cable calculations

[wolfiehogan]

hi, have a cable calculation question.
what size off cable do i need to run to supply a mushroom house.
its a 70 meter run of swa cable buried in the ground, the load is 12 amps lighting and sockets and a cooler taking 32 amps all this is single phase loads. there is also a 3 phase machine taking 15kw total power. can some body work this out for me show how you
work it out taking volt drop in to the equation
thanks

 

[i=p/u]

try find on site guide and is appendix 6, i9m heading for walk with kids if your still pleading , which i doubt i will help you,listen d me the spark

 

[Spudnik]

I havent got a clue whats going on here but i have edited out posts so that we can all start again.

 

[SimpleSimon]

try find on site guide and is appendix 6, i9m heading for walk with kids if your still pleading , which i doubt i will help you,listen d me the spark

Think your on the mushrooms mate.

 

[piccollo]

wolfiehogan, re your enquiry you are looking into the design & verification aspects, I will guide you as far as possible but cannot take any responsibility as I do not know the full parameters of the supply source. If we take the 2 main loads , 32 amp for cooler & 15kw total for a machine. I have assumed 15kw over the 3 phases as you have not given FLA or HP of motor. Total load on 1 phase is approx 58 amps therefore working on a 63Amp TPN supply / feed. Table 4D4a of BRB states min 16mm2. We now check volt drop, 5% of 400 =20volts max. From table 4D4B of BRB 16mm2 has volt drop of 2.4 mV/A/m, = 2.4 x 58 x 70/1000 = 9.8volts [ below 20 volts, so satisfies volt drop]. Protection for supply say 63 Amp BS88 fuse. Zs = 0.65 [ at 80% of max] therefore with a TNS supply max r1 + r2 = >0.3 ohms. From table 9A of OSG 16mm2 with 16mm2 cpc [ min due [assume presence of water supply] & to satisfy disconnection time] 2.3x 70/1000 = 0.16ohms. Zs = r1 +r2 + Ze, Zs = 0.16 + say 0.35 + 0.51, which is lower than 0.65.

Min size cable for this sinario is 4core 16mm2 swa. SWA will meet requirements as approx csa is 70mm2 which is greater than the required for a 63amp fuse. As previously stated this is aguide only. regards piccollo