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80% Maximum ZS from OSG and GN3

Newfutile

 we use the 80% to  compare against our measured ZS to compensate for the temperature of the wiring being less than 70 C .

we apply this to the whole maximum ZS  ,should it not be only applied to the R1+R2 ,as the ZE part may be at a different temperature and possibly wont be loaded up as much.

Or is it just safer and good engineering to apply the 80% to all?

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    well in a T an E cable, if the live cores are warmer than ambient , the CPC will be as well.
    singles in rattling about in trunking or conduit may well be a quite different temps so your R1 and R2 correction are not really correct. Equally even if things are tightly grouped even unloaded cable may actually be heated by adjacent cables.
    You can say even less about the stuff that is external and may be shared with other consumers, and is just as likely to be  running hot or cold on the day you test.
    However the assumption is just that, an assumption that it is all hot - if you can justify that it never will be, maybe you can relax the test limits, but there will be few cases where a fail becomes a pass, and to be honest if there are, I'd consider it a marginal design anyway.
    Mike

    Late edit, Sorry, that was rubbish. The assumption is that on the day you measure it is all cold of course - a low resistance day if you like, but that you may need the fuse or whatever to still operate at full speed on another day when it is all hot, so 125% more resistive and when   the fault current when hot is 80% of the cold test result. Moral keep your algebraic wits about you.

     Mike

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    well in a T an E cable, if the live cores are warmer than ambient , the CPC will be as well.
    singles in rattling about in trunking or conduit may well be a quite different temps so your R1 and R2 correction are not really correct. Equally even if things are tightly grouped even unloaded cable may actually be heated by adjacent cables.
    You can say even less about the stuff that is external and may be shared with other consumers, and is just as likely to be  running hot or cold on the day you test.
    However the assumption is just that, an assumption that it is all hot - if you can justify that it never will be, maybe you can relax the test limits, but there will be few cases where a fail becomes a pass, and to be honest if there are, I'd consider it a marginal design anyway.
    Mike

    Late edit, Sorry, that was rubbish. The assumption is that on the day you measure it is all cold of course - a low resistance day if you like, but that you may need the fuse or whatever to still operate at full speed on another day when it is all hot, so 125% more resistive and when   the fault current when hot is 80% of the cold test result. Moral keep your algebraic wits about you.

     Mike

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