EICR today

Evans Electric · Sep 14, 2016

We had the kitchen ring with high trip time for the RCBO the rest of the place was fine .

Trip time was 300mS , plus the tester dithered slightly , the two LED lights flicker, go dim then it trips.

Tried a second RCD tester ( Yes we are two tester firm) That flashed up reading of 7 which immediately faded , followed by "ERROR 5 " :C

Thinking its a faulty RCBO I swap with the next breaker but the same occurs, so wiring fault .

Readings were R1 = .22 / Rn = .38 / R2 = .43 / R1 + R2 = .69 Zs .3

We started checking ( not being paid for that) but there was a socket behind a built in fridge , for the fridge, old dear wouldn't let us remove the fridge ....." I should get the kitchen fitters back they will know how to remove it ." ( Two screws) Then didn't really want us to return to sort it so what do you do?

There,s something wrong somewhere but we've had to leave it .

The other trip times were :-

12

12

9

12

12

8

300

7.8

:C

Andy™ · Sep 14, 2016

did you try testing it with the probes on the RCBO and / or with the circuit disconnected?

ProDave · Sep 14, 2016

What were the IR tests?

If the customer won't allow you to investigate a fault, then you can only note the fault on the EICR and code it.

I always prefer to try and find faults and would prefer to fix a simple fault and give it a satisfactory than have to code it and quote for remedial work, but if the customer does not want you to do that, then you can't force them.

Was the occupier, the "customer" or is she the tenant?

Rob_the_rich · Sep 14, 2016

could be an N-E fault on the kitchen circuit. Found this quoted on the iet site from an etci blog

Neutral to Earth Fault
Under no circumstances should a connection be made between neutral and protective
earth downstream of the origin of the installation. If such a connection was made,
intentionally or accidentally, it would seriously compromise the safety of the installation
and undermine the level of protection provided by an RCD installed upstream of this
fault condition. If the Neutral becomes inadvertently shorted to earth on the load side of
the RCD (neutral to earth fault condition) due possibly to miswiring or insulation
breakdown, two problems will arise.
i) An effective loop or short circuit will be created between the neutral conductor
and the earth return path. This short will act as a load on the current transformer
in the RCD and cause the RCD trip point to rise, effectively desensitising the
RCD.
ii) The earth fault current will divide between two paths, part of the fault current
returning to the supply via the earth return path and part of the fault current
returning via the Neutral due to the neutral to earth fault. Thus the residual
current seen by the RCD will be less than the total earth fault current.

If your second tester is a Fluke mft, I think error 5 is neutral fault (missing?), not sure.

ProDave · Sep 14, 2016

Rob van you explain that.

In the event of a N-E fault, part of the return current will flow via N and part via E. so there will be an imballance between L and N and the RCD will trip. I have not seen any N-E fault that results in the rcd not working, I have only seen N-E faults as the reason for the rcd tripping (and doin it's job)

leesparkykent · Sep 14, 2016

I've seen neutral earth faults that stop the RCD from working correctly and also stop the test button from working. Ideally it should of been tested with the load disconnected as something plugged in could cause noise or if there is a capacitor or something of the likes could produce readings that are not acceptable and you might have a healthy RCD/RCBO. I cant remember the manufacturers of the top of my head (might be MEM) but you have to attach a fly lead to the RCBO for testing.........I couldn't tell you why though. RCD's/RCBO's can act in a strange way sometimes.

kerching · Sep 14, 2016

Had similar.........it was the CH prog buried in back of a cupboard

turned DP,switched spur off.....all back to normal!

just saying

ProDave · Sep 14, 2016

They say every day is a learning day, but I just can't understand the mechanics of how a N-E fault can do anything other than imballance the L/N currents and trip the rcd.

Evans Electric · Sep 14, 2016

Andy™ said:
did you try testing it with the probes on the RCBO and / or with the circuit disconnected?

