Strange RCD fault any ideas?

[ebee]

Reminds me possibly of the time a customer reported "that outside socket you fitted keeps tripping the RCD!"

I was about to go on holiday so I asked a mate of mine to take a peek

On my return he told me he got a shock.

kitchen ring circuit spurred off via DP switch to external socket which he used for a pond pump.

Over 6 months customer had changed the pond pump three times, each time thinking it had solved the problem , which it did for a while then trouble started again.

He then decided to feed pump via an inside socket on the same ring via an extension lead. Problem vanished so he concluded my outside socket was to blame.

My mate on hearing all this tale, layed himself on the grass by the side of the pond and proceed to drag the pimp by it`s flex so he could reach in and examine the pump. Trouble is he had not unplugged the thing first.

I guessed it as he was telling me, he put his hand in the water whilst lying on earth and got a belt from the pondwater or pump.

The pond water in the pond liner was LIVE. the extension running the pump was only two core no earth.

the pumps were all the same make of French Pumps.

Customer changed to an alternative make and problem never returned.

I did an ins res test on his pumps whilst immersed in water and they all were well down on L to E

 

[JohnW2]

... proceed to drag the pimp by it`s flex ...

An interesting concept

Kind Regards, John

 

[ebee]

I think pimp is french for pump . LOL

 

[flyingsparks]

You're probably 'done with this' now, but I suppose it would have been interesting to try SP switching with the other ('N') contacts of the original switch, to see if those contacts were 'better' and didn't result in the problem.

Anyway, well done for having (hopefully!) sorted thye problem!

Kind Regards, John

Yes I suppose I could have tried that out of interest. To be honest I had had enough of dealing with this fault! At least (for now anyway) I have cured it! Thanks for your input John, surprised there hasn't been a few more comments from some of the other regulars on this one?!

 

[JohnW2]

You're probably 'done with this' now, but I suppose it would have been interesting to try SP switching with the other ('N') contacts of the original switch, to see if those contacts were 'better' and didn't result in the problem.

Yes I suppose I could have tried that out of interest. To be honest I had had enough of dealing with this fault! At least (for now anyway) I have cured it!

Sure, as I implied, that's what I imagined! Mind you, I suppose the better one understands what went wrong, the surer one can be that one really has cured the problem for good Assuming you've still got it, an autopsy on the switch might be interesting - there might be obvious signs of something wrong with/around the switch contacts.

Thanks for your input John, surprised there hasn't been a few more comments from some of the other regulars on this one?!

Indeed. I thought exactly the same and have been feeling rather 'lonely' - I wonder why that was?! Anyway, I hope that I was at least able to give you some 'food for thought'!

Kind Regards, John

 

[ebee]

"Sure, as I implied, that's what I imagined! Mind you, I suppose the better one understands what went wrong, the surer one can be that one really has cured the problem for good icon_smile.gif Assuming you've still got it, an autopsy on the switch might be interesting - there might be obvious signs of something wrong with/around the switch contacts."

Well said John.

That`s why I was so pleased that the article featured explained in detail my strong suspicion about the DP switch on the immersion heater circuit.
Almost confirms my thoughts - well not completely but it does suggest I may well have been correct in my reasoning. I had many doubters .

 

[flyingsparks]

Well,k I tried to take the switch apart as carefully as possible. It kind of fell to bits, but here you can see where the L contacts have been arcing. Surprised its enough to make a difference to the RCD tho!

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• flyingsparks
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[JohnW2]

Well,k I tried to take the switch apart as carefully as possible. It kind of fell to bits, but here you can see where the L contacts have been arcing. Surprised its enough to make a difference to the RCD tho!

Thanks. Interesting.

What you experienced was obviously nothing to do with DP switching (not the least because it persisted when you changed to SP switching!).

How about this as a hypothesis as to what may have happened ... L was breaking first (or L one was the only pole which ever broke, when you used SP switching), with arcing at the L contacts. Arcing can result in a current with a lot of high frequency transients ('spikes'). There will be capacitance to earth on both L and N sides of the circuit, through which those high frequency transients can leak/flow. If there is a resistive load (like your heat gun), the amount of such 'leakage' will probably be similar on both sides of the circuit, thereby not resulting in any appreciable L-N imbalance. However, if there is a significantly inductive load, there will probably be appreciably more 'leakage' on the L side (passage of high frequency components to the N side being impairedbyvthe reactance of the inductice load) - such that an L-N balance can arise, seemingly potentially enough to trip and RCD (surprising though that may be!).

All very speculative, but it's the best I can think of at present!

Kind Regards, John