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.
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.
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.
