Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 74)

Current-measuring overload relays for protection of Ex e – motors must be equipped with a
phase failure protection.
Protection by temperature sensors
As an alternative to monitoring the current, the windings temperature can be measured directly.
If overload protection is exclusively provided by the installation of temperature sensors, then the
motor must be especially examined and certified. It should thereby be documented that the
temperature sensors installed in the stator windings trip reliably, even when the rotor is locked,
before the rotor reaches the critical temperature according to the ignition class.
Direct temperature monitoring is usually realized with PTC thermistors. See also Sections
4.1.2.3 and 4.2.4.3 .
Heavy-duty starting and high frequency of operation
Ex -motors with heavy-duty starting create additional requirements in hazardous areas. For
starting times that would result in tripping of the protective device set to the t
E
-time, precautions
are required to reliably avoid impermissibly high temperatures under all operating conditions.
Thus for example heavy-duty starting from the cold state is permissible as long as it does not
exceed 1.7 times t
E
-time and is specially monitored.
As the limit temperature of the respective temperature class may not be exceeded even during
start-up, especially adapted motors or protective equipment must be selected.
In the case of motors that are frequently switched, there is also a danger that the permissible
limit temperatures of the windings will be exceeded. A current-measuring protective device of
the motor by itself is not good enough to protect the motor. Additional monitoring of the coils by
temperature sensors can be the solution in this case. This is in turn only possible with machines
in which the stator is critical. In this case, motors of ignition protection type ”Flameproof
enclosures d” have an advantage as short-term exceeding of the limiting windings temperature
according to the temperature class is not relevant from the viewpoint of explosion protection.
The thermal limit in this case is determined entirely by the insulation material class (temperature
class).
2.4.7.5 ATEX 100a (Directive 94/9/EC)
For EEx- applications within the EU and the EEA (EU plus Iceland, Liechtenstein and Norway)
only devices and protection systems may be circulated that are certified accordingly under EU
Directive 94/9/EC (ATEX 100a or ATEX 95). This also applies to Switzerland on the basis of the
bilateral treaties with the EU.
Motor protective devices for the overload protection of motors of ignition protection type “e” are
subject to these regulations. These include for example circuit breakers and motor protection
relays that themselves are installed outside hazardous areas but that are required for the safe
operation of the motors with respect to explosion risks, which are installed inside hazardous
areas. Strict regulations are in force with respect to the inspection and certification of the
devices, their labeling and measures relating to production control and quality assurance at the
manufacturer.
In accordance with ATEX 100a, inspection and certification of devices performed by a recog-
nized standards institute (“Notified Body”; for example the “Physikalisch Technische Bundesan-
stalt Braunschweig PTB”) is required. In addition the “Notified Body” audits the production
monitoring and quality assurance systems of the manufacturer. The certification of the manufac-
turer is subject to periodic renewal.
Device labeling according to ATEX
The protective devices are in accordance with ATEX 100a to be labeled as follows:
• Name and address of the manufacturer
• CE-mark supplemented with the number of the notified testing institution
(for example 0102 for PTB)
• Type designation
• Serial number, where applicable
LVSAM-WP001A-EN-P - April 2009 2-46