Merlin G rcd fault

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M107

Billy-the-Kid
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This one has done my head in this afternoon so appologies if it sounds gobbledygook.

2x Merlin gerin boards;

Cu 1 has 100amp main switch with looped line neutral tails into second board (cu2).

Cu 2 has 100a 30mA rcd (with a module fitted to it ? ) as the main switch.

So in effect a split load allbeit over 2 cu's

Cu1 = heating / lights/cooker

Cu2 = all socket circuits/shed submain

The problem they have is that with all mcb's on both boards energised & appliances on sso in kitchen are operating, then they turn on the oven the rcd main switch of cu2 trips.

Rcd will not reset unless any one mcb on cu2 is turned off.

tested IR on kitchen ring / cooker / office ring / utillity ring / summer room ring & all passed with flying colours.

Dissconnected oven from circuit, (oh yeh thinks I ovens goosed) flick on the kettle & rcd trips.

Isolated all other circuits apart from oven & kitchen ring, turn on oven rcd stays in? :|

Start turning on fcu's & appliances in kitchen ...... **** it....... rcd trips.

All appliances on in kitchen cooker off reset rcd & start energising other circuits rcd trips, try this as a random pattern to find the offending circuit but makes no difference. Any order the circuits are energised the rcd trips at varying times and cant pin it down to one circuit.

Anyway customer said they had visitors comming X( (why call somebody out then) this afternoon so would be ok with the problem untill I can get back & take another look (that'll be mid october at the moment).

All I can think of is an over sensitive rcd & replace it.

Failing that it's isolate all circuits pull the neutrals & then reintroduce one at a time.

I dont often get stumpped but this one has me:(

Any ideas?

I need a beer now.........my head hurts.....

 

davetheglitz

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Can only think of a couple of possibilities:-

1) Have you checked that the neutrals of each CU are isolated from each other? Bit of a long shot - but you never know!

2) N-E fault on a circuit (possibly lighting - you didn't say that you had tested IR on that). The current flowing will be split between the neutral and earth so If a low current is taken then there is not enough leakage to earth to cause a trip - but if a high current device is used the leakage current will be high enough to cause a trip. This would give a seemingly random trip which ties in with what you are describing.

Hope this helps.

Dave

 

M107

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Cheers Dave.

You are right I didnt IR any of the lighting circuits, but will do when I get back there.

Twas getting me all harrassed so quite glad when the home owner said leave it for now & come back at a later date.

 

M107

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Got the ***er pinned down today it turned out to be the kids pool heater with a neutral/earth fault.

The pool was one of these cheap things from cost-co, so might be something to keep in mind if theres a few out there.

Kept me occupied for a while.

 
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Got the ***er pinned down today it turned out to be the kids pool heater with a neutral/earth fault. The pool was one of these cheap things from cost-co, so might be something to keep in mind if theres a few out there.

Kept me occupied for a while.
Useful info m8. Sorry it gave you a headache (never mind, have one of my Guiness Drink_, but at least we all know these could be suss!!

 

M107

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Permission granted soldier carry on & smug away at will :p

 
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