Aprilaire 50, 51 Installation Manual

Installation Instructions for

Models 50 and 51 Current Sensing Relays

Current Sensing Relays

GENERAL INFORMATION

MODEL 50 HUMIDIFIER WIRING DIAGRAMS

READ COMPLETE INSTALLATION INSTRUCTIONS BEFORE STARTING.

GENERAL INSTALLATION PROCEDURES FOR MODELS 50 AND 51 RELAYSMODELS 50 AND 51 RELAY

INSTALLED WITH MANUAL HUMIDIFIER CONTROL INSTALLED WITH AUTOMATIC HUMIDIFIER CONTROL

WARNING

120 volts may cause serious injury from electric shock.
Disconnect power to the furnace before attaching the
Model 50 or 51 Current Sensing Relays.

CAUTION

1. Load must not exceed recommended ratings. (See specifications)

2. Load must be wired in series with relay.

3. Do not power humidifier from furnace blower motor circuit.

1. Disconnect power before installing.

2. The Models 50 or 51 must be located at least 4” from any transformer.

3. Remove the screw from the bracket and place the common wire that will activate the relay

between the bracket and the plastic case.

4. If the current through the common wire is less than 4 amps, wrap it one or more additional

turns around the metal bracket.

5. Replace the metal screw in the bracket.

6. Complete the wiring as shown in the

appropriate diagram.

7. Read the checkout procedure.

8. Relay bracket must not come in contact

with metal.

1. Not approved for directly controlling motors of

safety related applications.

2. Always disconnect power before working on the

Current Sensing Relay or its connected load.

3. Follow all local electrical and safety codes,

the National Electrical Code (NEC), and OSHA
requirements.

90-1251 90-1249

90-908

90-909

10005113_B AA Model 50-51 Install 1/11/08 12:30 PM Page 1

LOAD

24 or

120 VAC

RELAY

COMMON

LEAD

4 Amp. min.

COMMON LEAD

120 VAC

CURRENT
SENSING

FURNACE

BLOWER

MOTOR

RELAY

COMMON

METAL BRACKET

24

VAC

TRANSFORMER

MODEL

50

HUMIDIFIER

METAL BRACKET

NOTE: SET THE WATER PANEL
CHANGE INDICATOR TO THE “OFF”
POSITION WHEN USING THE MODEL
50 CURRENT SENSING RELAY WITH
AUTOMATIC CONTROL.

COMMON LEAD

FURNACE

BLOWER

MOTOR

COMMON

CURRENT
SENSING

RELAY

AUTOMATIC CONTROL TERMINAL STRIP

R C A B ODT CfW/G H

24V

JUMPER WIRES REQUIRED

FOR THE AUTOMATIC DIGITAL

HUMIDIFIER CONTROL ONLY

HUMIDIFIER

MODEL

50

RESEARCH PRODUCTS CORPORATION

P.O. BOX 1467 • MADISON, WI 53701-1467 • PHONE: [phone] • FAX: [phone] • www.aprilairecontractor.com

10005113 1.08
B2202490B

MODEL 51 TYPICAL ELECTRONIC AIR CLEANER INSTALLATION

1. Disconnect power before installing.

2. Install the Model 51 on the common wire of the blower motor as

shown in the diagram.

3. Open the main power junction box on the side of the furnace. Run the

leads of the Model 51 relay into the junction box.

4. Connect the leads of the Model 51 relay in series with one of the

electronic air cleaner leads. Connect remaining lead and ground wire of
the electronic air cleaner. The 120 VAC source must be independent of
the furnace blower motor.

5. Check all wire connections, close junction box and restore furnace to

working order. Test proper functioning of the Model 51 by observing
that the air cleaner’s indicator lamp turns on when the blower runs and
turns off when the blower stops.

CHECKOUT PROCEDURES FOR MODELS 50 AND 51 RELAYS

1. Replace all safety devices.

2. Reconnect power to furnace.

3. Activate furnace blower motor.

4. Check load for operation – it should now be operating properly. (Check

indicating lamp or other condition showing the load is receiving power.)

5. Switch off the blower unit. The power to the device should shut off.

6. If the device is activated properly and turns off when the power

through the common wire is removed, installation is complete.

7. If the device is not powered when the blower is turned on then:

• Ensure the device’s ON/OFF switch is ON.

• Recheck all wiring.

• Check line fuses.

• Confirm that four (4) or more amps is flowing through the
common wire. Wrap additional turns around the bracket if
necessary.

SPECIFICATIONS

Model 50 Model 51

Voltage Range 21-24 VAC, 50-60 Hz 100-125 VAC, 50-60 Hz

Sensing Current Minimum of 4.0 amps Minimum of 4.0 amps

Operating Ambient Temperature Range 40°F to 104°F 40°F to 104°F

Dimensions 1” x 1-7/16” x 2-3/4” 1” x 1-7/16” x 2-3/4”

Load Ratings Maximum (12 watts) 0.50 amps Maximum (50 watts) 0.42 amps

Minimum (3 watts) 0.12 amps Minimum (3 watts) 0.03 amps

Case Color Black Yellow

Underwriters Laboratories Recognized Component N/A Yes

90-1264 90-1265

10005113_B AA Model 50-51 Install 1/11/08 12:30 PM Page 2

MODEL

51

BRACKET

BLOWER

MOTOR

COMMON

120 VAC

EAC

120 VAC

120 VAC

to EAC

JUNCTION

MODEL 51

COMMON

WIRE

ELECTRONIC AIR CLEANER

BOX

BLOWER

FURNACE