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Figure 2.2 - Flexible steel conduits for electrical cables

For most substation applications, there will be more than two
conductors in a conduit, so the maximum fill percentage will be
40%.
It is important to consider the length of the conduit run and the
number of bends in the conduit runs when determining the amount
of fill that is acceptable. The maximum fill percentage will not
guarantee an easy installation. Other considerations associated
with the fill of the conduit and the ease of installation is the
jamming ratio. While the NEC does not govern this, it does
contain an informational note about its occurrence.
There are many different requirements for ampacity de-rating of
cables.

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