Bathroom Fan, LED lights & Dimmer

Talk Electrician Forum

Help Support Talk Electrician Forum:

King Arthur

Well-known member
Joined
Jun 22, 2019
Messages
91
Reaction score
25
Looking at this for a friend (honestly!). Bathroom has six LED ceiling downlights on two circuits of two lamps (over the bath) plus four lamps. Both circuits controlled by separate dimmers. The 4-light circuit also has an extractor fan wired to it. Basically, the 4-lamps + fan are not working, the two lamps are working and dimming ok. Immediate suspicion was that the dimmer for the 4-lamps+fan had failed.

I removed the faceplate comtining the two dimmers and swapped the wires to them. As suspected, the 4-lamps+fan now work and the two lamps over the bath do not. So it looks like a failed dimmer, which should be an easy fix. So far, so good.

My question concerns the extractor fan. It's a basic two-wire fan and does not overrun (how could it with only two wires?). I've not checked but my guess is that it has simply been wired into the 4-lamp circuit. It's an old-ish installation with red/black wiring to the fan and was originally switched (the dimmer was only connected about one year ago), which was probably ok at the time. The light switches were, apparently, replaced with dimmers by a pro electrician about a year ago in full knowledge of the fan.

After replacing simple light switches with dimmers the fan speed varies as the LEDs are dimmed. Clearly this is not ideal and I'm wondering if this could have led to the failure of the dimmer after only one year?

I see three options here:
1. Replace the failed dimmer module. Perhaps it was 'just one of those things' although I'm sure we'd all expect it to last more than one year.

2. Replace the failed dimmer module with a switch. The existing dimmer module is fitted to the faceplate with a nut and is easily removed. The issue would be finding a suitable switch with a knob that matches the existing one - ie it would look like two dimmers on the faceplate but only one would actually dim. But that's just a cosmetic issue really.

3. Replace the failed dimmer AND replace the fan with a more modern fan with overrun facility. My understanding is that such units have a permanent live connection and a 'trigger' connection, which would be compatible with the dimmed lighting circuit - ie lights are switched on with any brightness which triggers the fan to switch on at full speed until lights are switched off. The problem with this option is getting a live connection to a new fan set into a fully-tiled bathroom.

If it was me, I would replace the dimmer with a simple switch and leave the fan alone but my friend insists she wants all the lights to be dimmable.

What does the panel think?
 
Last edited:

steptoe

of course Im wrong, ask my wife™
Supporting Member
Joined
Feb 13, 2008
Messages
24,422
Reaction score
166
Location
Gtr Manchester
I'd say you opinion of a fan on a dimmer is correct,
It shouldn't be done.
I'd also hazard a guess, that not only has it shortened the life of the dimmer switch, the fan has also probably been damaged.
 

Sharpend

"It Just Is"
Joined
Feb 13, 2012
Messages
9,193
Reaction score
661
Location
Here There and Everywhere
What are the connections at the switches? Is the fan wired into the switch or direct from lights, have you verified this? Have you found this connection?
What is the make up of the ceiling/walls plasterboard, render/skim etc.
 

King Arthur

Well-known member
Joined
Jun 22, 2019
Messages
91
Reaction score
25
I've not verified the circuit wiring but I'm pretty sure the fan is directly wired into the 2-led light circuit. I say this because the wires to the fan are red/black whereas the wires to the dimmer switches are blue/brown. That doesn't mean there couln't be a junction box somewhere in the ceiling I suppose.

My friend would ideally prefer the fan to be an overrun type but with an easily accessible isolator switch so it could be switched off if not needed, but the bathroom is already fully tiled on brick walls so changing the cabling would be a major job - not so much an electrical job but more of a building job (as these things often are). And probably quite expensive.

