time delay switches and extractor fans!

[Nigel]

Hi, in my cloakroom I have a light and extractor fan ( no windows ), the fan has a run on of a few minutes after the light switch is turned off which is fine and alll works dandy. The issue is that the switch for the cloakroom is on the outside, which again is fine but what tends to happen is that they switch on the light first, enter the room do their business and then close the door leaving the light and hence the fan on. It can be quite some time before someone realises that the light is still on - wasting power and melting ice caps etc.....

I was in B&Q the other day and saw a neat little timer delay switch with touch control, looked exactly what I was after, replaces a normal light switch, did a soft start of the light and remained on for a configurable number of minutes before switching off. I bought one of these and fitted it, all seemed ok, nice soft start of the halogen lamps and fan came on. after 5 minites light went off and fan remained on as I'd expected. What I did not expect however is that the fan just stayed on! and didnt go off at all even after the normal run on time had well elapsed.

I had to remove the switch an revert back to the old one.

Can someone please advice what is going on here and also what the solution should be - apart from putting the switch in the room...

regards

Nigel

[John Rumm]

This is a common problem with anything "clever" designed to replace a light switch. Because switch positions are typically not wired with a neutral, there is no easy way for electronic switch gizmos to draw power, other than by "leaking" a small amount of current through the bulb. This can cause a couple of problems; like those you are seeing. It can also break with non incandescent bulbs.

[Owain]

The "replaces the normal light switch" may be the problem.

To power the electronics of the switch, it passes a very very small current when off. This is not enough to light an ordinary bulb, but is obviously enough to trigger the fan's timing circuit.

You could use one of the more old-fashioned pneumatic timers which provide a definate on-off switching, but they tend to pop 'off' with quite a loud click which might be disturbing if people use the cloakroom at night.

If you can run a switched-live and neutral cable from the light back to outside the room you could use a neon faceplate (available through manufacturers' 'gridswitch' ranges) to give a polite "engaged" indicator outside the door.

Or replace the switch entirely with a PIR detector that uses a relay, which will provide a definate off.

Owain

PS The fan will require a triple-pole and earth Fan Isolator Switch somewhere, for isolation for mechanical maintenance.

[calums]

Your solution on this would be to replace the fan with a non timer fan. I dont know if you could even get away with just removing the constant supply wires from your existing one so that it is only being fed directly from the lights supply. No doubt someone will help with this. My gut feeling is that by simply removing the constant feed that this will solve the problem.

Be aware though that even with the light switched off, there will still be a live cable at your fan, so I would advise turning off your electrics before doing this job, and then just putting terminal blocks to isolate the cables that you remove. If at all in doubt with your electrics then call out an electrician. If you feel competent then keep the electricity turned on, put your old switch in. Put it in the off position and then use a multimeter to ascertain which cable/s are the constant feeds.

Good luck and stay safe Calum Sabey NewArk Traditional Kitchens 01556 690544

[John Rumm]

Might not be so good as the room has no other ventilation by the sounds of it.

A mechanical version of the switch would not exhibit the same problem:

[David Hansen]

On 27 Feb 2007 12:40:47 -0800 someone who may be "Nigel" wrote this:-

Replace the switch with a gridswitch plate with two spaces. In one space of the gridswitch fit a switch, in the other fit a neon indicator which comes on when the light is energised.

switches with neon indicators built in are available.

A good way of getting people to only pay quick trips I suppose.

[robert]

Neon indicators usually need a neutral to work if "illuminated when on" is required.

I have a similar problem of people leaving the bathrrom ligh(and fan) on and am resigned to pulling a neutral feed through to switch.

There dont appear to be any lowcost or unobtrusive PIR switches around. Robert

[John Rumm]

[calums]

Nigel I still stick by my 1st suggestion of removing the timer element of the fan (via one of the 2 methods mentioned). The fact that you now have a timer switch means that John's argument against disabling the timer is not valid. I am assuming that you will set the timer so the light and fan go off about 10 minutes after the person enters the room. Calum Sabey

[David Hansen]

On Wed, 28 Feb 2007 17:46:20 +0000 someone who may be [e-mail] wrote this:-

While that is best I'm not convinced that a low current through the protective conductor is a great problem. It might be if electric supplies were DC, as that could lead to high resistance joints being formed.

[robert]

could mount it in the ceiling with just PIR showing through hole. Robert

[John Rumm]

Why do you say it is no good for a bathroom? So long as it can be placed in zone three it ought to be fine.