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VERIFICATION OF THE MAXIMUM PERMITTED POWER OUTPUT AND CURRENT
The heat-tracing system has to be built in such a way that under consideration of voltage and resistance tolerances
the max currents, given in table 1, and the max specific power outputs, given in tables 2, 3, and 4 (depending on variant
in use) are NOT exceeded.
The specific power output of a single conductor polymer insulated heating cable has to be calculated considering of
the maximum voltage and minimum resistance for a given circuit length, using the formulas shown below.
To design such a heating system, nVent offers state of the art software (Trace Calc Pro) and detailed design guides.
Please contact nVent for more information.
2
U
max
p
=
spec
max
r
spec
p
l
spec
=
[A]
max
I
max
U
max
p
Specific power in W/m
spec
U
Voltage in V
l
Length of heating cable in m
r
Specific resistance of heating cable in
spec
I
Current in A
T
Conductor temperature in °C
conducteur
Remark: For heating cables with conductors with a temperature dependent resistance (e.g. copper or copper alloy
conductors), the specific resistance will be calculated for the relevant use temperature, using the
Temperature dependent resistance conductors:
r
= r
spec
spec
min
hot
∆T
T
=
conductor –20°C
Table 1 Maximum current for each variant
Maximum current
Configuration
cold lead
C (power connection)
1 x 2,5 mm
C (power connection)
1 x 4 mm
L (loop)
3 x 2,5 mm
L (loop)
3 x 2,5 mm
S (splice)
non applicable
W
2
l
m
min
(hot)
Ω
/m
(1 + α∆T)
min
cold
Max. temperature of use
180°C
2
180°C
2
150°C
2
180°C
2
180°C
1
α = 0,004
pour cuivre
K
I max*
25 A
32 A
25 A
20 A
32 A
α
-factor.
* for temperature related
reduction factors, see relevant
manufacturers data.
Recommendation for selection of cold
lead:
1 x 2.5 mm
and 1x 4 mm
withstand
2
2
temp. up to 260°C (e.g. PTFE)
3 x 2.5 mm
withstand temp.
2
(e.g. Silicon up to 200°C)
nVent.com/RAYCHEM | 9
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