Another college query

[davedwr1978]

Hi guys I need to find the installation method for a twin and earth cable run in a stud wall touching the wall in insulation for 13meters, I've referred to the regs and I have come up with install method 102 does this sound right to anyone ( page 67 OSG)

 

[Richard Burns]

Have a look at table 4A2, near the end there are the installation methods for twin and earth when covered with insulation, these then refer you to the appropriate current carrying capacity table.

102 is correct.
(what is on page 67 of the OSG?)

 

[davedwr1978]

Thankyou Richard I'm happy now I know I'm on the right path.

 

[davedwr1978]

hi Richard sorry to bother you again, i also have to find out the tabulated current, so using the factors of Ci - 0.51 and Ca - 0.94 i done the following of 20 divided by (0.94 x 0.51) which gave me 41.71 amps, then when i went to page 340 table 4d5, column 4 it says i need a CSA of 10mm2, is this correct as it seems very big to me or have i gone wrong somewhere?? its for a 4kw storage heater.

 

[telectrix]

( 4kW is 16.6667A, so 4 mm gives 32A so that would be my choice.

 

[malcolmsanford]

Yes if your cable is surrounded in insulation for those 13 metres then you use a derating value 0.5 for 500mm or more. So in affect you are halving the current carrying capacity of the cable

 

[davedwr1978]

16.6667A is 4000 divided by 240, i divided by 230v, on the paper it doesnt state 230 or 240v, not sure which one to use now,

 

[Leesparkykent]

16.6667A is 4000 divided by 240, i divided by 230v, on the paper it doesnt state 230 or 240v, not sure which one to use now,

use 230v

 

[davedwr1978]

cheers guys it makes sense now i m just happy im going down the right route, thanks again

 

[Leesparkykent]

Reference method 102, Ambient temperature 30°C and Conductor operating temperature 70°C the current carrying capacity of 2.5 T&E is 21 amps. Your 4kw heater is going to pull 17.39amps.

 

[davesparks]

( 4kW is 16.6667A, so 4 mm gives 32A so that would be my choice.

That's not going to help him pass his exams is it, the trainee section is really not the place for 'rule of thumb' guesstimates.

 

[Richard Burns]

Remember that reference method 102 tabulated current carrying capacity has already factored in the Ci correction factor so you do not need to do this again.