89
Do it Once. Do it Right.
®
TACO, INC.
, 1160 Cranston Street, Cranston, RI 02920
Telephone: (401) 942-8000
FAX: (401) 942-2360.
TACO (Canada), Ltd.
, 6180 Ordan Drive, Mississauga, Ontario L5T 2B3.
Telephone: 905/564-9422.
FAX: 905/564-9436.
Visit our web site at:
http://www.taco-hvac.com
Printed in USA
Copyright 2005
TACO, Inc.
SR 503
24 VAC
POWER
FUSE 1 AMP
THERMOSTATS
ZONE1 ZONE2 ZONE3
120 VOLT
CIRCULATORS
ZONE1 ZONE2 ZONE3
TO: "TT" ON AQUASTAT CONTROL
TO: "TT" ON AQUASTAT CONTROL
TO: 120 VAC POWER (HOT)
TO: 120 VAC POWER (NEUTRAL)
JUMPERS
N P ZC H X ZR
1
X
2
ZONE 2
POWER
ZONE 1
ZONE 3
THREE ZONE SWITCHING RELAY
WITH OPTIONAL PRIORITY
SR 503
24 VAC
POWER
FUSE 1 AMP
THERMOSTATS
ZONE1 ZONE2 ZONE3
120 VOLT
CIRCULATORS
TO: 120 VAC POWER (HOT)
TO: 120 VAC POWER (NEUTRAL)
TO: "ZC" ON AQUASTAT CONTROL
TO: "ZR" ON AQUASTAT CONTROL
ZONE1 ZONE2 ZONE3
JUMPERS
N P ZC H X ZR
1
X
2
ZONE 2
POWER
ZONE 1
ZONE 3
THREE ZONE SWITCHING RELAY
WITH OPTIONAL PRIORITY
Cold Start Boiler
Application
Tankless Coil Boiler
Application
Specifications:
PRODUCT
NUMBER
TRANSFORMER
MAXIMUM
DIMENSIONS OF ENCLOSURE
NUMBER
OF ZONES
VOLTAGE
COMBINED LOAD
WIDTH
HEIGHT
DEPTH
SR502
2 with Priority
120 VAC I
n
put
15 a
m
ps
10 1/4
"
6 3/4
"
2 3/4
"
SR503
3 with Priority
120 VAC I
n
put
15 a
m
ps
10 1/4
"
6 3/4
"
2 3/4
"
All Switchi
n
g Relays are relay type DPST, have a ther
m
ostat curre
n
t of .18, a
n
d have a si
n
gle phase
m
otor rati
n
g per zo
n
e of 1/3 hp (7.2A) @ 120 VAC.
Features:
External Indicator Lights
Priority
Simplified Wiring
Fully Enclosed Snap-Out Relays
Compact Design
Fuse Protected
100% Factory Tested
Isolated End Switch
Contractor Friendly PC Board Layout
Universal Thermostat Compatibility
UL Approved
24 volt Power Input or Output Terminal
Extended 3 Year Warranty
Made in the USA
The Taco Connection:
Combine the reliability of the Taco Zone Valves, Priority Zoning
Circulators, Thermostats, and the “00” family of circulators with the
advanced features of the Taco Zone Controls to achieve total system
integration. No matter the application, Taco now provides the products
to maximize system performance while simplifying both installation
and service.
External Diagnostics:
Externally visible lights show full functionality of the switching relay.
The green light should always be on, indicating that power is connect-
ed. When the thermostat calls for heat, both the appropriate circulator
and red indicating light is energized.
Warning:
Wiring connections must be made in accordance with all applicable electrical codes and these
instructions. Use copper wire only. Failure to follow this instruction can result in personal injury or
death and/or property damage. 10-18 gauge wire recommended for 120 VAC connections with 9 in.lbs.
max torque, 12-22 gauge wire for thermostat connections with 9 in.lbs. max torque, and 12-22 gauge
wire for 24 VAC source with 5 in.lbs. max torque.
Instruction Sheet
SR502 & SR503 Switching Relay
Operation:
When the thermostat calls for heat, the appropriate circu-
lator is energized and the isolated end switch (X
1
and X
2
) will start the
boiler.
Jumper Placement:
The jumper should be placed between terminals
ZC and H. Connect the isolated end switch, X
1
and X
2
to the boiler
aquastat control.
For zone 1 priority, remove jumper between
terminals P and ZC.
Power Input:
Connect 120 volt ac power input to terminals N and H.
Neutral wire to terminal N. Hot wire to terminal H.
Operation:
When any thermostat calls for heat, the boiler and appro-
priate circulator are energized when the boiler temperature is above the
set low limit.
Jumper Placement:
A jumper should be placed between terminals ZC
and X
1
. Connect terminal ZC to ZC terminal on the aquastat control.
Connect terminal ZR to ZR terminal on the aquastat control. Confirm
polarity is consistent between boiler aquastat and switching relay.
For
zone 1 priority, remove jumper between terminals
P and ZC.
Power Input:
Connect 120 volt ac power input to terminals N and H.
Neutral wire to terminal N. Hot wire to terminal H.
Note:
When using Alternative Wiring diagram, the boiler operating control’s ZC terminal will see the load of the circulator(s).
Warning:
When using Alternative Wiring diagram, wiring instructions must be followed so power originates from the boiler aquastat. Failure to
follow these wiring instructions may result in a secondary source of power being connected to the boiler that may activate it under certain cir-
cumstances, causing injury or death.