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Rcd

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Bazspark

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When visiting relatives house she mentioned RCD was tripping sometimes and would i take a look. MEM split board and had no tools so i got on chair pressed trip button and no trip, told her trip was probably faulty and would replace. Returned another day with few tools in car and replaced trip. pressed test buton and still no trip so i put rcd tester on it and all fine, checked polarity with independant earth and all fine, house is TT system and trip is 30mA feeding shower, garage and sockets. also checked house earth spike and it was fine also. didnt have a lot of time to investigate further as it was also family visit but find it hard to believe that 2 trips had faulty trip button and when i simulated trip with bypass between neutral and earth trip functioned. anyone got any thoughts:confused::confused:
 
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Mac

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  • #2
Sounds like you may have a neutral to earth fault somewhere.It could possibly be a central heating fault.Have you tested the immersion if it has one:confused:
 
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B

Bazspark

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  • #3
Sounds like you may have a neutral to earth fault somewhere.It could possibly be a central heating fault.Have you tested the immersion if it has one:confused:
I done a Continuity test on between Neutral and Earth on all circuits and all showed fine and even with circuits isolated by removing fuses the rcd refuses to trip on pressing the trip button but will trip manually:confused:.
 
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Mac

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  • #4
I done a Continuity test on between Neutral and Earth on all circuits and all showed fine and even with circuits isolated by removing fuses the rcd refuses to trip on pressing the trip button but will trip manually:confused:.
Have you tried unplugging everything in the house,appliances,electronic equipment or anything on a timer setting:confused:
 
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Bazspark

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  • #5
Have you tried unplugging everything in the house,appliances,electronic equipment or anything on a timer setting:confused:
No I only pulled cu fuses and then done continuity test on neutral and earth but I will try this next time. Diagram on RCD shows test button circuit is internal link with resistor between supply phase and load neutral and when i put my continuity tester across these terminals it tripped and RCD tester trips it but test button does not and didnt on old RCD so i am stumped for now.:confused:
 
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Mac

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  • #6
No I only pulled cu fuses and then done continuity test on neutral and earth but I will try this next time. Diagram on RCD shows test button circuit is internal link with resistor between supply phase and load neutral and when i put my continuity tester across these terminals it tripped and RCD tester trips it but test button does not and didnt on old RCD so i am stumped for now.:confused:
There is definitely something wrong in the house.Now i think back, my mate had this same problem a couple of years ago.He used to leave all his appliances on standby and there was enough earth leakage to trip the RCD,it used to happen during the night and even when he was out at work.Hope this helps?:confused:
 
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Bazspark

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  • #7
Thanks for input macca 5668 as 73 other visitors to thread are all stumped as well. Still cant understand why test buttons on two trips would not operate as polarity is correct going across trip so imbalance for test button should be no problem, also continuity test between neutral and earth should show up any problems and i done this test with cu fuses removed and then installed:confused:
 
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Spudnik

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  • #8
Did you do the continuity test between N & E disconnected from the bars?

maybe a silly question and not having much experience with MEM, but are you pressing the test button hard enough??

Seems strange that the RCD tester takes it out but not the button.
 
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Bazspark

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  • #9
Did you do the continuity test between N & E disconnected from the bars?

maybe a silly question and not having much experience with MEM, but are you pressing the test button hard enough??

Seems strange that the RCD tester takes it out but not the button.
No i just turned trip off and tested between neutral outgoing on trip and earth bar and i also checked between two neutral bars to see if if a neutral was on wrong bar but all seemed ok. i also thought that on old mem trip that because it was old that i didnt press button hard enough or maybe contact inside was not making so you can imagine my suprise when i installed new trip it also would not trip on pressing test button. I have had problems before for various reasons with jobs usually done by cowboys that i have had to follow up on and usually i am good at getting my head round problems like this but this one is baffling me. I also find that the best way to find if a problem is in wiring to do with polarity is to to run an independant earth lead from a spike outside and measure the voltage on the neutral.
 
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spark1

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  • #10
Have you measured for a voltage level at the Neutral at the RCD ?



spark1
 
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spark1

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  • #12
As its a split load are you sure the previous installer has seperated the two halve of the busbar correctly ?


spark1
 
P

pushrod

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  • #13
Faulty new RCD? - i had a duff new one the other day. Is it possible to substitute another in that you know is working.
 
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baldsparkies

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  • #14
Have you tried testing your rcd at 0 and 180 degrees of the waveform see if your getting similar tripp times on both tests along with your half full and five times. Iit may help show something adrift. You need to build a full picture. Also dont assume the new unit isnt faullty it does happen.

Don't you just love fault finding:)
 
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Bazspark

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  • #15
Checked what conductors i could see visually to make sure they were on correct busbar and all seemed ok but i will make sure next time all is correct but if neutral on wrong busbar would trip not be operating all the time. Done half test and trip would not operate and full and 5 times test were fine for times so i think next time i will diconnect load tails from trip and put rcd tester leads direct into trip and see if house is disconnected from supply is trip operating. Also replacing trips in mem boards is a pure torture as you have to dismantle half the board to get it out and i always find that when you go to put fuse holders back on busbar you find the screw is wrung, anybody else find this:confused:
 
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baldsparkies

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  • #16
Just popped home for a cuppa, anyway sounds like your only problem is with functional testing of the RCD all else is ok. (Is that right)

If so I would follow the advice of previous posts regarding changing the RCD again. As said, its not immpossible for the new unit to be faulty.

Remember the test button generates an inbalance through the coil using a line resistor, that generates an eddie current in the relays secondary winding and the generated voltage differance operates the relay, with this in mind have you checked the mains voltage under load ? Also dont forget to check your tripping times on both ends of the waveform ie 0 degrees and 180.

It doesn't sound like a low neutral to earth resistance otherwise the rcd would be nuisance tripping, or crossed neutrals at the neutral bar. That would cause tripping the moment the offending circuits were energised.
Hope this info helps
 
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Bazspark

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  • #17
I am going to change the trip again, thanks for input every one, I think my problem is myself refusing to believe two trips could be faulty and was hoping someone could give me a easy answer to save me having to change again. Will keep you all posted:)
 
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spadxiii1918

  • Thread Starter Thread Starter
  • #18
Does the MEM have a Functional earth cable?
The test button is usually a mechanical operation and shorts out as you described earlier. Could be faulty.
 
K

kung

  • Thread Starter Thread Starter
  • #19
How long has the fault been there ? did they have any work done just before it started or got a new bit of equip ? might be worth a check. All you can do is do tests/checks if all ok as said prob a faulty rcd although does sound strange that one.
Regards
Kung.
 
B

Bazspark

  • Thread Starter Thread Starter
  • #20
Does the MEM have a Functional earth cable?
The test button is usually a mechanical operation and shorts out as you described earlier. Could be faulty.
Yes the MEM trip had a functional earth cable which was properly connected to earth busbar and I have had some problems before with MEM trips which was why I thought it was the problem. The new trip I installed was a Hager and they have never given me any problems. Have not had a chance to revisit house yet but apparently New trip is not given nuisense tripping since but test button still not working. No new equipment in house and problem started about 3 months ago
 
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