Andy Wade wrote:
On 06/11/2010 15:46, Dave Osborne wrote:

Yes, you should definitely suspect the RCD.

I've never known an RCD fail by becoming over-sensitive.

Ah, I wasn't suggesting that the RCD becomes over sensitive, rather that
is is and has always been over sensitive.

An RCD that trips at 17mA is likely to be noticeably more of a nuisance
than an RCD that trips at 27mA.

I've known a
few though that have become insensitive and failed to trip when they
should. The test button is there for a purpose...

The test button is of limited facility. There's no substitute for
testing with an RCD Tester. I've had RCD's that didn't trip on the test
button but did trip on a "proper" fault and vice versa.