Lighting problem. load and connection

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I have 2 MCB's at 6A one for upstairs and one for downstairs.
I am adding some lighting for under the kitchen wall cabinets although am not sure whether to go for small fluorescent or ELV spots. I just want to check how to do a calculation to make sure the load is permitted.? is it purely adding watts used divided by 240v = current.


One other thing I need to do is relocate a switch for 2 normal ceiling lights. The switch has 2 physical switches on it and is supplied by 3 core + earth. The switch has L1 + L2 + common on top and bottom. Hanging down from each ceiling location is just one 7mm wide cable with L + N + E
What are my options here as it is difficult to start ripping apart the ceiling and I can see no junction box where these 2 cables must meet. Upstairs in this location a granite floor is laid. Is it allowed to permanently make the switch live then put a cover plate on it. So then I would only have to make a new route for the new switch and cable up to the ceiling light point.?

Any advice welcome
 
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Yes you load can be calulated using watts/volts the new nominal voltage is now consider to be at 230v.
so if you had a circuit with say 12 lamps rated at 100watts each
that would equal 1200 watt divide that by 230,
which will equal 5.22A.
As far as your switch drop, I would install a new cable with no joints, as joints need to be made accessible.
You could either have a lighting system that is loop in, which means the switch cables will be terminated at the light fitting this will make life a little easier than locating the other system of junction boxes.
But the odds are stacked in the favour of you having to break in to your ceiling, reagardless.
Hope this helps!
 
Yes you load can be calulated using watts/volts the new nominal voltage is now consider to be at 230v.
so if you had a circuit with say 12 lamps rated at 100watts each
that would equal 1200 watt divide that by 230,
which will equal 5.22A.

When making a calculation of the expected maximum demand, it is assumed that not all lights will be on at the same time.
This technique is known as diversity and has been discussed to death on here.

For a house, one can apply a diversity factor of 66%. So the 5.22A becomes 3.44amps. The 100w only applies to GLS tungsten lamps though. There are more complex rules if you are using discharge or fluorescent lighting due to harmonic currents etc.

However, its unlikely that a couple of under cupboard lights is going to cause you any issues with loading (unless you have had mystery tripping of the lighting cb due to marginal loading.)

A larger issue would be Building Regulations Part P - as this work is in a special location..
 
The OP asked about calculating load, not diversity!
That's another lesson ;)
But there is a chance that all lights on a single circuit, can be all on, so it's a grey area!
 
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OK thanks a lot Taylortwocities and prenticeboy. :)

As far as your switch drop, I would install a new cable with no joints, as joints need to be made accessible.
You could either have a lighting system that is loop in, which means the switch cables will be terminated at the light fitting this will make life a little easier than locating the other system of junction boxes.

Yes, I have made small hole in the ceiling to hopefully find a junction but all I find is both cables disappear into a joist hole. So I am prepared to lay a new cable from the new switch position to the light fitting but the problem is where do i get my live. If I remove the old switch I have live wires there. How would a pro make this safe , by tracing the cable back to the CU or junction and removing ? And to make my new "switch drop" none of my light fittings have power unless the switch is on. So again where would a pro get the live from, the junction i believe .? So I have the same problem of finding a junction and ripping apart the ceiling. Sorry if this is obvious but want to know how a pro would approach this if you have a finished house :)
 
Yes, I have made small hole in the ceiling to hopefully find a junction but all I find is both cables disappear into a joist hole. So I am prepared to lay a new cable from the new switch position to the light fitting but the problem is where do i get my live. If I remove the old switch I have live wires there. How would a pro make this safe , by tracing the cable back to the CU or junction and removing ? And to make my new "switch drop" none of my light fittings have power unless the switch is on. So again where would a pro get the live from, the junction i believe .? So I have the same problem of finding a junction and ripping apart the ceiling. Sorry if this is obvious but want to know how a pro would approach this if you have a finished house :)
are you sure the lights/switches are connected via junction boxes and not looped in at ceiling roses?
 
Tks for your reply.
Yes, All I have is a chock block and just cable going back into the ceiling void.
 
Tks for your reply.
Yes, All I have is a chock block and just cable going back into the ceiling void.
I don't understand.
You said you have followed the cables to joist and no futher, so how do you know they are in choc-boxes?
Anyway you need to find where the cable treminates, whether it be to boxes or loop method and replace the cable, only other method would be extending cable using mechanical fixings, they can be solderer or crimped not really advisiable for installation, there is also what is known as maintenance free junction boxes
http://www.tlc-direct.co.uk/Products/ASJ804.html
that seems to allowed but not favoured by some, they can be placed in your ceiling void.
I would always try to replace to whole cable, how far are you moving it?
 
I don't understand.
You said you have followed the cables to joist and no futher, so how do you know they are in choc-boxes?

Apologies let me explain. I have a fluorescent light connected to a choc box (small plastic connector) then a cable that disappears into the ceiling. Then I made a small hole in the ceiling where it meets the partition to find the same cable but it disappears into a joist (but i was hoping to find a junction :) )

Now in this same partition i have the switch that controls the light, so I went the other side of partition, made another small hole for my hand to "feel" both the cable from the switch and the cable from the light but no luck as both cables disappear at different directions into another joist. So no luck finding this junction :(

But yes the link is useful, thanks for that. So these maintenance free connectors do comply with BS 7671. So would it still comply if I used it in this wall partition at the switch position to permanently connect the cable. So this would mean I have permanent live supply to the light where I can wire a switch to drop down on the opposite side of the ceiling. Of course this would mean a cable that does not make a direct route and travels down a partition and back up again.
Thanks for all your help with this.
 
I understand better now.
What cables do you have coming from ceiling in to light fitting, just a set of red/black and earth?
If so
I would put the joint in the ceiling void, but if you leave a blank plate on the front of the old switch box you can use a normal connection block inside it, to make termination, fixing the earth to the metal back box terminal.
Then will still be accessible and cable routed in permitted safe zones, so complies
Link
//www.diynot.com/wiki/electrics:installation_techniques:walls
//www.diynot.com/wiki/electrics:installation_techniques:route
 

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