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

6 channel isolated thermocouple/mv input module
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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.

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