Harsco Industrial SC-2000 Installation & Owner's Manual page 18

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.
are available for purchase from Harsco Industrial, Patterson-Kelley.
acceptable, provided they do not exceed
always 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
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
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 (
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
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.
Harsco Industrial, Patterson-Kelley Technical Service 1.877.728.5351
240VAC
120VAC
circuit (external power supply)
120VAC
120VAC
motorized dampers with end limit switches
120VAC
. The Air Damper Interlock circuit for the end limit switch is
motorized air
) which allows the
18
Gas Fired Boiler
Other damper motor voltages are
N !
OTICE
Relay A, Relay B and Relay C are
rated for a maximum voltage of
and a maximum current
240VAC
capacity of . Connecting a
1/2 Amp
motorized damper which exceeds
the voltage or current capacity of
the relay could cause permanent
damage to the relay.
.
120VAC