Tripping RCD
- Thread starter Jevban
- Start date
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Some ( inexperienced ) electricians cannot see how a Neutral to Earth fault can trip an RCD when the MCB for that ciruit is switched OFF. They believe that because the Earth wire is connected to the incoming Neutral at the main fuse there cannot be a voltage difference between Neutral and Earth. Without that voltage difference they believe there cannot be a current through the fault to trip the RCD
One such electrician who was shown this diagram admitted that his training in fault finding had not covered this matter,
One such electrician who was shown this diagram admitted that his training in fault finding had not covered this matter,
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Any chance you could share this with us (removing your details)
So no receipt, no invoice no record, no tax or NI
Pretty sure that would be a Multifunction Tester.
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They may also believe that
"Current takes the path of least resistance",
which is not so.
Current flows in all available paths, in proportion to the "Conductance" of each "path",
which is the inverse of their "Resistance".
Hence, if there are parallel Earth and Neutral "paths" - of equal Conductance/Resistance -
the Neutral "path" will carry half the Current of that in the Line "path",
which will be detected by the RCD/RCBO as an imbalance of Current, between the Line and the Neutral.
Sorry I have not gone through all the information just the basics.
*You have had work done on external lights
*The lighting circuit used, was not connected a RCD protected circuit
*But RCD at Consumer Unit has started to trip
*Tripped when it rained.
Ok, so if lights are not connected to RCD. In reality you wouldn't expect that work to interfere or cause RCD trips.
The rain could be a factor, as RCDs don't like moisture ingress, but this would need to be related to a circuit that is covered by RCD protection.
If the lighting by chance had been connected by chance to RCD covered circuit again, moisture ingress is a possible cause. If the lighting circuit was using a either borrowed live or neutral from a circuit connected to the RCD, it possible this would trip when the lights were activated.
If the earth had been connected to the neutral side, you would also expect it to trip, but this would be more than likely a constant trip, not a random one.
It could be coincidental that trip has happened since the work on lighting has been undertaken.
Unfortunately, there's a whole host of possibilities and reasons behind RCD trips, in an ideal world it is best to have all circuits individually/separate to others protected by RCBOs.
The fault finding would be a process of elimination and ideally when the fault is present and active.
My thoughts other than insulation resistance testing, would be to disconnect a circuit at a time from the consumer unit and see what happens and which circuit causes the issue. It could be time consuming and inconvenient. Or alternatively Link out the RCD mod and install RCBOs to establish the circuit issue.
The other thing to consider, do you have an appliance on load that could cause the RCD to trip. All appliances can cause earth leakage and RCD trips. Is there a trend to the RCD tripping EG: kettle being boiled, oven being used, toaster being used, heating coming on, washing being washed or dried. dish washer being used. In short is there an appliance in use, when the RCD trips.
Then the other thing to consider is, have the new lights actually been connected to an RCD protected circuit and if the trip is happening in the hours of darkness and you have PIR sensor lights, is trip activated when the sensor is?
*You have had work done on external lights
*The lighting circuit used, was not connected a RCD protected circuit
*But RCD at Consumer Unit has started to trip
*Tripped when it rained.
Ok, so if lights are not connected to RCD. In reality you wouldn't expect that work to interfere or cause RCD trips.
The rain could be a factor, as RCDs don't like moisture ingress, but this would need to be related to a circuit that is covered by RCD protection.
If the lighting by chance had been connected by chance to RCD covered circuit again, moisture ingress is a possible cause. If the lighting circuit was using a either borrowed live or neutral from a circuit connected to the RCD, it possible this would trip when the lights were activated.
If the earth had been connected to the neutral side, you would also expect it to trip, but this would be more than likely a constant trip, not a random one.
It could be coincidental that trip has happened since the work on lighting has been undertaken.
Unfortunately, there's a whole host of possibilities and reasons behind RCD trips, in an ideal world it is best to have all circuits individually/separate to others protected by RCBOs.
The fault finding would be a process of elimination and ideally when the fault is present and active.
My thoughts other than insulation resistance testing, would be to disconnect a circuit at a time from the consumer unit and see what happens and which circuit causes the issue. It could be time consuming and inconvenient. Or alternatively Link out the RCD mod and install RCBOs to establish the circuit issue.
The other thing to consider, do you have an appliance on load that could cause the RCD to trip. All appliances can cause earth leakage and RCD trips. Is there a trend to the RCD tripping EG: kettle being boiled, oven being used, toaster being used, heating coming on, washing being washed or dried. dish washer being used. In short is there an appliance in use, when the RCD trips.
