RCD test button not tripping the RCD.

[Rednadnerb]

Hi all After working OK since it was installed a couple of months ago the RCD started tripping whenever anything was switched on. After failing to isolate the problem by disconnecting circuits we (the installer and I) realised that the RCD test button doesn't work, so after a quick dash to Screwfix we got an identical one and installed it but it's exactly the same! pressing the yellow test button does nothing. Could it be we have two faulty RCD's or is there something we're obviously missing?

[Andrew Gabriel]

Does the RCD have an earth connection? (Most don't, but a few do.) If it does, I might guess the earth connection is faulty.

[tony sayer]

In article , Rednadnerb scribeth thus

I might be wrong but you haven't got the input and output's reversed?.

Or a Neutral to Earth short?...

[Rednadnerb]

You got it, a neutral to earth short. We weren't thorough with our checks, it turned out to be a neutral wire trapped between the faceplate and the backbox. Thanks to you both.

Brendan.

[js.b1]

Do test RCD (or RCBO often).

I nearly got caught out in April 2009 when I cut through an outdoor cable. My spine is usually rough (left front quadrant spinal muscle is essentially missing on an MR scan) so I will drop anything if I sense problems. On that day I did drop some aluminium, severing a cable, the RCBO did not trip. I only knew because the cable steamed the puddle I was standing in. The RCBO would not trip by test button, it had been tested one year before and all figures were exactly in line with others & expectations).

Aside - having seen similar RCBO failures, they all ran signficantly warmer to those nearby. To the extent that a palm run along the top of the RCBO body (CU lid on) was "point hot". Terminal tightness was not an issue, nor load (unloaded).