Lighting and mains Heights and other Q's


Postby MrElectric » Sun Jul 29, 2007 10:39 pm

H All,
I recently purchased a property in England and was told:
1- The MCB fuses in the consumer unit need to in order of High to Low.
Is this true? Has anyone come across this?

Please can someone kindly help me with the following questions:

Q1 – I have read on the internet that light switches and mains sockets have to be at certain height.
The height for mains sockets has to be 450mm or above from the floor.
The height for light switches can be upto 120mm- maximum.
The property I have some of the light switches are above 1200mm and some of the main sockets are above 150mm and below 450mm. Do I need to re-install them? Is this a mandatory requirement nowadays?

Q2 - In order to install a wall mounted lamp holder (with 3 terminals earth, live and neutral). Can I take a mains to a switch and then to a wall mounted lamp holder. Is this OK and does it conform to 16th edition? If not what is the recommended approach?

Q3- In lighting loop or ring mains - Can you put a junction box to add in a new socket or a new light? If not what is the alternative?

Q4 - I have experience of domestic electrical installation and would like to become a certified competent electrician. I don’t wish to spend 4 years at a college. I have seen a number of quick part P and other electrical courses that can be completed in 5 days to 15 days in total. Is this true or just a money making game?

All replies greatfully received.

Many Thanks
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Postby sparx » Mon Jul 30, 2007 11:17 am

Hi, Mr E.
points in order:
1)No! very old idea when boards bus-bar was smaller & tried to get main load nearest sw. no longer relevent.
1a) Only new build & extensions to non-domestic.
2) Ok if by mains you mean from a lighting circuit, If from power cct then use a sw/fused spur with a 3A fuse.
3) yes or loop in at nearest point.
4)As a time served (5years on slave wages) fully quilified electrician I can only damn these courses to hell & back they are rubbish but if you can get away with it.......
regards SPARX
P.S. I used to lecture @ local tech. but quit due to the college introducing these 'bums-on-seats' short course, so somewhat biased. It's not possible to become a safe, qualified leckie in a year never mind a week in my humble opinion!!B.W.
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Postby MrElectric » Mon Jul 30, 2007 1:32 pm

Hi sparx,

Thank you very much for taking the time to reply to my posting.

Many Thanks :)
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Postby MrElectric » Mon Jul 30, 2007 1:53 pm

Hi sparx,

Please can you kindly tell me:

1- How many double sockets, spurs can you have on a ring mains ? and also what size cable can you use?
2- How many lighting lamps can you have on a lighting circuit? and what size cable can you use?

Many Thanks :)
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Postby sparx » Tue Jul 31, 2007 9:44 pm

Hi agn.
as long as one ring per 100M2 of floor area no limit to total # of outlets but must have no more as spurs than # 'on the ring' IE 20 'on-ring' less than 20 spurs.
cable for ring/spurs 2.5mm2
lights normal recommendation 10-12 points/cct. on 1.5mm2 , sw. wires can be in 1.0mm2 .
load limits max # on lighting cct, ie 12 X 100watts=1200w, 1200/230v =
5.2 Amps on normal 6A MCB is enough!
regards SPARX
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Postby MrElectric » Thu Aug 02, 2007 11:24 am

Hi Sparx,
Thanks for your reply.

Can I use 1.0mm for lighting throughout. It’s just a matter of convenience when trying to bend and fit cables into a ceiling rose. Is this OK?

Also when trying to interconnect smoke alarms do you use a 3 core & earth?

Cheers,
Mr E
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Postby sparx » Thu Aug 02, 2007 9:01 pm

Hi Mr E
on most circuits 1.0mm2 is adequate & as u say easier to fit in roses & small fittings, & wall lights.It's a little fragile to connect, so personally I use 1.5 for looped feeds and twin brn. 1.0mm2 for switch drops or 1.0mm2- 3 core for 2 ways. 1.0mm2 rated up to 11A so no prob with load only volt drop to consider for longer runs, If using one circuit for each level then average house fine on 1.0mm2,
Smoke alarms do need 3C /e for interconnecting,
BTW I have gone back to old fashioned way of wiring lights, where you take a single cable from each point back to a central Junction box, bn/blu for each light, brn/brn for sw cable and connect relevent cores together in J.B. an end to overcrowded fittings (and 1/2 the posts on here abt how to connect fittings!!!)
REGARDS SPARX
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Postby MrElectric » Fri Aug 03, 2007 10:35 am

Thanks for your reply sparx.
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Postby MrElectric » Tue Aug 28, 2007 3:04 pm

Hi Sparx,

I have 4 main smoke alarms to interconnect using a 3 core and earth cable. What size and type of cable should I use to connect from the fuse box to the first smoke alarm?

I can’t see how I can use a 3 core to connect to the fuse box.
The way I see it is- a quick sketch:

key:-
SM1-4 = Smoke Alarms
3C = 3 CORE and earth cable


CABLE TYPE:~~? ~~~~~~~~3C~~~~~~~~3C~~~~~~~~~3C~~~~~~
[FUSE BOX]------- SM(1)-------------SM(2)------------SM(3)-----------SM(4)
(6AMP FUSE)

Many Thanks
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Postby sparx » Tue Aug 28, 2007 8:05 pm

Hi , Gee this is getting a long time post, but to answer last? twin&E from consumer unit to first detector, the 3rd core just interlinks the outputs so one-on-all-on.
So L & N will have 2 cores in each but first & last det. will only have one in the link term.
Hope that makes sense, ie in your drawing SM(1) & SM(4) will have only 1 in link term each but SM(2 & 3) will have 2 in/out.
regards SPARX
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