Rockwell Automation 1747-L5xx SLC 500 Modular Hardware Style User Manual - Manual (Page 68)

Publication 1747-UM011G-EN-P - June 2008
68 System Installation Recommendations
Power Considerations Refer to the following sections regarding power.
Common Power Source
All chassis power supplies should have the same power source as the input and
output devices. This helps reduce the chance of electrical interference due to
multiple sources and grounds as well as helps maintain system integrity if
power is interrupted.
The processor detects the absence of power to any chassis in the system. If
power to any chassis is lost (or not yet applied), the CPU FAULT status
indicator turns on and all controller outputs in the local chassis are
de-energized. Output states in any remote chassis are determined by
configuration settings at that chassis.
This fault detection makes it necessary that you apply power to the expansion
chassis before you apply power to the chassis containing the processor to
avoid an unwanted fault. Of course, applying power in sequence is unnecessary
if all chassis have a common power source.
Isolation Transformer
In many industrial applications, a step-down transformer is required to reduce
line voltage to 120 or 240V ac. This transformer also provides isolation to
protect equipment from high voltage transients that may be generated on your
power distribution system.
ATTENTION
Your SLC 500 power supply can be damaged by voltage surges
when switching inductive loads such as motors, motor starters,
solenoids, and relays. To avoid damage to your SLC 500 power
supply in these applications, use an isolation transformer to
isolate the power supply from harmful voltage surges.