"Stepping up" 1mm t&e to 1.5mm

[richeighty1]

Good afternoon all,

First post here, so please be gentle...

I'm in the middle of adding an additional three 70w fluorescent strip lights to an existing 70w strip light in my garage (all run from a single switch).

Having made a similar addition in my last property (which is was a more recent build) I have wired the additional lights together in the same way using 1.5mm t&e.

However, having come to make the final connection to the existing light circuit I have discovered that the current wiring is 1mm t&e. Checking back I have discovered that this is the case through out the lighting circuit, all the way back to the MCB (B6).

Now, I know what I should probably do (i.e. strip out what I have done and start again with 1mm...), but would it be possible to step up the existing 1mm to 1.5mm, just for the additional three lights? Would it be unacceptable on the basis that anyone subsequently adding to the circuit would assume it was 1.5mm throughout, or is there a loading issue?

Many thanks for any thoughts.

 

[ban-all-sheds]

Just leave it - 1mm² is fine - absolute worst case current carrying capacity is 8A.

 

[richeighty1]

Sorry, I don't think I phrased that particularly clearly. I was planning on leaving the existing 1mm part of the circuit, it was just whether I could make my addition with 1.5mm?

Thanks.

 

[flameport]

You can use 1.5mm if you want - but there is no reason to do so.

 

[deadshort]

All good,


DS

 

[EFLImpudence]

Who started this fashion for 1.5mm²?

 

[DetlefSchmitz]

Who started this fashion for 1.5mm²?

I can remember a long time back before all this regulation when I was engaged to wire a new portacabin type playgroup building (so I was one of a team of volunteers). My experience was wiring at home and talking to retired electricians. Obviously nowhere near sufficient in today's terms.

Anyway the father of a then colleague was once an electrician, so I was given 'tips' by him. One tip was 'you can always spur off a socket' which means that a spur can spur off a socket which is already a spur, and so on - daft really'. I have no idea if the regulations were really worded like that back then. No-one could afford the regulations so who knows?

Anyway, the other thing he said was 'no need to buy 2.5, 1.5 and 1mm, because you can use the 1.5 for lighting and save buying a reel of 1mm'.

I did this during the playgroup wiring, (and really struggled to get the 2x1.5mm into the places needing this).

I believe that this was common 'knowledge' back then. Just a way to save money on a job.

Only saying this because the question keeps coming up here.

Don't get me started on the procedure for getting the job signed off by the Electricity Board...

 

[ban-all-sheds]

Anyway, the other thing he said was 'no need to buy 2.5, 1.5 and 1mm, because you can use the 1.5 for lighting and save buying a reel of 1mm'.

I wonder why he didn't say "...because you can use the 1mm² for lighting and save buying a reel of 1.5mm²"? What was his plan for using 1.5mm² on circuits other than lighting ones?

 

[deadshort]

You could use 1.5mm on 15a or 13a Radials into the 80's.

DS

 

[JohnW2]

You could use 1.5mm on 15a or 13a Radials into the 80's.

AFAIAA, you still can, in 2015, if you want. Indeed, if it Method C, you could even have a 20A radial wired in 1.5mm².

Kind Regards, John

 

[JohnW2]

Who started this fashion for 1.5mm²?

Perhaps eric, backed up by some VD calculations for very long lighting circuits

Kind Regards, John

 

[DetlefSchmitz]

Anyway, the other thing he said was 'no need to buy 2.5, 1.5 and 1mm, because you can use the 1.5 for lighting and save buying a reel of 1mm'.

I wonder why he didn't say "...because you can use the 1mm² for lighting and save buying a reel of 1.5mm²"? What was his plan for using 1.5mm² on circuits other than lighting ones?

I think (long time ago) it was for immersions. In the playgroup case, it was probably the handdryer circuit.

 

[EFLImpudence]

the other thing he said was 'no need to buy 2.5, 1.5 and 1mm, because you can use the 1.5 for lighting and save buying a reel of 1mm'.

As said, surely there must be more cases of 1.5 being wasted on lighting circuits than using 2.5 when 1.5 was actually needed.

 

[deadshort]

I do recall that local authorites specified 1.5mm for lighting but this was for physical reasons as the 1mm was a bit to flimsy for the house bashers to 'draw in' without damage.

That's my story, but at the time, cable was cheap ! 1977

DS

 

[westie101]

Certainly when I was training back in the '70s we were always advised to use 1.5 as it was physically stronger and less likely to being damaged on installation that 1.0

At that time the company probably employed 4 to 5 hundred electricians, so I think it had some experience in these matters.