Vulcan-Hart VSX24D Service Manual page 33

VSX SERIES STEAMER - ELECTRICAL OPERATION
Electro Mechanical - Auxiliary Low Level Cut-Off
This control serves as a safety backup to the main low level cut-off (LLCO) control to meet Cal-Code
requirements. The operation of the auxiliary control is identical to the main low level cut-off control but performs
a single function: 1) Provide auxiliary low level cut-off protection to shut off the heat source in case the water
level drops below the low level cut-off (LLCO) probe. A single LLCO probe identical to the LLCO probe on the
main low level cut-off control is connected to the auxiliary control.
The auxiliary control is powered by input voltage (120VAC) on terminals 1 and 2 which also connect to the
primary side of the internal transformer. The transformer secondary winding (300 VAC) will provide power to the
internal contactor coil through a series path going from one side of the secondary winding, through the contactor
coil, through the water level control probe, through the water in the boiler and to the boiler for ground. The other
side of the transformer secondary is attached to the LLCO probe which directs power to the other side of the
internal contactor coil.
When the main power switch is turned ON, the auxiliary low level control is energized but no switching occurs.
When the water level reaches the low level cut-off (LLCO) probe, the internal contactor coil on the low level
control is energized, closing the contacts on terminals 7 & 8. The internal contactor coil will remain energized
until the water level in the boiler drops below the LLCO probe.
When the boiler stops filling, press the manual reset button on the boiler control box. This closes and locks the
manual reset switch contacts to energize the heat source auxiliary control.
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