RCD Conundrum

[morph]

Comments welcome please :rolleyes2:

rcd trips once or twice a day been doing so for a couple of weeks
often trips during the night or when occupants are out


wylex 30 mA
serves four circuits
two rings
one radial socket
cooker

fairly new install 15 years
board updated 4 years ago during spruce up

ramp tested trips at 8 mA when tested at sockets in kitchen
19 mA when tested at board
cant test on up stairs sockets as they are all L-N reversal ! ( occupant admits to changing all the sockets for metal ones) will fix that tomorrow



why does the ramp test vary between test at sockets and test at board ?
( changed rcd and new one does the same)


would L-N reversal on adjacent circuit affect the rcd this way? seems it might

 

[morph]

The Cables were not isolated at the CU, so if it is a cable or JB or accessory that is breaking down, it would still allow enough leakage to affect your readings.

Don't forget that MCB's are single pole (in the UK at least) and don't in general isolate the N.

have some more time tomorrow to investigate , just did nt think the conductor insulation would have any bearing if not under load, thanks for the replies..

 

[netblindpaul]

morph,
This has been done recently, it is a function of the meter.
They are basic.
You are testing a capacitor in parallel with the RCD at the sockets, not the RCD itself.

 

[morph]

morph,
This has been done recently, it is a function of the meter.
They are basic.
You are testing a capacitor in parallel with the RCD at the sockets, not the RCD itself.

true indeed had not thought of that ,
generaly though the variance is not so significant

 

[Engineer54]

In other words the only meaningful values on a RCD test, are those taken at the CU. Tests taken at the socket outlets only basically prove the RCD is functioning, NOT the operating values of the RCD device!!!