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PTB 24 ATEX 1002 X
The rated data of the trace heating system
stated on the type label and any additional
data from the manufacturer shall be taken
into consideration.
4.1
Ambient temperature
To ensure adherence to the maximum permissi-
ble surface temperature, the ambient tempera-
ture shall not fall below or exceed (see type
label). When considering temperature condi-
tions, the effects of other existing heat sources
(process heat) shall also be taken into account.
These must not lead to an additional heating up
of the terminal box.
4.2
Electrical protective measures
4.2.1 Overcurrent trip
The rated trip range of the overcurrent protection
is determined according to the rated current of
the trace heating system as given on the type
label, or as stated in the specification of the trace
heating system. Preference is given to a C trip-
ping characteristic.
4.2.2 Residual current circuit breaker and
insulation monitoring (IEC 60079-
14:2024, Subclause 6.8.2)
In order to limit the heat rise due to earth fault
and earth leakage currents, in addition to the
overcurrent protection, the following protective
devices shall be installed:
–
It is necessary to use a residual current pro-
tective device (RCD) in a TT or TN system,
whereby the rated tripping current shall not
exceed 100mA. Preference shall be given
to residual current protective devices with a
trip-ping current of 30 mA. The maximum
switch-off time of the device must not
exceed 5 s at the rated tripping residual cur-
rent and 0.15 s at 5 times the rated tripping
residual current.
–
It is necessary to use an insulation monitor-
ing device in an IT system. This switches off
the supply as soon as the insulation resis-
tance falls to 50 Ω /Volt of the rated voltage
or lower.
Edition May 2024
Copyright
/
PTB 24 ATEX 1003 X
13
thuba Ltd., CH-4002 Basel
Switzerland
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