When adding a spur at an MCB do you....

[JulianC]

...just test your addition or test the entire circuit connected to the breaker, even though your addition is effectively separate from it?

To be more specific, customer wants an external PIR light fitted above their garage. The CU is a few feet away from where the light is going so it makes sense to spur off an existing lighting circuit at the MCB (there are no spare ways).

When fitting spurs in the past they've always connected into an existing circuit away from the CU and consequently, I've tested the entire circuit. However, this time the spur doesn't 'break in' to what's already there and is not reliant on the existing circuit for Zs and IR values. Your thoughts are appreciated.

 

[ukpablo]

i would have thought that the highest reading on that mcb would be recorded, whethet it be the spur in question or the furthest point in the original cct..........i.e, the whole cct is protected by that mcb in question?!.....just like any other cct................a spur on a ring is recorded as the highest on that cct etc.

thats what i would do?!

 

[JulianC]

Yup, that makes sense. One the other hand, seems like a load of unnecessary, unconnected work testing something I'm not touching or influencing. Bloody regs....

 

[ukpablo]

i agree...................all those bloody hoops we have to jump through eh!!!

 

[Des 56]

To the letter of the guidance, the highest reading is recorded,which is probably not your addition
To the letter of reality,what I would be more interested in than a number on a certificate is whether my install was Ok

To the guidance you will be ripping the installation to bits to obtain a reading that doesn't impact on your install and is a little irrelevent
I would test what I installed