17th edition wire calculations... new and old installs.

[michaelw6]

a couple of questions really.
1st.
On a periodic which has had new insulation installed the 17th edition calc on my pc up rates all cables so now there not up to regs, do you recommend a rewire on every test???
2nd.
I am currently fighting with a decision on a new build that the cable calc said the lighting up stairs needs to be a 10-16mm cable wow don't think ill get that in the down lights,lol
or I wire a radial circuit to every room.
Customer loves his down lights.

 

[roukel01]

How many lights you got on each circuit.... don't forget Part L requires 75% energy efficient lighting of 45 lumens per watt or higher these days.

Not sure about the insulation situation. It is happening everywhere with loft insulation upgrades being so cheap, perhaps try pulling some insulation off the cables??

 

[michaelw6]

Approx 9 down lights per room a few have more, 6 rooms upstairs 6 down. and its the cable lengths. killing me this job to bloody big...

 

[telectrix]

on 16mm cable you could run around 400 50watt downlights, and that's without low energy and diversity. how many has he got?

 

[michaelw6]

69 D/L upstairs some on dimmers. he is putting 1/4 energy but replacing once signed off so cant allow for that. approx 350 M cable.
68 D/L down stairs some on dimmers approx 400M cable not including the 6 extractors.

on 16mm cable you could run around 400 50watt downlights, and that's without low energy and diversity. how many has he got?

 

[SKY]

Is this on a single circuit? whats the MCB size?

 

[roukel01]

69 D/L upstairs some on dimmers. he is putting 1/4 energy but replacing once signed off so cant allow for that. approx 350 M cable.
68 D/L down stairs some on dimmers approx 400M cable not including the 6 extractors.

If the runs are that long, surley you need to be installing more C/U's around the building?

 

[roukel01]

"he is putting 1/4 energy but replacing once signed off so cant allow for that"


You shouldn't be siging 1/4 off, it has to be 3/4 nowadays.

 

[michaelw6]

thats what im trying to sort out!

 

[michaelw6]

thats the total cable thats why im thinking separate circuits.

 

[Martin Bradley]

Put up your calculations. so we can all have a look at it, you never know.
All infomation that you have, see what we can do.

 

[michaelw6]

supply voltage 230, Ze 0.35, mcb 60898 10A, T+E, method C, design current 9.90A with diversity, length of run 350M, temp 30, thermal insulation 50mm, number of circuits 2, max volt drop 3% @ 6.9V. i get 16mm cable?
can some one explain what im doing wrong or another way around this please?

 

[Simlec]

350M & 400M ???
Somethink not right there!
I take it you have just added up all the cable you have used? Which would not give you the circuit lenght!

 

[i=p/u]

just put in a separate board for lighting

 

[michaelw6]

thinking separate board for lighting on rcbos. the 350 m is from cu to last light fitting.