Yes Andy , while the circuit was in the adjacent breaker , tested the suspect breaker @ 20mS So being an 80 yr old lady we thought we'd give it an hour , see if we can find it , but she would'd let us take the fridge out for a start . When we said the socket shouldn't really be behind the fridge it was ..." Oooooh is it dangerous ...oooh dear the kitchen men did that ooooh I am worried now"

So we had to back pedal a bit . TBH

ProDave · Sep 14, 2016

Ah, so it's a new kitchen. I think you know where to look for the fault then.

Rob_the_rich · Sep 14, 2016

ProDave said:
They say every day is a learning day, but I just can't understand the mechanics of how a N-E fault can do anything other than imballance the L/N currents and trip the rcd.

I will try

say the fault is between the rcd and the testing point. The tester "diverts" some current from the line to the cpc, this cpc current then meets the neutral at the fault and some of the current flows down the neutral (less resistance, larger csa), so less imbalance.

leesparkykent · Sep 14, 2016

Evans Electric said:
Yes Andy , while the circuit was in the adjacent breaker , tested the suspect breaker @ 20mS So being an 80 yr old lady we thought we'd give it an hour , see if we can find it , but she would'd let us take the fridge out for a start . When we said the socket shouldn't really be behind the fridge it was ..." Oooooh is it dangerous ...oooh dear the kitchen men did that ooooh I am worried now"

So we had to back pedal a bit . TBH

So it tripped at 20ms when the load was disconnected?

Evans Electric · Sep 14, 2016

Rob_the_rich said:
could be an N-E fault on the kitchen circuit. Found this quoted on the iet site from an etci blog

If your second tester is a Fluke mft, I think error 5 is neutral fault (missing?), not sure.

Not a Fluke Rob ....all my testers are fairly old seperates , so RCD is a Megger . I won't be buying any new stuff these days.

ProDave said:
Ah, so it's a new kitchen. I think you know where to look for the fault then.

3 years old apparently .

Rob_the_rich · Sep 14, 2016

There is something going on with the neutral, as the Rn value is significantly higher than R1

Evans Electric · Sep 14, 2016

leesparkykent said:
So it tripped at 20ms when the load was disconnected?

Yes Lee.

Sharpend · Sep 14, 2016

This is a combination of a loose connection on the neutral and a squashed core in a back box, don't ask me to explain it but I have come across it before, had to pull every front and checked terminals one loose, tested fault had disappeared.

leesparkykent · Sep 14, 2016

Evans Electric said:
Yes Lee.

RCBO sounds fine to me. 20ms is the result you should record on the schedule of test results. As Rob the rich has pointed out there looks like a loose connection on the neutral or trapped insulation as the r1 and rn readings should be within 0.05 of each other.

ProDave · Sep 14, 2016

Rob_the_rich said:
I will try say the fault is between the rcd and the testing point. The tester "diverts" some current from the line to the cpc, this cpc current then meets the neutral at the fault and some of the current flows down the neutral (less resistance, larger csa), so less imbalance.

Okay, I can see that as a reason why testing in one particular place might not trip the RCD.

but the fact remains, any N-E fault will result in part of the normal load current going directly to E rather than N, so there will be an imballance, so why does the rcd not trip when a load is turned on?

Rob_the_rich · Sep 14, 2016

ProDave said:
Okay, I can see that as a reason why testing in one particular place might not trip the RCD.

but the fact remains, any N-E fault will result in part of the normal load current going directly to E rather than N, so there will be an imballance, so why does the rcd not trip when a load is turned on?

It is, or should be, a ring circuit, so if you plug the tester anywhere in the ring, some of the cpc current will be going down the neutral, as above, wherever the fault is in the ring. At x1 rated current of rcd, instead of 30mA going down the cpc, some will divert to the neutral, so the rcd sees maybe 15mA, enough not to trip.

Depending on the load the same thing happens, where high protective conductor currents occur, the rcd might not see any imbalance.

binky · Sep 14, 2016

so you are effectively saying a fault could be effectively by passing the cpc by using the neutral instead. I see your point.

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