Rockwell Automation 1790P-T4T0 CompactBlock LDX I/O Thermocouple Modules - Manual (Page 26)

Publication 1790-UM003A-EN-P - May 2002
2-12 Installation and Wiring
Field Wiring Connections System Wiring Guidelines
Consider the following when wiring your system:
General
• Route field wiring away from any other wiring and as far as
possible from sources of electrical noise, such as motors,
transformers, contactors, and ac devices. As a general rule, allow
at least 15.2 cm
(6 in.) of separation for every 120V of power.
• Routing field wiring in a grounded conduit can reduce electrical
noise.
• If field wiring must cross ac or power cables, ensure that they
cross at right angles.
• If multiple power supplies are used with analog millivolt inputs,
the power supply commons must be connected.
Terminal Block
• Do not use the module’s NC terminals as connection points.
• For millivolt sensors, use Belden 8761 shielded, twisted-pair wire
(or equivalent) to ensure proper operation and high immunity to
electrical noise.
• For a thermocouple, use the shielded, twisted-pair thermocouple
extension lead wires specified by the thermocouple manufacturer.
Using the incorrect type of thermocouple extension wire or not
following the correct polarity will cause invalid readings.
• To ensures optimum accuracy, limit overall cable impedance by
keeping a cable as short as possible. Locate the module as close to
input devices as the application permits.