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Edited this - as just read the DW bit. Please confirm - the DW is unplugged and just operating the DW benchtop isolation switch affects whether the RCD trips?
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Can you post a better picture of your fuseboard?
Discuss Strange RCD tripping problem in the UK Electrical Forum area at ElectriciansForums.net
Hi new to forum I work in France so work with aircon units, I think problem is capacitors in AC units because when turned on they store small amounts of electric they make the rcd think there is a fault, the dishwasher will also have capacitors and when you turn dishwasher on it will have same effect, you may also have some small earth faults and the capacitors just push it over edge, would use combined rcbs /mcb, to give less chance of tripping, can not remember what they are called in UK regards Ian
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O
Octopus
Can you post a better picture of your fuseboard?
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I agree with all the advice on thorough inspection and electrical wiring tests - including earth leakage current measurements. It's a good idea too to swap to an RCBO populated CU for the convenience and least disruption to the family.
I reckon moisture, water or damp air could be troublesome inside the external a/c units although our 4 split a/c mitsubishi units on top of a flat roof have been happily energised permanently and fed by an mcb on one side of a dual rcd board and never caused a trip.
What puzzles me about this problem is the involvement of the dishwasher circuit post the double pole grid switch - the dishwasher itself has been ruled out by unplugging it. I have a suspicion it has a relatively high impedance N-E somewhere between the switch and socket including in the socket or its back box.
I also observe that in the photo of the grid switches the neons for the dishwasher and cooker hood look noticebably dimmer than the other two - maybe a feature of the camera angle but seems odd to me. I'd be itching to open that grid switch box and CU and to check the correctness and tightness of all the connections.
The other aspect which might be a factor is that the tripping occurs when an MCB switch is made to power up - so some form of transient effect - which makes me ponder about the current/voltage disturbances in L, N and cpc caused by any input filters the a/c systems have - they are largely electronically controlled these days so will need protecting. I'd be keen to observe the L-N, L-E and N-E voltages and cpc currents during these switching events with DW switch on and off.
I note that the oven and hob are supplied from the same side of the CU - the former often being a villain for element earth leakage and N-E when the element controls are off.
Some electrician is going to have a fascinating time investigating and putting right!
I reckon moisture, water or damp air could be troublesome inside the external a/c units although our 4 split a/c mitsubishi units on top of a flat roof have been happily energised permanently and fed by an mcb on one side of a dual rcd board and never caused a trip.
What puzzles me about this problem is the involvement of the dishwasher circuit post the double pole grid switch - the dishwasher itself has been ruled out by unplugging it. I have a suspicion it has a relatively high impedance N-E somewhere between the switch and socket including in the socket or its back box.
I also observe that in the photo of the grid switches the neons for the dishwasher and cooker hood look noticebably dimmer than the other two - maybe a feature of the camera angle but seems odd to me. I'd be itching to open that grid switch box and CU and to check the correctness and tightness of all the connections.
The other aspect which might be a factor is that the tripping occurs when an MCB switch is made to power up - so some form of transient effect - which makes me ponder about the current/voltage disturbances in L, N and cpc caused by any input filters the a/c systems have - they are largely electronically controlled these days so will need protecting. I'd be keen to observe the L-N, L-E and N-E voltages and cpc currents during these switching events with DW switch on and off.
I note that the oven and hob are supplied from the same side of the CU - the former often being a villain for element earth leakage and N-E when the element controls are off.
Some electrician is going to have a fascinating time investigating and putting right!
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ABB Classification of RCDs upon detectable wave form - Residual Current Devices RCDs (Modular DIN Rail Products) - http://www.abb.co.uk/product/ap/seitp329/4bd0ec0528a84420c1256f5500557772.aspx
http://www04.abb.com/global/seitp/seitp202.nsf/0/740f1caaeb62137fc1257fe900545279/$file/Guia+Técnico+ABB+-+Diferenciais+Tipo+B_EN.pdf
I cannot get this problem out of my mind. At the moment the advice is to switch to an RCBO board (or to fit 2 new RCBOs for the two a/c systems). The question for me is what type of RCBO? I think there is a risk that using type A or AC RCBOs will not stop the problem of nuisance trips because of the nature of the inverter drive technology and its effect on the load current waveform. I cannot find any recommendation by Mitsubishi on what type of RCD device to use with their inverter a/c systems. During the course of this on-line research I have read some folk (and manufacturers) recommend not using an RCD to feed a/c equipment because of the problem of nuisance trips - sometimes when the a/c equipment has been powered down for some period and then powered up.
Looking at the references above it seems to me that the correct RCD type to use is Type B which does all that Types A and AC do. The Type B can detect those 'true' faults which have more complicated current waveforms generated by earth leakage from inverter electronics and supply filters and yet avoid nuisance tripping in the presence of 'normal' low level earth leakage currents as the supply filters do there job 'dumping' harmonics, noise and leakage to earth including power up/down transients.
Does anyone have any practical experience of selecting the correct RCD type for a/c systems using inverter technology?
On page 6/12 the second reference you will find:
With these properties, Type B RCDs turn out to be RCDs with high immunity to nuisance tripping caused by grid surges, electronic loads and EMC filters. Therefore, Type B circuit breakers are the ideal solution for all “difficult” loads, not only from the point of view of protection, but also in terms of service continuity
http://www04.abb.com/global/seitp/seitp202.nsf/0/740f1caaeb62137fc1257fe900545279/$file/Guia+Técnico+ABB+-+Diferenciais+Tipo+B_EN.pdf
I cannot get this problem out of my mind. At the moment the advice is to switch to an RCBO board (or to fit 2 new RCBOs for the two a/c systems). The question for me is what type of RCBO? I think there is a risk that using type A or AC RCBOs will not stop the problem of nuisance trips because of the nature of the inverter drive technology and its effect on the load current waveform. I cannot find any recommendation by Mitsubishi on what type of RCD device to use with their inverter a/c systems. During the course of this on-line research I have read some folk (and manufacturers) recommend not using an RCD to feed a/c equipment because of the problem of nuisance trips - sometimes when the a/c equipment has been powered down for some period and then powered up.
