Two questions


Postby Oz » Sun Apr 20, 2008 12:00 pm

1) I'm changing a light fitting. At the moment its a normal pendant light with three cables going to it, two small cables (about 8mm wide) one larger cable (about 10mm wide). They are all connected within the rose. The new light is very different. It has a decent sized earth but only very small push-in type live and neutral terminals (one each). There is easy access to the roof space above the light. I can see that the wider cable goes to the switch, one of the smaller cables goes to another light, the other disappears into the wall and heads down. How do I fit all the wires that are going to the original light into the new one?

2) I'm also swapping my electric shower. It has 6mm cable. What is the maximum kW output I can run on this size cable?


Many thanks in advance

Oz
Oz
Posts: 4
Joined: Sun Apr 20, 2008 11:32 am

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Postby BLAKEY1963 » Sun Apr 20, 2008 10:11 pm

[quote="Oz"]1) I'm changing a light fitting. At the moment its a normal pendant light with three cables going to it, two small cables (about 8mm wide) one larger cable (about 10mm wide). They are all connected within the rose. The new light is very different. It has a decent sized earth but only very small push-in type live and neutral terminals (one each). There is easy access to the roof space above the light. I can see that the wider cable goes to the switch, one of the smaller cables goes to another light, the other disappears into the wall and heads down. How do I fit all the wires that are going to the original light into the new one?

2) I'm also swapping my electric shower. It has 6mm cable. What is the maximum kW output I can run on this size cable?


Many thanks in advance

Oz[/quote]

OZ
I have just checked the project section of this site.
i think what would b of help 2 u is the sections on

CONNECTING AN ELECTRIC SHOWER PROJECT.

CHANGING A LIGHT FITTING

both sections have decent advice and fully understanable diagram 4
u to study.
get back 2 me once u have looked at sections.

personally with the shower as a rule of thumb any thing above a
7kw i would change cable for 10 mm2.
to get into projects click on PROJECTS at the top of the page.

BLAKEY1963
BLAKEY1963
Posts: 654
Joined: Wed Jun 13, 2007 10:57 pm


Postby ericmark » Mon Apr 21, 2008 7:58 am

2) Assuming the 6mm² cable is PVC
Ref Ref Ref Ref Ref Ref
100 101 102 103 A C
34 27 35 23.5 32 47
As you can see according to how the cable is run the amps is can carry vary in watts this becomes:-
7820 6210 8050 5405 7360 10810
Even the smallest shower may overload the cable. Because showers are used for such short times a small overload you may get away with so 7.5Kw on a 32 amp MCB is about the max (Ref C is direct in masonry and although it may travel part way like that 100 and 102 clipped to wooden joist and in stud wall are more likely limiting factors) If the cable runs through a wall with insulation and is not clipped or if in loft with insulation above level with joists then 6mm² will not run a shower. People have got away with a 8.5Kw shower on 32 amp MCB but if they have anything more than very short shower it will trip and in the end the trip itself will fail.
The 9.5Kw showers need 16mm² really but you can get away with 10mm² for short showers. Also as one uses 40, 45, or 50 amp MCB’s you need to be sure your whole supply can cope as some houses have only 60 amp supply. I have seen in old houses 6mm² tails from meter to consumer unit. Remember all electrical installations should be tested and new circuits and work in bathrooms and kitchens often needs Part P there are links in Projects section.
1) As to lamp I would retain existing rose but re-position above ceiling then feed new lamp from the flex. i.e. use old rose as junction box. Strictly speaking its not allowed as you don't need a tool to open a ceiling rose and it only has special dispensation when used as ceiling rose. But how many people are really going to go into your loft and mess with it?
ericmark


Postby Oz » Mon Apr 21, 2008 6:23 pm

Thanks BLAKEY1963. I've checked out these Projects. The light fitting should be fine now and thanks ericmark for the suggestion about using the existing rose as a junction box in the loft. I guess these things are obvious to you guys.

As far as the shower goes I might have to change my mind as it doesn't look as if I can get away with anything powerful enough as a straight 'old for new' swap. Either I will plumb in a hot/cold shower or rewire to accomodate a more powerful electric shower. This would mean the most disruption so probably my least preferred option. Anyway, I've checked and I only have a 60amp supply.

Thanks again to you both, much appreciated.

Oz
Oz
Posts: 4
Joined: Sun Apr 20, 2008 11:32 am


Postby Oz » Tue Apr 22, 2008 6:21 pm

My new light says "must be earthed". Does this just mean run an extra earth wire to the light fitting from the same earth point where the others meet up?

Cheers

Oz
Oz
Posts: 4
Joined: Sun Apr 20, 2008 11:32 am


Postby ericmark » Tue Apr 22, 2008 10:52 pm

Yes you will need to replace original two core cable for three core.
ericmark


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