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Benchmark 750-3000 Boiler Installation & Startup Manual
SECTION 2 – INSTALLATION
2.11.12 Interlocks
The unit has two interlock circuits for interfacing with Energy Management Systems and
auxiliary equipment such as pumps, louvers or other accessories. These interlocks are called
the Remote Interlock and Delayed Interlock (REMOTE INTL'K IN and DELAYED INTL'K IN in
Figure 2-11). Both interlocks, described below, are factory wired in the closed position using
jumpers.
NOTE:
Both the Delayed Interlock and Remote Interlock must be in the closed position for the unit to
fire.
2.11.12.1 Remote Interlock In (OUT & IN)
The remote interlock circuit is provided to remotely start (enable) and stop (disable) the unit if
desired. The circuit is 24 VAC and comes factory pre-wired closed (jumped).
2.11.12.2 Delayed Interlock In (OUT & IN)
The Delayed Interlock terminals can be used in one of two ways:
•
In conjunction with the optional external sequencing valve (see section 2.15: Sequencing
Isolation Valve Installation and Section 6: BST), a component of AERCO's on-board Boiler
Sequencing Technology (BST) solution. A cable of the boiler's wiring harness is connected
to these terminals on all units; if BST is implemented, the other end of that cable is
connected to the sequencing valve.
•
If BST is NOT implemented, the second use is typically in conjunction with the AUXILIARY
RELAY CONTACTS described in section 2.11.14, below. This interlock circuit is located in
the purge section of the start string. It can be connected to the proving device (end switch,
flow switch etc.) of an auxiliary piece of equipment started by the unit's auxiliary relay. If the
delayed interlock is connected to a proving device that requires time to close (make), a time
delay (AUX START ON DLY) that holds the start sequence of the unit long enough for a
proving switch to make (close) can be programmed.
To use this option, you must disconnect the harness from the Delayed Interlock terminals
and connect the proving device in its place.
Should the proving switch not prove within the programmed time frame, the unit will shut
down. The AUX START ON DLY can be programmed from 0 to 120 seconds. This option
is located in the Configuration menu (see Section 2.6: CONFIGURATION Menu, item 16, in
the Benchmark 750 – 3000 Operation and Maintenance Guide, OMM-0122 (GF-206)).
2.11.13 Fault Relay (NC, COM, & NO)
The fault relay is a single pole double throw (SPDT) relay having a normally open and normally
closed set of relay contacts that are rated for 5 amps at 120 VAC and 5 amps at 30 VDC. The
relay energizes when any fault condition occurs and remains energized until the fault is cleared
and the CLEAR button is depressed.
2.11.14 Auxiliary Relay Contacts (NC, COM, & NO)
Each unit is equipped with a single pole double throw (SPDT) relay that is energized when there
is a demand for heat and de-energized after the demand for heat is satisfied. The relay is
provided for the control of auxiliary equipment, such as pumps and louvers, or can be used as a
unit status indictor (firing or not firing). Its contacts are rated for 120 VAC @ 5 amps. Refer to
Figure 2-11 to locate the AUXILIARY RELAY terminals for wiring connections.
OMM-0121_D • GF-205 • 5/9/2019
Technical Support • (800) 526-0288 • Mon-Fri, 8 am - 5 pm EST
Page 38 of 122
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