80% rule

[Frosty69]

Hi people,
I was talking to my niceic assessor the other day and he mentioned in passing the 80% rule. Ive not heard of this directly before but I assumed he means the max zs not exceeding 0.8 of bs7671 value? So am I right in saying that for example on a B32 the max in regs is 1.16 but I should be hoping for less than 0.9?
Thankyou

 

[Bradzz]

Correct.

 

[telectrix]

not quite. the max. for a 32A type B is 1.44. the 80% of that is 1.15. this is because you are measuring Zsat ambient temp. ( say 20deg.) whereas the operating temp of the cable is up to 70deg. the 80% rule is to allow for the higher rfesistance at the higher temp.

 

[Guest 004]

Indeed, also some of my clients insist on me putting the 80% values in the max Zs box on the test sheets, and others 100%

In practice any circuit that reaches the 80% value, should be investigated further, and ascertain how to make it lower

 

[Sintra]

The max in the regs for a B32 is 1.44 of the top of my head. The 1.16 figure looks like the corrected value.

 

[Mr Mark Sparks]

note to self...
must type faster

 

[ezzzekiel]

yup wot he said

 

[telectrix]

why? if it's compliant.

 

[telectrix]

that's like saying you should drive at 25mph in a 30mph limit.

 

[giio]

Indeed, also some clients of my clients insist on me putting the 80% values in the max Zs box on the test sheets, and others 100%

In practice any circuit that reaches the 80% value, should be investigated further, and ascertain how to make it lower

they are wrong, that is not the max Zs,
the figures on the chart on the back of the niceic pad also have taken into consideration the 80% but you should not enter that on the forms

 

[tony mc]

Remember that BS 7671 gives max values and OSG gives corrected values in appendix 2.

 

[Bradzz]

on site guide figure, page 103 2D
to calc the correct ZS
230/(32*5)=1.44 B type breaker, this then gives BS7671 values.

 

[Guest 004]

they are wrong, that is not the max Zs,
the figures on the chart on the back of the niceic pad also have taken into consideration the 80% but you should not enter that on the forms

My clients are never wrong!

 

[Mr Mark Sparks]

that's like saying you should drive at 25mph in a 30mph limit.

do you still do 30mph in a 30 when its icey or do you correct you speed

 

[truckster]

My clients are never wrong!

I thought only ------ and lawyers had 'clients'

 

[Guest 004]

there you go, learn something new every day

 

[richy3333]

I thought only ------ and lawyers had 'clients'

PMSL!
How about a ----- sparky, could make your annual assessment interesting?!

 

[Frosty69]

Thanks for the fast replies and it was the osg I was reading from so they are the results taking into account the 80% rule. Thanks alot people

 

[Guest 004]

PMSL!
How about a ----- sparky, could make your annual assessment interesting?!

kronenberg is kicking in, and my eyes are getting blurry, is that annual or ----?

 

[telectrix]

only when i'm going backwards.