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Insulated Enclosures of Old and Earthing.

Zoomup
Can anyone remember the I.E.E. Regulation applicable, and the era, and even the reg. number, when it was stated that in certain situations an all insulated fuse box was to be used as opposed to a metal one?


Thanks,


Z.
  • 0
    I don't recall any regulation specifically demanding an all-insuated fuse box (although it might have passed me by). It might have been implied by more general regulations though - e.g. the need to provide shock protection, ADS not being practical in some situations (say with high Ze) so obliging a double/reinforced insulation approach for TT systems and similar.


    There's been a reminder of that in the regs for a while - e.g. 531.4.1 in the 17th - which became 531.3.5.3.2.201 in the 18th - but neither really demand an all-insulated approach - as it has always been possible to have a double/reinforced insulation system within metal enclosures.


      - Andy.
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    AJJewsbury:

    I don't recall any regulation specifically demanding an all-insuated fuse box (although it might have passed me by). It might have been implied by more general regulations though - e.g. the need to provide shock protection, ADS not being practical in some situations (say with high Ze) so obliging a double/reinforced insulation approach for TT systems and similar.


    There's been a reminder of that in the regs for a while - e.g. 531.4.1 in the 17th - which became 531.3.5.3.2.201 in the 18th - but neither really demand an all-insulated approach - as it has always been possible to have a double/reinforced insulation system within metal enclosures.


      - Andy.




    Thanks Andy, that is a good reminder. I am sure that I read about the need for all insulated distribution boards in the I.E.E. Regs. years ago on T.T. systems. What was a T.T. earthed system called before T.T? An installation with its own earth electrode and not supplied with an earth terminal from the distributor?


    Z.

  • 0

    I am sure that I read about the need for all insulated distribution boards in the I.E.E. Regs. years ago on T.T. systems. What was a T.T. earthed system called before T.T? An installation with its own earth electrode and not supplied with an earth terminal from the distributor?



    Depends how far back you go. At one point they didn't call it anything in particular - you could "Earth" things in almost any way you liked (from a supplier's terminal to just a metal plate buried on edge in the ground) - the only requirement then was that the resistance between any two exposed-conductive-parts anywhere within the installation didn't exceed 1Ω. In effect the entire installation was protected by supplementary bonding rather than ADS. From that point of view having an insulating CU isn't much of an advantage - as it'd be at pretty much the same potential as any other exposed-conductive-part anyway. Later on (14th say) they started talking about ADS and earth loop impedances, but still didn't really distinguish between TN and TT (even though PME does get a mention) - just noting that where the impedance was too high for 'excess current protection devices' to provide ADS you'd need some other device to provide 'earth leakage protection' (usually an ELCB). In those days ELCBs were normally all-insulated anyway, and installed in the tails before the CU, so there would be little need for the CU itself to be all/double/reinforced insulated. Come the 15th we had full TN-S/TN-C/TN-C-S/TT/IT descriptions.


      - Andy.
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    National Wiring Rules (i.e.

    ET101: 2008).

    (From Andy post)They do seem to have an odd requirement for CUs to have a fuse on the incomer (usually 63A).

    Not the subject of discussion but  that rule appear to be  super seeded. Hear is a list  below of updated rules And for the main fuse (Now MCB) The MCB shall be located in a weatherproof enclosure having a degree of protection IP55 and made of non-conducting self-extinguishing material (750'C).


    Question ? What sort of box is that or is just a way of regulators passing the buck on to others to sort out.

    https://safeelectric.ie/contractors/wp-content/uploads/sites/2/2018/12/Dec-2018-Newsletter-Final.pdf

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    jcm:

    National Wiring Rules (i.e.

    ET101: 2008).

    (From Andy post)They do seem to have an odd requirement for CUs to have a fuse on the incomer (usually 63A).

    Not the subject of discussion but  that rule appear to be  super seeded. Hear is a list  below of updated rules And for the main fuse (Now MCB) The MCB shall be located in a weatherproof enclosure having a degree of protection IP55 and made of non-conducting self-extinguishing material (750'C).


    Question ? What sort of box is that or is just a way of regulators passing the buck on to others to sort out.

    https://safeelectric.ie/contractors/wp-content/uploads/sites/2/2018/12/Dec-2018-Newsletter-Final.pdf

     




    Regarding the main over current device (M.C.B.) This is a bit worrying. I would prefer a nice robust H.R.C. cartridge fuse myself for proven reliability, longevity and safety.


    "b) In the case of installations having a maximum import capacity (MIC) less than 50 kA, the MCB shall have a rated short-circuit breaking capacity of at least 9kA."


    Z.

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