Cable sizes for lights

[brizospark]

Was carrying out a PIR today.
10 x low bay lights supplied via 20A MCB
Cable to klix units is 2.5 which is fine but from klix to lights is 1.5

should this be reported (20A MCB too large for 1.5mm)

 

[Mr Mark Sparks]

in theory yes but if the fittings are fused then the flex cant pull more than ?amps so its ok

 

[i=p/u]

thats what i dont get, if the load is not going to exceed the cable , what does it matter where/what circuit you come off?? someone put me on my hole.. with simple awnser or agree

 

[brizospark]

i=p/u your thoughts are fine in theory but if there is say a fault with the fitting and it was drawing 19A for instance then the 1.5mm flex would not be able to handle this and the MCB would not trip

 

[johnboy6083]

mopst of the clicks i have ever fitted, have been fitted to lights that have incorporated a fuse. if the light started pulling too much current, then the 1.5mm cable is protected by that fuse. this is called backfusing. if the cables is damaged, then the device further up the line will protect the cable from short circuit, Zs permitting.

 

[brizospark]

yes but i have seen cases where there are no fuses internally within the fitting

 

[johnboy6083]

i dont think that flourescent lights are capable of overload.

 

[brizospark]

johnboy any elec. equip. is capable of overload if there is a fault with the wiring to it

 

[Deleted member 26818]

This is no different from using 0.75mm² for pendants, or spuring off from a RFC in 2.5mm².
The cable upt to the Klix has to be sized to carry the current of the whole circuit, whereas the cable from each Klix only has to carry the current for that particular fitting.

 

[johnboy6083]

if theres a wiring fault, then that would be a short circuit, and ZS permitting, that will be taken care of by the circuit OCPD

 

[brizospark]

yes i see what you guys are sayin about it being the same as a spur. Still, I don't agree with it! The MCB should, IMHO, be protecting the entire cabling for the circuit

 

[One_of_them]

I find the ballast usually takes the "hit" instead of the wiring.