Product Overview

© 2012 A 274 - 01/12 6 of 8
Application A 274-6
Concept Drawing: This is only a concept drawing, not an engineered drawing. It is not intended to describe a complete system, nor any particular system. It is up to the
system designer to determine the necessary components for and configuration of the particular system being designed, including additional equipment, isolation relays
(for loads greater than the control’s specified output ratings), and any safety devices which in the judgement of the designer are appropriate, in order to properly size,
configure and design that system and to ensure compliance with building and safety code requirements.
Electrical
System Description: The Boiler Control 274 controls two, Lo/Hi fire boilers to provide setpoint operation for the dedicated
DHW tank. When a valid DHW Demand is present from the DHW Sensor, the DHW pump relay turns on. The DHW
relay in this mode is used as the DHW recirculation pump and operates continuously in the occupied period and cycles
with the DHW demand in the unoccupied period. The boilers are sequenced based only on the DHW Sensor. The Boiler
supply sensor is not required. Outdoor design is turned off.
The 274 has a combustion air contact which opens and closes
a damper when a boiler is to fire. A combustion air proof ensures the damper is open before firing a boiler.
Mechanical
S1 = DHW Sensor 082
C1 = C.A, Proof
M1 = C.A. Damper Motor
P1 & P2 = Boiler Pumps
P3 = DHW Recirculation Pump
S1
P1 P2
120 V (ac)
274
Potable
Supply
P3
DHW
Tank
M1 C1
S1
Boiler 1
Lo Stage
6
DHW
5 4
Sup
3
+
2
-
1
Do not apply power
274
N
720
Power
L
8
tN4 Com Out Boil Com BRet/ Relay
1
910
Relay
2
11 12
Relay
3
13 14
Relay
4
15 16
C.A./
Alert
21 22
Boiler
Demand
23 24
DHW
/Setp
Com
Dem
25
Pr.
Dem
19
Prim
P1
18
DHW
/P2
17
Boiler 1
Hi Stage
Boiler 2
Lo Stage
Boiler 2
Hi Stage
N
115 V (ac)
L
P3
M
M1
C1
C
24V(ac)
R
Class 2
Transformer
Demands
Setback
Off
EMS
Rotate
Fixed Last
Pump Sequencer
Exercise
Off
Fixed Lead
First On / Last Off
First On / First Off
274 Switch Settings:
Essential Control Settings:
Mode = 3
DHW Mode = 6