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Hi everyone,

I have just installed a two-speed bathroom/toilet ventilation fan (back and forth on/off switches, in bathroom and in toilet, with a speed toggle switch in the bathroom). Here is my circuit diagram: (sorry, not a professional here, hope it's all clear). The right and left circuits are identical, the left was just to help me figure out where the wiring would go.

It all works fine except for one thing: when I turn on the bathroom light, the fan stops/will not start! Otherwise it works fine.

I suppose this is because I took the live wire from the (existing) light circuit (10A light circuit - I'm in France if that matters) and hooked it up to power my fan circuit. It might be worth noting that the fan on/off (back and forth) and the light on/off (simple) switches are on a double switch, side by side.

Thanks to anyone who can help me out!

Andrew

Your wiring diagrams look to be correct.

Suggestions:

i) Check the fan instructions on how the connections are to be wired;

ii) check wiring to the double switch unit;

iii) check original wiring to lamp;

iv) have you marked all switched live wires with red identification tape and clearly distinguished between the two fan on/off wires?

v) does the light glow dimly when lamp is switched off and the fan is on low speed and a little brighter the fan is on high speed? If yes, then you have wired fan N to lamp switched L.

vi) move to Germany (where the wires have a higher chance of being what you expect them to be)?

:)

Hi signality,

Thanks for taking the time.

i) Fan instructions very simple: N, LA (fast) and LB. No ground. Wire it up and go. Pretty sure that is okay because it is working after all.

ii) Pretty sure this is okay too. The double switch unit lets you do a simple on/off or a back-and-forth setup. I have done one of each. Both work - but not at the same time!

iii) Haven't touched original wiring, apart from where it arrrives at the switch. I doubled off the L and N wires just before the switch and hooked them up to the double switch unit as mentioned above. I have a feeling that the problem is in the switch unit, but don't know why exactly.

iv) No, no red tape, but all wires are colour coded: back and forth wires = purple; high/low speed wires = brown; N = blue, L between switch 2 (toilet) and speed toggle switch = red. This more or less corresponds to local standards, but I could be mistaken.

v) No dimming of the lights at all in any circumstances (halogen spots, 2 x 35W I think).

vi) Been there, but only worked in tiling and demolition next to my studies, didn't get into electricity at all. Perhaps I should give it a shot?

Did I mention that if the fan is on when I turn on the light it stops, but starts up again when the light is turned off?

Could the light be "parasiting"' all the electricity, absorbing it all so that there is not enough to power the fan? There are other lights on this circuit which do not affect the fan at all.

I'll have to sleep on it and see if the kids let me rack my brains for more than 5 minutes tomorrow.

Thanks again and take it easy.

Andrew

"Did I mention that if the fan is on when I turn on the light it stops, but starts up again when the light is turned off?"

You did hence my suggestion of (v). Note that the light glowing dimly is only when the light is OFF but the fan is ON.

Does the fan turn slowly or buzz when the light is on?

"Could the light be "parasiting"' all the electricity, absorbing it all so that there is not enough to power the fan?"

Unlikely. If you replaced the light with a higher power light and it only glowed about the same brightness as the old one then that might be your problem but you'd have noticed that the light wasn't as bright as it should be with the original bulb anyway.

"halogen spots, 2 x 35W"

Aaaaaah. I'd guess that the spots are low voltage and are driven from a transformer.

Are you sure you've wired the fan to the live side of the transformer that feeds the spots?

Are you sure the transformer for the spots is not itself driven from a low power mains isolation transformer (like the 20W types used for shaver sockets).

The current drawn by the spots or the fan may be OK but the total current drawn by the fan + the spots may draw so much current that the output of this hypothetical isolation transformer drops too low.

Nah ... the light from the spots and the fan speed would both drop ...

Hi signality,

Greater minds than I will understand why and how, but I seem to have found the solution. I went higher up in the circuit wiring and found that the electricians who did the installation used an orange wire for the N of the light (which I had connected the fan N to). This orange wire was not connected to the N wire (blue) for that circuit. No idea where it goes.

I found the blue N wires a bit higher up, made sure they were all actually Ns and on the same circuit I want to use, and connected the fan N to that.

So now I guess I can move on to my drop ceiling ...

Thanks for your help and have a great day.

Andrew