Rule of thumb tabulated

[bhamoggy]

Can anyone tell me when the 80% is exactly applied ?

Not sure when to use the Zs in BS7671 or multiply by .8

 

[Andy™]

7671 does not include 80% values. you should use 80% of 7671, or OSG (which are 80%)

 

[bhamoggy]

Yeah I know 7671 doesn't include 80% values. It's only OSG that does, that's not my question is it.

I want to know when to apply the 80% of 7671 values?

When do I use the regs values and when do I use the tabulated 80% value

 

[Zeespark]

Regulation values when you are designing a circuit/job, rule of thumb value when you test the said works.

AndyGuinness

 

[sparkytim]

Hi

The 80 % value is to allow for the difference in temperature between the value of Loop impedance measured when testing and the actual value under fault conditions.

So when TESTING the maximum acceptable value must be the 80% value to ensure disconnection will occur within the time requirement for that protective device.