Possible Appliance fault tripping RCD

[AJshep]

Just come back from an interesting fault.
Typical RCD tripping randomly. The customer was not using anything in particular, at any time.

Anyway I carried out Insulation Resistance on every circuit, each circuit was above 200M L-E and N-E and the
RCD tests were good.
The place was rewired in 2010 by a Domestic installer who did quite a nice neat job !!
I also removed the cover of the boiler to check for moisture and also carried out Insulation Resistance tests at 250v between L-E and N-E the readings were above 1M

Went round the kitchen carring out Insulation Resistance tests between L-E and N-E (only 250v just incase ) on the plugs for the Toaster, Fridge, washing machine etc.
Everything was above 200M

I'm the second spark to look at this and was just about to leave with my tail between my legs when the elderly customer mentioned that the last time it went she was talking to a friend on her laptop.

The laptop has recently been moved from upstairs to downstairs and is plugged in to a socket constantly turnned on and charging all the time because the plug is a little hard to get to.

So I got my test kit out and tested the IEC type lead that plugs into the Power supply

L-E 0.17 Mohm
N-E 0.26 Mohm
Obviously not good, and ive told the customer to get a new one, and not constantly charge her computer.

it's been disconnected all day because another member of the family went round earlier to unplug stuff to see if they could help. Has anyone ever had this before ?

I'm thinking as the lead gets warmer the fault gets worse causing the RCD to trip.

 

[buzzlightyear]

if the say you did a test on the appliance was it pat tested and failed .
. most appliances if faulty will trip the RCD.

 

[AJshep]

The appliance wasn't or has never previously been PAT tested as such, I just used my Insulation Resistance tester on the plugtop one clip on the Earth the other on the L or N pin.

Yeah I know most things would just trip the RCD but using ohms law 0.17M still isn't quite enough to trip a 30mA RCD.

That's the annoying thing

 

[Richard Burns]

I often find that the readings measured (normally on circuits) are higher than would be necessary to trip an RCD but the RCD still trips!
Cheap IEC leads often have poor connections but at the sort of reading you are getting I would suspect the lead got wet at some point, it does not seem to be a near copper to copper contact, possibly if water is inside the cable sheath the slight warmth of running will allow it to migrate to the terminals.
However this is all supposition and changing an IEC lead is much easier than defining the fault, if it works, then problem solved.
(What a bad approach to testing).

 

[buzzlightyear]

I had one the other day customer saying she had a tingling every time
she use the dish washer, opened the sink cupboard up ,holly f88k ,the appliance engineer put a moulded plug on a extension lead .and the washing liquid all over the plug and the extension lead ,the customer said he could not put the moulded plug in the socket under sink .
fixed the under the sink .
got a call same customer ,the dishwasher having tingling off it .
pat tested it . failed the pat test .told her, she said it worked .yeah .
blaming me for F.F faulty dish washer . I could have put her head in the F.F dish washer .pratt

 

[AJshep]

That's how I've left it with the customer, the customer is happy but it's always satisfying to have a clear cut answer !

the lead is an original but I assume the conductors are pretty small, I can't find a pic of the lead to show everyone but it's like an IEC lead, the comnection end is more rounded though a bit like a 3 leave clover !

 

[Fitzy]

Damage to laptop charger cables like this is very common, because people regularly wind the cables around the charger block very tightly and this eventually damages the flex cable, another common fault is the laptop charging pin/socket on either the laptop or the lead gets damaged causing a short circuit.

 

[stevethesparks]

One problem I 've had twice in the last year was an older type digital TV causing RCD trips. It ended up being the aerial somehow causing a return loop that was the cause.

 

[westward10]

I have never had an IEC lead fail an IR test no matter how much it has been deformed, earth continuity yes with Chinese imports. As in #4 I could only put it down to water ingress.

 

[Octopus]

What's the background leakage across the property?

 

[AJshep]

What's the background leakage across the property?

Well intailly i would have said pretty low !
I got readings of greater than 200M on all of the circuits.
However when I carried my Insulation Resistance tests I had everything unplugged, it was only once I had confirmed that circuits were clear that I started looking into appliances.

I'm always a bit dubious of carrying our IR tests on appliances that's why I step my meter down 250v and only Test between the Lives and Earth.

My initial thought was the boiler as it was one of the things that would be running all the time when I carried out An IR test on the boiler itself (250v on Lives -Earth) I got around 1.07M ohm so I suppose theres two resistances I should parallel up, then when you factor in other equipment that I did not test the background leakage could infact be the tipping factor.

 

[Octopus]

^^ you lost me ......

IR tests are irrelevant

Have you got an. Earth clamp meter?

 

[AJshep]

Sorry Murdoch,
I completely misunderstood !
Yes I have however I had no access to it at the time (saturday) as its locked up at work.
Just had my hand tools and my MF testkit.

That would have given a nice starting point !

 

[Octopus]

My first test in such visits is the full RCD tests, followed by getting the earth clamp metre out.

IR tests then follow

 

[AJshep]

I can see the logic of that. I expect that saves a bit of time. If I'm honest it wasn't something that initially sprung to mind.

Im going to have to buy a new one anyway, In a couple of weeks.
What's the scale on yours ? think the one at work lowest is 200mA