Tripping RCD - Unusual

[leolec]

Got a call out yesterday to look into a problem which has stumped me, and it seems many others before me.

Wylex 16th ed Box (installed 2005 by qualified registered spark who left good cert), 2 lighting, and door bell on main breaker together with a Hager bell transformer, shower sockets immersion, etc on 100a 30ma RCD.

When kitchen 18" fluorescent is switched "off", it regularly trips the RCD which obviously its not attached to.

The owner worries that on leaving the house and turning off the light the RCD will trip and the freezer will defrost during the day.

The lights switch is below a shower cubical, there is a socket on the opposite side of the door frame at light switch height, I've done an insulation test on the plaster work above the light switch say about 3 foot above and get 190meg and above the socket and get similar.

I started thinking about back EMF but can't figure out how anything from the fluorescent call leak across to the neutral of socket or shower or immersion circuit especially given that the RCD never goes when everything is on or if a bulb blows.

I measured trip times and the RCD seemed to react OK but don't have a ramp tester so I only suspect the RCD is OK

The only thing I can come up with is to put a bayonet fitting in the kitchen to try and move towards proving leakage out of the flurry (which others have replaced twice)

Any suggestions thoughts would be very welcome

 

[chrish_1977]

Just an obvious one, but the neutral from lights is not on the rcd side, I know it should trip when switched on but worth checking

Chris

 

[Octopus]

A temporary change of kitchen light fitting would be a sensible "start" - if the client will agree!

 

[leolec]

Thanks Chris/Murdoch, I think she'll agree they've been trying to fix it for some years now, the only reason I didn't do it yesterday was purely the fact that I can't think of how 30ma might be getting back to the RCD

 

[SPARTYKUS]

Is the socket backing onto the light switch linked somehow?

 

[MarkieSparkie]

My first step would be to wire a snubber across the switch contacts to eliminate any switching spikes.

 

[leolec]

Something like a 0.1uF 240v inline with a 100ohm @ 5w ?

 

[Octopus]

Maybe the lighting circuit is wrapped around the heating pipes and that's what's providing a route back??

 

[ackbarthestar]

Something like a 0.1uF 240v inline with a 100ohm @ 5w ?

The capacitor will need to be rated for 500V since they are rated for peak voltage and not rms Volts

 

[SPARTYKUS]

The capacitor will need to be rated for 500V since they are rated for peak voltage and not rms Volts

You're showing off now :devil2:

 

[leolec]

Thanks everyone, gonna try the snubber asap will keep you posted

 

[ackbarthestar]

You're showing off now :devil2:

I can also drive no-handed with a blind fold, available for demonstration runs on a road near you !:43:

 

[MarkieSparkie]

You could use, as I do, a integrated RC network in a single package such as Evox-Rifa PMR209MC6100M100 or PMZ2081MD6100M100J105 see link below.
http://uk.rs-online.com/web/p/rc-network-capacitors/2067881/?origin=PSF_432983|cav
Buy RC Network Capacitors Radial contact supp,100nF 100R 250Vac Evox-Rifa PMZ2081MD6100M100J105 online from RS for next day delivery.

 

[leolec]

Snubber installed over 12hrs ago wts

 

[davelerave]

i've had that problem
afaik taking out the pfc cap stops it happening

 

[davelerave]

just another idea to throw out there if the snubber didn't work
anti-nuisance trip rcd's or even try a diffferent rcd ?

[URL]http://www05.abb.com/global/scot/scot209.nsf/veritydisplay/7115a45a1e2da408c1256cbc0054f193/$file/2csc421002b0201.pdf
[/URL]

 

[baldelectrician]

Had a similar problem with an old Grundig telly- I found out the telly discharged the charge in the tube through the ariel cable.

as others have said- change the light

 

[davelerave]

hasn't it already been replaced twice?

 

[davelerave]

think my memory was back to front
seems to be switching on fluorescents with pfc caps
and switching off fluorescents without pfc caps
according to rcd handbook dec 2010 which i downloaded
and as already said arcing of contacts
so hopefully the snubber solves it

 

[leolec]

Mark/Dave Update, fitted snubber on Friday, had an email from the customer on Sunday saying all was well, fingers crossed! (I think they would normally have experienced a trip by then), haven't heard a thing since so....................

Carl