Can a faulty Extension Box (V1) cause my incoming mains supply RCD to trip?
With the extension box manually bypassed and L connected to 3 & 4, my HW & CH works properly albeit with no Tado control. With the extension box in place the RCD trips! Can anyone throw any light on the problem please? Tado chat says the extension box can’t cause the problem!
Answers
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What if you connect L and N to extension box and nothing else? If that doesn’t trip then I’d say the ext kit is likely ok.
I think I broadly agree with them here and I’m not sure I 100% trust all heating wiring.
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The RCD will be tripping when earth leakage current exceeds a permitted threshold. Tado devices are Class 2, meaning they have no earth protection. So it shouldn't be possible for the extension box to leak electric current to earth.
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Thanks. If it’s not an earth leakage problem then it must be an overcurrent problem? Tado chat said the Ext Box is a simple relay and couldn’t cause the problem but this can’t be right. Surely there are electronic components inside that could fail, e.g, power supply for the wi-fi comms and the circuit to drive the electronic relay. The Ext Box is not fused which seems weird to me.
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If the issue is over current then the MCB will trip. I'm not saying the problem is not earth leakage, just that the extension box shouldn't cause this type of problem. With central heating systems earth leakage usually occurs when water comes into contact with the electrics. It could be an old circulation pump where water is seeping into the motor, a motorised zone valve where water is leaking into the motorised head, or internal to the boiler.
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Thank you. It can’t be a component external to the ext box that has failed because as soon as the ext box is bypassed everything works properly and the rcd doesn’t trip! My curiosity is what can happen inside the ext box that can cause the rcd to trip?
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