Can I use 0.5mm^2 flex for a pendant light?

[Steve T]

Hi all,

Got an antique light fitting that for some reason she wants putting up (can't say I love it haha) however it didn't come with any electrical fittings, so I'm trying to create a compliant solution. We want to use a brass lampholder with gold flex just going straight down from the brass base, basically what's already in the picture just brass and gold flex so it looks nicer. A few questions you'll probably want answers to already:

1. I will be earthing the brass base, with a brass m4 machine screw and nut and ring crimp since the connections sit inside it (wago connectors-there is space) so that bit should be safe. (1 cable at fitting not loop in)

2. The gold flex must be 3 core since the brass lampholder (one designed for pendants with strain relief) requires earthing.

3. Strain relief- haven't got a perfect solution for this for the cable coming out of the brass base, plan is to use a ziptie or two tight round the flex sheath which does stop it getting pulled out of the base, I'm aware this probably isn't really ideal but there's very little weight on the flex, only the lamp and lampholder, and the lamp ends up almost touching the glass shade anyway, so can't really see it being a problem.

But my question is firstly does my plan sound reasonable? Obviously this will be homemade and not type tested but I'm not selling it so shouldn't be too big an issue.

Secondly, can I use 0.5mm^2 gold flex for the lampholder mainly since TLC (where I'm ordering everything for this) don't sell 0.75mm and a smaller diameter looks nicer? I'm aware that pendants generally use 0.75mm^2 and have heard somewhere that 0.75mm^2 is the minimum allowed size flex on a 6A lighting circuit but not sure of the source or validity of that info. Also have seen many lights that appear to have 0.5mm^2 or smaller flex used?

Thanks for any advice on this!

 

[brianmoooore]

Why are you using a brass lamp holder when it's not visible?

 

[Steve T]

Why are you using a brass lamp holder when it's not visible?

You can see it clearly in real life just not from the angle that picture was taken

 

[Spoon]

and have heard somewhere that 0.75mm^2 is the minimum allowed size flex on a 6A lighting circuit but not sure of the source or validity of that info.

Table 52.3 of the regs.

 

[Pretty Mouth]

I think it may be okay to use 0.5mm for the flex from the base down to the lampholder. I have a pre-wired GU10 lampholder here that is wired with 0.5mm conductors, so someone must have thought it a good idea anyway

 

[timhoward]

If you expand the description on TLC site you’ll see the current rating the 0.5 sq mm flex. It’s 3amps.

I think it may be okay to use 0.5mm for the flex from the base down to the lampholder. I have a pre-wired GU10 lampholder here that is wired with 0.5mm conductors, so someone must have thought it a good idea anyway

I was waiting to see what other people said with interest!
I was torn between that table in section 5 which at first glance prohibits it.... and then thinking that the load will be nowhere near the 0.5 sq mm flexes limit and a protective device below the CCC could probably be omitted in these circumstances.

Is the answer that it would be ok but technically you shouldn't?!

 

[Pretty Mouth]

I was waiting to see what other people said with interest!
I was torn between that table in section 5 which at first glance prohibits it.... and then thinking that the load will be nowhere near the 0.5 sq mm flexes limit and a protective device below the CCC could probably be omitted in these circumstances.

Is the answer that it would be ok but technically you shouldn't?!

I suspect either it comes under manufacturer's regs rather than BS7671, or omission of overload protection due to nature of the load would apply.

Along similar lines, I believe it is acceptable to install a regular pendant set on a 16A circuit, in which case the .75mm flex wouldn't be protected against overload.

 

[Steve T]

Cheers guys, looks like technically I shouldn't use 0.5mm flex, thing that mainly made me think about it was the light fittings I've seen with clearly 0.5mm or smaller flex used within, for example a 4 spotlight bar fitting I got from screwfix years ago used flex that was definitely smaller than 0.5mm probably around 0.25mm yet it had the relevant certification to be installed in the UK and the instructions even mentioned having it on a 6A lighting circuit even though the CCC of the wires was clearly less than 6A.

 

[Lucien Nunes]

The load is fixed, it can't possibly draw 3A or anywhere near that without exploding, so the 6A MCB only needs to provide fault protection. In which case you might apply the adiabatic equation to check whether 0.5mm² works on a B6.

Historical note: There used to be a specific exemption for the internal wiring of light fittings and similar, in which a particular size of conductor called 'fittings wire' was permitted despite being too small for the circuit. I can't remember its actual CSA or which edition was the last to include it.

 

[pc1966]

A quick check on the typical let-through curves for the Hager B6 MCB has around 6,000 A2s at 3kA PFC so adiabatic would be 0.54mm using k=143 from Table 54.2 so a touch high for 0.5mm to be considered OK (of course other MCB might be different and typically lighting circuits won't see 3kA PFC, etc)