Wiring for replacement bathroom fan

[Phil54]

Hi,

I'm replacing an old (blown) bathroom fan (with an overrun timer) with a new one, and adding an isolator switch (3 pole) at the same time.

I WILL test with a meter before connecting up, but as the wiring is all in a very awkward to get at spot in the back of the loft behind the water tank, and in a very cramped spot, I'd like to confirm my assumptions with any passing sparky before clambering back into my tight spot.

The old fan (circa 1965) has a 3-core + earth cable going to it. Colours are - red, yellow. blue. bare earth.

As I'm adding an isolator, I need a couple of meters of new cable, and I'm assuming I'll connect :-


red to brown (live)
yellow to black (switched live)
blue to grey (neutral)
earth to, well, earth.

And then, obviously, the new cable to the new fan as per supplied instructions.

As I say, I'll meter it to confirm, when someone else is here to do the switching, but does that seem likely (bar daft wiring in the past) to be correct?

Many thanks.

PS. Probably should say .... it's domestic and not three phase.

 

[securespark]

Buy (if you have not got already) a multimeter to test the votages.

Tenner from Maplin.

 

[PrenticeBoyofDerry]

As I'm adding an isolator, I need a couple of meters of new cable, and I'm assuming I'll connect :-
red to brown (live)
yellow to black (switched live)
blue to grey (neutral)
earth to, well, earth.

You assume correctly but remember to sleeve the cables to identify whether they are phase, neutral or earth.
Are you linking the fan up to light?

 

[Phil54]

Buy (if you have not got already) a multimeter to test the votages.

Tenner from Maplin.

Got several, from a cheapy digital job to a venerable old ex PO (when what's now BT was still the Post Office, and they still did phone lines), to my favourite, an ancient Avo.

As I said, I will meter prior to connecting. Electronics, I'm familiar with, and have both qualifications and about 30 years experience. Household wiring, though, not so much.

 

[Phil54]

You assume correctly but remember to sleeve the cables to identify whether they are phase, neutral or earth.
Are you linking the fan up to light?

Noted, on the sleeving.

And yes, to taking the connection from the light. Or rather, the existing connection comes from the light fitting.

It's a loop-in system with the bathroom light coming from a junction box between bedroom lights, and the feed for the extractor fan being taken from the existing bathroom light. The (already existing, as per house-builders original job) cable went to the old fan. I'm rerouting that to a fan isolator switch, and adding new cable from the isolator back to the new fan.

In other words, a dead simple job. I just want to get a heads up to my assumptions about cable colours, though I'm also aware that in those days (mid-60s) things weren't always wired quite how they should be. And judging by the standards I've already found in this place, the monkeys that built it could have done just about anything.

Put it this way. When I first bought the place, I made a daft mistake. I put up a shelf and assumed that power cable would run pretty much vertically from a power point, so drilled a mounting hole about three feet from that line, and several feet above. But no, the idiot that wired the house ran the cable at about a 30 degree angle off the vertical, diagonally across the wall, and naturally, I found the exact path of the cable with the drill.

So, having channelled out the wall, replaced the damaged cable, wired a new fuse and brushed the scorch marks off the fuseholder, I now don't make many assumptions about wiring. And neither the plumbers nor the chippies did a better job.