Didn't think was possible

[Pondy]

Ok guys, thought I would share this with you, have a call to a one bedroom flat with rcd tripping . It's the main flat ring which is the one. It's a tns system, incoming supply is pyro. 16th edition board(crabtree), lights and smoke on none rcd side,kitchen, flat, cooker and unknown circuit on rcd side. the unit is in the kitchen. The kitchen has had a new ring and cooker circuit installed I'm guessing at the same time as the board was installed.
Originally the flat had one ring and so they have though crimped in a couple of places where was in the kitchen and these are behind double blank plates. I have inspected these crimps and they are fine.
This is the part I really can't get my head around, even with all circuits off and all neutrals out and even the main neutral coming out of the rcd removed, but all earth's still in place the rcd still trips when trying the flat ring. I will be re booked to fix, the guy is using an extension lead from the kitchen for power in the bedroom and lounge. All items have been unplugged.
Coincidentally I'm not sure whether this could be related, the ze is around 3.5 ohms and the zs on the kitchen ring is around 80 ohms. The r1.r2 and rn is .13 .26 .13 respectively. I done a zs at home and it was fine, new batteries in my fluke tester., so doubt tester at fault. I haven't done any insulation resistance testing yet as time was short. Just baffled by the rcd tripping with no neutral. Your thoughts or suggestions would be most grateful.

 

[uksparks]

3.5 ohms for Ze? That's very high, is this fed straight from the meter from cutout? You will not meet disconnection times on your sockets with that.

 

[Pondy]

Yea I know the max ze for this system is 0.8ohm
. Will be contacting the supplier. I moved the kitchen ring over to the non rcd side temporary and same reading

 

[Plonker 3]

I hope you then put it back on the RCD side once you had done this?

 

[Pondy]

Yes of course. It was only temporary to make sure rcd wasn't giving me the high reading

 

[tony mc]

Ok guys, thought I would share this with you, have a call to a one bedroom flat with rcd tripping . It's the main flat ring which is the one. It's a tns system, incoming supply is pyro. 16th edition board(crabtree), lights and smoke on none rcd side,kitchen, flat, cooker and unknown circuit on rcd side. the unit is in the kitchen. The kitchen has had a new ring and cooker circuit installed I'm guessing at the same time as the board was installed.
Originally the flat had one ring and so they have though crimped in a couple of places where was in the kitchen and these are behind double blank plates. I have inspected these crimps and they are fine.
This is the part I really can't get my head around, even with all circuits off and all neutrals out and even the main neutral coming out of the rcd removed, but all earth's still in place the rcd still trips when trying the flat ring. I will be re booked to fix, the guy is using an extension lead from the kitchen for power in the bedroom and lounge. All items have been unplugged.
Coincidentally I'm not sure whether this could be related, the ze is around 3.5 ohms and the zs on the kitchen ring is around 80 ohms. The r1.r2 and rn is .13 .26 .13 respectively. I done a zs at home and it was fine, new batteries in my fluke tester., so doubt tester at fault. I haven't done any insulation resistance testing yet as time was short. Just baffled by the rcd tripping with no neutral. Your thoughts or suggestions would be most grateful.

I can't get my head around what you are saying re neutrals remove and RCD still trips when trying flat ring can you explain how you are testing !!

Are you connecting the ring only both Line & Neutral of the RFC ?

Have you tested the RCD on its own no loads to see if its faulty?

IMO a IR test of the FRC must be high on the list of testing especially when you have you test gear out !

I would not rule out any of the other ccts either!

The maths re you ZE and results just don't add up either with that 80 ohms figure !!!

 

[Engineer54]

My question is, where are you taking your Ze reading from? The flats CU or at the main incoming supply to the building??

If at the flats CU, that's known as Zdb it's basically a Zs value, and you have a problem on the sub-main supply cable between the main incoming supply and the flat.

If it's at the main incoming supply to the building then you have a ''REAL'' problem, that is not only affecting the flat you're working in but all the other flats as well. If that's the case, cease all work in this flat and call the DNO emergency hotline, which you should have done immediately you found the Ze fault in the first place!!!...

 

[Pondy]

E54, that's a very good point and one which I overlooked, annoyed at myself for not thinking about that, I was there on an emergency basis and will be going back this week. That's why I wondered whether my tester was faulty as I know it's not possible, either that or I'm doing something wrong. Just to clarify the other bit, with all neutrals out of the board and the neutral taken out the outgoing side of the rcd it still tripped on the flat ring

 

[Pondy]

E54, the first thing I will check is the ze at origin. I'll let you know

 

[Octopus]

Are you saying that you removed all the load neutrals and the RCD trips? Removing neutrals isn't likely to prove anything really IMHO