User manual

Publication 1747-UM011F-EN-P - May 2007
70 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.