GeneralAire GA51 User Manual

24-volt and 120-volt Current Sensing Relays

Installation Instructions

General Filters, Inc. 43800 Grand River Ave., Novi, Michigan 48375 • Phone: [phone]

Fax [phone] • www.generalaire.com

Designed to interface with humidifiers and most heating and cooling systems.

It senses current rather than measuring voltage, making it more reliable. It is less expensive than using traditional flow switches,
pressure switches or other types of relays. The relay installs around the blower motor’s common lead and interface easily into the
circuitry.

The current sensing relay case is constructed from high-impact plastic. The lead wire bracket is protected by a soft sponge insert, in
order to prevent damage to the motor/blower wire and/or accidental contact with any metal.

Important:

The wire lead bracket needs to carry a minimum of 5.0 amps for proper operation. If the current draw is less than 5.0 amps,

wrap the lead wire around the bracket so that it passes between the bracket and relay housing two or more times.

Caution:

Turn off all power to the furnace motor circuit and cabinet.

GA50 24-volt and GA51120-volt Current Sensing Relay

General Installation Procedures

1. Follow the step-by-step instructions for

Common
Blower Lead
5 Amp. Min.

L
O
A
D

24 or 120 VAC.

mounting the General Filters humidifier,
found in the humidifier installation
manual. DO NOT connect the electrical,
water supply or drain at this time.

2. Please follow these wiring instructions:

A. Turn off electrical power to the

furnace. Attach the current sensing
relay around the common lead of
the furnace blower motor. The relay
must be located at least 3” from any
transformer. Make sure, the relay’s
metal bracket does not touch any
other metal. (See detail A)

Model X Wiring Diagrams

GeneralAire Model 1137 GeneralAire Model 1042 DME GeneralAire Models 1042 LH, 1099LH & SL16

B. Use a wire nut to connect one lead

wire. Use a wire nut to connect one
lead wire from the current sensing
relay to one of the 24V wires from
the humidifier. (X) (Additional wire
length may be needed.)

C. Use a second wire nut to connect

the remaining lead wire from
the current sensing relay to the
humidistat (Y).

D. To complete the circuit, use a third

wire nut to connect the humidistat’s
second lead wire to the 24V lead
from the humidifier (Z).

3. Follow the instructions supplied with the
humidifier to complete the installation.

COMMON LEAD

DETAIL A

120 V

GeneralAire Fan Powered Humidifier

CURRENT SENSING
RELAY

120 V 24 V

GeneralAire Bypass with Temperature
Compensating Auto Control

METAL BRACKET

CURRENT SENSING
RELAY

120 V 24 V

COMMON LEAD

FURNACE BLOWER
MOTOR

GeneralAire Bypass with manual control

24-volt and 120-volt Current Sensing Relays

120 VAC

GASI

EAC

Model Air Cleaner Installation

Installation Instructions

1. Install the air cleaner according to the
manufacturer’s instructions.

2. Install the GA51 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 and run the leads of the GA51 relay
into the junction box.

120 VAC

2 x 4

Electrical

Box

EAC

4. Connect the leads of the
GA51 relay in series with
one of the electronic air
cleaner leads. Connect the
remaining lead and ground
wire. The 120 VAC source
must be independent of
the furnace blower motor.

Checkout Procedures

1. Replace all safety devices.

2. Reconnect power to furnace.

3. Activate furnace blower motor.

4. Check load for operation. It should now be working properly. Check
indicating lamp or other conditions showing that 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.

5. Check all wire connections, close junction box
and restore furnace to working order. Test proper
functioning by observing that the air cleaner’s
indicator lamp turns on when the blower runs and
turns off when the blower stops.

GASI

EAC

120 VAC

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

• Ensure the device’s power switch is in the “ON” position.

• Recheck all wiring.

• Check line fuses.

• Confirm that five or more amps is flowing through the control wire.
Wrap additional turns around the bracket if necessary.

Technical Specifications

24-volt and 120-volt Current Sensing Relay

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

Sensing Current Minimum 5 amps Minimum 5 amps

Operating Ambient Temperature Range 40˚F - 104˚F 40˚F - 104˚F

Dimensions

Load Ratings Maximum (12 watts) 0.50 amps

GA50

24-volt Model

Minimum (3 watts) 0.12 amps

GA51

120-volt Model

Maximum (50 watts) 0.42 amps

Minimum (3 watts) 0.03 amps