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Cable sizing Query for Harmonic Filter

seansasta
Hi, I'm looking for some advice on best practice & regulatory requirements in relation to the following project.

I have a main switchboard with a "future" PFC cubicle (ABB SACE EMAX E2.2H 3P+N 1250A EKIP TOUCH LSIG W/D); we are installing a Harmonic Filter (COMSYS ADF P300-360/480), which has a power rating of 249KVA (360A). The ADF is to be located within 25m cable run of the PFC feeder cubicle and I am proposing H07ZZ-F single core cables installed in trefoil (3+earth) as the supply cables. We have CT reference terminals available in a marshalling cubicle on the main switchboard monitoring the main incomer. The ADF has it’s own incoming fuses
My query is in relation to the proposed cable sizing versus the protection settings of the supply breaker. The most I can turn the ACB overload trip down is 0.4 x In (500A)…..Is it OK (reg compliant) to size the cables based on load rather than the minimum supply breaker setting…I’m proposing 1c 185mm (360A max with a derating factor of x1.3 to avoid overheating), Table 4F2A doesn’t have a specific example of 1c 185mm x3 for 3ph power and I am wondering do I need to change the 1250A ACB to an 800A (which I’d rather not do!)?
Any advice would be appreciated?

Regards, Seansasta
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    this nagging in my head from my years of sparking that the downstream cable should be rated at or above the breaker setting that feeds it

    It's actually quote common to have things otherwise - just consider a 20A cable feeding an unfused spur from a domestic ring circuit fed by a 32A MCB.


    For fault conditions the only considerations are the c.s.a & material of the conductor and its allowable temperature increase (usually determined by its operating temperature and maximum temperature the insulation can withstand for short periods) - i.e. "k" and "S". Factors that affect the long term current carrying capacity of a cable (grouping, thermal insulation and so on) don't come into it as they're all related to how well the cable can loose heat - while the fault conditions are (usually) considered to be adiabatic.


       - Andy.
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  • 0
    this nagging in my head from my years of sparking that the downstream cable should be rated at or above the breaker setting that feeds it

    It's actually quote common to have things otherwise - just consider a 20A cable feeding an unfused spur from a domestic ring circuit fed by a 32A MCB.


    For fault conditions the only considerations are the c.s.a & material of the conductor and its allowable temperature increase (usually determined by its operating temperature and maximum temperature the insulation can withstand for short periods) - i.e. "k" and "S". Factors that affect the long term current carrying capacity of a cable (grouping, thermal insulation and so on) don't come into it as they're all related to how well the cable can loose heat - while the fault conditions are (usually) considered to be adiabatic.


       - Andy.
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