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EICR C3 mixed manufacturer breakers

Martyn
I know this will have been discussed in the past but we are on Amd 1 of the 18th now so I thought I would renew it.


The Best practice guides list mixed manufacturer breakers in a consumer unit or distribution board as a C3.


As far as I am aware Bs7671 does not have a Reg on it beyond manufacturers instructions and given EICR's are based on this standard perhaps it is justified on that basis.


Most on here will be familiar with the 16kA 'rule' in BSEN61439 Annex ZB or its predecessor BSEN60439 Annex ZA


I avoid C3's like the plague because they give all the wrong signals to a client and clearly by definition are for things which are a breach of the regs, I'm not too keen on the insurance risk of a C3 either.


My question here would be what fault rating can one apply to an enclosure where there are mixed breakers given a manufacturer will only have certified their equipment with their devices?


Enjoy!


Martyn
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    I would argue that a fault has already occured by dint of the assembly having insufficient fault rating for the installation.




    Err no. The fault has only occurred when you are called out to take a look at the smoking remains and twisted metal hanging off the wall... 

    It could however certainly be C2 - if the next big fault that comes along that should operate ADS, instead blows the thing to bits.

    So single fault to danger, not already dangerous.




    Like others I can count on the fingers of one foot the no. of times I have ever seen an MCB fail catastrophically  in anything other than film taken during a lab test set up.


    The Americans estimate the energy density  from arc events  using these formulae  . I am aware that in the UK we do not normally, but in the US they calculate a rating in joules per cm2 for exposure, and then assume the energy spreads out from the source, to get a safety distance.

    However, work beckons,  and I'm having "fun" with the formulae in the forum software , so rather than cock it up I will come back and do it properly in another post, probably tonight.


    However, even for an open arc, at the risk of spoiling the conclusion, so long as the arc is cut suitably short by a suitable up stream fuse, you do not need much weight in the way of containment until >>10kA  at mains voltages (less for an arc partly dissipated in tearing up the case of a breaker.) You could probably make a safe CU out of plastic.  ?


    Given how most modern  enclosures are steel, and would stop the max legal  air gun pellet of 12 joules with an impact area of less than 1cm2  it is quite informative to compare that to yjr  incident energy from the un-restrained arc flash in a typical box.  In general a bigger box has an easier time, as the energy has space to be spread more thinly.

     


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  • 0

    I would argue that a fault has already occured by dint of the assembly having insufficient fault rating for the installation.




    Err no. The fault has only occurred when you are called out to take a look at the smoking remains and twisted metal hanging off the wall... 

    It could however certainly be C2 - if the next big fault that comes along that should operate ADS, instead blows the thing to bits.

    So single fault to danger, not already dangerous.




    Like others I can count on the fingers of one foot the no. of times I have ever seen an MCB fail catastrophically  in anything other than film taken during a lab test set up.


    The Americans estimate the energy density  from arc events  using these formulae  . I am aware that in the UK we do not normally, but in the US they calculate a rating in joules per cm2 for exposure, and then assume the energy spreads out from the source, to get a safety distance.

    However, work beckons,  and I'm having "fun" with the formulae in the forum software , so rather than cock it up I will come back and do it properly in another post, probably tonight.


    However, even for an open arc, at the risk of spoiling the conclusion, so long as the arc is cut suitably short by a suitable up stream fuse, you do not need much weight in the way of containment until >>10kA  at mains voltages (less for an arc partly dissipated in tearing up the case of a breaker.) You could probably make a safe CU out of plastic.  ?


    Given how most modern  enclosures are steel, and would stop the max legal  air gun pellet of 12 joules with an impact area of less than 1cm2  it is quite informative to compare that to yjr  incident energy from the un-restrained arc flash in a typical box.  In general a bigger box has an easier time, as the energy has space to be spread more thinly.

     


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