Then the other thing to consider is, have the new lights actually been connected to an RCD protected circuit and if the trip is happening in the hours of darkness and you have PIR sensor lights, is trip activated when the sensor is?
Hello all
I had another more experienced and very expensive electrician out yesterday ,( my 66 th birthday spent knee high in death and destruction of my house lol) and he found corroded back boxes that were from ac rewire likely 30 plus years ago look to have caused the earth leakage. He screwed the faceplate back on and within minutes every think tripped again...he has left the faceplate off and made the wires secure, made 2 radials in that socket circuit as the problem was between 2 sockets one of which had been disabled when I had a kitchen refit 4 years ago and the earth between these two was problematic. The lad previous to this had identified the problem was between a socket just outside my kitchen and the two I'm talking about, but doesn't seem to have realized the impact the corrosion in the back box caused. It's raining heavily here and so far, my electric is staying on. This last electrician had a megger or magga( apologies im not sure of the right name ) and it was showing earth connections where there should have been none when all was disconnected. I hope all this is making sense to you all. He also found loose wires in the lights at the top of the stairs where the first lad had clearly been pulling on the cables
It's been an expensive few weeks ,!
I had another more experienced and very expensive electrician out yesterday ,( my 66 th birthday spent knee high in death and destruction of my house lol) and he found corroded back boxes that were from ac rewire likely 30 plus years ago look to have caused the earth leakage. He screwed the faceplate back on and within minutes every think tripped again...he has left the faceplate off and made the wires secure, made 2 radials in that socket circuit as the problem was between 2 sockets one of which had been disabled when I had a kitchen refit 4 years ago and the earth between these two was problematic. The lad previous to this had identified the problem was between a socket just outside my kitchen and the two I'm talking about, but doesn't seem to have realized the impact the corrosion in the back box caused. It's raining heavily here and so far, my electric is staying on. This last electrician had a megger or magga( apologies im not sure of the right name ) and it was showing earth connections where there should have been none when all was disconnected. I hope all this is making sense to you all. He also found loose wires in the lights at the top of the stairs where the first lad had clearly been pulling on the cables
It's been an expensive few weeks ,!
The term "Mega" is the SI term for Million (10⁶) - Prefix "M".
This is used colloquially to refer to a device which measures the resistance of insulation, which (hopefully) will be in the "Millions of Ohms" range.
The device applies a "Test Voltage" of around 500 V - much at the "Top End" of the normal Rated voltage of any such insulation.
The lowest value "acceptable" under these conditions is likely to be 1 MΩ.
However, one should be very suspicious of any such a low value, read under these 500 V testing condition.
This is used colloquially to refer to a device which measures the resistance of insulation, which (hopefully) will be in the "Millions of Ohms" range.
The device applies a "Test Voltage" of around 500 V - much at the "Top End" of the normal Rated voltage of any such insulation.
The lowest value "acceptable" under these conditions is likely to be 1 MΩ.
However, one should be very suspicious of any such a low value, read under these 500 V testing condition.
Some use the name when referring to any make of test device and even as a verb - as is also done with 'Hoover'.
Any particular weather event ?
Hi
Not that I'm aware of. It was middle of the night. Heard a noise...looked at my bedside alarm clock and it was off, as was the whole house.
I really thought we had sorted it. I may have to bite the bullet and pay for the downstairs sockets to be rewired.
Jan
Not that I'm aware of. It was middle of the night. Heard a noise...looked at my bedside alarm clock and it was off, as was the whole house.
I really thought we had sorted it. I may have to bite the bullet and pay for the downstairs sockets to be rewired.
Jan
My money is on the fridge freezer
If you have a wooden suspended floors downstairs, and there is a junction box lying on the ground below, sometimes if it rains the water table rises and it can get wet below the wooden floor.
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I wonder what the noise was !
If you do have any electrical work done,
ask for a quote on the extra cost of having
the RCD (Residual Current Device) on your Consumer Unit removed and
the MCBs (Miniature Circuit Breakers) "protected" by this RCD
replaced by
RCBOs (Residual Current circuit Breaker with Overcurrent protection.)
As a "guide", the cost of each RCBO itself should be between about £15 and £20
(Of course, "labor" will be extra.)
Having RCBOs on each circuit will make it much easer to determine on which circuit any "leakage" exists.
As a side issue, if you have any "equipment" replaced,
the equipment which has been replaced is still your property.
The person replacing it should
advise you of this,
and
offer to "return" it to you'.
You may then request that the installer disposes of the replaced equipment
but
that is up to you to decide.
Maybe so.
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