We have a two way switch for an exhaust fan. The fan is out of sight from the switches.

So, the problem we face is we have no clue if the fan is on or off looking at the switch.

I tried to see if there are two-way switches with indicators attached (like this one for a one-way switch).

But there are none. They have a stand-alone indicator lamp, however.

Will it be OK if I connect the stand-alone indicator lamp is series with the exhaust fan?

BTW, this is at home on a 220-240V 5A circuit.

  • Where does power come into this circuit? At the fan, or at one of the switches? May 26, 2018 at 5:02
  • how much current does the fan motor use, the size of the circuit-breaker is not important.
    – Jasen
    May 26, 2018 at 5:28

4 Answers 4


If you want a solution that doesn't require running any additional wires, you might consider getting a couple of 1000:1 current transformers. Run the common leg of each switch through a transformer, and put a couple of back-to-back diodes across the secondary. If one (or both) of those diodes is an LED, it will light up whenever load current is flowing in the circuit.

For example, 5 amps of load current will put 5 mA through the LED. But modern LEDs will light up quite nicely on much lower currents.

  • Beat me to it!! (Well, I was writing too much.) Great answer!
    – jonk
    May 26, 2018 at 5:06
  • the fan probably does not use 5A, 1200W gets you quite a breeze! 100:1 might be a better transformer. or put several turns through the core,
    – Jasen
    May 26, 2018 at 5:30


Figure 1. A perverse solution requiring two neon lamps. Both neons will light when the fan is off.

How it works:

  • There is always one of the pair of wires between the switches at 'live' potential.
  • If the fan is on the other wire will be disconnected at both ends. The neon lamps will turn off as there is no neutral connection.
  • If the fan is off (as shown in Figure 1 then the top wire will be live and the bottom wire will be connected to N through the fan which provides a relatively low resistance path (compared to the neons). The neons will light.

Note that the fan can never be fully isolated from mains using the switches in this scenario.

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Figure 2. A green panel-mount neon indicator.

One of this style of indicator could be mounted on the face of a 2-way UK switchplate to give a professional looking finish. I'd go with green to indicate the fan is "off" rather than the usual red for "on" but bear in mind that the neon lamps usually give off an orange glow which is rather pale by the time it gets through the green filter.

  • There are light switches with built in neon lights. They are normally wired so as to light up in the dark so you can find them. I have rewired a couple of them in my house to work like you describe. In Germany (where I live,) it is common to have the light switch for the bathroom outside of the bathroom. As an American, I prefer them on the inside of the bathroom. So, to keep peace with my wife we have both. The outside switches have neon lights, and light up when the lights are on inside the bathroom. You can can see if the toilet is occupied even when the door is closed. :)
    – JRE
    May 26, 2018 at 9:20
  • Except, the way I wired it, the neons would light when the fan is on.
    – JRE
    May 26, 2018 at 9:22
  • The OP probably doesn't have a neutral available.
    – Transistor
    May 26, 2018 at 9:25
  • In mains wiring, there must be a third wire in that cable, commonly neutral. You need 3-wire (+earth) cable to wire 2-ways because neutral must be returned at the same physical location hot is taken. Otherwise 3 big badnesses happen: a) imbalance of currents in the cable, this being AC, causes eddy current heating, high EMFs and other kinds of mischief. b) dumping the motor's current return on any random handy neutral can overload that neutral, and neutrals don't have fuses. c) Current imbalance will break a future per-circuit RCD/AFCI installation. May 26, 2018 at 14:13
  • Other than that, your solution is not perverse at all. I'm impressed that it seems to conform with Code AFAICT (and you weren't even trying). Leaking current through loads is already allowed; lighted switches do it. The installation is electrically "neat"; it doesn't require alteration to an existing n-way circuit. It could happen right inside the switch, which could be UL listed. Well done. May 26, 2018 at 14:22

Any indicator light, (I don't know what a stand-alone light is), is not going to be able to carry the current to a exhaust fan. The lamp will burn out, or the fan will simply not operate if connected in series. Depending on the type of lamp. For your own safety, I recommend a qualified electrician.

  • not necessarily, I've seen small lamps rated at up-to 1A filament current, that's more than many fans use.
    – Jasen
    May 26, 2018 at 5:29

For series connection to work you'd need lamps that use the same current as the fan.

it quick search indicates the motors in small extraction fans typicaly use about 0.4A of current, so for series connection you'll need lamps that will work ok with the same current, and at as low voltage as possible.

you can get 2W 3V lamps and two of them in series with a 230V fan motor would have little effect on the fan speed but should glow orange but that's assuming 0.4A - the exact current needs of the motor will determine which lamp should be used.

Although they are low voltage parts you'll need insulated housings for the lamps as they will be live to full mains voltage when the power is on. (one of them will always be live, the other switched)

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