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

 

[telectrix]

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

leakage on circuit/s. IR test required. or get an earth leakage clamp meter on the job.

 

[morph]

hi Tel
question is realy more why the diffence in value in ramp test , AFAIK leakage would not actually alter the ramp test ( nothing being usedat time of test)
at 8 mA i am not surprised it goes. I/r test would be the obvious usual approach if not for the premature rcd

 

[spark 68]

Hi Morph,

As the 30mA RCD (if it is working correctly) can trip at anything above 15mA (1/2 Idn), this means on your ramp test tripping at 8mA the circuits have approx 7mA or more leakage already, and if this is varying it suggests either something is breaking down/dampness, or something which may not be faulty (ie. normal leakage) is pushing it over the edge.

As Tel says a leakage clamp meter would help greatly here, or an IR test on the individual circuits.

It could also be that there are too many items using this RCD with normal leakage leading to nuisance tripping.

Without either (earth leakage) clamping individual circuits or testing the IR of the individual circuits you will be playing time consuming guessing games.

 

[morph]

if i had a ELC meter i would have used it , thing is just about everything was off hence my confusion in the different ramp readings , going back to sort out the L-N reversal as they had to think about the cost ( big posh house i am sure they are skint ...not

 

[PC Electrics]

What results do you have for your IR tests.

IR test (at 250V) the heating controls esp the pump.

 

[morph]

Hi Morph,

As the 30mA RCD (if it is working correctly) can trip at anything above 15mA (1/2 Idn), this means on your ramp test tripping at 8mA the circuits have approx 7mA or more leakage already, and if this is varying it suggests either something is breaking down/dampness, or something which may not be faulty (ie. normal leakage) is pushing it over the edge.

As Tel says a leakage clamp meter would help greatly here, or an IR test on the individual circuits.

It could also be that there are too many items using this RCD with normal leakage leading to nuisance tripping.

Without either (earth leakage) clamping individual circuits or testing the IR of the individual circuits you will be playing time consuming guessing games.

this is partly the problem as they are both computor boffs and have 4 kids all on pc;s too
i can only think that while i thought most things were off in fact they were not and hence the varying ramp readings, i only had a couple of hours today so did nt dig too deep

 

[PC Electrics]

if i had a ELC meter i would have used it , thing is just about everything was off hence my confusion in the different ramp readings , going back to sort out the L-N reversal as they had to think about the cost ( big posh house i am sure they are skint ...not

You didn't adequately impress upon them just how dangerous this situation is then!

 

[morph]

You didn't adequately impress upon them just how dangerous this situation is then!

i did indeed
its been like that for 4 years and it works fine so it must be fine

 

[spark 68]

Hi morph,

What I would be doing (in the absence of a EL clamp), would be to start disconnecting (both L and N) of individual circuits one at a time, and repeating the Ramp test, to see where it improves, then IR test the suspect circuit/s, average readings on ramp tests for 30mA RCD's tend to be around the 20-25mA mark IME,

Or do as above but IR test each individual circuit to find the culprit/s.

 

[morph]

Hi morph,

What I would be doing (in the absence of a EL clamp), would be to start disconnecting (both L and N) of individual circuits one at a time, and repeating the Ramp test, to see where it improves, then IR test the suspect circuit/s, average readings on ramp tests for 30mA RCD's tend to be around the 20-25mA mark IME,

Or do as above but IR test each individual circuit to find the culprit/s.

agreed , i have now been asked to sort up stairs socket issue so i will fix that and then look at I/R
it was just the fact that with other circuits isolated and most things unplugged on down ring that the ramp was 8 and 19 at board that seemed odd
if nothing is on how does the ramp result vary so much ?

 

[PC Electrics]

Issue a danger notice.

Appliances will work fine with reverse polarity, but that does not diminish the danger. Such is the danger that modern electronically controlled boilers are designed to detect reverse polarity and will go straight into lock out, thus forcing the owner to call in expert help.

 

[netblindpaul]

It varies because the meters we have to test it can't cope with testing in this manner.

 

[spark 68]

if nothing is on how does the ramp result vary so much ?

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.

 

[morph]

It varies because the meters we have to test it can't cope with testing in this manner.

thanks for the reply , could you expand a little please