nvent Raychem T-M-20-S/+X+Y/EX Manual page 9

5.3 Installation of the temperature sensor of the safety temperature Limiter
The T-M-20-S/+x+y/EX knows two methods of limiting the surface temperature of the heating cable.
On the pipe surface
The first method consists of using the surface temperature of the pipe as reference and preventing
powering the heating cable when the pipe temperature is above a calculated value. This value is
depended on the make of the cable and the design of the heating circuit. Use TraceCalc Pro
determine this value and document the calculation in your filing. The sensor is installed identical to the
normal temperature sensor, at the top of the pipe, firmly attached to the surface by means of glass
tape. Special attention needs to be taken that the sensor lead does not cool the pipe/sensor; nor that
moisture could enter the insulation, cooling the capillary or reducing the insulation capacity in this area.
On an artificial HOT-SPOT
The second way of surface temperature limiting is to create an artificial hot-spot. In order to guarantee
the limiter sensor measures the highest possible temperature of the installation, the temperature
sensor of the limiter shall be installed on an artificial hotspot. Only use the 10 mm insulation pad for
this purpose.
Artificial hot-spot
Important guidelines on sensor positioning and installation:
• The correct position is on top of the pipe.
• Fix the insulation pad with sufficient glass tape. (GT-66 or GS-54)
• Guide the heater from the bottom of the pipe to the insulation pad and fix it well so that it keeps its
position.
• The sensor needs to be attached with sufficient glass tape to the heater. Use two bands of glass tape
to ensure its position.
• The capillary needs to leave the insulation so that no moisture can enter the cladding insulation
system. Fix the capillary to the pipe with glass tape if needed to ensure the
stability of the hot spot system.
• Make sure that the nominal insulation thickness is respected over the hot spot, it might be necessary
to use oversized insulation shells.
Limiter temperature setting:
• The limiter value (T
minus 20 K. (10K due to standards, 10k due to heat loss by sensor)
) needs to be set at the maximum allowed surface temperature (T
lim
to
®
)
max
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