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Topic Title: Central extraction ventilation unit
Topic Summary: ..wiring
Created On: 31 October 2017 09:51 PM
Status: Read Only
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 31 October 2017 09:51 PM
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SKElectrical

Posts: 1122
Joined: 01 February 2009

Just checking how wiring of these units is done.
The unit serves air extraction for 2 bathrooms whose lighting is on 2 separate circuits.
The fan appears to have its own separate supply too.
Fan unit requires 3 core (Perm for trickle and overrun, Switch for boost, and N).
The one I saw today had 2 contactors next to it ( I didn't look inside) but am I right in think the individual switched lives from each bathroom connects to A1 of separate contactor (with the load being linked across top & bottom before feeding the fan as Sw boost function)?
Is this how they're usually done?
 31 October 2017 10:20 PM
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AJJewsbury

Posts: 15989
Joined: 13 August 2003

Sounds reasonable - contactor coils (both L and N) supplied from the various lighting circuits, contacts paralleled up to switch the boost line, using the fan circuit's L for supply. Other methods include wireless connections, or a humidistat or, ahem, "air quaility" sensor in the duct or fan unit itself so it boosts automatically when needed - the trickle function in effect sampling the air in all the extract rooms continually.
- Andy.
 31 October 2017 10:40 PM
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SKElectrical

Posts: 1122
Joined: 01 February 2009

Thanks Andy ive not done them before.
I should've checked when i was there but time was dwindling after swapping out 2 storage heaters for convectors.
(Incidentally, make sure you tell your cust to turn off their storage htrs the day before or else the bricks are unworkably hot.
Thx again.
Simon
 01 November 2017 02:42 AM
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leckie

Posts: 4389
Joined: 21 November 2008

Or install a PIR in each room in parallel.
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