DIY Doctor

1mm² T&E on lighting circuit

Postby chris_on_tour2002 » Thu Jun 05, 2008 10:07 pm

hi folks,

still renovating the house that we moved into in november. pulled up the floorboards in my son's bedroom to fit the last radiator on the new heating system and noticed some 1½mm² cable going into a junction box under the floor - old red and black T&E with white sheathing so obviously done last time the house was rewired (badly) 20 years ago.

what caught my eye is the 1mm² cable with grey sheathing, the newer type, that also goes into the junction box so clearly an extension of existing. closer investigation shows that the new T&E is feeding the outside light by the front door.

all the outside lights are on a separate loop. the run of the 1mm² cable is about 4 metres and to change it for 1½mm² cable would be a great pain. so can i leave it as it is? i know that normally the same thickness of cable as the circuit should be used when adding a spur.

the light fitting uses a low energy bulb and is the only light being fed from the 1mm cable. what concerns me is that the light is a dusk til dawn so its on permanently throughout the night.

i will change it for 1½mm² but only want to do it if absolutely necessary! any advice greatly appreciated.
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Simply Build It

Postby ericmark » Fri Jun 06, 2008 10:12 am

If taking the regs view if the cross sectional area of a cable reduces it should be fused at the point of change or if no branches then at destination. In real terms lights normally have ceiling roses which mean the maximum overload size feeding lights is 6 amp and 1mm cable is more than required for that current so I would not worry about it. Also grey sheaving also used for 90 deg C instead of 70 deg C cable so don't jump to conclusions just because of colour.

Postby chris_on_tour2002 » Sat Jun 07, 2008 7:25 pm

thanks ericmark, i thought that it would be ok, as you say 1mm more than enough for 6amps but thanks for the confirmation and putting my mind at rest. i shall leave well alone.
Rank: Project Manager
Posts: 1024
Joined: Thu Aug 30, 2007 9:14 pm

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