Pentair Raychem NGC-20-C-E Guide D'installation, D'utilisation Et De Maintenance page 13

2.3.2.2 Installation of the temperature sensor of the safety temperature Limiter
2.3.2.2.1 On the pipe surface
2.3.2.2.2 On an artificial HOT-SPOT
INDUSTRIAL HEAT TRACING SOLUTIONS
The Raychem NGC-20-CL-E knows two methods of limiting the surface temperature of
the heating cable.
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 to 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 sensor tip or reducing the insulation capacity in this area.
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.
For this method you should use the Raychem NGC-20-LIM which comes with all the
needed parts.
Only use the 10 mm insulation pad supplied with the Raychem NGC-20-LIM for this
purpose. The offset value has been verified and proven with this insulating pad and the
sensor as supplied with the thermostat.
Figure 7: Artificial hot-spot
Important guidelines on sensor positioning and installation:
• The correct position is on top of the pipe. See Figure 7.
• 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 lead wire needs to leave the insulation so that no moisture can enter the cladding-
insulation system. Fix the lead wire 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 ) needs to be set at the maximum allowed surface temperature
lim
(T ) minus 10 K.
max
• T = T – 10. Temperatures in Kelvin or Celsius.
lim max
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