2.4.1.5
Shielding
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NOTE: IEEE C2 requires the cable conductor shield
to have sufficient ampacity to withstand the effects
of available fault current without damage to the
conductor (except in the vicinity of the fault).
The designer should provide the expected maximum
available ground fault current, so the cable
manufacturer can size the shield. Testing has shown
that for grounded medium voltage systems where a
bare ground fault return conductor is installed with
phase conductors in metallic duct, 3% - 14% of the
available fault current returns along the cable
shield. A separate ground fault return conductor
(bare copper wire or metallic duct) should always be
provided. For circuits not installed in metallic
duct, with a ground fault return conductor supplied,
the shield can be sized to conduct (until the
protective device operates) 15% of the available
fault current per cable. Where the available fault
current is unknown or cannot be determined, the
designer should provide a # 2/0 AWG bare copper
ground conductor and delete the ground fault
ampacity statement.
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Cables rated for 2 kV and above shall have a semiconducting conductor
shield, a semiconducting insulation shield, and an overall copper [tape]
[wire] shield for each phase. The shield [tape] [wire] shall be sized to
meet IEEE C2 requirements for a ground fault availability of [_____]
amperes.
2.4.1.6
Neutrals
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NOTE: Where high impedance grounded neutral systems
are employed, add the following requirement for the
neutral to be fully insulated. For high impedance
grounded neutral systems, the neutral conductors
from the neutral point of the transformer or
generator to the connection point at the impedance
shall utilize [copper] [aluminum] conductors,
employing the same insulation level and construction
as the phase conductors.
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[Neutral conductors of shall be [copper] [aluminum]. employing the same
insulation and jacket materials as phase conductors, except that a 600-volt
insulation rating is acceptable.] [Concentric neutrals conductors shall be
tinned copper, having a combined ampacity [equal to] [1/3 of] the phase
conductor ampacity rating.]
2.4.1.7
Jackets
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NOTE: PVC is acceptable for duct applications.
Polyethylene is exceptional for direct burial and in
duct applications where there is significant amounts
SECTION 16375A
Page 21
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