My DIY suggestion is to swap out the failed dimmer for a 'dummy dimmer' switch module, which will keep the appearance of a dual dimmer switch plate but would just operated as a push-on-push-off switch for the 4-led lights and the fan, leaving the other dimmer to operate the 2-led lights over the bath. I buy such a switch from TLC for about a fiver whereas tracing the precise circuit, re-wiring it for a new overrun fan plus any associated disruption to the decor will necessitate a pro electrician and will cost . . . . well, you can make your own guess, but it's going to be several £100s.

She would certainly PREFER the latter but doesn't think it's worth the money, which is usually the deciding factor in these things. We all know that anything is possible if money is no object.

The really annoying thing is that it was a pro-electrician who wired the fan and dimmers in the first place. C'est la vie.

Thanks for all the comments.
 
Last edited:

King Arthur

Well-known member
Joined
Jun 22, 2019
Messages
91
Reaction score
25
I've not checked for accessibility above the ceiling but she definitely wants the lights on two circuits so no real point investigating further.
 

King Arthur

Well-known member
Joined
Jun 22, 2019
Messages
91
Reaction score
25
I don't know and haven't looked. Not much point cutting/pulling up boards when replcing a dimmer module with a switch module is the simplest/cheapest option.
 

King Arthur

Well-known member
Joined
Jun 22, 2019
Messages
91
Reaction score
25
Yes, well my DIY recommendation and her decision.

But what would a pro-electrician advise? (bearing in mind it was a pro electrician that wired the fan into a dimmer circuit in the first place!).
 

SPECIAL LOCATION

Trailer Boy - Electrician.
Supporting Member
Joined
Mar 28, 2008
Messages
13,657
Reaction score
342
But what would a pro-electrician advise? (bearing in mind it was a pro electrician that wired the fan into a dimmer circuit in the first place!).

I don't think it was any type of electrician pro or not IMHO.. sounds more like a cowboy...!
(did you check for horse manure & horseshoe prints on the lawn?)

I would be 'Very' interested to see the standard bathroom fan manufactures wiring instructions that suggest their equipment can be connected to a supply via a dimmer switch?

Two questions that need answering that relate to your best solution are:-
(1) Are cables accessible in a loft void above the bathroom?
(2) Can new/additional/replacement cables be pulled down the walls to the switch position?

e.g. depending on the above answers..
possibly you could convert the fan to 12v.. (fit the transformer/timer in loft void)
pull new cable down wall to trigger 12v transformer/timer to operate fan.. and leave lights as 2x dimers.

🍺
 

King Arthur

Well-known member
Joined
Jun 22, 2019
Messages
91
Reaction score
25
I don't think it was any type of electrician pro or not IMHO.. sounds more like a cowboy...!
(did you check for horse manure & horseshoe prints on the lawn?)

I would be 'Very' interested to see the standard bathroom fan manufactures wiring instructions that suggest their equipment can be connected to a supply via a dimmer switch?

Two questions that need answering that relate to your best solution are:-
(1) Are cables accessible in a loft void above the bathroom?
(2) Can new/additional/replacement cables be pulled down the walls to the switch position?

e.g. depending on the above answers..
possibly you could convert the fan to 12v.. (fit the transformer/timer in loft void)
pull new cable down wall to trigger 12v transformer/timer to operate fan.. and leave lights as 2x dimers.

🍺
I was using the 'pro electrician' decription in the sense that they were earning a living from the trade and advertising themselves as such. It's easy for the person in the street to be fooled.

Besides, this forum is supposedly full of 'pro electricians', all dutifully qualified' and yet disputes and disagreements requently break out when the 'regulations' are discussed. If genuinely 'pro electricians' can disagree about regulations what hope is there. Are the regulations really that complex or so ill-defined that they allow too much scope for interpretation?

As for the 'best solution' in this particular case, I accept that 'best' is itself subjective. A 'pro electrician' might well suggest an invasive exercise of re-configuring circuits, at very significant cost to the customer, or they might suggest replacing the failed dimmer with a simple switch costing a fiver.

I guess a 'pro electrician' isn't going to make a living doing the latter.
 
Top