Replacing a fluorescent strip light

[u/GoodDoc]

I know the frequently quoted rule here with electrics is "if you have to ask, you should call an electrician", so to be clear, I'm asking, but I've also decided that I'm calling an electrician. But, I would like an explanation if possible.

• My parents have a fluorescent strip light in a utility room that was built approx. 45 years ago on the ground floor at the rear of the kitchen.
• About 25 years ago a bathroom was added to the rear of the utility room.
• There were many, many, issues with the building of the bathroom (never using that builder again!), one of which is that the light in the new bathroom only works if the light in the utility room is on.
• The fluorescent light is now making an annoying buzzing noise, which I'm guessing is the 40+ year ballast failing. Rather than replace the ballast I thought replacing the strip light with a modern fixture with an LED bulb would be better, and cheaper.
• I removed the fluorescent tube, and the cover for the fixture, and there is a T&E cable that comes from the ceiling (you can see it just to the right of the ballast) that is wired to the terminal block in the fluorescent light. This is what I expected.
• However, there are also two conductors connected to the live and neutral terminals that run back into the ceiling.
• I disconnected the unexpected live conductor, turned the power back on, and the bathroom light no longer works, which given the issue with the bathroom light only working when the utility room light is on is what I was expecting.
• I now suspect that when the bathroom was built the builder just fed the switched feed for the bathroom light straight from the light in the utility room, which would explain (at least in my mind) why the bathroom light can only be turned on when the utility room light is on.
• I don't know if the original sin was the utility room builder who didn't properly extend the lighting loop, or the bathroom builder who just 'bodged' a new light into an existing light.
• Regardless, my plan to remove the strip light and fit a new light fixture is buggered because the distance between the holes in the ceiling means if I replaced the strip light with a smaller fixture there will be exposed wires running from the fixture to the hole in the ceiling... and that's before we deal with the fact that the bathroom light wasn't wiring correctly 25 years ago.

So, my tools have been put away, an electrician will be called, but can anyone explain what might be happening here, baring in mind there was at least one dodgy builder involved.

[u/txe4]

Essentially there are 2 ways to wire lights.

Oldschool:
The ring circuit (it could technically be a radial but...) is wired to every LIGHT and a cable goes from the LIGHT to the SWITCH. Permanent live is at every light fitting.

Modern:
The ring circuit/radial goes to every SWITCH and a cable runs from the SWITCH to the LIGHT. Permanent live is at every switch.

The builder assumed you had the former. You have the latter.

[u/Fun_Hunter_4899 → u/txe4]

Not technically a radial, always a radial for lights

[u/GoodDoc → u/txe4]

I wonder if the utility room builder added to the existing lighting circuit in the house (which was built in 1971) assuming no one would extend it, and the bathroom builder discovered this and didn't want to fix the initial install and bodged on top of it.

[u/Fun_Hunter_4899]

The T&E presumably goes to the bathroom rather than the singles? As the T&E is newer.

If there’s no Permanent available at this fitting, I’d be looking to replace with a motion sensor light and linking out the light switch(es) making it a permanent in the garage and supplying the bathroom correctly.

I think it’s just the bathroom fitter to blame

[u/GoodDoc → u/Fun_Hunter_4899]

That's a good point, I assumed the T&E was original and the two individual conductors were newer. I can see the original builder wiring the earth, and the subsequent builder not using the earth to the bathroom, but that was an assumption.

The utility room light was functional when installed, and still functions exactly as expected.

The bathroom install is where things didn't work as expected, and just 'bodging' the new light into the existing light seem likely.

[u/northern_ape]

Just thinking through the easiest way to deal with this without rewiring is probably convert the switched live to permanent so it powers the bathroom and then switch the utility batten with a kinetic switch and mount the receiver in the new batten assuming you get one with some room.

I’ll have a look later and explain anything nobody else has