I know it's not the best video, as it was taken on my very old phone, but here's a neutral cable which had a bit of a high resistance joint. Who can explain this then?
Cooker DP switch tripping RCD
- Thread starter Fidget7
- Start date
I know it's not the best video, as it was taken on my very old phone, but here's a neutral cable which had a bit of a high resistance joint. Who can explain this then?
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You're essentially asking the same question which I asked, and I haven't got a clue - it doesn't make much (any?) sense to me.
I can but presume that we are seeing the result of the RCD's sensitivity to something ('spikes'?) other than 'conventional' L-N imbalance. Could it perhaps be that there are 'spikes' which have components at such high frequency that they manage to put 30mA through stray capacitance (from N to E in this case), and thereby create the imbalance? - although that feels a bit far-fetched to me.
Kind Regards, John
Where would you find something to verify that john.
Neutrals breaking last and making first were common with 4 pole switches i recall, but not heard that with double pole
If an appliance has earth leakage, when switching on, a percentage of current would go to neutral and a percentage to earth.
If the neutral was switching late then i would assume a higher percentage of current would take the earth path, possibly tripping rcd
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Only by hunting through technical datasheets, I guess, and I may well be wrong about that - but it's not a central part of what I was saying, anyway!
Kind Regards, John
Ah - now that's a whole new ballpark
I was talking about the proposal (as I understood it) that a switch 'malfunction' alone could cause an RCD to trip - and I still can't see how it could.If you introduce a fault to earth in the appliance, then the goalposts move totally - and I'll have to have a little think about what the consequences of non-synchromous L and N switching might then be!
Kind Regards, John
Okay, some thought here...if I were to introduce a second switch into the equation so we have the existing switch putting power to a junction box, split to one appliance (oven say) then a separate feed from the jct box to a separate switch powering perhaps the hob. So what we have is only one appliance switching at a time...as currently two appliances are getting power at the same time from the same switch...adding a second switch would mean only one appliance at a time.......or am I over complicating it ?
As you imply, that's appreciably more complicated than temporarily changing back to the (one) old plastic switch - which I would think is what you should try first.
Kind Regards, John
I suspect that when you wiggled the neutral connection the fleeting connection contained frequencies other than 50hz, which as well as having the possibility of having effects on the RCD itself, also increased the leakage to earth through any capacitive load (filter networks in just about any electronic device) as well as leakage to earth through cable capatance as well.
Have you posted that before rob, I've got a feeling of deja vu....
I suppose if you have an earth leakage clamp thats got a wideband and max/min hold setting you could probably prove the above but I've not really got access to a workshop atm
No matter how the switch operates it alone cannot create an unbalance on Live and Neutral in the sense coil of the RCD.Ah - now that's a whole new ballpark
For there to be an un-balance there has to be a path to ground or a path that enables some of the current to by pass the sense coil.
The comments about high frequency components created by an arcing switch are valid. That together with capacitive paths to ground and/or CPC may result in enough leakage to trip an RCD.
The impedance of a capacitor decreases as the frequency increases. Insulation testing with DC will not discover stray ( or intentional ) capacitive paths between conductors so apparantly good wiring ( with DC testing ) may in fact be significantly leaky at 50 Hz AC.
No matter how the switch operates it alone cannot create an unbalance on Live and Neutral in the sense coil of the RCD.Ah - now that's a whole new ballpark
For there to be an un-balance there has to be a path to ground or a path that enables some of the current to by pass the sense coil.
Its probably vaguely possible, opening the neutral first / closing the live first will result in all the wiring of the appliance being at 240v with respect to earth instead of just that on the live side for the short time it takes the other pole to close. Not normally a problem but if there was a high resistance fault on the neutral side to earth then you could get RCD trip if the poles closed in the wrong order.
The intermittant nature could then be due to the switch not always breaking the poles in the wrong order, speed of operation of switch, nature of high impedance fault (with a cooker it could be boiled over water leaking into something which then dries out most times before morning, etc, etc)
That really depends upon what you mean by 'alone'. As I have already said, and as you now appear to agree, high frequency components resulting from arcing at the switch could conceivably go to earth via capacitance (much more so from the N than the L, if its the N which is arcing) to a sufficient extent to create enough L-N imbalance in the RCD to cause it to operate.
Kind Regards, John
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