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Discuss RCD tripping under high load on 2 circuits in the Electrical Forum area at ElectriciansForums.net

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I’m in desperate need of someone with great fault finding knowledge. I have a dual rcd consumer unit as seen in picture. The left hand side rcd trips when anything with a high output like a tv for example is turned on in any sockets protected by the left rcd. The left rcd also trips when trying to switch on any light switches also protected by this rcd. The left rcd also trips if I use an appliance in the kitchen which is protected by the right hand side rcd, the appliances still work in the kitchen but they trip the left rcd and the rcd will not reset until I turn off whatever I’m using in the kitchen. I have had an electrician come round to investigate who left still scratching his head and told me that a full test would need to be carried out on the consumer unit as the faults were not pointing to one specific thing as 2 circuits are tripping the left rcd and not just 1. My house is 4 years old and I have owned it since new, one problem I have had since owning the house is the bath leaks onto the living room ceiling. I’ve had the builders out twice for this but that problem still persists. It has been like it for 4 years so I’m not sure if it has finally caused a problem? To summarise, any high output appliance used in the sockets protected by the left rcd trips the left rcd and also the light switches protected by the left rcd trip the left rcd. Everything in the kitchen works but using them causes the left hand rcd to trip. I have switched the rcd units with each other to eliminate the possibility of an over sensitive rcd but it made no difference so I have now swapped them back. I have checked the wiring on the sockets and light switches protected by the left rcd but couldn’t see any damage/loose connections. Any advice would be greatly appreciated as I’ve been trying to diagnose this problem for a week without any proper testing equipment. Kind regards, SimonBEFFC282-6288-4391-AC11-F77B4E618D21.jpeg60E833DB-D563-4B43-83DB-1A2411C783DA.jpegBDB1A794-4FF9-46E7-B4A2-6CC9ADCD43ED.jpeg
 
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Get another electrician is my opinion.

With it being only on the left side you must have a minor fault on the left side circuits which is only becoming an issue when you are under a higher load. Any decent electrician should be able to split the circuits up and find the fault. It may be two very small faults that when together and connected through the neutrals are creating a bigger fault on any kind of load.

I've had this before and turned out to be a small fault on a dishwasher not the circuits itself.


I take it the electrician used a multimeter to test the circuits
 
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Get another electrician is my opinion.

With it being only on the left side you must have a minor fault on the left side circuits which is only becoming an issue when you are under a higher load. Any decent electrician should be able to split the circuits up and find the fault. It may be two very small faults that when together and connected through the neutrals are creating a bigger fault on any kind of load.

I've had this before and turned out to be a small fault on a dishwasher not the circuits itself.


I take it the electrician used a multimeter to test the circuits
Thank you for your reply. The electrician who came round was actually a friend who I think thought it was going to be easier to diagnose than what it seems. He didn’t have any equipment with him but instead of waiting on help of friends I have another electrician coming round early next week to hopefully diagnose. Just wondered if anyone else has come across anything like this before, it’s interesting to read about your similar past fault tho.
 

Des 56

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Because a certain level of imbalance or leakage is required for a Rcd to operate,occasionally a neutral-earth fault on a lighting circuit will have insufficient current flow to cause that Rcd to operate
Sometimes when a heavy load is then used the current flow through that fault path then becomes high enough to operate the Rcd,the fault may not be with the load just used it could be via the lights or elsewhere but the symptoms can sometimes cause confusion
Needless to say ,the only sure way of determining whats at fault is by the use of test meters
 
RCD's are very finiky devices,
they won't tolerate any inter connection between the neutrals and the earth lines on the load side of the RCD.
so go thru all your circuits and make sure all neutral lines are keep completely independant of the earth lines.
 

Wilko

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Hi Simon, sorry to hear about your electrical problems. It likely won’t take long for an experienced Electrician to find :) .
 

Midwest

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One of the last jobs I did, was a CU replacement, kitchen & bathroom refurb. After I’d finished, I was called back a few weeks later to fit the bathroom vanity mirror.

Met by the kitchen fitters, who said there was no power upstairs. RCD had tripped. Quick look round, and spy a new socket on the landing, where the fitters had plugged in their hoover. Removed faceplate, and found neutrals pinched by faceplate screws.

Apparently, the client got a ‘mate’ in, and installed the landing socket. Obviously not tested.

Had anything like that OP?

PS, if the house is relatively new, do you have the original electrical installation certificate?
 
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Lucien Nunes

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Classic symptoms of a typical N-E fault, usually on a circuit on the RCD that is tripping. But the loads that trigger it need not be on the same circuit, or even the same RCD, as any load on the CU will cause voltage drop on the supply side.

So, one circuit on the left RCD almost certainly has an N-E fault. Testing required to find which. Bear in mind it can also be something plugged into a socket, so try unplugging everything from the left RCD's sockets. However if very light loads such as individual lights trip it, the fault is more likely to be on that circuit. BTW the TV is not a heavy load, 100 watts or so unless its over 40 years old.
 
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Sintra

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@Simonw586 Looking at the first picture it looks like there is no neutral on the outgoing side of the right hand RCD. The neutral going to the right hand neutral bar appears to be coming from the main switch and not the outgoing side of the right hand RCD. Can you check that out and confirm?
 

telectrix

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Ha, ha, I’ve just noticed my spell checker converted you into a famous singer, sorry about that !
that's nothing .Once I had to text an Eastern lady customer, named Alka. when the text had gone, I noticed that the predictive text had called her AlkaSeltzer. She was not amused.
 

Lucien Nunes

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it looks like there is no neutral on the outgoing side of the right hand RCD
It does look exactly like that, but I can't see how it can be. Circuits on the R/H RCD work, so that neutral bar must be correctly connected as the line appears to be. As there appear to be at least two neutral jumpers in the main switch outgoing terminal, not having one in the RCD would mean four cables disappear down behind the DIN rail but only three emerge underneath. It seems unlikely that someone would have left one unconnected, or put three in the main switch which I think we'd be able to see, so all the evidence points to this being a trick of the camera angle and in fact the neutral output link from the R/H RCD is sharply bent over towards the back of the CU just hidden by the RCD body.
 
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Hi all, thank you for your replies, the problem has now been resolved. It was a cable that had been crushed in the loft supplying the first floor lighting circuit. The neutral had been crushed exposing the wire onto the earth wire. Strange how this was causing the sockets to trip the rcd also but the main thing is it’s fixed!
 

Lucien Nunes

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Strange how this was causing the sockets to trip the rcd also
Thanks for reporting back, glad it's fixed. That behaviour might seem odd but electrically it's exactly what one would expect. The N-E fault on the lighting circuit will cause an imbalance in the RCD whenever there is any potential difference between N & E at the CU to drive current through it. That includes voltage drop due to loads on both different circuits on the same RCD, and loads on the other RCD, even loads next door if the supply is TN-S. The amount of load needed to cause a trip depends on how close to the supply the meeting point is between the faulty circuit and the load. Hence, small lighting loads on the faulty circuit itself would trip it, but on the other RCD only heavier loads such as the cooker would do so.
 

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