Fun at the inlaws!!! Live to earth reading 0.2 m ohms??

[Oll13]

Hi all,

I left the forces to work for myself in 2007. I did my part p, (as part of a package for plumbing work for bathrooms, kitchens etc) and felt it gave me enough knowledge for what I needed.

Been wanting to do some more q's and get full status but not really justified it timewise/expense (although I really must now!)

Currently staying with the outlaws (17th century cottage - mostly rewired a couple of years ago, on a split board) As a favour I said id install a replacement power shower. Turns out plumbing needed moving also the flex needed to be extended.

Since the new shower has gone in, when its live (doesnt have to be running) the whole house trips out, usually after 20mins or an a hour or so. Of course its all my fault, it was fine before blah blah. Checked the obvious, disconnected the fused spur, no more tripping. Called trition, they sent an engineer today - no fault with the shower or the new cable running from FCU to it. £68 call out! cheers

The guy said there was a live to earth fault on the ring. I tested the IR on my Fluke and getting readings 0.2M OHMS - 0.4 M OHMS phase-earth at all sockets and the FCU for shower. Disconnected entire house appliances - used a Fluke socket tester on all sockets - all ok, readings still the same. Started plugging things back in but something will eventually trip the RCD, not necessarily the same thing, but eventually it will go 20mins/ 1 hour ish. The IR still reads 0.2 -0.4 M OHMS at all skts. So I disconnect shower at FCU and now it has stopped tripping yet the reading is still 0.2-0.4 M OHMS at each socket.

Im a bit confused where to go from here? There are quite a lot of outdoor sockets, outdoor JBs in stables, decking etc, but all are ok with Socket tester. The only other thing ive done is some painting and decorating for them and loosened skt plates etc, but ive been round and checked all them incase id nicked a wire - nope. They've also had a carpet replaced upstairs where the shower is with one new threshold fitted (kept existing grippers)........???

Sorry for the essay................. not sure how to fix this, i have a decent tester just not quite enough knowledge but im a fast learner.... and im keen to get out of here without the finger pointed at me...

Many thanks in advance

Ollie

 

[Dayo]

is the split board a dual rcd board? if yes can you move the fcu that feeds the power shower over to the other side then if the other rcd trips at least you know its not the rcd being faulty

 

[Dayo]

have you got an rcd tester? try it on half trip and see what happens.

 

[Oll13]

Yes it is a dual rcd board - I'll certainly be trying that first thing, thank you! Will post back my result............

 

[Oll13]

Ive just looked at the board, the stickers say Main Switch on one side (lighting etc) and RCD controlled circuits on the other (rings) but both switches look same?? am i being thick but are these both RCDs? Im guessing if i take them out it will become clear - trouble is there is a massive cupboard built all around it!

My Fluke is a 1652, it does do RCD Time and RCD Trip, just not quite sure on how all the settings work to get half trip......

 

[Deleted member 9648]

You are going to have to check very carefully that you have disconnected everything from the ring and then IR test.(dont forget to disconnect the Neutrals from the DB....if you are still getting a low reading start splitting the ring at various points and testing untill you can isolate the area with the low reading....try and think about how the circuit is wired and proceed in a logical fashion. You should also IR test other circuits fed by the RCD to ensure they are not a contributing factor.
One thing which springs to mind is your reading of 0.2-0.4 megs....a surge protected lead will give an IR reading of approx 0.3 megs,and these are sometimes the cause of RCD's tripping,check none are plugged in......you say the whole house trips???....that would suggest there is an RCD main switch??

 

[Johnny-G]

It sounds like a split load board with just one side RCD protected, if the 'main switch' hasn't got a test button then it's just that, a main switch and not an RCD.
If you set your Fluke to do auto RCD tests, the first 2 are 1/2 trip.

 

[Oll13]

Sorry, to clarify its just the right hand side RCD (with the rings on) that trips all the sockets out. Occassionally there is one MCB that wont go back up, but no set pattern to it. But if you try again it will usually go back up.

They do have surge protected extensions for the tv, but all has been disconnected and still the same.

Both switches look exactly the same, both have test functions?

Im going to try the RCD tests then start splitting the circuits and try and locate the gremlin. Trouble is there are spurs and rings going everywhere like spaghetti - worst ive ever seen!

Thank you for all your suggestions so far.........

 

[Oll13]

Okay done the RCD tests using my FLUKE 1652:

RCD TIME TEST; x 1/2 = 310ms and 310ms @ 180 (1VAC)
x 1 = 8.7ms and 8.1ms @ 180 (1VAC)
x 5 = 7.6ms (9VAC) and 7.4ms (4VAC)

RCD TRIP TEST @ 30ma = 18mA and 18mA @ 180

Was initially getting err4 on screen, which I believe indicates fault voltage, I hadnt unplugged all the stuff outside, done that now and its all cleared.

Any comments/ suggestions? Cheers

 

[malcolmsanford]

It should not be tripping on the 1/2 test, so if it is tripping in 310mS then it is a faulty RCD. The best way to test it is ramp test it. I think the Fluke 1652 has that capacity, I know the 1351 don't have it.

If you can't unplug everything then test the RCD at the CU. Isolate all the MCB's that is on that RCD so that there is no load and then test the RCD with the probes.

 

[Dayo]

does it trip at 1/2 test tho, i think 310 ms on these meters means it hasnt tripped it actually might show >310ms

 

[Johnny-G]

My 1652b shows >2000ms when it doesn't trip @1/2, I *think* the original displays the same range

 

[Geoffsd]

You need to reset your meter to UK data.

Go to the Fluke website and download the manual if you don't have one.

 

[SimpleSimon]

The guy said there was a live to earth fault on the ring. I tested the IR on my Fluke and getting readings 0.2M OHMS - 0.4 M OHMS phase-earth at all sockets and the FCU for shower.

Just to clarify. What is the rating of the pump? is it one that can be used on a ring or needs a dedicated supply? a tripping time of 20-60 mins could indicate an overload and the readings could be a breakdown of insulation due to overloading the ring.
Could that is.....

 

[Oll13]

Hi all, thank you so much for your help.

What a fantastic site, its good to see some comradery on here - I've missed that from forces life.....excellent forum!

Well after lots of testing I finally located a moisture ridden junction box underneath the decking at the far end of the garden! Took most the day, but got there eventually. I've isolated the spur!! from one of the internal ring mains!! that is feeding the multitude of lights and sockets on the decking and hey presto all readings back to normal......................hmmm funny how im no longer hearing 'must be the shower you fitted!!'

Just to clarify earlier points raised from previous posts:
You were correct, the RCD wasnt tripping on the 1/2 test just displaying >310ms.
And the power shower is fine to be on an FCU on the ring, doesnt need a dedicated supply as it is only 150W rating, merely spinning a small motor as opposed to an electric shower for example. Also I didnt mean I had the shower running for 20-60 mins before tripping, just simply had the supply to to unit live and it would eventually trip within 20-60mins.

All sorted for now though, so thanks again for all your help.......

See you around the forum!

Ollie