Is an RCD required with 18th no socket and cables in trunking TT supply?

[ericmark]

I think there should be a RCD due to the supply if there is a power failure being TT, the electrician showed me the loop impedance reading of 0.37 ohms but since realised he tested the wrong wire, I could not believe the reading hence him showing me, the wire went in the direction of earth rod but actually went to the inverter. However both him and me at the time thought the earth rod reading was 0.37 ohms, so even with TT the 3 kW emergency supply would not need a RCD to trip.

So they fitted two double RCD type A sockets, and a FCU to supply the central heating. It is the latter I am thinking should have an RCD FCU my worry is some heating guy turning off the wrong FCU and getting a shock, there are two one next to the other, so would be an easy error.

But surface cables except for one to the thermostats, where it goes about 1 meter behind tiles, but this was the case in 2004 I think when the garage was made into a flat, however it was supplied by a split board, and the central heating boiler was supplied from the main house with no RCD, one pump from the flat CU, the other one from a 13 amp socket in the flat so at least three circuits and two independent distribution boards. But the design (If you can call it designed) was 2004 before the 17th edition.

I changed this so all now from one FCU, which was supplied from a RCBO until solar fitted. So two pumps, two motorised valve two port, two thermostats one mechanical one Nest Gen 3, and a relay should be two but second not fitted yet, plus the boiler and two distribution units and the extra low voltage supply to main house thermostat are all now from the FCU in the flat kitchen.

I assume the paperwork as yet not received I only have the compliance certificate will have the disconnection times of the two RCD sockets, to be frank never used RCD sockets so never filled in paperwork for them, and if a RCD FCU is required then also disconnect time for that, my RCD tester has failed so can't test myself, I can test tripping current with some resistors etc, but can't measure 40 mS with a stop watch.

So the installers have a 150 mile round trip to correct, so can't see them being keen to come here, so expect them to try to wriggle out of coming, fitting the FCU is easy but not sure how to isolate it, there are four isolators, two for DC, two for AC, but seem to remember them turning off one under the inverter,

it says DC switch, I assume supply to/from battery, not sure it that isolates the EPS (UPS) supply, it is clearly marked EPS supply, not what isolates it. I had expected it to come from the second CU they fitted, but it does not seem to, if it did then I would have thought they would have used a RCBO. So don't know how to isolate maybe remove the UPS plug?

So what I want is ammunition when the guy phones back so I can get it done safely for any heating guy to work on.

 

[Murdochcat]

Don’t pay the balance until you have the questions answered and the certificates is my advice

 

[ericmark]

I have a week left to change my mind and say rip it all out again. Which is not the way I want to go.

 

[plugwash]

I would not expect the supply in the case of a power failure to be TT, I'd expect it to be either IT or TN-S.

 

[JohnW2]

I would not expect the supply in the case of a power failure to be TT, I'd expect it to be either IT or TN-S.

I've been getting a bit confused by eric's references to 'power cuts'.

I suspect he's talking about 'loss of the CNE' in a TN-C-S installation, in which case the usual 'earth' is then 'lost' as well as the neutral. In that situation, the only 'earth' (if any) connected to the installation's MET will be that due to bonded extraneous-c-ps and/or an explicit earythj electrode (if there is one) - so essentially TT (or 'nothing'). A power cut would obviously not result is loss of a TN-S earth (unless the power cut were due to total severing of the supply cable, including the sheath).

Kind Regards, John