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Topic Title: MCB downgrade
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Created On: 12 May 2013 08:37 AM
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 12 May 2013 08:37 AM
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darrenscruton

Posts: 62
Joined: 02 November 2005

Hi,

I've been given a job to carry out some remedial work in student accommodation, there are about 150 individual units all with there own kitchen units.

The work request has come thru and one of them is to downgrade the MCB for the cooker from 40A to 32A. it is 6mm T+E and in an insulated ceiling and then buried in plaster down to the CCU.

I told the main contractor that it would need to be a RCBO as there is no RCD protection and i was changing the characteristics of the circuit and that an insulation cert would then be filled out. They are adamant that they want an MCB and a minor works.

I did ring the NICEIC and ECA help lines for the first time and guess what, NIC said i was right, eca said i was wrong.

What does anyone think would be the correct way.

Thanks for any replies.
 12 May 2013 09:36 AM
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daveparry1

Posts: 6169
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Mcb and minor works i'd say. You're not altering the circuit as such, just making the existing safer,

Dave.
 12 May 2013 09:51 AM
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leckie

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If for example the circuit was within a 1-way consumer unit, say an old Wylex 104 with a 40A mcb, and you were replacing the consumer unit with a 1-way board with a 32A mcb or rcbo, you would require to notify the work, and issue an EIC.

BPG6 says that if a circuit requires additional protection from an rcd to comply with regs, including for cables in walls, then this protection should be provided. It also says that the building regs require that the installation should not be left in a less safe condition than before the work is carried out. Bit confusing because the installation would not be any less safe, but the advice is still to install rcd protection.

From the perspective of the circuit, is there a difference between replacing the MCB only to the existing board, or replacing the board itself? I would say not, so the advice in the BPG6 would still stand.
 12 May 2013 09:52 AM
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OMS

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I did ring the NICEIC and ECA help lines for the first time and guess what, NIC said i was right, eca said i was wrong.


Not suprising - don't forget that the NICEIC, despite all thier claims to the contrary, are just basically focused on domestic installations, God love 'em.

The ECA on the other hand are quite capable of seeing the distinction between a cooker circuit in someones house and one in a student acomodation unit - particularly an existing one, and where, presumably, the MCB downgrade has arisen from the outcome of an EICR where some regimentally insane tester has decided that the thermal insulation requires the cable to be upgraded or the MCB downgraded.

Anyone with a modicum of common sense would evaluate it properly and determine that no action of any kind is required - but I guess that's not the game the main contractor or you are in, is it.

regards

OMS

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 12 May 2013 10:02 AM
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leckie

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Well I agree OMS, why on earth do you keep persisting in using common sense!

On the other hand, if the OP is being offered work why turn it down? And if you are carrying out the work some sort of cert needs to be issued. My own opinion is the same as Daves, MWC and ok to fit an MCB, but my example and reading of the BPG6 seems to indicate that the NICEIC are taking that view. As usual the ECA are more sensible.
 12 May 2013 10:05 AM
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daveparry1

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I still say that as the circuit isn't being altered or extended there's no need for it to be rcd'd, after all if the existing 40a mcb was being replaced due to failure no one would be saying he'd have to fit an rcd would they!

Dave.
 12 May 2013 10:11 AM
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dg66

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Originally posted by: daveparry1

I still say that as the circuit isn't being altered or extended there's no need for it to be rcd'd, after all if the existing 40a mcb was being replaced due to failure no one would be saying he'd have to fit an rcd would they!



Dave.


Agree, i can feel a common sense overload coming on

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Dave(not Cockburn)
 12 May 2013 10:46 AM
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OMS

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Originally posted by: leckie

Well I agree OMS, why on earth do you keep persisting in using common sense!

Sorry !!


On the other hand, if the OP is being offered work why turn it down?

Indeed - I wasn't suggesting that, the evaluation of the presumed EICR coding should have been made earlier is my point - ie it's a non-job.

And if you are carrying out the work some sort of cert needs to be issued. My own opinion is the same as Daves, MWC and ok to fit an MCB, but my example and reading of the BPG6 seems to indicate that the NICEIC are taking that view. As usual the ECA are more sensible.

