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Topic Title: Cable sizing
Topic Summary: Variable MCCB
Created On: 06 March 2013 01:34 PM
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 06 March 2013 01:34 PM
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carllangwood

Posts: 8
Joined: 08 February 2012

When sizing cables is it a requirement to rate the cable for the full rated current setting of the MCCB, or is the cable sized to the adjusted setting?
 06 March 2013 01:45 PM
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OMS

Posts: 19747
Joined: 23 March 2004

If you wish, it may be the adjusted setting - see 433.1.1 (i) as an example of where the adjusted setting may be used in the cable sizing exercise.

It depends on what setting you are "adjusting" as to the relevant circuit parameters you decide - so for example you may reduce the current carrying capacity of a cable required based on adjusting the overload long time pick up to use a smaller cable - but you may need to increase the size if you put in longer short time pick up (say under short circuit) as an aid to discrimination.

In summary - whatever permitations of settings you pick - then you design against those and pas the setting informatopn on to the installer.

Just be careful that the settings can't be adfjusted after you complete the installation however (ar at least have a warning in place of the implications of doing so) - adjustments that need a key or tool to initiate are the usual solution.

Regards

OMS

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