Selection of low voltage fuses and common fault handling methods

1. Selection of fuse type

The fuse is mainly selected according to the condition of the load and the magnitude of the short-circuit current of the circuit. For example, for the protection of small-capacity lighting lines or motors, RM10 series non-filled sealed tube fuses should be used; for short-circuit currents, RL series spiral fuses or RT series with high breaking capacity should be used. Filled tube fuses with packing; for the protection of silicon rectifiers and thyristors, fast fuses should be used.

The form of the fuse should also consider the use environment. For example, tubular fuses are often used in large equipment and large-capacity substation applications; plug-in fuses are often used in vibration-free applications; spiral fuses are often used in machine tool distribution; Electronic equipment generally uses a fuse holder.

2. Selection of melt rated current

1 For resistive loads such as lighting circuits and electric heating equipment, because the load current is relatively stable, it can be used as overload protection and short-circuit protection, so the rated current Irn of the melt should be equal to or slightly larger than the rated current Ifn of the load, ie

Irn=1.1Ifn

2 The starting current of the motor is very large, so the motor should only be short-circuit protected. For a single motor that protects long-term operation, the melt cannot be blown when the motor is started.

Irn≥(1.5~2.5)Ifn

Among them, when the light load start or start time is short, the coefficient can be close to 1.5; when the load is restarted, the start time is longer or the start time is more frequent, the coefficient can be close to 2.5.

3 For the fuses protecting multiple motors, considering that the melt is not blown when a spike current occurs, the rated current of the melt should be equal to or greater than 1.5 to 2.5 times the rated current of the largest motor, plus the rest of the simultaneous use. The sum of the rated currents of the motors, ie

Irn≥(1.5~2.5)Ifnmax+∑Ifn

The rated current of a motor with the largest capacity among the Ifnmax-multiple motors;

∑ Ifn - the sum of the rated currents of the remaining motors.

3. Selection of the rated voltage of the fuse The rated voltage of the fuse should be equal to or greater than the rated voltage of the circuit in which it is located.

The common faults of fuses and their treatment methods are shown in the table.

Common faults of table fuses and their treatment methods