System; Section 3.7 Field Wiring Connections; System Wiring Guidelines - Spectrum Controls 1769 Series User Manual

3-8 Compact™ IO Isolated Thermocouple Module
Section 3.7
Field Wiring
Connections
User's Manual Pub. 0300244-01 Rev. A

3.7.1 System Wiring Guidelines

Consider the following when wiring your system:
General
•
Power and input wiring must be in accordance with Class 1, Division 2 wiring
methods, Article 501-4(b) of the National Electric Code, NFPA 70, and in
accordance with the authority having jurisdiction.
•
Channels are isolated from one another by 500 Vdc maximum.
•
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.
•
Do not tamper with or remove the CJC sensors on the terminal block. Removal
of one or both sensors will reduce accuracy.
•
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 ensure 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.
Grounding
The possibility exists that a grounded or exposed thermocouple can
!
become shorted to a potential greater than that of the thermocouple
itself. Due to possible shock hazard, take care when wiring grounded or
Attention
exposed thermocouples. See Appendix B, Using Thermocouple
Junctions.