Discuss Voltage N to CPC causing Fan timer to continuously Run in the Electrical Forum area at ElectriciansForums.net

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Hi All,

Bit of a tricky number. I have recently installed lights / fans /toothbrush chargers and shaver sockets to a bathroom and En-suite. The house had been rewired a few weeks before(not by me). I tied into the existing lighting circuit and everything works fine apart from both extract fans with timer. The fans run on but never stop. I replaced both thinking it might be a bad batch. The ones i replaced did the same thing. with further investigation i discovered that i was getting 40 - 90 v between earth and neutral. I'm assuming this is effecting the run on timer. I have carried out ins res on every cable i installed and everything was clear. When i used my test lamps to check the other lights on the circuit i found i was getting the same issue. Does anyone have any ideas? Also the all circuits are on rcbo's but it isn't tripping.R1+R2 is fine and getting a decent ZE at consumer unit.
 
Sounds like a broken cpc between consumer unit and light fitting.
start by testing loop impedance at fan or light fitting.
p.s. What is the earthing method at the property?
 
The findings you are reporting don't add up. If the continuity of earth and neutral are both OK, and the EFLI is good at the board, then there cannot readily be 40-90V between them. The only situation that could give rise to those conditions at the same time, would be high resistance in a TN-S supply neutral, which is now 40-90V above earth but this would make the L-N supply voltage 40-90V too low, which is bound to cause other symptoms - lights dim and flickery and appliances malfunctioning. That voltage range is typical of a broken / floating CPC, which I would double, triple check for at this point in case that R1+R2 check was in error.

Then there is the oddity that a floating CPC or voltage N-CPC shouldn't affect the fan operation anyway. It's possible that a high resistance connection in the neutral to the light, could prevent it serving to discharge any inbound capacitive leakage to the SL below some threshold voltage, and expose the unduly sensitive nature of the trigger input. But then again that high resistance would probably manifest as flickery lights, and it couldn't be in the neutral common to both fans and lights as then each fan's SL and N terminals would be at the same potential and the fan wouldn't trigger.

So I would ignore the behaviour of the fans to begin with and try to get a set of voltage and loop impedance readings both at the board and the end of the circuit that don't conflict with each other.
 
I was going to say much as @Lucien Nunes said that "40 - 90 v between earth and neutral ... R1+R2 is fine and getting a decent ZE at consumer unit" simply does not add up without something very strange and noticeable at the supply neutral, or something bonkers like a high inductance/transformer in the tested circuit's N or CPC tested.

Check N-E at the supply, check Zs at the supply and PSCC, also Zs at the circuit, check for any non-trivial currents in the CPC with a clamp meter, etc.
 

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