Looking at the references above it seems to me that the correct RCD type to use is Type B which does all that Types A and AC do. The Type B can detect those 'true' faults which have more complicated current waveforms generated by earth leakage from inverter electronics and supply filters and yet avoid nuisance tripping in the presence of 'normal' low level earth leakage currents as the supply filters do there job 'dumping' harmonics, noise and leakage to earth including power up/down transients.
Does anyone have any practical experience of selecting the correct RCD type for a/c systems using inverter technology?
On page 6/12 the second reference you will find:
With these properties, Type B RCDs turn out to be RCDs with high immunity to nuisance tripping caused by grid surges, electronic loads and EMC filters. Therefore, Type B circuit breakers are the ideal solution for all “difficult” loads, not only from the point of view of protection, but also in terms of service continuity
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The advantage of 2 or more RCBOs is that it means if there are other small earth faults on system they do not add to what ever the a/c units are doing and the a/c units might not take a trip out on there own, and if they do you can go back to the a/c company and say it is your system sort it out
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Picking the right protection - https://www.electricalreview.co.uk/features/9258-picking-the-right-protection
In this reference I have just read:
Now let’s turn to RCBOs. In principle, as these are functionally an MCB and an RCCB in the same device, it would be possible to produce versions with a huge range of combinations of MCB and RCCB characteristics. In practice, manufacturers limit themselves to the most commonly used combinations, such as a Type B or C MCB characteristic with a Type A or AC RCCB characteristic. Where other combinations are needed, it often means that an RCBO can’t be used and that the necessary protection must be provided by using a separate MCB and RCCB. Some manufacturers, however, offer field-fittable residual current units that can be used to convert an MCB into an RCBO, and this makes possible a wider range of combinations.
In this reference I have just read:
Now let’s turn to RCBOs. In principle, as these are functionally an MCB and an RCCB in the same device, it would be possible to produce versions with a huge range of combinations of MCB and RCCB characteristics. In practice, manufacturers limit themselves to the most commonly used combinations, such as a Type B or C MCB characteristic with a Type A or AC RCCB characteristic. Where other combinations are needed, it often means that an RCBO can’t be used and that the necessary protection must be provided by using a separate MCB and RCCB. Some manufacturers, however, offer field-fittable residual current units that can be used to convert an MCB into an RCBO, and this makes possible a wider range of combinations.
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Hpi type:
Modular devices Hpi type RCCBs - http://www.export.legrand.com/EN/modular-devices-hpi-type-rccbs_63.html
Hpi seem similar to UK type B RCCB - not sure yet if they are the same.
Modular devices Hpi type RCCBs - http://www.export.legrand.com/EN/modular-devices-hpi-type-rccbs_63.html
Hpi seem similar to UK type B RCCB - not sure yet if they are the same.
#61 - correct. We had DW unplugged all day yesterday and could replicate tripping.
Coincidentally we had the DW replaced a few months ago and the original one had been hard wired in, so as part of the installation the electrician changed the fixed wiring to a single socket. So this is also new and presumably tested.
Coincidentally we had the DW replaced a few months ago and the original one had been hard wired in, so as part of the installation the electrician changed the fixed wiring to a single socket. So this is also new and presumably tested.
Hopefully new electrician coming on 15th. I will invite him to comment if he can or cannot resolve it. That will obviously be much more useful than my observations.
I will point him to this thread but would you recommend I ask him any specific questions ? I am not suggesting that as a professional he wouldn't know what to do. Just in case it helps.
I will point him to this thread but would you recommend I ask him any specific questions ? I am not suggesting that as a professional he wouldn't know what to do. Just in case it helps.
T
Toneyz
Is the only reason the A/C set up is protected by RCD as it is due to the type of C.U. you have already.If you do get the C.U. set up changed/reconfigured and the wiring is all surface you may not need the RCD/RCBO element.Do the A/C installers usually put on MCB only.
Not sure I understand your questions / comments.
To my simple mind:
Never previously had a single rcd trip. A/C installed by what I believe is reputable experienced company. Almost immediately frequent RCD trips. Could prevent them by isolating A/C both internally and externally. Seemed a no-brainier to me. Called the A/C company who said an electrician should be consulted. Persisted and they sent an engineer who identified the link with the dishwasher circuit.
Since then no-one can work it out and all we have is repeated and sometimes frequent RCD tripping.
I will go with the transfer to all RCBOs if only to avoid disconnection of fridge freezer, internet routers etc.
To my simple mind:
Never previously had a single rcd trip. A/C installed by what I believe is reputable experienced company. Almost immediately frequent RCD trips. Could prevent them by isolating A/C both internally and externally. Seemed a no-brainier to me. Called the A/C company who said an electrician should be consulted. Persisted and they sent an engineer who identified the link with the dishwasher circuit.
Since then no-one can work it out and all we have is repeated and sometimes frequent RCD tripping.
I will go with the transfer to all RCBOs if only to avoid disconnection of fridge freezer, internet routers etc.
T
Toneyz
What I mean is depending how the A/C circuits are installed they may not need RCD/RCBO protection under the regs, but as they type of consumer unit that you have they have had to be installed on one and are adding to the leakage current making it trip.
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