Installation And Maintenance Instructions
NELSON HEAT TRACING SYSTEMS, Tulsa, OK 74146
Bulletin No. 27277- Z 11-08-07
1 of 3
Model
TH4X325
Line sensing bulb and capillary type
Model
TH4X325-2
DPST Relay - Line sensing bulb and
capillary type
Model
TA4X140
Ambient sensing probe type
Testing of the Switch
Testing of the switch may be done before or after
final installation. If bench tested, the switch should
be re-tested when installed in the final application.
Be sure switch can be tested without affecting other
equipment. Check nameplates for elec trical rating
and circui try (normally closed or normally open) of
switch. Cycle switch a few times to check operation.
Set-Point Adjustment
Turn adjustment knob counter-clockwise to increase
set-point.
Description
The remote bulb and capillary types are used to
sense the fluid media temperature.
The local mount types are used to sense ambient
temperatures for freeze protection applications.
Caution:
Do not use these switches for hazardous
environments. Sensing bulb and probe
must not exceed specified proof
temperatures.
Installation
Caution:
This switch should be installed by a
trained service person.
Switch
Mounting:
Switch may be mounted in any position.
Sensors:
Install bulb toward the bottom of pipe or
vessel, away from heat sinks and
approximately 90° from the heat tracing
cable. Always secure both bulb and
capillary and wrap with proper insulating
tape. Orient the local mount probe for
optimal ambient temperature sensing
away from heat sources.
Enclosure: Type NEMA 4X .
Enclosure temperature limits:
-40 °F TO 160 °F (-40 °C TO 71 °C).
Wiring
All electrical wiring must comply with local and
national electrical codes.
Caution:
Electrical rating must be within range
stated on switch nameplate. Failure to
stay within rating may result in damage
to, or failure of electrical contacts.
Electrical
Rating: Standard Switch: 22A @125,250,480VAC.
DPST Relay: Coil - 240VAC,4VA
Contacts - 22A @ 208/240 VAC.
HEAT TRACING TEMPERATURE SWITCH
FOR ORDINARY AREAS
Wiring (continued)
Electrical Connection:
Clamping screw terminals on insulated terminal block
via 3/4 NPT (female) conduit connection. Use 105°C
rated copper conductors only.
Standard SPDT snap-switch models, TH4X325 &
TA4X140, may be wired normally open or normally
closed, per Figures 1 - 4. Contact positions (C, NO,
NC) are clearly identified next to terminal block.
Wire code for built-in jumper wires to terminal block:
Purple= Common
Blue= Normally Closed
Red= Normally Open
DPST Relay model TH4X325-2, may be wired per
Fig. 5. Circuit 1 (2 positions) are for first conductor
of heating cable & first phase of power supply.
Circuit 2 (2 positions) are for second conductor of
heating cable & second phase of power supply.
Contact positions for both circuits are clearly identi-
fied next to the terminal block. Note that the other
2 positions of the terminal block are not used.
Relay contacts for both circuits are wired to close
on falling (decreasing) temperature.
The braid of heating cable must be connected to the
ground screw provided on every switch.
Agency Approvals
Underwriters Laboratories, Inc.
Temperature Indicating and Regulating
Equipment File No. E56247, Guide No. XAPX.
Canadian Standards Association listed for
Temperature Indicating and Regulating
Equipment File No. LR34555,
Guide No. 400-E-O, Class 4813.
