Harsco Industrial SC-2000, Installation & Owner'S Manual

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Gas Fired Boiler
18
Harsco Industrial, Patterson-Kelley Technical Service 1.877.728.5351
A normally-closed motorized combustion air damper with end limit switch is required for Category II vent
installations, and is optional for Category IV vent installations.
120VAC
motorized dampers with end limit switches
are available for purchase from Harsco Industrial, Patterson-Kelley. Other damper motor voltages are
acceptable, provided they do not exceed
240VAC
. The Air Damper Interlock circuit for the end limit switch is
always
120VAC
which is sourced from the boiler itself. All end limit switches must be rated for a minimum
120VAC
.
Motorized dampers must be powered from an external power supply
other than the boiler.
Figure 3.5.1
shows a sample installation in
which Relay C is user-selected to operate a
120VAC
motorized air
damper. Relay C is normally-open, so when the boiler is in standby,
the combustion air damper remains closed. Once a call for heat is
received, Relay C closes the
120VAC
circuit (external power supply)
which provides power to the damper motor, opening the damper.
Once the motorized damper is fully-open, its end limit switch
completes the Air Damper Interlock circuit (
120VAC
) which allows the
boiler to proceed to ignition.
NOTE:
The NURO control allows the user to allocate Relay A, B or C for use with a motorized combustion air
damper.
Figure 3.5.1
shows Relay C in use for the motorized combustion air damper. Depending on the
user-configuration, Relay A, Relay B, or Relay C can be selected to operate the combustion air damper.
Figure 3.5.1
N
OTICE
!
Relay A, Relay B and Relay C are
rated for a maximum voltage of
240VAC
and a maximum current
capacity of
1/2 Amp
. Connecting a
motorized damper which exceeds
the voltage or current capacity of
the relay could cause permanent
damage to the relay.
External power supplies are required for Relay A, Relay B and Relay C. Because power is provided from an
external source, the power is still present when the boiler is turned off. Check all voltage sources have been
disconnected prior to servicing. Failure to do so could result in electrocution, injury, or death.