Wylex RCD's

[PhilB]

Hi, My name is Phil and I am based in Warwickshire, whilst I have many years of experience in the electrical industry I have recently come across a problem that I cannot recall seeing before. I installed some new fluorescent fittings in the local community hall and upon carrying out a Zs reading on the said lighting circuit the 30mA triple pole & neutral Wylex RCD fitted at source by another electrician (nobody at the hall recalls who it was) operates.

My meter is a Di-Log 9083P and is fully calibrated and puts 15mA through the circuit on a Zs test therefore the RCD should not operate. It also operates if I plug the 13amp plug lead into any random socket outlet and carry out the same test. Would this signify a fault within the RCD itself or am I over looking something staring me in the face?

When it does trip it cannot be reset for a bout 5 to 10 minutes even if the main isolator is switched off. Also being commercial does an RCD have to be fitted at source? There are members of the public using the hall & the kitchen at various times, most of the installation is in surface steel conduit with some of it buried into the walls. There are also various incidents of random nuisance tripping but this is very difficult to investigate as we all know.

Many thanks for any help/suggestions on this matter

 

[spark 68]

First off I would do a ramp test on the RCD itself with nothing else connected, to see at what mA it is actually tripping at, this would confirm whether or not the RCD is actually working correctly before I would start looking for further problems.

 

[Olec]

As above, ramp it, think your meters got that feature

 

[PhilB]

Many thanks for that Spark 68 & Olec. Will try that don't know why I didn't give that a thought originally.

 

[telectrix]

i would swap the RCD out. then do your Zs testing. ( it's the easiest option to prove faulty or eliminate, without starting a lengthy fault-finding exersise)

 

[jase1638]

I had a similar problem when tring to carry out RCD trip time. When carrying out the test the RCD would immediatly trip with a reading of 0 secs at both 0+180 degrees, and also when i used a socket tester the RCD would trip. the was strange as all seemed fine under normal usage i.e plugging in the kettle.

I swapped the RCD and all was good. Seems that the RCD was just a little too sensitive.

 

[Engineer54]

My initial suspicion, would be a faulty RCD device, the thing has probably never been user tested for the period it's been installed, come to that or via a EIR...

RCD devices are not the most reliable bit's of kit to provide protection as yet, (especially over periods counted in years) even though far too many electricians foolishly put almost total trust in them. Which is why they should always be considered as ''Additional'' protection on TN installations. I don't particularly like the use of a sole up front RCD, or RCD's looking at several circuits on TN systems either, far better to have RCBO's... At least you are then confining any fault to a single circuit (as it should be)

 

[PhilB]

Thanks to all that have replied. The client is seriously considering the RCBO option as an RCD at source does contavene regulations. It was fitted some years ago by another contractor. Even when I isolate the RCD completely from all other circuits and leave just one radial circuit connected and carry out a Zs test it still operates :/ Doing a ramp test it will sometimes trip immediately or sometimes at 27mA. The earthing arrangements are all in order.