interesting extractor fan mistake

[laurencewithau]

Hi everyone. I've just installed an in-line shower extractor fan with timer, isolator switch and independent ( or so I thought) pull cord switch.
It all worked perfectly when I tested it the evening I completed the work.
I pulled the cord, the fan came on, I could feel with my hand the powerful suction at the ceiling grille, and the fan continued for about 15 minutes when I switched it off at the pull cord.
The next day, a bright sunny day, I pulled the cord and nothing happened.
Wanting to investigate further, I switched the light on: and, lo and behold, the fan came on.
The previous evening the light had been on throughout the testing, so I hadn't noticed anything amiss.
The only explanation I can think of is that when I found a lighting cable to cut into in the crawl space, I accidentally used the actual switch cable from the light switch to one of the four junction boxes, one for each of the four ceiling lights, such that all the lights come on at the same time.
I did not notice because, of course, the neutral wire, where I cut the cable, does not have any red tape around it to mark it as the switch live, this only being found at the switch, not elsewhere on the cable.
this is an interesting mistake because, with one proviso, I now have an extractor fan that works off the light switch but only if I want it to.
When the pull cord switch is off, the light switch activates only the lights; when the pull cord switch is on, the light switch activates both lights and fan, both of which go off with the light switch.
This would be useful if, say, you had children who could not be relied on to switch the fan on before taking a shower but would very likely switch the light on.
In that case you could simply switch the pull cord switch on beforehand, so that the fan would go on with the lights.
The one drawback concerns the timer, which would work, after the shower, only if your kids left the light on when they exited the bathroom.
Here are some questions:
1/ Did I really cut into the switch cable or is there some other explanation?
2/ How can I avoid making that mistake in the future?
That is, how can I tell, without cutting the cable, that the cable is not the one with the switch live?
3/ Is there a simple way of re-wiring so that the timer works even if the light is turned off?
Or do I have to start again and find a non-light switch cable? Which takes us back to question 1/ how do I test the cable?
I hope that I don't have to find another feed cable, because the crawl space is inaccessible except by cutting a square hole in the ceiling and working with my head and shoulders and one arm inside the crawl space.
That is why it took me almost a week.
I don't think I could face doing it again, because when I first cut the hole and squeezed my head and shoulders and one arm through it, I also managed to squeeze my other arm in as well.
But then I was well and truly stuck.
My wife was downstairs but I knew I could not call her because she uses social media a lot.
She would, I know, have run for her camera and posted the photos on Facebook and to her mobile phone contact friends, some of whom I am acquainted with. But also, she has a camcorder, and I was in a panic in case she used that, too.
I did manage to extricate myself, but only by squeezing my torso up and down an inch or two until the edges of the plasterboard broke off and the hole got bigger. The hole is now covered by a rather large ventilation grille.
Thanks for reading all this and for any help or comments.
I hasten to point out that I do still love my wife.

[Someone-Else]

You need to invest in a multi meter, that way you can find out what does what (Via testing at junction boxes you have) as to what does what.

[ahfix]

I made the same mistake when I installed a remote extractor unit, I identified the correct cable but somehow managed to cut the wrong one.

Come morning I couldn't understand why the extractor wouldn't work ...

ah

[laurencewithau]

Hi ahfix. I know that feeling. But as I said, it's quite useful to have the control I now accidentally have: apart from having to leave the light on for the timer to work, and then coming back to switch it off.
next time, I'll do as someone-else suggests and use a multimeter. I n fact, I'm about to get really carried away and install a cooker hood extractor in the kitchen. At least I'll have loft access for that (it's a bungalow), but the problem with cooker hood fan, which will be twice as powerful as the bathroom one, is that there won't be enough ventilation in the kitchen unless I do something about it. Should be fun, and no doubt I'll mess it up and be back here asking to be rescued.

[OchAye]

On a positive note, the cooker hood extractor does not have a timer