Special Considerations; Class I, Division 2 Applications - Allen-Bradley SLC 500 User Manual

Special Considerations

Allen-Bradley PLCs
The recommendations given previously provide favorable operating
conditions for most controller installations. Some applications may
involve adverse conditions, such as excessive line voltage variations
and/of excessive noise, as described below. Additional measures can
be taken to minimize the effect of these conditions.

Class I, Division 2 Applications

When installing peripheral devices (for example, push
IMPORTANT
buttons, lamps) into a hazardous environment, ensure
that they are Class I, Division 2 certified, or
determined to be safe for the environment.
Excessive Line Voltage Variations
The best solution for excessive line voltage variation is to correct any
feeder problems in your distribution system. Where this does not
solve the line variation problem, or in certain critical applications, use
a constant voltage transformer. If you require a constant voltage
transformer, connect it to the power supply and all input devices
connected to the SLC 500 controller.
Connect output devices on the same power line, but their connection
along the power line is normally made before the constant voltage
transformer. A constant voltage transformer must have a sufficient
power rating for its load.
Excessive Noise
When operating the SLC 500 controller in an environment with a high
amount of electrical noise, give special consideration to the possibility
of electrical interference.
The following reduces the effect of electrical interference:
• SLC 500 controller design features
• proper mounting of controller within an enclosure
• proper equipment grounding
• proper routing of wires (power, communications, control lines)
• proper suppression added to noise generating devices
Selecting Your Hardware Components
Publication 1747-UM011C-EN-P - December 2001
2-25