Bathroom Switch Wiring Question

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gedc

355 posts

Ultimate Geek

#319006 12-Mar-2025 23:57

Switch controls the typical 3 in 1 Extractor fan, light and heatlamp plastic box that sits in many NZ bathroom ceilings. Was wired so that the heat lamps only activate when the extractor fan is running but extractor fan and lights can operate independently of each other.

Button for lights has broken so replacement ordered. I thought i understood the wiring but the more i look at it, the more i can't figure it out. Sparky on route to resolve in a few days so this is for knowledge purposes only.

Switchplate is safely back onto the wall but hoping someone can talk me through this as i can't figure it out.

As per pics - Top switch is for heat lamps, middle is for lights and bottom is for fan. Neutrals appear to be connected inside the wallbox and a switched live from the bottom switch.

I assumed that live in/out to common on middle switch. Switched via 1 which operates lights....The fan ( bottom button) - when switched - supplies power via long brown wire to the top switch which in turn allows heatlamps to come on if needed.

What is the short brown wire purpose from middle switch to bottom switch? I guessed it was switched power but given the fan works even if the light isn't switched i couldn't figure it out. Where is the fan getting the power from if the light switch is not activated - meaning the brown wire is not live.

Having typed all that out and looking at the pics again, could power be coming in on 1 on middle module and switched via common instead ? Why would there be two wires coming out of common then ?

Thanks for your thoughts.

pdh

331 posts

Ultimate Geek

#3353344 13-Mar-2025 00:30

Are you quite sure you haven't erred in your allocation of functions ?

If the top switch controls the lights
and the middle controls the heat lamps
then it all makes sense.

It's a little (visually) confusing that the (red) wire to the fan leaves from the back of the middle switch - it would be more intuitive if it were connected to the switched side of the bottom switch. Into the terminal at the other end of the short brown wire. Electrically identical - just a wee bit harder to figure.

evnafets

536 posts

Ultimate Geek

Lifetime subscriber

#3353347 13-Mar-2025 06:40

My basic electronics knowledge(not a sparky)

Power comes in on the 'top' of a switch.
Turning on the switch completes a circuit to the 'bottom' of each switch.

The 'live' wire supplying all the electricity here is the red wire coming in to the 'top' of the light switch (middle).
The brown wire connecting lights and fan passes that power on in parallel to the fan (bottom)

So the lights and fan both have power supplied to their 'top'.

Switch on the lights and it will send power down the two red wires (two lights?)
Switch on the bottom (fan) and it will send power down the black wire sheathed in red (presumably to the fan) and also the brown wire to liven the heat lamp switch.

So the heat lamp switch is only powered when the fan is 'on'

SATTV

1642 posts

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#3353358 13-Mar-2025 09:13

Not a sparky but did have EST-A & B ( we were not allowed to replace light switches but could connect 3 phase motors etc. )

The sparky has done a dodgy and no longer legal sleeve a black wire with red tape / tube )

Heatlamp - Top switch/ power comes in on the brown, when switch is tuned on it goes out the red.

Lights - Power comes in on the single red and livens the fan switch for independence from the short brown wire. When the switch is on it looks like it powers 2 lights?

Fan - Power comes in from the light switch on the short brown, when turned on it goes to the Heat lamp switch on the longer brown wire and powering the fan on the sleeved black wire.

There are hundreds of thousands of these in NZ, I don't know why sparkies don't use 3 phase cabling as it would be so much easier having three different colours and it all being in one cable.

John

I know enough to be dangerous

gregmcc

2145 posts

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#3353376 13-Mar-2025 10:06

SATTV:

Not a sparky but did have EST-A & B ( we were not allowed to replace light switches but could connect 3 phase motors etc. )

The sparky has done a dodgy and no longer legal sleeve a black wire with red tape / tube )

Heatlamp - Top switch/ power comes in on the brown, when switch is tuned on it goes out the red.

Lights - Power comes in on the single red and livens the fan switch for independence from the short brown wire. When the switch is on it looks like it powers 2 lights?

Fan - Power comes in from the light switch on the short brown, when turned on it goes to the Heat lamp switch on the longer brown wire and powering the fan on the sleeved black wire.

There are hundreds of thousands of these in NZ, I don't know why sparkies don't use 3 phase cabling as it would be so much easier having three different colours and it all being in one cable.

John

Sleeving a black wire red is still allowed, it the sleeving of a green wire to another colour that is not allowed. ASNZS3000, 3.8.2(a)

looking at the switch wiring, middle switch controls lights, bottom switch (fan) only gets power when middle switch is on, top switch (heat) only gets power when bottom switch is on.

gedc

355 posts

Ultimate Geek

#3353733 13-Mar-2025 18:25

Thanks everyone. I grabbed the DMM to check the feeds and have it figured out. I made the mistake of assuming the 2 reds in the middle switch module were in and out onto the next thing on the circuit. They are indeed only out as a previous poster noted. No voltage on them until middle is switched live.

Top - Heat

Middle - Light

Bottom - Fan

Lights and Fan operate independently of each other. Heat ONLY operates when Fan is switched live via the long brown wire.

The '240V in' is the single red wire in the middle switch - the brown taps off that to also feed power to the fan switch - hence allowing both lights and fans to be switched on/off without the other.

Regarding the two red wires in the middle switch. Took me a bit of wandering around the bathroom to figure it out. DOH. There is a single light in the main unit in the ceiling but that accounts for one wire. Turns out there are two small led's in the sink/vanity unit that also come on alongwith the ceiling light....Presume that's the second switched feed.

Thanks for the inputs. All makes sense now :)

Cheers