How to select the load switch for the crane load switch box?

When selecting a load switch for an overhead crane load switch box, several factors must be considered to ensure safe and reliable operation. Here are some key selection points:

Rated Voltage:The rated voltage of the load switch should match the supply voltage of the overhead crane. Common overhead crane supply voltages are 380V, 400V, etc. The rated voltage of the selected load switch should not be lower than the actual operating voltage of the overhead crane to ensure reliable connection and disconnection of the circuit under normal and abnormal conditions.

Rated Current:Determine the rated current of the load switch based on the sum of the rated currents of the motors of each mechanism of the overhead crane. The current changes during starting, braking, and overload conditions of the crane must also be considered. Generally, the rated current of the load switch should be greater than the maximum operating current during normal operation of the overhead crane, with an appropriate margin, usually 1.2 to 1.5 times the sum of the rated currents of the motors, to handle possible short-term overload situations.

Breaking Capacity: The load switch should have sufficient breaking capacity to quickly cut off the circuit in case of short circuits, overloads, and other faults to protect equipment and personnel. Breaking capacity is usually expressed as the effective value of the short-circuit current and should be selected according to the short-circuit capacity of the overhead crane's power system. For example, in power systems with a large short-circuit capacity, a load switch with a high breaking capacity should be selected, such as a current-limiting fuse combination switch or a contactor with a high short-circuit breaking capacity.

Operating Frequency: Overhead cranes have a high operating frequency, and the load switch needs to frequently connect and disconnect the circuit. Therefore, a suitable load switch should be selected based on the actual operating frequency of the overhead crane. For overhead cranes with a high operating frequency, a load switch with a high mechanical life and electrical life should be selected, such as an AC contactor, to ensure that it maintains good performance and reliability under long-term frequent operation.

Arc Extinguishing Performance: When cutting off the load current, the load switch will generate an arc. Good arc extinguishing performance is crucial for the safe operation of the switch. For overhead crane load switches, products with special arc extinguishing devices are usually selected, such as load switches using air arc extinguishing, vacuum arc extinguishing, or magnetic blow arc extinguishing technologies. For example, in some overhead crane applications with high safety requirements, a vacuum contactor is selected as the load switch, which has good arc extinguishing performance and a high electrical life.

Protection Level: Consider the working environment of the overhead crane and select a load switch with an appropriate protection level. If the overhead crane operates in an environment with a lot of dust, moisture, or corrosive gases, a load switch with a higher protection level should be selected, such as products with an IP54 or IP65 rating, to prevent dust, moisture, or corrosive substances from entering the switch and affecting its performance and life.

Control Method: Select a load switch with the corresponding control method according to the control requirements of the overhead crane. Common control methods include manual control and electromagnetic control. For overhead cranes with a higher degree of automation, an electromagnetically controlled load switch, such as a contactor, is usually used to facilitate remote control and automated operation; while for some small or simple overhead cranes, a manually controlled load switch may be sufficient.

Coordination with Protective Devices: The load switch should work well with the overhead crane's protective devices, such as fuses and thermal relays. For example, the breaking characteristics of the load switch should match the fusing characteristics of the fuse to ensure that the circuit can be accurately and quickly cut off in the event of a fault, achieving reliable overload and short-circuit protection. At the same time, the rated current and operating characteristics of the load switch should also be coordinated with the thermal relay to achieve overload protection of the motor.