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Installation
Guide
SG Series
225 & 300 kVA
3.9 POWER WIRING OF PARALLEL UNITS
To guarantee good
Load
sharing between the units of a parallel system, we recommend it is
recommended that the cable length from the input distribution board (5) to the output
distribution board (10) are the same length for each unit (a+b = c+d = e+f = g+h = i+l = m+n =
o+p = q+r). Tolerance:
+/-10%
.
The AC input power of the
Bypass
must be the same for all units of the parallel system - no
phase shift allowed between units.
It is strongly recommended that no transformers, automatic circuit breakers
or fuses should be inserted between the unit’s output and the
Load
common
bus bars.
However, it is recommended that a disconnect or isolation switch be inserted
in order to totally isolate a unit if needed
Verify that power wiring and control wiring are run in separate conduits or cable trays.
UPS input cables must be run in separate conduits from the output cables.
Fig. 3.9-1 RPA Parallel System
1
= Rectifier
c
= Unit Number 1
2
= Inverter
2
= Unit Number 2
3
= Electronic
Bypass
3
= Unit Number 3
4
= Manual
Bypass
4
= Unit Number 4
5
= Input
Utility
Distribution
5
= Unit Number 5
6
= Unit Output Load
6
= Unit Number 6
7
= External Battery MCB
7
= Unit Number 7
8
= External Battery fuse
8
= Unit Number 8
9
= External
Battery
10
= Common Busbar and Output Load Distribution
In a
RPA configuration
with 3-wire kit, it’s most important to connect the
Neutrals of the UPS outputs together (see
Fig .3.8.2-2 and 3.8.3-2
).
Cable section for this connection shall be not less then
AWG 1
