Any idea please...

[sythai]

Evening All

Had bit of a strange experience last thing today. Wonder if anybody could advise please.

Apprentice working upstairs changing a light (loop in/ 3 plate) circuit isolated at MCB. At the same time I was putting cover back on CU, so for additional isolation ( just in case I knocked the MCB on) I tripped the RCD.

As the RCD tripped he got a belt?

Circuit tested out fine, polarity, Zs, IR all acceptable. New Hager RCD all good within limits.

Have I missed something obvious.

Many Thanks

Sy

 

[Darkwood]

Inductive loads ??? you switch off the power you create a back emf with nowhere to go until your mate bridges to earth at the right timing... a good tickle could be had in theory...well my guess anyway.

Capacitors in the circuit also as you have isolated the mains they can't dissipate as quickly and waits till you bud becomes the next capacitor in the circuit...

 

[Marvo]

Possibly a run capacitor discharging from a CSR motor like a fridge compressor for example, this is one of the problems with isolating both poles simultaneously.

 

[Darkwood]

Dam Marvo just added same thing before i saw your post....

 

[sythai]

Thanks chaps for your help :icon14::icon14:

 

[Marvo]

Dam Marvo just added same thing before i saw your post....

No probs, we can share the credit

This phenomenon wouldn't be unusual and it's more than likely a combination of things creating a potential, there's very little you can do about it, it's one of those things that experience teaches you to be aware of.

 

[Darkwood]

Well at least Sythia has found a use for his apprentice .. he probably saved himself getting a good tickle lol.

 

[sythai]

Did make me laugh though.

The little menace gave me a belt the other week, turned off wrong MCB and I really blew my top on him. So we're 1-1 now.

Seriously many thanks and something to be aware of in future.

 

[Darkwood]

Did make me laugh though.

The little menace gave me a belt the other week, turned off wrong MCB and I really blew my top on him. So we're 1-1 now.

Seriously many thanks and something to be aware of in future.

Hope he turned around after getting the wrong mcb and relayed the safe testing procedure... he'd have been 2-1 up if he had ...tut tut lol :lol:

 

[moospark]

Did make me laugh though.

The little menace gave me a belt the other week, turned off wrong MCB and I really blew my top on him. So we're 1-1 now.

Seriously many thanks and something to be aware of in future.

I would never take anybodys word as gospel that the circuit was dead. Then stick me fingers in.

 

[Darkwood]

It just reminds me.. if you could see half the cock-ups my apprentices have made over the yrs then its just common sense not to trust their abilities to get things right lol... i'd never trust any of mine and do recall a number of occasions when they have got the wrong breaker.

 

[telectrix]

might be that when you press the test button on the RCD, the line is briefly connnected to E through the fault resistor, so he'd get a tingle from the cpc atr the light.

 

[D Skelton]

might be that when you press the test button on the RCD, the line is briefly connnected to E through the fault resistor, so he'd get a tingle from the cpc atr the light.

That was my thinking too

 

[Engineer54]

It's good to hear that we have some members here, that are training Apprentices!! At the end of the day, they will go out into the real world remembering all those little tickles and know the reasons behind them too!! lol!! Another aspect of gaining experience under the umbrella of qualified and knowledgeable mentors!!

 

[sythai]

Appreciated Eng54..... One of the best decision I've made taking him on, he ticks all the boxes (99% of them anyway) so really dont mind spending the extra time with training so he can hopefully evolve and become part of the business longterm.

Was able to explain today the possible reasoning behind his little buzz, so we both learnt something new there :yesnod: