Bathroom (loft) extractor wiring with humidistat

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Kinnectus

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I have tasked myself (along with any professional help such as electrician, of course) with installing an in-line extractor fan in the loft - to service the bathroom (and landing if it needs it).

I have a Vent-Axia ACM100T (timed) in-line extractor.

I have also decided that I'd like a humidistat installed to better automate when the fan comes on if it needs to. For this I have purchased a Manrose MAN1361.

1) Having read some previous threads on here as the ACM100T installation guide does not state the maximum current for the timer versions (ACM100T) but one member has confirmed that, typically, the unit can be connected using an existing lighting (6A) circuit (hence the lack of fuse/protection in the instructions). I'm fine with this as it is very logical. Our lighting and other circuits are all protected with MCBs (recently had new consumer unit installed). BUT, The instructions also show the non-timed versions requiring a 3A FCU, which leads me to my next step...

2) Now, as I'd like to incorporate an external "control" (MAN1361) the manufacturer has stipulated the humidistat should be protected by a 3A isolator. The external control has both humidistat and timed over-run (I bought the extractor first and then thought about a humidistat, before anyone asks).

See diagram below.

Question(s):

1) Is this an acceptable circuit?
2) Can I use the external control isolator to power both the control unit AND the fan?

Please assume I shall also be incorporating a 3 pole isolator directly before the fan (as per manufacturer guidelines).

Diagram:

Bathroom_Extractor_Fan_3.jpg


Manufacturer installation guides:

Vent-Axia ACM100T: https://www.vent-axia.com/sites/default/files/409945_a_0.pdf
Manrose MAN1361: https://www.tlc-direct.co.uk/Technical/DataSheets/Manrose/MR1361_Instructions.pdf

I've tried to incorporate both manufacturer guidelines into the circuit diagram.

I've incorporated a double pole switch to replace the ceiling pull cord - to ensure complete separation of circuits.

I would like to install the FCU in a landing stairs cupboard (next to the bathroom) as it has a suitable feed to a double socket in the loft - I'm confident this can be spurred off for the extractor solution I'm proposing.
 
Neither the fuse nor the 3 pole isolator switch is required electrically.

Fuses are to protect the cable, NOT the appliances.

Also it will not work with the fan Permanent Live and Switched Live joined together.

If you have an isolator it should also isolate the timer and functional(light) switch - plus the FCU already does that so in your diagram the isolator is pointless.
 
But an FCU as shown will do the job of an all-pole isolator for the fan without the need for another isolator.
 
Thank you, all. My mind has been put at ease.

Now, an additional thought, which may or may not be any point in installing... an additional dedicated timer so I can program daily/weekly scheduled activation of the fan.

I have found the following Greenbrook T205-SCR digital timer (https://www.screwfix.com/p/greenbro...ay-fused-digital-timer-spur-switch-230v/7643g) that is, essentially, a double pole isolated, single pole switch activated upon the timer configuration. Datasheet (with schematic) show here: http://www.greenbrook.co.uk/eshop/files/files/T205-Ins-June-18.pdf. I note, however, that the fuse is 13A. Fine. Could this be changed for a 3A (to match the FCU)? Would it be worth changing the fuse knowing the FCU is rated considerably lower?

My updated schematic (including change by EFLImpudence):

Bathroom_Extractor_Fan_4.jpg
 
You don't need to change the fuse, you have a 3A in the FCU.
Also you don't need the outgoing Load Neutral wire from the timer back to the supply.

It's your house but I have to say I can't think of why the timer would be needed.
 
Kinnectus said:
Thank you, all. My mind has been put at ease.

Now, an additional thought, which may or may not be any point in installing... an additional dedicated timer so I can program daily/weekly scheduled activation of the fan.

I have found the following Greenbrook T205-SCR digital timer (https://www.screwfix.com/p/greenbro...ay-fused-digital-timer-spur-switch-230v/7643g) that is, essentially, a double pole isolated, single pole switch activated upon the timer configuration. Datasheet (with schematic) show here: http://www.greenbrook.co.uk/eshop/files/files/T205-Ins-June-18.pdf. I note, however, that the fuse is 13A. Fine. Could this be changed for a 3A (to match the FCU)? Would it be worth changing the fuse knowing the FCU is rated considerably lower?

My updated schematic (including change by EFLImpudence):

View attachment 153936
Click to expand...

As I have said you don't need the fcu. Put a 3a fuse in the timer if you like but it won't have any discrimination against a 6a MCB in your CU.
 
ban-all-sheds said:
View attachment 153958

:confused:
Click to expand...

The 13A in the picture is just straight from the manufacturer's instructions.

My text along the side "T205-SCR (Timer)(With 3A fuse)" is me suggesting I'd fit a 3A fuse (in place of the 13A it'll come pre-fitted with). As has been said, however, it makes no sense to change the fuse as the FCU is rated at 3A.

Lol... no extra-curricular horticulture moonlighting... promise! We've got a condensation problem that rears its head after bath/shower, but also from cooking and when we wake up the next morning.

The reason I want the timer is that the humidity sensor might not guarantee to come on, so if I can set specific times of day/night for it come on then every little helps.
 
winston1 said:
As I have said you don't need the fcu. Put a 3a fuse in the timer if you like but it won't have any discrimination against a 6a MCB in your CU.
Click to expand...

Thanks winston1. The only reason I put the FCU in was because it's in the manufacturer's instructions. The lights are on a 6A MCB but I'd like to keeps the lights separate from this install.

I'd need to double check, but the circuit I'm looking at spurring off (a radial, I'm pretty confident) was from an old immersion heater that was removed many years ago when the previous owner had a combi-boiler installed.

The circuit was re-purposed by our electrician to feed a double socket in the loft, and that's it - because the wiring was already right below where we wanted the double socket.

I'd like to extend the radial to feed the proprosed installation. This way I'll know 100% where the main source is coming from and not risk the lighting circuit because, essentially, I have no need to touch it.
 
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