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Topic Title: Cable in Ground/Duct
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Created On: 26 August 2013 11:46 AM
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 26 August 2013 11:46 AM
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greghenderson17

Posts: 6
Joined: 26 August 2013

Hello,

I am currently working on a project which has a sub-main cable running a total length of 190m. For 160m the cable is run in the ground (Method E) and for the final 30m the cable is run in duct (Method D).

When producing the cable calculations and applying appropriate grouping factors, should I allow for the worst case scenario (I.E. Method D) or apply 'Method E' for the calculation as over 80% of the cable run is via this method?

Any advice would be greatly appreciated.

Thanks,
 26 August 2013 03:46 PM
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Legh

Posts: 3472
Joined: 17 December 2004

Welcome Greg,
As a rule of thumb apply the worst case correction factor, but then there are other factors that might influence your design such as loading, and diversity.

edit: You'll most likely comply anyway when you've considered the volt drop over that distance.....

Legh

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http://www.leghrichardson.co.uk

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Edited: 26 August 2013 at 03:54 PM by Legh
 27 August 2013 11:02 AM
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AJJewsbury

Posts: 11290
Joined: 13 August 2003

Alternatively you could treat it as two cables in series - do the calculations for each (160m underground, 30m duct) separately and add together (v.d. Zs etc). Occasionally that might give you a bit of extra wiggle room (e.g. recognising that the v.d. in the cooler section of cable won't be quite as bad as for the other section and so on, or perhaps allowing a buried section to run >70 degrees while keeping the above-ground section to <= 70 degrees to suit terminations etc), although unless things are really tight the saving probably doesn't justify the extra effort.

- Andy.
 27 August 2013 11:44 PM
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weirdbeard

Posts: 1456
Joined: 26 September 2011

I agree with much of which other posters have suggested.
 30 August 2013 10:04 AM
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greghenderson17

Posts: 6
Joined: 26 August 2013

Thanks for the advice guys!

-Greg
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