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Topic Title: Installation Conditions - Cable Size
Topic Summary: Maximum length that can be ignored
Created On: 09 November 2017 10:14 AM
Status: Read Only
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 13 November 2017 08:21 PM
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broadgage

Posts: 2435
Joined: 07 August 2007

Originally posted by: Apostolos1983

Thanks everyone. I think the sensible thing would be to go to the bigger CSA through the whole length. I do not think the client would like additional points of failure (junction boxes).

So, to return to the original question, there is not any definite answer in the regs about the max length we could ignore the change in the installation conditions.

Thanks!


I am not aware of any defined limit on the distance that may be ignored, but common sense and engineering judgement suggests that it must be very short, such that the heat may be conducted away along the length of the cable.
I have heard a limit of ten cable diameters suggested for small cables, and twenty cable diameters for large cables.
Definitely not a road crossing though !

In general, upsizing the whole cable run is more economic for smaller cables, and jointing to a larger size more economic for large cables.
In yet other cases, it may come down to standard lengths of cable.
If the length on cable tray was 104 meters before the road crossing, and the cable came on 100 meter drums, then I would be inclined to joint to the larger size 4 meters before the road crossing thereby using exactly a whole drum with no waste.
If the load was only 12 meters from the far side of the road, then I might run the larger cable from the road crossing to the load, thereby eliminating one joint.
IET » Wiring and the regulations » Installation Conditions - Cable Size

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