The OP has clear instruction from his client - fit a 32A MCB and provide a MWC for each one altered - personally i agree that's the proper course of action. I wouldn't take the guidance in BPG6 and use it in anything other than a domestic setting - 'cos that's what it was written for - being a bit unkind, but probably truthfully, it was aimed at the guys who have short cycle training and operate from the OSG rather than BS 7671

Installers (as opposed to electricians) love simple rules - it's based on a mentality of "wire, fire and f**k off"




regards

OMS

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Failure is always an option
 12 May 2013 12:08 PM
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slittle

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Originally posted by: OMS

Originally posted by: leckie



Well I agree OMS, why on earth do you keep persisting in using common sense![IMG][/IMG]



Sorry !!





On the other hand, if the OP is being offered work why turn it down?



Indeed - I wasn't suggesting that, the evaluation of the presumed EICR coding should have been made earlier is my point - ie it's a non-job.



And if you are carrying out the work some sort of cert needs to be issued. My own opinion is the same as Daves, MWC and ok to fit an MCB, but my example and reading of the BPG6 seems to indicate that the NICEIC are taking that view. As usual the ECA are more sensible.



The OP has clear instruction from his client - fit a 32A MCB and provide a MWC for each one altered - personally i agree that's the proper course of action. I wouldn't take the guidance in BPG6 and use it in anything other than a domestic setting - 'cos that's what it was written for - being a bit unkind, but probably truthfully, it was aimed at the guys who have short cycle training and operate from the OSG rather than BS 7671



Installers (as opposed to electricians) love simple rules - it's based on a mentality of "wire, fire and f**k off"









regards



OMS



I'd agree OMS, do as asked but really it's a no brainer.

I've always felt that the ECA have been for it's members and taken a more sensible approach whereas the NIC have championed the customer so much they've forgotten what the real world is


Stu
 12 May 2013 03:10 PM
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leckie

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I have alway preferred the ECA to the NIC having been in both for many years. I wonder, now that there is certain amount of "partnering" with the Electrical Safety Register, etc, if they will soon be agreeing on most matters.

Regarding the OP, whilst I agree that the sensible answer is to carry out the works as required by the client, providing you agree that their instructions are compliant, if this work was assessed by the NIC and they think that an RCBO should have been fitted and a EIC issued this may present a problem. Personally in this case I would probably fit the MCB and take the loot.

Edited because i misread the OP!

Edited: 12 May 2013 at 04:02 PM by leckie
 12 May 2013 03:13 PM
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sparkingchip

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Any socket on the cooker switch?
 12 May 2013 03:46 PM
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geoffsd

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Originally posted by: darrenscrutonThe work request has come thru and one of them is to downgrade the MCB for the cooker from 40A to 32A. it is 6mm T+E and in an insulated ceiling and then buried in plaster down to the CCU.

Detractors -

I assume the grounds for your derision are the fact the cable will not be overloaded by the cooker - fair enough - but -

Does the fact that the CCC of the cable (in insulation) is less than the rating of the MCB and is not compliant not matter?

How does this response compare with the oft quoted response that a 44A shower will be alright on a 40A MCB because the shower will not be on for very long?

Would examples such as these be entered in the 'departures' section of certificates, what would be the explanation and would this be satisfactory?
 12 May 2013 04:48 PM
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OMS

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What type of insulation are we talking about would be the first question Geoff.

How do you know what the CCC of the cable is in insulation, you don't know what insulation.

The BS 7671 values of cable in insulation assume a particular thermal resistance - which is rarely achieved in practice.

How do you even know if the MCB is actually required to provide overload protection - the cooker rating may well be less than the cable rating.

Students don't spend very long cooking in my experience - it's why god invented MD's - I'm loving it.

OMS

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Failure is always an option
 13 May 2013 12:06 AM
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whjohnson

Posts: 716
Joined: 24 January 2009

If concern or doubts are expressed about the suitability of the use of 6.00mm singles, why not use tri-rated instead of the normal 70' stuff?

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