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Page 37
"ALTERNATE" Continued
COMMUNICATION (RS 485) WIRING
From: System Control Module
To: Boiler Module
• Shielded communications cable - Belden #9842 must be used.
Polarity must be observed. Make use of wire color coding to ensure polarity.
• The shielding [foil wrapper - bare wire (drain)] MUST be grounded.
Grounding is done at the (System Control) only. DO NOT ground at boiler monitor.
• Note: Equivalent shielded cable must be suitable for RS 485 communication applications;
must have 100-140 ohm impedance; and less than 30 picofarad per foot capacitance.
• Install in conduit with no other wiring.
SYSTEM CONTROL
TERMINAL
Dia. #11
RS 485 Communications Cable Schematic