Bathroom lighting circuit

[comfused]

Hi all,

This post relates to the lighting circuit in a bedroom currently in the process of being converted into a bathroom. The existing bathroom is downstairs, the bedroom is upstairs.

An existing 60W ceiling rose has been removed. The wiring is recent and dates from 2004 and consisted of two cables. One to the switch and one to the ring. This appears to be a spur which I wasn’t expecting. The changes described below relate to this connection.

I am adding:

- Six 35W halogen lamps, ceiling-mounted in IP44 enclosures running from two 12v transformers. The transformers are supplied by 1.5mm T&E, 12V supply is 0.75mm twin flex connected in series to 3 lamps each. This sounds a bit on the thin side to me. Perhaps the 12V supply should be 1.5mm T&E to junction box then each halogen individually wired from this?
- One 1.5mm T&E direct from switch to a mirror heater. Approx 30W.
- One 1.5mm T&E direct to a shaver point.
- Connection to extraction fan including 35W lamp. I haven’t done this yet as I don’t have any 3 core plus earth. Is it acceptable to do it with 2 x 1.5mm T&E and if so, how?

I will also be adding a 10mm shower cable from the consumer unit which is only 8 feet away. However, I’ll be getting an electrician to do this and check everything else for part p.

Questions:
1. Should the 0.75mm flex used to wire the 12V halogen lamps be thicker or individually cabled to each lamp from a junction box?
2. If I can’t get hold of any three core plus earth, how can I achieve the same with 1.5mm T&E.
3. Do I have to have a switch on the fan, mirror heater, shaver point or shower?

Background:
This house is very cold. The loft insulation consisted of some pink rock wool around 50mm thick at best combined with the usual carpet, rugs, mats and bits of Christmas decorations dating from the 70s. This has now been cleared but has revealed 4” joists which won’t work with my shiny new 200mm rock wool as I also want to board the whole space. So, as I was given around 20 lengths of 5x2 I have now glued and screwed them to the existing joists giving me 9” and plenty of room for both 200mm insulation and boarding. All halogen lights are now surrounded by 360mm sq boxes with at least 50mm clearance and all cables are housed in at least 25mm trunking where they run near or in insulation.

 

[Steve]

1. 0.75 is borderline. 105 watts at 12 volts is about 9 amps (though only a small section of cable actually carries this, since it branches off to lamps). And the lamps are wired in parallel. However, bear in mind you cannot run this cable at this current through insulation (can someone do the calcs?). And its not recommended to modify a pre-assembled lamp set (as this sounds like). The transformer must be accessible - they will fail at some point. It would be less hassle to use mains downlights, fitted with CFLs. Less energy, more light, less current.

2. You can get hold of 3c+e.

3. fan - 3 pole isolator mounted at ceiling height or outside the bathroom.
mirror heater - 10A pull cord
shaver point - no switch required
shower - 50A pull cord.

PS. This light point is not a spur, its the last point on a RADIAL circuit. Lighting isn't a ring circuit.

Also, have you already arranged an electrician to check off your work? This is actually not allowed, but some will do it.

Your LEGAL options are:

1. Notify building control before commencing work, and THEY arrange one of their electricians to test and certify your work at as many stages as they see fit, depending on the scope of the work.
2. Employ an electrician to carry out ALL of the work for you, though you may save money by doing the "donkey work" yourself.

 

[comfused]

Thanks Steve,

From what you say, it seems that my best option would be to get a properly qualified electrician in. I have the details of the company who completely rewired the house a few years back so they would probably be best placed to do the work as they presumably can remember what went where.

By "donkey work", I guess you mean making the Electrician's job as easy as possible by removing obstructions etc. If this is the case, I’ve already done it as the loft space has been cleared and there’s a clear path from new bathroom (an empty room at present) to the consumer unit.

Back to the lighting though. The connectors in the 12v kits are never long enough so I have no option but to cut them. It sounds like my best bet for the bedrooms would be to use 15A 2 core cable which would give me up to 180W – ie. more than enough as I will likely be using 3 x 20W Halogens or 3 x 5W LEDs (or a combination of both).