76 Planning the electrical installation
Symmetrical shielded cable is recommended for the AC output cabling; see section
Recommended AC output power cable types below. Compared to a four-conductor
system, the use of symmetrical shielded cable reduces electromagnetic emission of the
whole inverter system.
Note: When continuous metal conduit is employed, shielded cable is not required. The
conduit must have bonding at both ends as with cable shield.
To operate as a protective conductor, the shield conductivity requirements according to
IEC 61439-1 are shown below when the protective conductor is made of the same metal
as the phase conductors:
To effectively suppress radiated and conducted radio-frequency emissions, the cable
shield conductivity must be at least 1/10 of the phase conductor conductivity. The
requirements are easily met with a copper or aluminum shield. The minimum requirement
of the cable shield is shown below. It consists of a concentric layer of copper wires with an
open helix of copper tape or copper wire. The better and tighter the shield, the lower the
emission level.
Cross-sectional area of
the phase conductors
Minimum cross-sectional
area of the corresponding
protective conductor
S (mm
2
) S
p
(mm
2
)
S <
16 S
16 < S <
35 16
35 < S S/2
1 Insulation jacket
2 Copper wire screen
3 Helix of copper tape or copper wire
4 Inner insulation
5 Cable core
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