Induced voltage.

AMTC electrical · Feb 24, 2024

Hi
Just replaced a bathroom extractor fan. I didn't alter any wiring.
Both old & new have live & switched live. Trouble is, once activated, the fan won't turn off.
Vent axia say there's an induced voltage. Not enough to switch fan but enough to keep it running. Sure enough, there seems to be 37v.
They say to run in a new, seperate switch live.
Any advice/thoughts welcome

Bsharp · Feb 25, 2024

I presume your are talking about a timed fan? Line/switched line and neutral???

Bsharp · Feb 25, 2024

Firstly I’d double check (presume you have) that the cores are actually what you’d expect I.e. brown -line
Black -switched line & grey - neutral. Presuming these are correct and when tested the 240 does actually drop off to 37v when light turned off and timer over run has stopped. Then I suppose it could be induced voltage

If it is then maybe try swapping the neutral and switched line cores around (obviously at both ends and mark accordingly) possible having the neutral between the line and switch line may eliminate the induced voltage. Never tried if just something that popped into my head. Hmmmmmm

pc1966 · Feb 25, 2024

It is unlikely that "induced voltage" is able to actually run anything, sick a voltage tester that draws a couple of mA for LEDs on it and it collapses to near-zero.

As @Bsharp suggested, check the permanent and switched lives are as expected. Also some fans just have problems with timers and go bad, if nothing else explains things that is a possible reason.

Bsharp · Feb 25, 2024

pc1966 said:
It is unlikely that "induced voltage" is able to actually run anything, sick a voltage tester that draws a couple of mA for LEDs on it and it collapses to near-zero.

As @Bsharp suggested, check the permanent and switched lives are as expected. Also some fans just have problems with timers and go bad, if nothing else explains things that is a possible reason.

Yer reckon your correct, never seen a fan running via induced voltage only ever had dimly lit LEDs. But with fans “always running” as you say timers can go bad also when waiting for an over run to stop this can seem like an endless amount of time.