Inner thermal overload cut-out switches
(per CEI 2-3/IEC 34-1)
The electrical protections on the motor power line may not be sufficient to protect against
overloads. If the cooling conditions worsen, the motor overheats but the electrical conditions
do not change, which inhibits line protections. Installing built-in protections on the windings
solves this problem:
bimetallic device “PTO”
this is a normally-closed electromechanical device that opens when
the threshold temperature is reached; it automatically resets when
the temperature falls below the threshold level. Bimetallic devices
are available with various intervention temperatures and without
automatic reset, per EN 60204-1.
Tr= Opening temperature (motor stops)
Ti= Re-closing temperature (motor works again)
PTO is not allowed in motors “Delphi Ex - II 3G Ex nA” and other ATEX motors for
Gas environments
PTC thermistor device
this device promptly, positively adjusts its resistance once the
threshold temperature is reached. Motors “Delphi Ex - II 3G Ex nA”
and all motors from type 160 to type 355L are equipped with 3 PTC
thermistors in the winding, with temperature intervention of 120-
130°C in Class F motors (standard) (150-160°C in H Class motors,
not Delphi Ex)
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General