32 Rockwell Automation Publication 750-RM003A-EN-P - April 2018
Chapter 1 Selection Considerations
Note the following regarding user-supplied 240V AC primary control power:
• If an external user-supplied 240V AC primary control power source is
used, it should be 240V AC, 50/60 Hz, 1 PH, and must have the neutral
conductor grounded.
• User-supplied branch circuit protection is required to protect the 240V
AC control circuit connectors and bus bars.
• If the primary control bus must also supply 240V AC control power to
existing common bus inverter drives then the external supply must be
sized for these additional loads.
• If the total 240V AC control power current exceeds 100 A, you must
split the control bus and apply separate 240V AC control power to
groups of drives.
• Calculate the required external control 240V AC control circuit current
from the loading data that is shown in Table 6 on page 31
.
a. Add the current required for applicable Entry and Exit wiring bays.
b. When selecting an external control transformer power or VA rating,
multiply the total current requirement by 240V AC. Multiply this
value by 1.25 to ensure the transformer can supply inrush currents.
EXAMPLE Quantity 1 x frame 11 PowerFlex 755TM bus supply, IP54 enclosure
with optional entry wiring bay.
– External 240V AC control current required =
(34.6 + 0.39) = 35.0 A
– Is the total 240V AC control bus current less than 100 A? Yes.
– Calculate the VA rating of the external transformer =
35 A x 240V x 1.25 = 10,500 VA
A standard size control transformer rated 12…15 kVA is an
acceptable solution for this example. The control power option (-C1)
control transformer for this example is rated 15,000VA.
ATTENTION: DO NOT connect external 240V AC control power if an internal
control transformer is installed. Severe damage to the PowerFlex 755T and
external power supplies could occur.
IMPORTANT The PowerFlex 755T product control bus bars and splice kits are not
compatible with other enclosure bus bar systems that may have been used
with PowerFlex common bus inverters. If it is necessary to connect to
existing control bus bars, the migration solution designer is responsible for
the proper design and installation of any bus bar transition equipment.
Transition cells are expected to be available from Rockwell Automation at a
later date.
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