Flooring a garage loft

[James Abley]

Hi,

I had this done at my old house, and would like to have the same again. I thought how hard can it be, so I'm doing it myself this time. The last place had the bar code left on the boards, so I know what to get there. The only question I have really is about how to re-wire the lighting? The current setup has the wires going across some boards which I'm going to rip up and replace with the new flooring. I need to re-do those wires, plus I guess stick in some sort of junction box so that I can run a couple of lights up in the new loft along with a switch by the loft hatch / ladder. I'm no electrician though. I've previously installed a junction box to run a security light off the front of the garage. That's the limit of my electrical experience:

• What kit I need to add in the new lighting along with a light switch?

• How do I ensure that I'm not overloading the circuit?

• What have I missed?

All expertise gratefully received.

Cheers,

James

[Roger Mills]

Is the garage part of the house, or detached? Is it heated?

If you have cables running over the joists, and you want to fit boards, you have several options.

One is to drill holes through the centres of the joists, and to feed the cables through. But you'd obviously have to disconnect and re-connect the cables in order to do that. Also, there are rules about where - along the length of the joists - you are allowed to drill holes without causing structural problems.

If you *don't* want to disconnect the cables, the options are either to notch the tops of the joists to accommodate the cables, or to fit battens to the joists to space the boards clear of the cables. Again there are rules about where you can cut notches.

When you box cables in, technically you are reducing their heat dissipation capacity, and need to restrict the amount of current which they carry - particularly if they pass through heated or insulated spaces - but it's probably not an issue in your case.

With regards to extending the lighting circuit in order to install additional lights and switches, you need to understand what you've already got, and how it's wired - 'cos there's more than one accepted way of wiring lighting circuits. Also, you need to distinguish between lighting and power circuits. If you don't know what you're looking for, it's probably safest to employ an electrician.

[Roger Mills]

Both. The building regs include rules about where holes and notches can be in order not to compromise the structural integrity. They have been quoted in this NG in the past, but I can't quote the exact details offhand.

Assuming it uses 1 or 1.5 M^2 cable on a 5 or 6 amp fuse, there's no danger of overloading it by adding another couple of lights.

In the garage, or in the house?

Your terminology worries me slightly when you say things like "it can't be too difficult". I would be happier if you demonstrated that you knew how you were going to go about it, and were simply seeking confirmation of your method.

[John Rumm]

"To meet current building regulations, the hole does not want to be more than 0.25 times the total joist height - so a 2" hole on a 8" joist is about the limit. It should also not go closer to the end of the joist than 1/4 of the span (so no nearer than 1m from the end of a 4m joist), and no closer to the centre than 0.4 times the span."

[John Rumm]

Modern lighting circuits are usually wired using the "loop-in" method:

each light position has a cable in, another to the switch, and (unless its the last light on the circuit) another cable out to the next light.

So adding more lights is really a case of taking a power feed from a convenient light on the existing circuit and extending in the same way. You can use a ceiling rose, the light fitting itself (if it has space for the terminals) or a 4 terminal junction box to do the loop in wiring.

Check the circuit breaker rating. Chances are its 6A. That limits the total power to just under 1400W. To assess the size of of the existing circuit then count 100W (or the actual rating if larger) for each light position and just add em up. Sounds like you probably have over 1200W spare!

[PeterC]

Is it necessary to allow for PF with CFLs? In the loft I have 7x11W CFLs, so 77W, but the PF is poor and so they're about 145VA. The 30W CFL in another fitting is about 31VA - pity that the lower wattage ones aren't as good.

[John Rumm]

No, because according to the sizing guidelines the smallest power you count is 100W - which is way more than a CFL even allowing for PF.

You still treat the 7x fittings as 700W of load; since you could realistically expect someone to install GLS bulbs and need to allow for it.

[PeterC]

OK, thanks. It'd stand that but 100W lamps might melt something; I'd better put in dome ally reflectors/heat shields. I woudn't put even a 40W GLS near anything that might suffer from the heat, but I've seen several things melted by over-powered lamps.

[John Rumm]

Many fittings are limited to 60W in reality.

[NT]

[<me9]

Bbbbutt! you can no longer get GLS blubs greater than 60w (or so they say).

I haven't used a GLS lamp for years.

[John Rumm]

Most shops seem to have stocks of 100W ones again...

[Frank Erskine]

On Mon, 03 Aug 2009 00:22:20 +0100, had this to say:

That doesn't mean that they aren't availabubble....

I bet you still hfr some Swan lamps though - in your torch, your oven, your microwave, your sewing chamine - even your car!

[PeterC]

Reality doesn't bother a lot of people - 100W in a 60W socket in a spherical paper shade: there seems to be a burning smell. (Or the 'instant' shower unit on 2.5!).

[PeterC]

I have them only where I need light immediately but for a short time. There's a 60W on the landing (for airing cupboard) but I recently put an

11W CFL in the hall as I have people staying and leave that light on if they're late back; the CFL is brighter than the 60W bulb.

[<me9]

I've a couple of supermarket (beginning with T) torches with 3W leds. Impressively superbright, but expensive.