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BS 61439 Assemblies

MG
Was talking to a switchboard manufacturer and he mentioned that the switchboards manufactured to BS 61439 are only tested to 70 degrees C, so all the cables attached to/from it must be calculated for 70 degrees. The only reference in the standard which makes some sense about this is section 10.2.3.1 attached. This means that all the XLPE cabling out there which is rated at 90 degrees is under-utilised and is useless.


Many designers I assume, are not aware and proceed in producing the calculations in Amtech or similar with cables to set operate at 90 degrees and think all is ok.

f5a9c7ec6b00da11eb458554d1bc6af5-huge-image.png
  • 0
    Well there is an assumption about cable routing that the ends with the switch gear on are the most thermally insulated and hottest running point. This is not always the case, as the middle of the run may be hotter due to  lower ventilation and/or  grouping factors, while in many cases at the ends the cores tend to be split out and may or may not be better cooled depending what else is in the box.

    There is a second assumption that all XPLE cables run to switch gear - this may not be the case (line taps in a box anyone).

    There is a third assumption that kit with 90C rated terminals does not exist, but it does. Actually some breakers have hot terminals by design due to internal dissipation, and the cable cools the breaker, not the other way about.

    I agree it needs more thought than some folk may use, but " This means that all the XLPE cabling out there which is rated at 90 degrees is under-utilised and is useless. " is a bit sweeping.
  • 0
    Alright, let me rewrite "all the majority of XLPE cabling out there which is rated at 90 degrees is under-utilised and is useless."

    I was really surprised because the said manufacturer starting with S and has a green logo is a major player in the market. To be fair though it is not the manufacturer's issue though, they follow the standards.


    I was really surprised though !!!
  • 0
    Amtech and the like are only as good as the user, SISO seems to apply here. 


    90 degree cabling can be useful where there are large temperature differentials throughout a run, a cable may pass through a thermally insulated section which may then raise its temperature under full load to 90 degrees, the terminations may still be at 60 degrees for example. 


    I recently requested of software company a cable thermal effects dialog where this could be modelled throughout a run, I can see plenty of use cases where increasing the CSA might be undesirable just for a section that may run hotter than 90% of the cable.
  • 0
    MG, see Notes 1 and 2 to Tables 4E1A, 4E2A etc. (of BS 7671).


    Whilst I'm sure you are correct that many will be unaware of this situation, on the flip side many people are aware of it - and it has been discussed numerous times on here (as well as text books, training courses etc). The previous (and no doubt later) replies will give a flavour as to the debate which often ensues as to how much of an "issue" it is in any given scenario.

    My post isn't intended to re-open the debate, but simply to let you know that it has been covered many times ?
  • Former Community Member
    0 Former Community Member
    MG:

    Was talking to a switchboard manufacturer and he mentioned that the switchboards manufactured to BS 61439 are only tested to 70 degrees C, so all the cables attached to/from it must be calculated for 70 degrees. The only reference in the standard which makes some sense about this is section 10.2.3.1 attached. This means that all the XLPE cabling out there which is rated at 90 degrees is under-utilised and is useless.


    Many designers I assume, are not aware and proceed in producing the calculations in Amtech or similar with cables to set operate at 90 degrees and think all is ok.

    f5a9c7ec6b00da11eb458554d1bc6af5-huge-image.png


    I think you may be mixing up 70C with what is actually a temperature rise of 70K above the ambient. The switchboard should not allow the terminals for external conductors to exceed a 70K rise above 20C - ie 90C. Busbars etc can rise to as high as 105C.


    The manufacturer is of course at liberty to state a temperature rise less than this for the device to deliver FLC  - but I'm pretty certain Schneider don't do this as their ACB's and MCCB are widely used in third party switchgear.


    Regards


    OMS


  • 0
    I did some googling on their website and found the below. Two of their specification engineers also agree that they quote the switchboards to be only permitted to accept 70 degree cables. As far as the standard they are manufactured to, is not very clear about this 70 degree property. Could not find any reference to that apart from that section talking about testing.

    3555ff38f4e35b5fb71db49937f6c1d3-original-image.png

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