1mm cable on commercial lighting ccts

[binky]

some time ago I read a paper on how 1mm lighting drops to individual lights are compliant with regs for commercial lighting ccts wired to say  C16A MCB ie where OCPD is in excess of the rating of the cable. Does anyone have a copy, or can anyone point in the right direction of said document  please.

 

[Andy™]

providing the cable cannot be overloaded, i.e fixed load on the end of it, and its adequately protected against fault current by the C16 then it would be OK

hate 1mm cable

 

[binky]

I know that bit Andy, but I have seen a paper which gives a full justification of this position, just can't think who it was by (one of the lighting manufacturers I believe). 

 

[Evans Electric]

Just wondering why you're looking at that Binky  ?

I think 1.00   T/E   is excellent for house bashing  and 1.5 is probably  OTT  for smaller houses .    Lets face it , upstairs lights ...max  0.5A    yet they get us worrying about  cables under  3 ft of insulation  etc  .   

Commercial / industrial  the runs are usually much longer , heavier loads say with fluorescent lighting .   

I see 1.5mm on kitchen jobs  looping ,say, 10  LED downlights  at 5W   and think its a waste & made the connecting more difficult.   

 

[binky]

Having a trade counter argument Evans, if I go to my local Tesco and go up onto the mezzanine floor where the sell loads of stuff like kettles and clothes you can see the cable runs are in 2.5mm to cope with voltage drop over long lengths. MCBs I've seen in such places are usually 16A C curve, at each light fitting (florries twin 5 or 6ft) 1mm flex cable drops to light fitting from ceiling rose. This is standard practice and has been for decades. Regs state that where a fixed load cannot overload the cable it is acceptable to use  a cable smaller than would normally be protected by the OCPD, but I also know I have seen a 2/3 page full justification of this which goes into great depth about how it complies. Just can't remember where I saw this or who wrote it, which is annoying!

Got another argument as well, if a ruined building has no floors or roof and is generally just an empty shell, does it have an equipotential zone???  To me it is no different to a field.

 

[Evans Electric]

Don't think I've seen that particular document TBH  Binky .      I agree , as you say , we drop to a small flex say, from a Greg rose to a fitting without worrying about the back up breaker.

I remember a huge warehouse at a local brewery where we had to upgrade the sw/wires & N  from the lighting panel    to 4.0mm  as the originals were cooking  feeding the the high bay fittings .

I notice our local ASDA has changed hundreds of fluoros to LED now . 

 

[SLIPSHOD & SLAPDASH]

I only use 1.0 on domestic jobs nowadays. Easy to terminate 2 cables into better lights & never a problem on a 6A B breaker. On our shop fitting jobs we nearly always use Klik distribution boxes wired in 2.5 to a 6A C with 0.75 flex to each light, all shop jobs are wired in LSZH cable.

 

[Rob.]

Having a trade counter argument Evans, if I go to my local Tesco and go up onto the mezzanine floor where the sell loads of stuff like kettles and clothes you can see the cable runs are in 2.5mm to cope with voltage drop over long lengths. MCBs I've seen in such places are usually 16A C curve, at each light fitting (florries twin 5 or 6ft) 1mm flex cable drops to light fitting from ceiling rose.

I've done the above myself in the past, 2.5mm ring for the lights in a silo. At each point they spurred off with a click fixture. 

However, devils advocate in me would argue that fluorescent lights with the wire wound ballasts can be overloaded, I've seen it when the ballast fails. As I'm sure a lot of people on here have also seen, certainly smelt it. 

 

[Andy™]

ballast may be overloaded, but the cable isnt