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Installation Instructions for 

Installation Instructions for 

Model A50 Current Sensing Relay 

Model A50 Current Sensing Relay 

CAUTION

CAUTION: 

For proper operation, the wire lead sponge bracket must carry a minimum of 4.0 amps.                               

If the current draw is less than 4.0 amps, wrap the lead wire around the bracket so that it passes                            

between the bracket and relay housing two or more times. 

For Installation of a Humidifier with a Line 

Voltage Motor and a Low Voltage Control 

IMPORTANT: 

Use a 120V power source 

other than furnace motor circuit. The 
humidifier can be powered off the hot 120V 
line before it enters the furnace.  

CAUTION: 

DO NOT connect the 120V power to the 

furnace motor circuit. It can be powered off the hot 
120V line before it enters the furnace.  

1.

 

To mount the unit, follow the step-by-step instructions 
noted in the humidifier installation manual. 

DO NOT 

connect the electrical, water supply or drain at this 
time. 

 

2.

 

Follow

 

these wiring instructions:

  

a)

 

Turn off electrical power to the furnace. Attach the 
Model A50 Relay around the common lead wire of 
the furnace blower motor (see Detail A). 

The relay 

must be located at least 3" from any trans-
former. Also, the metal bracket on the relay 
must not touch any other metal. 

 

b)

 

Using a wire nut, connect one lead wire from the 
Model A50 Relay to one of the 24V wires from the 
humidifier (A). Additional wire length may be 
needed. 

c)

 

Using a second wire nut, connect the remaining 
lead from the Model A50 Relay to the humidistat 
wire (B).   

d)

 

Using a third wire nut, complete the circuit by 
connecting the second lead from the humidistat to 
the 24V lead from the humidifier (C).  

3.

 

Complete the installation by again referring to the 
instructions supplied with the humidifier.  

 

For Installation with a Separate 

Transformer 

CAUTION: 

DO NOT connect the 120V/24V step-down 

transformer power to the furnace motor circuit. It can 
be powered off the hot 120V line before it enters the 
furnace.  

1.

 

To mount the unit, follow the step-by-step instructions 
noted in the humidifier installation manual. 

DO NOT 

connect the electrical, water supply or drain at this 
time. 

 

2.

 

Follow these wiring instructions:

 

a)

 

Turn off electrical power to the furnace. Attach the 
Model A50 Relay around the common lead wire of 
the furnace blower motor (see Detail A). 

The relay 

must be located at least 3" from any trans-
former. Also, the metal bracket on the relay 
must not touch any other metal.

  

b)

 

Using a wire nut, connect one lead wire from the 
water valve to the 24V transformer (A).  

c)

 

Using a second wire nut, connect the other lead 
wire from the water valve to the humidistat (B).  

d)

 

Using a third wire nut, connect one lead from the 
Model A50 Relay to the other terminal of the 24V 
transformer (C).  

e)

 

Using a fourth wire nut, complete the circuit by 
connecting the other Model A50 Relay lead wire to 
the humidistat (D).   

3.

 

Complete the installation by again referring to the 
instructions supplied with the humidifier.  

IMPORTANT: 

Use a 120V power source 

other than furnace motor circuit. The 
humidifier can be powered off the hot 120V 
line before it enters the furnace.  

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