RCBO keeps tripping without reason
- Thread starter pads69
- Start date
Sponsored Links
It does if you have a resistance fault!
A neutral-earth fault could do that... the current which flows through the fault need not have come from the circuit in question. I know that seems a strange answer at first, but it becomes apparent why if you draw out the fault path
Sponsored Links
OK some observations and test results.
Observations -
during the evening last night the RCBO kept tripping with nothing plugged in (or DP off)
but during the night, I put the boiler on and wife put the dishwasher on - but the RCBO stayed on all night!!!
Tests
1 - the ring is complete (both L & N) - zero ohms.
2 - neither L nor N connect to any other circuit on the CU
3 - L-E, and N-E, and L-N all measure 38M for the ring.
4 - connected L&N across all the CU and the measure 34M between LN-E.
The max age of the wiring in the house is about 28 years
Observations -
during the evening last night the RCBO kept tripping with nothing plugged in (or DP off)
but during the night, I put the boiler on and wife put the dishwasher on - but the RCBO stayed on all night!!!
Tests
1 - the ring is complete (both L & N) - zero ohms.
2 - neither L nor N connect to any other circuit on the CU
3 - L-E, and N-E, and L-N all measure 38M for the ring.
4 - connected L&N across all the CU and the measure 34M between LN-E.
The max age of the wiring in the house is about 28 years
Your insulation test results...... taken with a proper insulation tester @ 500V or with a multimeter on 'ohms' range?
Tracing obscure reasons for RCD and RCBO tripping requires careful examination of insulation resistance between ALL conductors and ground / earth. This requires disconnection of both Live and Neutral at the consumer unit before insulation resistance tests are carried out.
The fault shown is a dead short. In reality a resistive fault will also cause a trip as will capacitive faults.
Almost all insulation resistance testing is performed with a DC test voltage. This will find resistive leakage paths but will not find leakage paths involving capacitive effects which the RCD will find and react to by tripping.
The fault shown is a dead short. In reality a resistive fault will also cause a trip as will capacitive faults.
Almost all insulation resistance testing is performed with a DC test voltage. This will find resistive leakage paths but will not find leakage paths involving capacitive effects which the RCD will find and react to by tripping.
True, but we know what he means. Presumably he doesn't have a means of measuring very low resistances. In fact, he seems to have undertaken a true 'continuity test'Not possible.
I imagine he means 'after the L & N of the circuit in question have been disconnected from the CU - i.e. there are no cross-connections with any other circuit.
Does seem a bit surprising. I wonder what is the highest resistance his IR tester can display?
Again odd, particularly given his results in (3) above. Again, I wonder what is the highest resistance his IR tester can display.
Kind Regards, John
As he has an IR tester I assumed it would take low ohms measurement.True, but we know what he means. Presumably he doesn't have a means of measuring very low resistances. In fact, he seems to have undertaken a true 'continuity test'
Possibly or even probably but, pedantically, not what was said and how can he be certain.I imagine he means 'after the L & N of the circuit in question have been disconnected from the CU - i.e. there are no cross-connections with any other circuit.
It won't be 38.Does seem a bit surprising. I wonder what is the highest resistance his IR tester can display?
More than 34.Again odd, particularly given his results in (3) above. Again, I wonder what is the highest resistance his IR tester can display.
I didn't think that (m)any 'standalone' IR tests had such a facility?
True - but do you mean "how can we be certain" ?
One wouldn't think so, but identical answers for L-N, L-E and N-E would seem very improbable!
Well, we know it's at least 38MΩ! My point was that if the true IR of three results for individual pairs of conductors which were displayed as 38M were actually >38MΩ, then 34MΩ for L+N/E would be a little more credible.More than 34.
Whatever, I think we are agreed that the figures are rather odd!
Kind Regards, John
Oh. I thought they all did. I may be wrong.
No. I meant, whilst looking for a fault, how can he be certain.
Quite possible. Copper superconducts at 0 Kelvin and the OP does say that the boiler is on the faulty circuit. I believe Copper Oxides exhibit superconductivity at higher temperatures, so older cables would help.
Thanks John for making mostly correct assumptions
1) - yes - continuity round the ring.
2) - yes - L&N disconnected from CU - then checked for cross-connections
3) - see below
4) - see below.
My meter has ranges from 20m >> zero ohms (multi-meter)
My insulation tester goes up to 2000M
After the first set of tests, I discovered the burglar alarm was still plugged in !!
So re-tested and checked insulation for each circuit individually disconnecting from CU as tested.
Fuse--------Circuit--------------- LN------------NE------------LE
1 -----------Shower ----------- >2000 ------- >2000 ------ >2000
2 -----------1st Fl Light ------- >2000 -------- 134 --------->2000
3------------Gnd Light -------- >2000 -------- 149 --------->2000
4 -----------Base Light -------- >2000 ------- >2000 ------>2000
5 -----------1st Fl Ring --------- 1600 --------- 780 ----------1200
6 -----------Gnd Ring ------------ 390 ---------- 34 ----------- 420
7 -----------Base Ring ---------- 1170 ---------1100 -------- 1000
8 -----------Cooker ----------- >2000 ------- >2000 ------>2000
9 -----------Freezer ----------- >2000 ------- >2000 ------>2000
10 ----------Frid/Freezer ------ >2000 ------- >2000 ------>2000
......All in M ohms
yes - I have swapped the RCBOs for gnd and 1st Floor - always gnd floor which trips.
The results above indicate the Gnd floor 'NE' is suspect - but cannot see anything. By the way all wiring is exposed in basement so didn't have to lift floor boards to visually inspect.
1) - yes - continuity round the ring.
2) - yes - L&N disconnected from CU - then checked for cross-connections
3) - see below
4) - see below.
My meter has ranges from 20m >> zero ohms (multi-meter)
My insulation tester goes up to 2000M
After the first set of tests, I discovered the burglar alarm was still plugged in !!
So re-tested and checked insulation for each circuit individually disconnecting from CU as tested.
Fuse--------Circuit--------------- LN------------NE------------LE
1 -----------Shower ----------- >2000 ------- >2000 ------ >2000
2 -----------1st Fl Light ------- >2000 -------- 134 --------->2000
3------------Gnd Light -------- >2000 -------- 149 --------->2000
4 -----------Base Light -------- >2000 ------- >2000 ------>2000
5 -----------1st Fl Ring --------- 1600 --------- 780 ----------1200
6 -----------Gnd Ring ------------ 390 ---------- 34 ----------- 420
7 -----------Base Ring ---------- 1170 ---------1100 -------- 1000
8 -----------Cooker ----------- >2000 ------- >2000 ------>2000
9 -----------Freezer ----------- >2000 ------- >2000 ------>2000
10 ----------Frid/Freezer ------ >2000 ------- >2000 ------>2000
......All in M ohms
yes - I have swapped the RCBOs for gnd and 1st Floor - always gnd floor which trips.
The results above indicate the Gnd floor 'NE' is suspect - but cannot see anything. By the way all wiring is exposed in basement so didn't have to lift floor boards to visually inspect.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
