RCD spur nuisance tripping.

[John B]

Hi all,

Any ideas on this one greatly appreciated.

Powerbreaker rcd spur supplying manrose LV extractor fan and ADS 28watt 2D Ip65 bulkhead in wetroom trips ocasionally for no apparent reason.
All wiring to wetroom is new, supplied from rcd spur and does not feed any other circuits in the house. The rcd spur is supplied from the house lighting circuit, 60898 B 6A mcb with no rcd protection at source. (obsolete senate consumer unit).
TNS system, R1R2 is 0.85 ohms, Zs is 1.47 ohms, insulation resistance is 150 mega ohms + on L, N and cpc and rcd tripping time is 50 and 25ms respectively.
Light fitting, rcd spur and timed extractor fan lv unit all changed for new but fault still exists.
Greatly appreciate any ideas to resolve the issue as have just about run out of ideas myself.

Thanks

 

[truckster]

As it's a wet room I would suspect moisture ingress but a standing leakage current on the cpc could be causing a problem when other stuff in the house is switching.

 

[John B]

Thanks truckster but everything bone dry and Ip65 rated.

 

[mickys86]

Is there nothing else being supplied by the RCD that could be affected by moisture?

Does the light have a switch?

 

[Electro-tech]

Obviously you tested at X 1/2 the RCD rating,without being rude. Could it be a faulty RCD Spur, ie; is it staying latched in a power cut.

 

[John B]

nothing other than the wet room light, light switch and lv fan is supplied by the rcd, the light switch is outside the room and the timed lv control pack in the loft.

 

[John B]

yes tested at X1/2 and no trip, changed rcd spur just in case it had an intermittent fault but problem still exists. Also e-mailed powerbreaker technical helpline but surprise, surprise they have not replied and phone line appears to be on permanent voicemail.

 

[pushrod]

Have you done a ramp test on the rcd? What has not been replaced on the circuit? I would get the customer to keep a log of when the rcd trips in relation to how long fan has been on before tripping, time of day and when shower(?) has been last used re humidity/condensation to see if that can shed any light.

As it's a wet room I would suspect moisture ingress but a standing leakage current on the cpc could be causing a problem when other stuff in the house is switching.

Hi truckster- what is your line of thought there? - there is an effective earth to the house and the rcd will be working on current balance between L and N on just the spur?

 

[truckster]

I believe that a standing current on the cpc from anywhere in the house can affect the rcd, same as some rcd spurs won't set if there is no effective cpc. If something is switching and either leaking or sending out a dc pulse into the cpc that may affect it. The tranny for the fan may produce a dc pulse but equally anything in the house could also be contributing. I think as a first measure I would change the make of RCD as they do vary. I use Windsor.

As great as they are, RCD's are a PITA when they misbehave.

 

[pushrod]

Cheers truckster - no expert on this by any means so could be talking out of my bum but thought it was rcbos with there functional earth lead that would be more sensitive to other earth faults than an rcd. Will do a bit of reading later and see if i can find anything

Edit :john B - i assume this is an elv fan unit (12V) you are talking about with a timer built into a transformer?

 

[John B]

Thanks pushrod and trukster, yes its an elv fan unit, not ramp tested the rcd spur as its been changed and only thing that has not been changed is the fan unit itself which is dc and isolated from ac side and not earthed.

 

[mickys86]

I know it seems a silly answer. (but all technical stuff has failed LOL)

Are all the fittings done up correctly?? Is there any chance that the ip rating could have been lowered by anything? Fixings or even the rubber seal missing??

Good luck!

 

[pushrod]

Have done a little research and it seems that many rcbos use a functional earth to get a few extra features such as tripping if the supply voltages drops below 50V and monitoring the neutral to earth. Most ordinary rcd works completely independent of the earth and so don't do this, but there are a few types that can do this as well. Maybe yours is one of them, might be worth trying to retrieve the specification leaflet from the bin .

If you have an earth leakage clamp meter i would stick it over the tails (or earth) and see if there are earth leakage problems with the rest of the installation. If there is - it's probs worth trying a different make of rcd to use. If you haven't got an ELCM and haven't got the spec of the present rcd might be worth swapping over to a different type anyway and keeping that for another job