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5

ELECTRICAL WIRING

TOOLS NEEDED:

One (1) flathead screwdriver.

Conduit opening facing
toward float chamber

Conduit opening facing
away from float chamber

Manual reset button
on No. 2m Switch

a.

The No. 2 switch can be positioned with the conduit opening 
facing toward or away from the float chamber. These are the 
only positions in which the switch will function properly.
See drawing at right.

b.

On initial fill-up, push the 2M manual reset button after the 
proper water level is reached to energize the burner. If a 
low water condition occurs and the water level has been 
restored, push the reset button to energize the burner.

c.

Follow the wiring diagrams below to wire the No. 2 Switch.
Terminals C and NC are the low water cut-off switch.
Terminals C and NO are alarm switch. If the electrical load 
exceeds the rating of the switch, use an auxiliary relay or 
motor starter.

USED AS A MAIN LINE SWITCH
AND/OR LOW WATER ALARM

USED AS A PILOT SWITCH TO COIL
OF RELAY OR MOTOR STARTER

N.

O.

N.C.

C.

N.

O.

N.C.

C.

Neutral

120 V.A.C.

Supply Hot

Low
Water
Alarm

Burner
Circuit

Line

Load

SCHEMATIC OF SWITCH OPERATION

Water Level Normal
Burner On
Alarm Off

Low
Water
Alarm
Terminals

Low Water
Cut-Off
Terminals

C.

N.O.
N.C.

Water Level Low

Burner Off

Alarm On

C.

N.O.

N.C.

N. O.

N.C.

C.

• To prevent electrical shock, turn off the electrical power before making electrical connections.
• This low water cut-off must be installed in series with all other limit and operating controls installed on the 

boiler. After installation, check for proper operation of all of the limit and operating controls, before leaving 
the site.

Failure to follow this warning could cause electrical shock, an explosion and/or a fire, which could result in
property damage, personal injury or death.

!

WARNING

Cover Removal and Installation Procedure

• Using a flathead screwdriver, remove the one 

(1) screw that secures the switch cover.

• Place the cover on the switch housing and, 

using a flathead screwdriver, tighten the one 
(1) screw to approximately 2 ft•lb (2.6 N•m).

Do not use automatic water feeders with manual reset LWCO’s.

Failure to follow this warning could cause flooding, property damage, personal injury or death.

!

WARNING

Summary of Contents for McDonnell & Miller 63 Series

Page 1: ...INSTRUCTION MANUAL MM 206H 246746...

Page 2: ...the diagram that represents your boiler c Crosses should be used at each right angle connection for inspection and cleaning d Make sure the blow down valves are full port e While the burner is operati...

Page 3: ...riser going to the radiation or to the compression tank IMPORTANT The horizontal equalizing pipe should be below the horizontal run going to the radiation If it is not an air pocket will be created a...

Page 4: ...te the installation as described in the low water cut off installation instructions 6 After all piping assembly has been completed refill the system with water turn on all electrical supply and bring...

Page 5: ...N C C N O N C C Neutral 120 V A C Supply Hot Low Water Alarm Burner Circuit Line Load SCHEMATIC OF SWITCH OPERATION Water Level Normal Burner On Alarm Off Low Water Alarm Terminals Low Water Cut Off T...

Page 6: ...k for a build up of scale or sediment between corrugations of the bellows b Cause Contacts are fused together Test Remove switch and operate manually to verify proper switch operation Solution Replace...

Page 7: ...es no longer operate properly If you choose to replace the switch es order the proper McDonnell Miller replacement switch or switch assembly and follow the Repair Procedure provided More frequent blo...

Page 8: ...ngs and other wear parts or consumables all of which are not warranted except as otherwise provided in the quotation or sales form will be free from defects in material and workmanship for a period of...

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