Extraction motor

[pjb1]

Hi
Been asked by a customer to wire up a 15kw extraction motor the only figures i have at present are 3 phase 400v
Start current star delta 80.7 Amps
Run Current 26.9 Amps
done a quick cable calculation

15000/1.732*400*0.8=27.06A per phase

Will be using 3core Swa cable and the run is about 80 metres looking in the brb refer table4d4a comes at using 4mm seem a tad small to me considering the run length?
I haven't done alot of Industrial calculating so am getting stuck any help would be appreciated Thanks

 

[malcolmsanford]

Personally on a distribution cable like that I would go up to 10mm for that long a run.

Though you will have a large inrush current of 80 amps as long as you can conform to Regulation 525.4 regarding product standards or manufacturers recommendation then you should be ok.

As you are just using 3 core I assume you are going to be utilising the SWA as the CPC. You will find that a normal 70c SWA may not give you a good enough CPC, you will have to do the Adiabatic equation, or run a seperate CPC. XPLE should be fine though. The XPLE will give you an higher current rating capacity, but the VD per meter is virtually the same.

Is the controls for this motor remote? ie 80 metres from the motor, check to see if you need a neutral at the motor end. perhaps for a brake or something.

 

[pjb1]

Thanks Malcolm
I was thinking more along the lines of a 10mm 3 swa due to the length of run,and the high start up current.

I'm a bit rusty on calculating cable sizes and protective devises, Would any of you like to help me out?
I've been studying a pvc_xlpe.pdf.
Looking to see if the armour would be a suitable earth.

 

[malcolmsanford]

Well for the volt drop you just do mV/A/m x Ib X length /1000

So for 6mm it would have been 6.4 x 27.06 x 80/1000 = 13.85 then the temp factor of x 0.923 = 12.78 so just over the 11.5 v

So for 10mm 3.8 x 27.06 x 80/1000 = 8.23 x 0.923 and so 7.59 volts.

 

[Engineer54]

According to my table data on SWA cable, a 3 core 10mm PVC/SWA/PVC cable has a SWA CSA of 44, the minimum required CSA for the armouring to meet CPC requirement being 22.6. So i would say that the armouring can indeed be utilised as your CPC....

 

[pjb1]

Thanks Engineer54
John
Both the 6mm and 10mm are within the 5% for volt drop of 20 volts?

Calculation for the protective devise rating.
Iz>In
brb states 58A cable rating