# Different Sized Cable



## truth (Feb 13, 2008)

Hi
Can we use existing 2core x 70mm2 and 2 core 50mm2 (850m length) cables to carry a 3 phase supply (3 phase and neutral). 

Load : 5KW
Purpose : to feed the UPS unit

Concerns would be from the voltage drop and the terminal voltage difference at the end point. I have worked out the voltage. They are within the limit. 
The reusage of the existing cables will save enormous money (cables, trenches).
No Nearest secure power supply is available. Either to run a new cable or reuse the existing cables.

Could You advise Your opinion please.
Thanks


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## 5volts (Jan 11, 2008)

Is the smaller cable going to be able to handle the current?


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## frenchelectrican (Mar 15, 2007)

I am not too sure what the UK regulation related to the % of voltage drop max you can be allowed but what i did figured out [ after i change from metric size to the standard size then back to metric after i got the figures done]

is the entrie run will use the 70mm2 and 50mm2 combined or what ??

with the 50mm2 at 415 volts with 5 KW load @ 3 phase you will have about 6 volts [ i did figured with 25mm2 {about the same as #4 wire size } and you will have 10 volt drop at end of the run.[ this baised on 2.5 % max drop]

[ 50mm2 is about the same as #1 wire size ]
[ 70mm2 is about same between 2/0 and 3/0 size ]
[ 850 Metre is same as 2200feet btw ]

Merci, Marc


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## frank (Feb 6, 2007)

You can. The only thing neccessay to keep an eye on is that the two seperate cable runs do not travel in different directions. They must all pass through the desired route side by side and through any metalwork in particular. Min cable sizing is of course the 50mm,

Frank


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