earth loop impedance reading

[who took my fluke?]

hi lads, tested an installation yesterday using a robin installation tester (had it about 2 years). testing the external earth loop i had 0.17 ohms (TNS supply) this seemed very low to me as the PSCFC will be near the 2K mark. Does anyone else agree that this is too low??

 

[plugwash]

don't worry about loop impedance being low at least on domestics its high you've got to watch out for.

The PSCC you give is still easilly within the normal ratings of domestic MCBs (6KA) and even if it was higher than that you have back up protection from the service fuse (iirc a BS1361 which is what they tend to fit has a breaking capacity of 15KA a BS88 iirc has an insanely high breaking capacity).

 

[who took my fluke?]

thank you for your quick reply plugwash, much appreciated.

 

[Adam_151]

don't worry about loop impedance being low at least on domestics its high you've got to watch out for.

The PSCC you give is still easilly within the normal ratings of domestic MCBs (6KA) and even if it was higher than that you have back up protection from the service fuse (iirc a BS1361 which is what they tend to fit has a breaking capacity of 15KA a BS88 iirc has an insanely high breaking capacity).

I thought they were normally bs88 which is breaks somewhere near 80k , think some bs1361 have something like 33k, (there are two types, 1 and 2, IIRC) with 2 being 33k, and 1 being 15k

* reads boring stuff on the iee forum too much *

 

[plugwash]

it seems to vary by region different aprkys claim different things but i think a 15KA breaking is about the lowest you will see on a service fuse.