Sequence of Operation
4-2
750-368
CBEX Elite 100-1200 HP
4.2 — Circuits and Interlocks
The burner control circuit is a two-wire system designed for 115 VAC, 60 Hz, single-phase power.
The electrical portion of the boiler is made up of individual circuits with controls that are wired in a manner
designed to provide a safe system. The program relay (standardly the CB780E) provides connection points for
the interconnection of the various circuits.
The controls used vary depending upon the fuel burned and the requirements of applicable regulatory bodies.
Refer to the boiler wiring diagram to determine the actual controls provided. The circuits and controls normally
used are listed below and are referred to in the following sequence of operation. Components may vary.
Circuit Components/Controls
Limit Circuit
• Burner Switch (BS)
• Operating limit control (OLC) - pressure or temperature
• High limit control (HLC) - pressure or temperature
• Low-water cutoff (LWCO - Level Master)
• Gas-oil selector switch (GOS) - combination burner only
• Oil drawer switch (ODS) - oil burner
• Low gas pressure switch (LGPS)
• High gas pressure switch (HGPS)
• Fuel valve interlock circuit
• Main gas valve auxiliary switch (MGVAS)
• Oil valve auxiliary switch (OVAS)
Blower Motor Starter Circuit
• Blower motor starter (BMS)
• Combustion air proving switch (CAPS)
• Atomizing air proving switch (AAPS) - if provided
Running Interlock Circuit
• Blower motor starter interlock (BMSI)
• Combustion air proving switch (CAPS)
• Atomizing air proving switch (AAPS) - if provided
Running Interlock and Limit Circuit
• Low oil pressure switch (LOPS)
• High oil pressure switch (HOPS)
• High oil temperature switch (HOTS)
• Auxiliary low-water cutoff (ALWCO)
Pilot Ignition Circuit
• Gas pilot valve (GPV)
• Ignition transformer (IT)
• Gas pilot vent valve (GPVV) - if provided
Flame Detector Circuit
• Flame detector (FD)
• Main fuel valve circuit
• Man gas valve (MGV)
• Man gas vent valve (MGVV) - if provided
• Oil valve (OV)
• Main fuel valve light FVL)
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