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A little sum

lyledunn

I have 30m 16mm2 4-core swa 90C thermosetting run at 70C. I want to establish Z1+Z2 using PD CLC/TR 50480:2011 as set out in the IET design guide and will be using wire armour as cpc. The vector equation is;

(Z1+Z2) =(R1+1.1R2) + (0.3)x milliohms per metre.

Line is 1.51, (x can be ignored), DC resistance of wire armour is 3.1. All at 20C
There is no explanation but I assume that the line is raised to 70C and the wire armour to 60C.

Would some kind soul check my understanding. I make the impedance of line and cpc at design temp to be 0.162 ohms. 
This is purely academic.

  • 0

    Is the Line impedance of 1.51 milli-ohms/m correct  ? Table F.2 of BS 5467 (and Table F.7A of EIDG) have that at 1.15 milli-ohms/m. I think it's a typo in the post, as it looks like you've used the correct value in the calculation?

    Assumption for armour operating temp at 60 deg C for SWA operating at 70 deg C is confirmed by Table 6.1 of GN6, and also PD CLC/TR 50480 itself ... although I have also seen calculations which assume both armour and cpc initial temp is 70 deg C (and that would be OK for ADS disconnection times as it under-estimates the fault current)

    I concur 0.162 ohms with 1.15 milli-ohms per metre line conductor,  and armour at 60 deg C initially.... and 0.167 ohms assuming armour at 70 deg C initially

  • 0

    You are a star GK!

    yes, line should be 1.15.

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