Wassssuuuuup? Bathroom Extractors!

[TheCovidYears]

Is that still a thing? "Wassssup", I mean. Not bathroom extractors.

Anyway, my fellow bored apes, I need assistance with no clear picture as to what I have, only guess work.

New build 2020
Upstairs we have crap EnviroVent, asthmatic blowing out a candle through a straw style extractors.

These only come on with the lights (useless) and only if the 3 pole (I'm guessing) switch above the door is "on".

All over the house, we have "loop in switch" wiring. Therefore, without checking, I'm, expecting to find 4 cables going to the light switch.

1x LNE in (from previous light
1x LNE out (to next light)
1x TC or TCE for the light(s) - there are 4 spots in the bathroom
1x 3CE for the 3 pole isolator to provide a switched line to the extractor.

I might be wrong. Who knows.

What I want to do is:
A PIR / Occupancy Sensor and let this do the timing (ie, irrespective of the lights)
A new inline manrose extractor in the loft, in case I take a midnight dump (no overrun option)
Retain the 3P isolator, but might need to swap this for a 3amp FCU

So, can I repurpose the 3P isolator to effectively be the next "light" in the chain of loop in switch by running LNE into it, and out of it (to the next light). Only thing here would be that even "off" the isolator switch still carries a perm live.
Then, power the PIR / Occupancy sensor from the 3P isolator, which will handle switch line itself (ie, closes the circuit when it detects heat / movement).

Or, have I massively overcomplicated this, or massively misunderstood.

 

[Adam_151]

Or, have I massively overcomplicated this,

Yes.

I don't see what you think you need alter the cirucit to loop the supply through the three pole isolator, leave all that alone. Chances are you'll have a 3 core & e that goes to the current fan with L-N and SW live, put it into a joint box, don't connect SW-L to anything else, take a 3C & E or a 4 core flex to the PIR with L-N-E and returning a second switch live which you can send to your new fan alongside N and E.

 

[TheCovidYears]

Yes.

I don't see what you think you need alter the cirucit to loop the supply through the three pole isolator, leave all that alone. Chances are you'll have a 3 core & e that goes to the current fan with L-N and SW live, put it into a joint box, don't connect SW-L to anything else, take a 3C & E or a 4 core flex to the PIR with L-N-E and returning a second switch live which you can send to your new fan alongside N and E.

Ahhh, so doing it this way, and not connecting the SWL means it will still work even if the light switch is off? Genius.

 

[ericmark]

I would say a heat recovery unit works far better than an extractor fan, but not even convinced we need extractor fans, in a shower the problem is the chimney effect, cool air enters bottom of shower enclosure, and leaves top distributing the moist air throughout the room. Remove the shower cubical, (as with a wet room) or seal it at the bottom, and the room does not get anywhere near as wet.

Be it smells or moisture, we want the fan to activate on leaving the room, not entering. And to do it with as little noise as possible specially at night, the heat recovery unit is likely a good compromise.

The heat recovery unit can use the pipe through the wall as the heat exchanger, and can run for much longer without pumping all the expensively heated air outside, but I have found a shower which seals on the bottom of cubical does not fill room with steam, so no fan required.