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80 Guidelines for planning the electrical installation
Cable type
Symmetrical shielded (or armored)
cable with three phase conductors
and a shield (or armor), and separ-
ate PE conductor/cable
1) A separate PE conductor is required if the conductivity of the shield (or armor) is not sufficient for the PE use.
Alternate power cable types
Cable type
EMT
Four-conductor cabling in metal
conduit (three phase conductors and
PE). For example, EMT, or four-
conductor armored cable
Shielded (Al/Cu shield or armor)
four-conductor cable (three phase
conductors and a PE)
PE
A single-core cable system: three
phase conductors and PE conductor
on cable tray
L1
L2
L2
L3
L3
L1
L1
Preferable cable arrangement to
avoid voltage or current unbalance
between the phases
1) Armor may act as an EMC shield, as long as it provides the same performance as a concentric EMC shield of a shielded
cable. To be effective at high frequencies, the shield conductivity must be at least 1/10 of the phase conductor conductivity.
The effectiveness of the shield can be evaluated based on the shield inductance, which must be low and only slightly
dependent on frequency. The requirements are easily met with a copper or aluminum shield/armor. The cross-section of
a steel shield must be ample and the shield helix must have a low gradient. A galvanized steel shield has a better
high-frequency conductivity than a non-galvanized steel shield.
Use as input power cabling
Yes
PE
1)
Use as input power cabling
Yes
Yes
1)
Yes
WARNING!
If you use unshielded single-
core cables in an IT network,
make sure that the non-con-
ductive outer sheath (jacket)
L3
of the cables have good con-
L2
tact with a properly grounded
conductive surface. For ex-
ample, install the cables on a
properly grounded cable tray.
Otherwise voltage may be-
come present on the non-
conductive outer sheath of the
cables, and there is even a
risk of an electric shock.
Use as motor cabling
Yes
Use as motor cabling
Yes with phase conductor smaller
2
than 10 mm
(8 AWG) Cu, or motors
up to 30 kW (40 hp)
Yes with motors up to 100 kW
(135 hp). A potential equalization
between the frames of motor and
driven equipment is required.
No
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