HI everyone
Hope you've had a good week. Had a call from a client at the end of today. For the last 6 weeks (not sure why he left it so long to call) the RCD for his tenants property has been tripping while the builders are working on the ground floor flat (GFF). The set up is a bit odd. Converted to flats probably in the 80's. Main head has 2 x 60A fuses and is TNCS. Each flat has its own switched isolator, then 16mm T and E to the respective CU's. The GFF still has a 60A rewardable fuse in the isolator. The first floor flat (FFF) switched isolator (my clients) has been 'upgraded' to a 100mA time delay RCD and switch, presumably someone thought this would give protection to the buried supply cable. This is what is now tripping. Both boards now have RCBO's. Before the recent building work, the ground floor one didn't.
The builders apparently turn off the main switch of the GFF CU each night and at the weekend. When it's off, the 100mA RCD doesn't trip. Neither my client nor his tenants have witnessed the tripping, but have come home after work to find it's tripped OR that there has been a power loss (eg clocks need resetting) so the builder must be resetting it. Builder seems to think the issue is EITHER loss of power from the street (in which case he'd loose power as well, but he's not reported it) or that the tenants hairdryers are causing the 100mA RCD to trip but only after they've gone to work! Hmm. He's not said explicitly that he's rest the RCD but he must have (unless its a special self resetting one that I don't know about)
I just popped in to run some quick tests. Neither 16mm T and E supply cable is damaged. Ze is within limits, I loop tested 1 socket in the ground floor flat and it was fine so I assume polarity to the GFF CU is OK. All RCD's tripping within required times. I didn't have my megger with me, so couldn't ramp test.
Since the issues have only started since the builders started work and all was fine and dandy before, it MUST be something the builders have done that's now creating the fault? I tested the installation about a year ago and there was a previous test cert from 2010.
I'm a bit stumped and would welcome any thoughts on where to go next. I did suggest getting UKPN out to check the supply, is it worth this?
many thanks
BB
