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Surge protection devices without overcurrent protection

Zs

Hello all, greetings from a desk day.

I am just off the phone with our genius SPD lady at SPD.  I mentioned the latest Fusebox distribution board which does not have an overcurrent device for the SPD.  The device is a Fusebox SPD1MT2 type 2 direct to busbar surge protection device.   She tells me that it is not compliant in accordance with section 524.4.5 and am inclined to agree.

www.fusebox.shop/.../spd1mt2

So, I installed one a week or so ago.  Purchased in good faith, and guilty of assuming an overcurrent device would be there,   I was a touch surprised when I saw no MCB for the SPD.

Their website states product description states 'with No MCB required'. 

I'm reading now that overcurrent can (in italics) be built into the device but my conversation with SPD hinted at some industry 'naughtiness'.  

Any views? Where do we stand with that then, in terms of compliance as installers?

thank you, 

Zs

  • Hi,

    I don't think Regulation 524.4.5 exists in the latest version of BS 7671, unless I'm mistaken?

    As per the datasheet below it looks like the SPD relies on upstream fuse protection (<=100A gG required).

    Kind regards, 

  • in reply to Bh

    Interesting. thank you for finding that.  It does say that, and it says its a Gg so  That must be the incomer?  So, I wonder if that regulation for 'overcurrent with respect to short-circuit currents is being met?  It does still exist in the brown book. And, I might stick my neck out and question as much as 100A protection in terms of disconnecting the device.

    I'm sure the manufacturer wouldn't have done anything untoward, but I'm designing for a TPN thatched residence right now and I must turn every stone.

    Zs

  • in reply to Bh
    Bh said:
    I don't think Regulation 524.4.5 exists in the latest version of BS 7671, unless I'm mistaken?

    No, but 534.4.5 does.

  • in reply to Chris Pearson

    Apologies, my typo.

  • Zs said:
    Any views? Where do we stand with that then, in terms of compliance as installers?

    I would seek written confirmation from the manufacturers that the device is compliant.

    As an aside, like other SPDs, this one has a red/green flag, but what use is that to anybody when it is hidden under an opaque cover?

  • Their website states product description states 'with No MCB required'. 

    As I understand it, such devices are meant to have in-built overcurrent protection (if only a blob of solder type "fuse" which when opens also releases a spring lever that triggers the red 'replace' flag) - the upstream gG fuse is only needed for backup protection (like making M6 MCBs good for 16kA).

       - Andy.

  • in reply to AJJewsbury

    There certainly are designs with what is in effect an combination indicating fuse and thermal trip in series internally, and even versions where the indicator actuates a contact that can sound an alarm. 

    ~Does the little circuit in the side indicate anything of use ?
    I'd expect and hope that the 100A fuse is not normally the thing that pops - if it was, that would be very awkward in many  situations.
    Perhaps on a supply with a massive PSSC and an unlucky dead short failure of the MOV - but mostly MOVs fail by leaking more and more and then becoming unpleasantly hot - hence the thermal trip aspect to the internal fuse - the blob of low melting point solder alluded to above.
    Of course the main objection is none of this, but rather that it appears to be pink ! 
    Mike

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