Planning the electrical installation 35
Thermal overload and short circuit protection
Thermal overload protection
The drive protects itself and the input and motor cables against thermal overload
when the cables are dimensioned according to the nominal current of the drive. No
additional thermal protection devices are needed.
WARNING! If the drive is connected to multiple motors, a separate thermal
overload switch or a circuit breaker must be used for protecting each cable and
motor. These devices might require a separate fuse to cut off the short circuit current.
Protection against short circuit in motor cable
The drive protects the motor and motor cable in a short circuit situation when the
motor cable is dimensioned according to the nominal current of the drive. No
additional protection devices are needed. The drive trips on a motor phase short
circuit and will not restart unless AC power is removed. Remove all power from the
drive, correct the short circuit and restart the drive. The motor outputs are fully short
circuit proof according to EN 61800-5-1.
Protecting against short circuit in the supply cable or drive
Protect the supply cable with fuses or circuit breakers. Size the fuses according to
instructions given in Technical data on page 136. The fuses protect the input cable in
short circuit situations, restrict drive damage and prevent damage to adjoining
equipment in case of a short circuit inside the drive.
Fuses
Recommended fuses are listed in Recommended fuses, circuit breakers and wire
sizes on page 136. Alternative fuses must be compatible fast acting types.
Circuit breakers
It is highly recommended that fuses are used instead of circuit breakers. Circuit
breakers should only be used when absolutely necessary. UL compliance can only be
achieved when using the recommended fuses.The use of circuit breakers does not
guarantee UL compliance and provides protection for the wiring only, not the
MicroFlex e150. Your local ABB representative can help you in selecting the breaker
type when the supply network characteristics are known.
Motor thermal protection
According to regulations, the motor must be protected against thermal overload and
the current must be switched off when overload is detected. The drive can be
configured to include a motor temperature input that protects the motor and switches
off the current when necessary. For more information about motor thermal protection,
see Thermal switch connection on page 57, and the Mint keyword
MOTORTEMPERATUREINPUT in the Mint WorkBench help file.
Brake output short circuit protection
The brake resistor output is fully short circuit proof according to EN 61800-5-1.
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