Derating factor depends on ambient temperature & how u r
laying the cable ie., in Air,Duct,Burried.
normally the current carring capacity of a perticular cable
is calculated at 40*c, but if u lay the cable in air then
it includes the temparture around it,if it increases more
the 40*c then the conductor gets heated up by increasing
the resistance in it thus the current carring capacity of a
given cable decreases, so we will derate the cable
Die electric factor depends on the temperature around the
cable, method of cable laying etc..if cable is to be design
for 35 deg c and if temperature increases above 35 deg c
then resistance of cable increases (positive temp.
coefficient), so its current carrying capacity will
decreses...So current paseed through cable will decreases,
it menas its capacity will down..it's called derating
current and notrated current...and same effect is done for
cable laying method...By using good insulation and proper
method of cable laying reduces its effect...
derating factor depents on withstand level of ambient
tempreature,when it increase at tat time resistance of
cable is increase so current carrying capacity of cable is
decrease so it will derate the cable rating..
then based on the cable fixed in a cable tray and the
distance between the cable in tray...
Answer 9 is the most comprehensive...
U get loads of standards based on the country u r in..
If in duct-
1) Soik Thermal resistivity : Basically the max temp in the
surrounding. 40*C is the standard.
2) Conductor grouping : Due to arrangement of multiple
conductors there is a development of an EM field which
opposes the flow and thus we need to consider this factor.
3) Temp. Derating Factor : In this the arrangement of cables
in a conduit is of prime importance. It should be in such a
way that all cables have a minimum space to dissipate heat
into the surroundings. The cables can touch each other but
anyone cable should not be fully surrounded by other cables.
4) Burial Depth : Depends on the length below ground where
the conduit is laid.
The cable derating factor is the reduction from its present
capacity for a certain gradual amount due to intermittent
ambient temperature, insufficient space, unbalance flux,
higher voltage dropped, depreciation, etc.
To minimize the cause and effect conduct proper survey and
proper wiring to withstand on the cable loads and locations.