When the electric line Kengzi moving factory is short-circuited, it will burn out the electrical equipment because of the large short-circuit current, so it must be protected by the electrical equipment of Shenzhen Kengzi moving factory company. Common short-circuit protection appliances include fuses and overcurrent relays. As for the harm of overload, Shenzhen Kengzi Moving Factory Company is not only related to the size of overload (that is, the current exceeds the multiple of current) but also related to the length of overload. The overload current is not as large as the short-circuit current of Shenzhen Kengzi Power Plant Company (generally not more than 10 times the rated current), so short-term overload is allowed. This is an off-peak risk overload. However, the preparation of electric waste for heating is beyond the scope allowed by Shenzhen Kengzi Moving Factory Company, and it will be burned if it is overloaded for a long time. This is a dangerous overload and must be protected. The common overload protection appliance is the thermal relay of Shenzhen Kengzi Moving Company. The common electrical appliances of cranes include not only the electrical appliances and protective appliances of Shenzhen Kengzi Moving Factory Company, but also the executive appliances, that is, the electrical appliances used to complete or perform some mechanical operations of cranes, such as the brake electromagnet of Shenzhen Kengzi Moving Factory Company. 1) Single and double beams In general, the lifting weight is below 50t, the span is within 35m, and there is no special use requirement, so the single beam type should be selected. If the portal is required to be large in width and high in working speed, or heavy and long workpieces are often hoisted, the double-beam portal crane should be selected. 2) The span of the span gantry crane is an important factor affecting the quality of the crane itself. When selecting the type, the span should be reduced as much as possible under the premise of meeting the equipment use conditions and meeting the span series standards. 3) Determine the wheel track a) Meet the stability requirements of the gantry along the crane track b) The overall dimensions of the goods should be able to smoothly pass through the plane steel frame of the leg c) Pay attention to make the wheel track b directly proportional to the span s, and generally take the wheel track b = (1/4— 1/6) s. 4) When working, the overall dimensions of the gantry are between the goods in the freight yard and the traffic of transport vehicles. Generally, when loading and unloading vehicles within the span, the distance from the door leg should be kept above 0.7m.