Honeywell UMC800 - Manual (Page 20)

Pre-Installation Considerations
Introduction
12 UMC800 Controller Installation and User Guide Release F
4/01
Electrical considerations
The controller is considered “open equipment” per EN 61010-1, Safety Requirements for Electrical
Equipment for Measurement, Control, and Laboratory Use, Part 1: General Requirements. Conformity with
72/23/EEC, the Low Voltage Directive requires the user to provide adequate protection against a shock
hazard. The user shall install this controller in an enclosure that limits OPERATOR access to the rear
terminals.
Controller grounding
PROTECTIVE BONDING (grounding) of this controller and the enclosure in which it is installed shall be
in accordance with National Electrical Code (ANSI/NFPA 70) and local electrical codes.
Taking electrical noise precautions
Electrical noise is composed of unabated electrical signals that produce undesirable effects in
measurements and control circuits.
Digital equipment is especially sensitive to the effects of electrical noise. You should use the following
methods to reduce these effects:
• Supplementary bonding of the controller enclosure to a local ground, using a No. 12 (4 mm 2 ) copper
conductor, is recommended. This may help minimize electrical noise and transients that may adversely
affect the system.
• Separate External Wiring - separate connecting wires into bundles (see Table 4) and route the individual
bundles through separate conduits or metal trays.
• Use shielded twisted pair cables for all Analog I/O, Process Variable, RTD, Thermocouple, dc millivolt,
low level signal, 4-20 mA, Digital I/O, and computer interface circuits.
• Use suppression devices for additional noise protection. You may want to add suppression devices at the
external source. Appropriate suppression devices are commercially available.
• Refer to document 51-52-05-01 How to Apply Digital Instrumentation in Severe Electrical Noise
Environments for additional installation guidance.