Testing of the Switch
Testing of the switch may be done before or af ter final
installat ion. 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.
HEAT TRACING TEMPERATURE SWITCH
FOR HAZARDOUS LOCATIONS
NELSON HEAT TRACING SYSTEMS, Tulsa, OK 74146
Bulletin No. 27278-AD 3-10-08 1 of 3
Installation And Maintenance Instructions
Model
TH7325
Line sensing bulb and capillary type
Model
TH7325-2
DPST Relay - Line sensing bulb and
cappilary type
Model
TA7140
Ambient sensing probe type
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:
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 appro-
ximately 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 or heat sinks.
Enclosure: Type NEMA 4.
Enclosure temperature limits:
-40 °F to 140 °F (-40 °C to 60 °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 @ 125,250,480 VAC.
DPST Relay: Coil - 240VAC, 4VA
Contacts - 22A @ 208/240VAC.
Agency Approvals
Hazardous Locations (Division I)
Class I, Groups B,C & D
Class II, Groups E, F & G
Class III
File No. E58658 File No. LR34556
Job Identification 1Z1A0.AE
0081
LCIE 07 ATEX 6093 X
II 2 G D
Ex d IIC T6 *
Ex tD A21 IP6X T80°C*
-40°C
<
Tamb
<
+60°C
* Relay Model - T4, T130°C
Wiring (continued)
Electrical Connection:
Clamping screw terminals on insulated terminal block
via 3/4 NPT (female) conduit connection. Use only
copper conductors, 75°C rated for standard SPDT snap
switch models, & 125°C rated for relay model (TH7325-2).
Standard SPDT snap-switch models TH7325 &
TA7140, 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 wire to terminal block:
Purple = Common, Blue = NC, Red = NO
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 identified 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.
APPROVED
