Electrical Interference; Grounding - Control Technology 2500 Series Installation And Operation Manual

intended as safeguards against the failure of critical components and the effects of such
failures or the inadvertent errors that might be introduced if programs are changed while the
equipment is in operation.
Operator Safety Switches
Power should be configured so that it can be manually removed from all output devices. You
must provide a method that is independent of the control system for disconnecting power
from the outputs when a machine is not operating or the operator must reach into the
machine. A non-electronic switch or directly wired relay must be used to disconnect the
power.
Emergency Stop Switch
You must provide a method for disconnecting power from the outputs if an emergency
situation is encountered with the machine operation. Use a non-electronic switch or relay
that is wired external to the controller and that is easily accessible.

2.1.2 Electrical Interference

Electrical interference can adversely affect the operation of control equipment. The major
sources of electrical interference in an industrial environment are devices that use high
voltages and current, such as motors and welders. Electrical interference can be conducted
directly through wiring or inducted via electromagnetic coupling.
To ensure a reliable control system, you will need to determine the source of the electrical
interference and employ suitable techniques to eliminate it.

2.1.3 Grounding

It is very important that the all equipment is properly grounded. Lack of proper grounding
may cause intermittent or erratic operation or may cause the control system to fail. A
properly installed grounding system will provide a low-impedance path to earth ground,
which will give all PLC internal filtering devices a good ground return for reference. The
earth ground of the building site typically provides reliable grounding; however, if excessive
ground current is present, a separate grounding electrode should be installed.
A common practice is to provide a central ground bus bar as a single point of reference
within each enclosure, connecting all chassis and power supply components to the bus bar.
The bus bar is then connected to earth ground. When connecting to the bus bar, use 1 inch
copper braid or No. 8 AWG wire. To ensure good connections, scrape paint or other non-
conductive coatings away from mounting studs and from enclosure surfaces where
mounting bolts and washers make contact.
In addition to connecting the controller rack and power supply to earth ground, you must
ensure that the power supply, controller and all modules installed in the base are installed
securely and that the thumbscrews are tightened.
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2500C-8-TC Installation and Operation Guide