- Andy.
 07 November 2012 05:38 PM
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daveparry1

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I have seen that writen somewhere but as Andy said it's not a regulation,

Dave.
 07 November 2012 06:10 PM
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OMS

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It depends on what you are thinking of but i suspect it may have an origin in the continuous and intermittent rating of the DB - say a 60A DB would only be designed to supply say 45A continuous with odd excursions up to 60A.

Providing spare ways is never a bad idea though, decide what spare capaity you allow for them. As an example if you have a design current for 6 ways of a DB that comes to 43A that's an average of 43/6 = 7.2A per way. So adding two spare ways gives you 43A + (7.2 x 2)A = 57.4A. That's you design ciurrent for the submain or tails.

If then you get to the wholsaler and he has no 8 way boards but plenty of 10 way boards then you have 6 used ways, two spare (on the basis that you've allowed for them to be used) and two blanks (on the basis that your design hasn't made any allowance for an connection to them)

There is a world of difference between spare ways and blanks

regards

OMS

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Failure is always an option
 07 November 2012 06:14 PM
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mrlondon

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An old customer has been told that the dual RCD 10way board i fitted with 9 of the 10 ways being used doesn't comply with current regulations.
The spare capacity was originally 2 but 1 has since been used by an additional cooker circuit.

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Mr_London

 07 November 2012 06:24 PM
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OMS

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Sounds like complete nonsense to me, mate - who said it and are they short of work ?

Tell your client to ask for a regulation or a reference to the guidance document stating this.

Regards

OMS

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Failure is always an option
 07 November 2012 06:27 PM
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mrlondon

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thats what im thinking, they originally said my CU didnt comply because "All the upper floor lights/electricity should reside on one section and all the lower floor lights/electricity should reside on the other section. "

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Mr_London

 07 November 2012 06:39 PM
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daveparry1

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Shows just how much they know then doesn't it!
btw, is it a 16th compliant board, ie just one rcd, if so that could be why they're saying it doesn't comply,

Dave.
 07 November 2012 06:51 PM
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OMS

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Originally posted by: mrlondon

thats what im thinking, they originally said my CU didnt comply because "All the upper floor lights/electricity should reside on one section and all the lower floor lights/electricity should reside on the other section. "


arguablly, the opposite would be best practice - ie upstairs lights with GF sockets and vice versa if it's resilience you want - sound like a complete numpty to me

regards

OMS

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Failure is always an option
 07 November 2012 06:52 PM
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mrlondon

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its a wylex dual RCD consumer unit

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Mr_London

 07 November 2012 07:05 PM
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mrlondon

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this is funny, the electrician is quoting from this.
https://dl.dropbox.com/u/10058031/16000.pdf
See point 2 under design.

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Mr_London

 07 November 2012 07:16 PM
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mrlondon

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i traced the PDF to here.
http://www.fairfaxcounty.gov/d.../guidelines/16000.pdf

FAIRFAX COUNTY, VIRGINIA, USA!!!!!!!!!!!!!

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Mr_London

 07 November 2012 07:17 PM
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daveparry1

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That's all based on commercial installations I should think.
Btw mrlondon I didn't know how long ago you fitted the board, I thought it might have been before 17th, hence me asking if it was a 16th board,

Dave.
 07 November 2012 07:23 PM
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OMS

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It's an extract from an NEC design code - the voltages and reference to illumination levels in foot candles should tell you it's american in origin and they way the arrange electrical installations in the states is fundamentally different to the origins of BS 7671 in IEC documents.

Go tell the guy that he's an idiot and remind him that information gleaned from t'internet is not knowledge - it's still just information

regards

OMS

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Failure is always an option
 07 November 2012 07:55 PM
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mikejumper

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Originally posted by: mrlondon
Some one told me that domestic consumer units should be fitted to allow 25% or 2 spare way capacity, had a look the the big green book but couldnt find anything, could anyone help?

The only time I've seen that specified is on architects drawings.
So it could be something out of the architects equivalent of the BGB.
 07 November 2012 07:57 PM
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AncientMariner

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With 277 volts he must be going through light bulbs at a fair old rate...

Cheers!

Clive

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Clive S Carver GCGI IEng MIET
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