Timer Fan needs LS but I only have L & N

[davedo]

Hi,

I have a new Vent Axia vasf100t, it needs L, N & LS (switched live?). I am replacing a 30 year old Xpelair which did not need LS. Some facts
1. I have a light switch (that obviously turns on the lights)
2. I have a second switch to control the Xpelair.
3. The Xpelair cannot operate without the lights being turned on

Obviously the fan switch is in-line with (and after) the light switch. I do not know if the fan switch is a one or two pole switch.

A friend fitted the Vent Axia by using only the L & N, this appeared not to work (he did not wait the 15 seconds for the fan to start ... this fan has a delayed start). So then added a live to LS jumper on the fan, when the mains was turned back on - the fan PCB blew up with a puff of smoke close to the terminal block.

I can replace the broken fan with the model without a timer, as this only has L&N (no LS). However, would prefer the timer model ... how should the LS be wired in to a L & N cable feed? Or does the whole switch wiring need changing to reflect the 3 pole isolator as per http://www.vent-axia.com/files/pdf-downloads/446652 B.pdf

Lesson learned ... get an electrician not a friend to do work!

Thanks

Dave

 

[EFLImpudence]

You can connect the switched live (from the switch) to both L and LS

plus N and E, of course but

obviously the timer function will not work,

 

[davedo]

@EFLI, thanks for this - of course the L is needed to allow power to continue after the light is switched off, i.e. the timer function. However, any ideas why the PCB blew up with the L & LS jumpered together i.e. both coming from the switch?

 

[EFLImpudence]

any ideas why the PCB blew up with the L & LS jumpered together i.e. both coming from the switch?

Not from what you write - something else must have been wrong.

 

[ldoodle]

L is permanent live, so take from the loop in/loop out from the light
LS is from the switched live at the light

When you turn the light on, LS turns the fan on too. When you turn the light off, LS is obviously 'dead' to the fan, so the L (permanent live) still powers the fan for the desired time. Once the timer is reached, it kills L.

Do you have a fan isolator? If not, you ideally need to think about getting one - it goes between the source (light in your case) and destination (fan).

PS: Why are the rockers on MK fan isolators the wrong way round?

https://www.electricalsupplies.co.u...wCf9DF0LD-89oNnOe16fOVhJ2KikCGiWSHxoCkTDw_wcB

 

[Taylortwocities]

PS: Why are the rockers on MK fan isolators the wrong way round?

Because it is a ISOLATOR. Look at your consumer unit. Which way are the MCB/RCD/main switch when they are off , up or down??

 

[ldoodle]

Good point. But why do MK seem to be alone in this design?

https://www.google.co.uk/search?q=f...fOOuO7AbnwIGACg&sqi=2&ved=0CAcQ_AUoAg#imgrc=_

 

[ldoodle]

To be fair, maybe the UK is upside down.

US light switches are up for on and down for off. Not sure what the rest of EU is though.

 

[davedo]

@ldoodle, great explanation - thanks for that. I sort of worked out the purpose of the L and LS from teh diagram after reading the earlier post. However - I really do not want to start messing with new cable runs in the loft space, I need a qualified electrician to do that. Thus I am going to get a normal non-timer version and that will just connect nicely to the L & N that the old Xpelair used to use

I contacted Vent Axia - he said the jumper I added in the fan from L to LS was OK and should not have blown the board, I am hopeful for a refund on a faulty unit - either from the supplier of after send back to Vent Axia for checking

 

[JohnW2]

Because it is a ISOLATOR. Look at your consumer unit. Which way are the MCB/RCD/main switch when they are off , up or down??

Which is 'up' and which is 'down' with a rocker switch?

Kind Regards, John

 

[Taylortwocities]

Rocker, yes, I think i'll go and sit in mine…..

 

[EFLImpudence]

Which is 'up' and which is 'down' with a rocker switch?

Attach something (matchstick?) at a right angle to the rocker and it will become apparent and obvious.

 

[JohnW2]

Which is 'up' and which is 'down' with a rocker switch?

Attach something (matchstick?) at a right angle to the rocker and it will become apparent and obvious.

Well, yes - but, since switches don't usually come with attached matchsticks, it's far from so 'apparent and obvious' when the switches are in service!

Seriously, though, although I don't disagree with your conclusion, I've come across people who (whilst accepting that 'down is on' with a toggle switch) have the opposite view of 'which way around' a rocker switch should work!

Kind Regards, John
Edit: crucial typo corrected!

 

[EFLImpudence]

have the opposite view of 'which way around' a toggle switch should work!

rocker ?

Yes, perhaps but that doesn't make them right.

A rocker is just a toggle without a toggle.

 

[Iggifer]

Nothing to stop you putting all your light switches upside down....should you so choose

I hate it when 2 way light switches are both in the 'on' position but in actual fact off, I have to switch them both