A right head scratcher

[drew84]

Need help recently called out to a fault where the rcd would trip when iron plugged in and used for half hour to an hour into most sockets on ground floor but when plugged into 1st floor socket seemed ok
ground and 1st floor sockets are on same circuit and only happens with the iron which has been replaced
IR is ok getting around 8Meg acoss circiut and earth loop's fine

please help

 

[mister]

The RCD its self sounds iffy. have you tried swapping it?

Try a ramp test also.

 

[drew84]

thanks for that will try

 

[Kamikaze]

In general any insulation resistance reading below 50megs to earth will make a RCD trip off randomly. And below 15megs it’s almost impossible to keep it in. I’m surprised it stays in at all.

 

[andyb]

What's the problem?
1/2 hour should be plenty of time for her to do the ironing.

 

[drew84]

andyb: i think shes got nothing else to do lol Kamikaze: i've never come across that before as do alot of agricultal work and due to damp have low readings and never suffer with random tripping and the rcd stays on

 

[MarkieSparkie]

Kamikaze you're scaremongering by a factor of 1000 (you mean kohms surely) . Roughly 230V/15kohms=15mA threshold for a 30mA RCD to start tripping in normal circumstances.

 

[Deleted member 9648]

In general any insulation resistance reading below 50megs to earth will make a RCD trip off randomly. And below 15megs it’s almost impossible to keep it in. I’m surprised it stays in at all.

Generally below 0.5 megs before problems are likely.........up until a few years ago 0.5 megs was the minimum allowed.........the readings quoted by kamikaze are good and will not result in random tripping.

 

[SirKit Breaker]

I have never had a RCD tripping with IR of 8meg, some of the circuits i have put RCd's on are much lower than that, again no problems.
Wirepuller is right in what he says.

Cheers........Howard

 

[Richard]

In general any insulation resistance reading below 50megs to earth will make a RCD trip off randomly. And below 15megs it’s almost impossible to keep it in. I’m surprised it stays in at all.

It this defintly true? the reason I ask is i'v got to got and take a look at a fault for a friend and it's probibly going to come to stripping the board and megging stuff - so it's handy to know that! I'v got plently of experience installation BTW, but don't get the chance to go faulting much!

thanks

 

[telectrix]

think kamikaze just had a blonde moment. or his light sabre needs recharging

 

[telectrix]

It this defintly true? the reason I ask is i'v got to got and take a look at a fault for a friend and it's probibly going to come to stripping the board and megging stuff - so it's handy to know that! I'v got plently of experience installation BTW, but don't get the chance to go faulting much!

thanks

anything outside the house would be the first place to look.

 

[Richard]

Cheers Telectrix

 

[telectrix]

once you have eliminated everything that's plugged in, that is. had one last week. had just found a damaged cable in an outside socket which was tripping both RCD and MCB. fixed it, only to get a call the next day. tripping on the kitchen circuit ( different circuit, same RCD. ) . lady had 24 guests for lunch. was her Hostess trolley, pulled out from under the stairs, last used in 1980. element knackered.

 

[Kamikaze]

Kamikaze you're scaremongering by a factor of 1000 (you mean kohms surely) . Roughly 230V/15kohms=15mA threshold for a 30mA RCD to start tripping in normal circumstances.

Lol…no, it may have sounded like that but I was not on about earth leakage current as such. It was just a rough rule of thumb. For example if all the circuit breakers inside a distribution board are switched off and there was a pressure fault between neutral and earth (i.e. = possibly low insulation resistance below 50 Mega ohms) then it is not uncommon for the main RCD to trip off.
Anyway, only a logical approach with insulation resistance tests, completely disconnecting the ring circuit affected and unplugging/disconnecting everything from that ring will lead to the solution to this problem.