Isolating power to mutpil CU for Ze

[Mr. Anderson]

I've just looked at a job in a residential home where I need to replace a sfcu. The circuit is on a old cu and I've noticed that the main earthing is in 6mm and has thermal damage, I've quoted to also upgrade this. My question is the cu is on a SP TN-S and has 3 cu coming direct off the supply (3 main earting conductors). It's impractical (but not impossible) to disconnect power to all consumer unit to take a Ze reading, would you guys take the Ze reading for the one consumer unit with all parallel paths from the other cu connected (not a true reading), remove the power to the other cu so you can remove the main earthing to those cu (wont take long and is safe but is going to cause problems for all at the house) or remove all parallel paths from the other cu whist keeping the power to them on (not safe)? P.S. It might just be my computer but I cant seem to drop down a line to start a new paragraph?

 

[Zebra Stripe]

Hard one to judge without being there as it were. You need to discuss it with whoever is in charge at the residential home, as you may find that you can isolate the whole install for a short period during the day.

If you cant isolate the supply to all 3 DBs, then all you can do is a Zdb at each board. Don't remove the earthing conductor from the MET while any of the boards are powered up for obvious reasons.

 

[Mr. Anderson]

Common sense prevails! Thanks>

 

[Silly Sausage]

I'm sure you need a single point of isolation for the whole installation, so if you can negotiate a short shutdown, you could get one in and get your Ze.
With the added advantage of some extra work!

 

[Zebra Stripe]

Depends what you define as an "installation". Its possible imo to say in this instance that there are 3No installations, each with their own integral main switch located within each DB. I think this is acceptable as long as each switch is labeled as such.