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Hi Folks, so doing some testing on an installation today and when i carried out the PFC test i was getting a reading of 11A? I tested and retested and kept getting the same result! So, the installation in question is a shed that has had a split load board installed (by someone else) which is feeding several circuits. this is turn is fed from a DB in the house. the DB in the house main earth seems to be a pipe and the guys who did the install said this needed to be rectified and they were going to contact the supplier about it. So they provided a temp earth in the form of an earth rod. earth fault loop test at db = 21.7 Ohms. Im getting earth fault loop tests for all my circuits come back fine, just this PFC coming back at 11A? any ideas? re-checked my tester on my board at home and got a perfectly good reading....any ideas?
 
ok, so next questions...sorry im applying for my stroma so need to know this **** (i think). Does anyone have an easier way of working out diversity? looking in the onsite guide it seems to say that ring mains are rated at 100% and lighting circuits are rated at 66% so if the board contains only a lighting circuit and a ring main that should be 35A? (ring 100%=32A and lighting = 66% 3A)? also breaking capacity? seems to be 10kva for pretty much any kind of breaker except industrial? comments...also i may have had a few beers whilst working this....the calculations not the install ;p
 
ok, so next questions...sorry im applying for my stroma so need to know this **** (i think). Does anyone have an easier way of working out diversity? looking in the onsite guide it seems to say that ring mains are rated at 100% and lighting circuits are rated at 66% so if the board contains only a lighting circuit and a ring main that should be 35A? (ring 100%=32A and lighting = 66% 3A)? also breaking capacity? seems to be 10kva for pretty much any kind of breaker except industrial? comments...also i may have had a few beers whilst working this....the calculations not the install ;p

Diversity can be worked out any way you choose and is subject to the experience and judgement of the designer of the installation.
A good and commonly used rule of thumb for domestic type installations is a factor of 0.4 of the total of the rating of the breakers.
You can also work a more accurate from total connected loads and then applying your chosen diversity factor.

The rating of most modern domestic breakers to BS60898 will be 6kA. Older breakers such as BS3871 can be as low as 2 or 3kA.
 
I think we might all be wrong as defined in the BGB
Ipf = prospective fault current
Isc = short circuit current

BYB has deleted the Isc although this is in connection with 712.433 and refers to DC overload I think.
However, there maybe an error as the acronym 'Isc' no longer exists but a few pages back the definition does

Ah! Now I know why tel always calls me 'Prospective'.
 

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