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Basic Installation 3-13MN1919
3.4.3.3 Supplying input power from a variac (variable transformer)
When AC power is supplied from a variac, the MicroFlex’s pre-charge circuit may not operate
correctly. To ensure that the pre-charge circuitry operates correctly, increase the variac
voltage to the desired level and then power cycle the 24VDC control circuit supply. This will
restart the pre-charge circuit and allow it to operate correctly.
3.4.4 Power disconnect and protection devices
A power disconnect should be installed between the input power supply and the MicroFlex for a
fail-safe method to disconnect power . The MicroFlex will remain in a powered condition until all
input power is removed from the drive and the internal bus voltage has depleted.
The MicroFlex must have a suitable input power protection device installed, preferably a fuse.
Recommended fuses are shown in section 3.4.5. Recommended circuit breakers are thermal
magnetic devices (1 or 3 phase as required) with characteristics suitable for heavy inductive loads
(C-type trip characteristic). Circuit breaker or fuses are not supplied. For CE compliance, see
Appendix C.
Circuit Breaker
L
N
From
supply
L
N
From
supply
Fuse
L
N
L
N
Figure 4 - Circuit breaker and fuse, single-phase
Circuit Breaker
Circuit breaker or fuse are not supplied.
For CE Compli ance, see Appendix C.
L1
From
supply
Fuses
L2
L3
L1
L2
L3
From
supply
L1
L2
L3
Figure 5 - Circuit breaker and fuse, three-phase
Note: Metal conduit or shielded cable should be used. Connect conduits so the use of a
line reactor or RC device does not interrupt EMI/RFI shielding.
3.4.4.1 Using 2 phases of a 3-phase supply
Power may be derived by connecting two phases of an appropriate three-phase supply (L1
and L2 for example). When supplying AC power in this way , the voltage between the
two
phases must not exceed the rated input voltage of the MicroFlex
. A two pole breaker must be
used to isolate both lines. Fuses must be fitted in both lines.
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