insulation resistance problem

[christoff54]

hello

domestic install ir on ring >500 on p-e >500 on p-n o.oo mohms on N-E

iam I right in saying that there is a neutral to earth fault? Also ccu is new 17th twin rcd's both fail rcd test and earth loop test trips rcd on final ring.

driving me mad any ideals on finding fault

Thank

Chris

 

[WarrenG]

Seems strange that both RCD's are failing? O.K. some quickies:

• Is the supply ok?
• Are the neutrals in the correct neutral bars i.e. not crossing over?
• Meter O.K.?

I think you have an earth fault but where?

 

[slocm3105]

That reading you are getting is definitely a N-E fault. A couple of questions:

Did you install the new 17th edition CU?

If yes, check things mentioned from above post, but, prob wrongly wired installation. It is quite common that N and E are wired wrong ways round. I don't know how they manage it, but i come across it very often.

So,

1. disconnect at board and go to furthest point in house from board and split at the socket outlet.
2. IR Test each of the newly formed radials seperately,
3. On the faulty radial go to half way point between the sockets and split again testing each half of the split circuit.
4. Basically carry on this process until you have found the culprit.

Once found, if it is a leg of cable then disconnect tht length and leave the split ring main as 2 radials and put on seperate 20A breakers in the CU otherwise, correctly terminate and away you go .

And of course re-test the rcd's.

Hope this helped




Matt

 

[mrloy99]

hello

domestic install ir on ring >500 on p-e >500 on p-n o.oo mohms on N-E

iam I right in saying that there is a neutral to earth fault? Also ccu is new 17th twin rcd's both fail rcd test and earth loop test trips rcd on final ring.

driving me mad any ideals on finding fault

Thank

Chris

You will probably find that a "cut" 3.5mm socket screw has penatrated the neutral at one of the sockets.I'd check the kitchen first as maybe a tiler
has screwed up the sockets and not checked that he wasn't trapping any wires.As for your loop test tripping the rcd,I find that loads of times even on the D-log setting.A pain in the arse,but you might have to bridge out for the duration of test.You should find your fault first though.At least one of your rcds sound faulty,ie with a N-E fault your rcd SHOULD be tripping rcd all the time

 

[christoff54]

this is what bugs me both rcds stay on, there not tripping and the not on rdc test auto (function on my tester).

still iam going back there this week so I'll let you know how i get on

 

[Spudnik]

hello

domestic install ir on ring >500 on p-e >500 on p-n o.oo mohms on N-E

iam I right in saying that there is a neutral to earth fault? Also ccu is new 17th twin rcd's both fail rcd test and earth loop test trips rcd on final ring.

driving me mad any ideals on finding fault

Thank

Chris

To be honest, from what you are describing i would say that its a possible borrowed neutral somewhere in the installation.

 

[mrloy99]

hello

domestic install ir on ring >500 on p-e >500 on p-n o.oo mohms on N-E

iam I right in saying that there is a neutral to earth fault? Also ccu is new 17th twin rcd's both fail rcd test and earth loop test trips rcd on final ring.

driving me mad any ideals on finding fault

Thank

Chris

maybe a very daft question but are you physicly removing all cables from their terminals on your suspect circuit while doing the test?You should also ensure that no appliance are plugged in.Are you still getting short circuit between N/E using continuity scale or just on meg ohms?

 

[Tiger]

i would say there is something hiding somewhere that isn't unplugged , fused spur somewhere?

 

[Spudnik]

i would say there is something hiding somewhere that isn't unplugged , fused spur somewhere?

You still shouldn't have a N/E fault, unless it is in something that is till plugged in or connected.

 

[WarrenG]

this is what bugs me both rcds stay on, there not tripping and the not on rdc test auto (function on my tester).

still iam going back there this week so I'll let you know how i get on

Have you actually checked to see if the RCD's will trip on a functional test i.e. the RCD test button?

 

[Tiger]

You still shouldn't have a N/E fault, unless it is in something that is till plugged in or connected.

is that not what i said ???

 

[dannybruff]

Asuming you have disconnected the N & E at the board and are testing there and not at the socket it could be either a borrowed neutral OR earth from another circuit, therefore the low ohms will be the reading back to the board off the neutral/earth of the shared circuit and to the supply. Asuming its a TNC-S system. Turn main switch off to diagnose this. OR, If theres still low ohms reading, you've probs got either a damaged circuit or the work and expertise of a non electrician.

 

[christoff54]

Hi guys

thanks for your help everyone.

but I found the fault.

 

[m4tty]

what was it then ????

 

[claire_r]

hehehe read through all that....racking me brains as everyone else trying to think what it could be....as i have had this fault before....and then....anti climax...no answer to what it was in the end hehehe !