Another tripping rcd.....

[polo1]

In case I've missed something- 40a mcb in an old Simplex cu feeding a standalone, plastic cu consisting of a 63a, 30ma rcd as main switch and a 40a mcb. 10mm t&e serving a 9.5 kw Mira shower via a 45a dp switch.
Random tripping of the rcd when the shower is off ( power to the switch internal to the shower, but shower not running).

Rcd ramps at 22ma, x1 & x5 results fine, Zs what you would expect with measured Zdb and length of cable. Insulation resistance 999 on all combinations and resistance of heating tank fine. All connections tight. Cable run in loft is visible, no damage.

I wasn't able to ir test N-E on remaing circuits due to not being able to isolate on this first visit (am going back when house is unoccupied) but any thoughts meantime??

 

[Had8Lives]

Could this be a dodgy neon? Either in the shower or isolator switch?

 

[Richard Burns]

Is there any water dripping /spraying inside the shower cover?

 

[polo1]

Is there any water dripping /spraying inside the shower cover?

Nope, totally dry. Ran the shower for a good 15 mns. No signs of water ingress or leak at inlet.

Interesting point about dodgy neons; shower has two neon, these are only on when the shower is actually running. The 45a switch has one neon, and the switch is typically left in the on position.

 

[Deleted member 9648]

How would a dodgy neon trip an RCD?

 

[PEG]

It could,but the reason would may be apparent, if the lids have been off.

I take it the Simplex has no RCD? What bonding is present,are the other supplied accessories in the bathroom supplied from the non-RCD DB,such as lights,immersion,etc, are there sections of pipework separated by plastic... lots of opportunities for other electrical shananagins

 

[Deleted member 93172]

Have you tested the RCD on a ramp test to prove its ok.

 

[Richard Burns]

Have you tried tapping (gently) on the side of the RCD to see if it trips as it may be just so worn that any vibration can cause a trip. 22mA on a ramp test is a bit low (passes but a bit low) so may indicate ease of switching, perhaps?

 

[polo1]

All, thanks for the responses.
Simplex board has no rcd; all other circuits off this board. Main & equipotential bonding is in place. Ramp test result in op.
Peg, all appears to be copper piping with no plastic connections/inserts.
And yes Richard, I did try tapping on the rcd - I learned that "trick" a good few years ago!

 

[Had8Lives]

How would a dodgy neon trip an RCD?

It was just a thought. I was thinking of a flickering neon causing an inbalance between live and neutral or possibly the sleeving of a neons wires having broken down and allowing shorting to earth.