Interesting Fault.

[securespark]

Unfortunately, I left my trusty K800i at home today.

I came across an installation today where the RCD had tripped. Interestingly, it was tripping when both ring finals attached to it were energised.

I plugged my Martindale into a socket. When the RCD was reset, all three neons glowed. When the RCD tripped, only the second two illuminated (neutral fault).

Guess what I found when I opened up the CU?

After my diagnosis, the customer swore the board had been installed 9 months prior, but I could not for the life of me see how.

 

[RF Lighting]

Did you find a copy of the daily telegraph from 1994?

Were the unused ways on the busbars from the RCD and also non RCD side touching?



<edit> to correct spelling

 

[Lectrician]

Live fed from NON RCD side, neutrals on RCD side?

 

[leeco]

live feed from rcd neutral on the non rcd side

 

[pompeygit]

Did you give him a sardonic grin???????

 

[securespark]

Well done guys! Didn't take you long: I knew it wouldn't...

No, I didn't find an old paper, but the guy telling me the fault had only just started & that the board was fitted 9 months ago did not tally...

Not only were they touching, Rob, they were sandwiched together in an MCB terminal...

So yes, Leccy, the live was from the incomer & the neutral via the RCD...

Hence the "OK" reading when the RCD was energised & the "neutral down" reading when the RCD tripped. Of course, as the live & neutrals were mixed up, as soon as you put any load on the system, out pinged the RCD.

Must've thought I was born yesterday.

 

[securespark]

Did you give him a sardonic grin???????

No... I'm very wary of using that kind of response.

We offer maintenance & breakdown services.

One of our terms & conditions is that we will not repair stuff that is wrongly installed.

I once went to a job where a customer had a "faulty switch". When I got to the job, it was a chrome 3 gang switch that had quite obviously been wired up completely wrongly. Lights were in series with other lights etc...

On top of that, they'd replaced two fittings in the kitchen & managed to b@lls that up, too.

I told her I would not repair it as it was installed incorrectly.

She insisted it had been installed 4 months prior & had only just gone wrong. She was extremely upset at my suggestion that she was lying & I ended up repairing it anyway...

So this time I told the client that, as the CU is wired at the moment, it is wrong & would exhibit the kind of faults I was witnessing.

 

[rssteve]

did you explain there was no way this could have just gone faulty? or did he say nothing was plugged into the circuits since then.

 

[pompeygit]

I had an interesting fault today please don't don't pillory for my contraventions of EAWR. Some months ago I bought a 3phase RCCB for a fiver and have wondered for some time if it was kosher. I was at a factory today with some spare time so I thought I would give it a test. There was TPN isolator on the wall which I isolated at the DB. I then wired up the rcd correctly from the live side of the isolator with the door open. Then I energised it from the DB. I pushed the test button all OK. Got my tester out to see what the trip time was. Clipped a croc on the earth inside the isolator and put the other prods on L1 and N. All ok so pushed test button. On 1x trip went up to 2000ms and no trip. Was having a brain dead day. Tried again still nothing.........then it dawned on me....I guess we all have moments like this.......

 

[securespark]

...that you had a 3ph RCCB but 1ph connections...

 

[flyingsparks]

Surely the RCCB would still have tripped if only one phase was connected instead of 3, or were you putting the test meter on the incoming side?

 

[pompeygit]

All 3 phases were connected.......yes flyingspark I put my probes on the incoming side....took me 10 mins to realise???? Doh

 

[pompeygit]

I then got a reading of 23ms!

 

[securespark]

On the incoming side???

 

[pompeygit]

SS........no on outgoing!!!!!!!! Then all ok and got 23ms. Think because it was hanging upside down I got confused(fairly easy these days) and kept testing incoming and getting no result