Garage lighting question, and an earthing question

[slippyr4]

Hi All,

I'm currently rewiring the garage and the attached brick shed. Am using a wylex garage CU (RCD + 6A + 16A MCB - B's), and using plastic 20mm conduit and singles.

Question is if lighting *must* be loop-in? It'd be far easier, and use less copper, if i could run the garage lights and the shed light as "radials" from the same 6A MCB. This would result in two wires attached to the one MCB. Is that allowed? or should I really loop off the one light along to the next?


Second question - the CU is supplied by a 4m run of 2.5mm^2 3c SWA. To connect the armour banjo at the CU end to the CU's earth bar, what cable size should I use? will 2.5mm be ok? or should it be thicker? it'll only be about 20cm long.

thanks

slip

 

[ricicle]

Slip,
Its perfectly ok to have 2 cables in the same mcb.As for the earth it is best practice to have it the same size as live,so 2.5mm in your case.

ricicle

 

[industryspark]

firstly, are you aware of part p? this work is notifiable.

plastic 20mm conduit and singles

someone will correct me if im wrong (havent got my regs on me) but not sure if this is aloud in a garage environment. steel conduit in my opinion would be much better and offer far better protection!

personally id go from one light to the next to keep it simple and the way most people know but there's nothing wrong with a star configuration no.

you sure that 2.5mm swa is going to be enough for your needs? you may want to future proof it for additions later on.

 

[Lectrician]

20mm galv conduit in a domestic garage

20mm PVC will be fine - and better than most!

I would be more than hoppy with the two cables in the breaker.

Couple tips - Run the conduit high level, using circular tee-boxes to drop to accessories. The sockets and lights can share the conduit, and can also share an earth (2.5). I would wire the lights in 2.5 aswell - saves buying a drum of 1.5 of each colour!

Take the neutral directly to the light fitting, and take the live to the fitting via a switch. Dont do what domestic sparks think is correct ......... taking the live to the light fitting, and then back to the switch and back to the light! (as a standard T+E loop in/out).

Use circular boxes (terms, angles, throughs, tees etc) instead of inspection elbows. Pull your own bends where possible (buy yourself a bending spring.......and not a plumbers one!.....seen that so many times with DIY'ers!).

If you are fitting flourescents, fit two conduit boxes to the ceiling - normally a through and a term, and set them at the correct distance to fit the BESA fixings of the flourescent fitting. DONT wire through the flouresent - If ever you need to change it, it is an arse! Many flourecents these days are a little narrower than the conduit box lids, so use a lit aswell, with a 20mm hole in it. (between box and light).

Dont make any joins in any circ box.

Use Female adaptors - not males. AND MAKE SURE YOU DO USE ONE! So many people dont, and just push the conduit in the hole.

Make sure you have a circ box every 3m or so, and only have 180deg of bends between accessories/boxes. IE, two 90 or a 90 and two 45's.

May have missed something...?

 

[slippyr4]

firstly, are you aware of part p? this work is notifiable.

Yep. I've got a building notice.

someone will correct me if im wrong (havent got my regs on me) but not sure if this is aloud in a garage environment.

It's perfectly allowed - domestic. Besides, you're allowed to clip T+E to the walls in a garage, which also offers virtually nil mechanical protection. Working with steel is too fiddly for me (as a DIYer).

you sure that 2.5mm swa is going to be enough for your needs? you may want to future proof it for additions later on.

Too late to change that now. But the run is so short that I can pull 30A off it, should I need to. But in realism, all i'll have running at once is a power tool and some lighting. So i'm looking at worst case 16A total load. So 2.5mm^2 should do the job nicely.

thanks
#
slip

 

[Lectrician]

With a 16 a 6 amp breaker, max demand is only 24amp.

Why do these garage CU's always come with 16amp breakers?? I would prefer to see a 20.

Also, PVC SWA is only rated to 28 amp when ducted in the ground or clipped direct, Higher when directly in contact with the earth.......So, as you will have a length in the garage and house clipped direct, your max rating is 28amp.

You should therefore have it protected by a 20amp breaker, or 25 if your CU will accomodate one (some makes don't produce one).

 

[plugwash]

PVC conduit while it won't stand direct use of say a drill is more than sufficaiant to resist glancing blows from most tools.

 

[industryspark]

i stand corrected!

probably had my garage in mind which is steel conduit, but then again its more like a workshop than a garage!

Yep. I've got a building notice

good man.

sounds like you've done a couple of these before Lectrician!

 

[Lectrician]

A couple? I am more commercial/industrial than domestic - Do it all the time

 

[slippyr4]

Thanks for the tips Lectrician. Most of the conduit is already in place. It's all right at the top of the wall, and I have (inspection) tees to come down to switches and accessories.

I've already bought drums of 2.5mm, and a length of 1.5mm earth (my electrical supplier sells that by metre) but i was planning on splitting some spare 1.5mm T+E to get the brown and blue - i have some left from the house. Is that a no go?

Re: Lighting - in the garage i have a 5' and a 3' fluorescent. They have female conduit adaptors fixed into the ends of them, and since they are in line on the ceiling, i have a branch of conduit coming from the wall to between the lights, and then tees to go to each one. So it should be easy to remove the lights individually in the future if necessary.

basically, the CU is on the wall that's shared between the shed and garage, and the garage light switch is next to it. Hence my question about loop-in being necessary - the lights are in opposite directions. I'd planned to route live to the switch and then to the light, not bothering with a permanent live at the light - but that was of course dependant on loop in not being necessary.

What's a BESA fitting?

thanks

slip

 

[Lectrician]

I really don't like inspection elbows/tees. They don't help you pull in/out cables.

I wouldn't use your 1.5 T+E - the cores are solid, and not designed for pulling into conduit - 1.5mm singles are stranded.

Also, Wire the sockets with 2.5 L and N, and a 2.5 Earth - With singles it is best practice to use the same size.

If the flourescents only have a single conduit entry on them, then this should be ok for changing in the future.

BESA fixings are standardised fixing centres. The dimension from screw to screw on a conduit box lid will marry with the fixing holes/orientation of light fittings, ceiling roses, many socket back boxes, spot lights, wall lights, etc etc.

 

[slippyr4]

so one of the round conduit terminal thingies should fix straight onto the back of the fluorescent fitting then (aside from your previous comment that it might be too narrow)?