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Switchboard heating
The heating resistor, placed in the bottom of the switchboard, maintains the internal
temperature 10 °C higher than the external temperature.
When the switchboard is not in operation, the heater compensates the dissipated
power normally emitted by the switchboard.
The power of the heating resistor is calculated:
b
b
using the equation: Pr = (
D
T x S x K) - P
b
b
or using the charts below, based on the exposed surface area of the enclosure
and the desired difference in temperature.
Chart to determine the heating resistor for small wall-mounted enclosures
(exposed surfaces
y
1 m
2
)
Chart to determine the heating resistor for all types of enclosures
Calculation data
P :
power dissipated by the devices, connections and busbars (in Watts)
P
r
:
power of the heating resistor (in Watts)
T
m
:
maximum internal temperature in the device zone (in °C)
T
i
:
average internal temperature (in °C)
T
e
:
average external temperature (in °C)
D
T
m
= T
m
–
T
e
D
T
= T
i
–
T
e
S :
total free surface area of the enclosure (expressed in m
2
)
K :
thermal-conduction coefficient of the material (W/m
2
°C)
K = 5.5 W/m
2
°C for painted sheet metal
D :
ventilation throughput (in m
3
/h)
Note:
the dissipated power of each device is provided by the manufacturer.
Add approximately 30 % to account for the connections and the busbars.
Thermalmanagement
of switchboards
Heating
Additional information
Thermal characteristics
Dd381788.eps
Dd381789.eps