silly question? R1+R2

[madeinengland]

i have an assignment in which i have to describe the sequence of tests. also have to describe how the tests are done and expected values.for insulation restistence i know its 1 M ohm minimum. but is there a maximum R1+R2 value

 

[stretchyboy]

It would depend on the type of over-current protection and circuit details, before you can determine the limit that R1/R2 should be.
There are tables which tell you the maximum Zs for a type of mcb/cable etc but dont forget that this is the external and internal impedance of the circuit and not the Ze + R1R2.
We use Amtech so we have the charts that they provide and it is self checking as you produce a certificate. But you should be able to download a chart from any decent mcb manufacturer and even some cable manufacturers.

 

[Guest123]

Hi.

1 Mohm is the minimum for a 500V test. Dont forget there are 250V and 1000V tests too.

Technically there is no max for R1+R2 but, too high a reading could lead to the loop impedance being to high to achieve the disconnection time of the relevant protective device.