PRODUCT INSTRUCTIONS
LIMIT SWITCHES
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NAM1819 REV A.
WIRING AND MOUNTING
Unless specifically designed for such service, limit switches
SHOULD NOT BE
submerged in or
splashed with oils, coolants or other liquids. CONSULT FACTORY. In order to maintain a NEMA type 4
rating, a UL type 4 rated connector must be used. If a connector less than a type 4 rated is used, the
system enclosure rating will become the rating of the connector.
Limit switches
MUST NOT BE
used in locations where temperature or atmospheric conditions are
beyond those for which they have been specifically designed. Power from different sources MUST
NOT BE connected to the contact of one limit switch unless specifically designed for such service. The
temperature rating of the field installed conductors must be at least 90°C.
Limit switches
MUST BE
used within their contact ratings. Refer to switch label on cover for electrical
ratings and the appropriate limit switch bulletin for acceptable environmental conditions in which the
switch has been designed to function properly.
Limit switches
SHOULD BE
mounted rigidly and in readily accessible locations, with suitable
clearances to permit easy service and replacement when necessary. Cover plates
SHOULD
face the
maintenance access point. Refer to Figure B for terminal connections.
Limit switches
SHOULD BE
placed in locations where machining chips do not accumulate under
normal operating conditions to avoid chip interference with a lever operation.
Opposite polarities
MUST NOT BE
connected to the contacts of one limit switch unless the limit switch
is specifically designed for such service. See Figure B for terminal markings for field wire type–copper.
The terminal tightening torque shall be 20-25 in./Ibs.
ACTUATOR CONSIDERATION
Where relatively slow motions operate the limit switch, a snap-acting or snap-lock design
SHOULD
BE
used.
Where relatively fast motions are involved, cam arrangement
SHOULD BE
such that the actuator does
not receive a severe impact.
Where relatively fast motions are involved, cams
MUST BE
designed such that the limit switch will be
held operated long enough to operate relays, valves, etc. See Figure A.
Limit switches
MUST NOT BE
operated beyond the manufacturer’s recommended travel. Operating
positions and lever travel terminology are illustrated in drawing below. For specifications of a specific
switch, refer to the switch datasheet.
NOTE:
When loosening or tightening the pipe plug or set screw used to clamp the actuating lever in
the desired position, care must be exercised to restrain the shaft/lever assembly so as not to transmit
the applied torque to the switch itself.
Cam or dog arrangements
SHOULD BE
such that the actuator is not suddenly released to snap back
freely unless specifically designed for such service.
For limit switches with lever actuators, the actuating force
SHOULD BE
applied as nearly perpendicular
to the lever as practical and perpendicular to the shaft axis in which the lever rotates.
A limit switch actuator
MUST BE
allowed to move far enough for positive operation of the contacts.
Limit switches
MUST BE
mounted in locations which will prevent false operation by normal movements
of operator or machine components.
Limit switches are designed for proper performance with the actuators with which they are supplied.
Supplementary actuators
SHOULD NOT BE
used unless the limit switches are specifically designed
for them.
Operating mechanisms for limit switches
MUST BE
so designed that, under any operating or
emergency conditions, the limit switch is not operated beyond its overtravel limit position. A limit
switch MUST NOT BE used as a mechanical stop.
WARNING:
A SWITCH IN A PROTECTIVE INTERLOCKING CIRCUIT SHOULD BE USED WITH AT LEAST ONE
OTHER DEVICE THAT WILL PROVIDE A REDUNDANT PROTECTIVE FUNCTION, AND THE CIRCUIT
SHOULD BE SO ARRANGED THAT EITHER DEVICE WILL INTERRUPT INTENDED OPERATION OF THE
CONTROLLED EQUIPMENT. (PROPOSED NEMA ICS 2-225.95 St’d.)
SERVICING ENERGIZED INDUSTRIAL CONTROL EQUIPMENT CAN BE HAZARDOUS. SEVERE
INJURY OR DEATH CAN RESULT FROM ELECTRICAL SHOCK, BURN OR UNINTENDED ACTUATION
OFCONTROLLED EQUIPMENT.
RECOMMENDED PRACTICE IS TO DISCONNECT AND LOCK OUT CONTROL EQUIPMENT FROM
POWER SOURCES, AND DISCHARGE STORED ENERGY IN CAPACITORS, IF PRESENT. IF IT IS
NECESSARY TO WORK IN THE VICINITY OF ENERGIZED EQUIPMENT, ONLY QUALIFIED PERSONNEL
SHOULD BE PERMITTED TO PERFORM SUCH WORK , USING ALL APPLICABLE SAFETY PRACTICES
AND PROTECTIVE EQUIPMENT.
EXPERIENCE HAS SHOWN THAT THE MECHANICAL AND ELECTRICAL OPERATING LIFE OF A LIMIT SWITCH
IS INFLUENCED TO A LARGE DEGREE BY PROPER INSTALLATION AND APPLICATION PROCEDURES. THIS
PUBLICATION IS INTENDED TO BE USED AS A GUIDE.
The user should refer to NFPA 70B, RECOMMENDED PRACTICE FOR ELECTRICAL MAINTENANCE,
published by the National Fire Protection Association, for additional information.
