Introduction to the usage specifications for bolts, nuts, and washers

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Basic requirements for bolt connections: When ordinary bolts are used as permanent fasteners, they must meet the following requirements: 1. For typical bolt connections, flat washers should be placed under the bolt head and nut in order to increase the load-bearing area. 2. Flat washers should be placed on the bolt head side and the nut side respectively; generally, there should not be more than 2 flat washers on the bolt head side, and no more than 1 flat washer on the nut side. 3. For bolts and anchor bolts designed to prevent loosening, nuts or spring washers with anti-loosening features should be used, and the spring washer must be placed on the side of the nut. 4. For bolted connections subjected to dynamic loads or in critical areas, spring washers shall be installed as required by the design, and these washers must be placed on the side of the nut. 5. When using inclined surfaces to connect I-beams and channel steels, inclined washers should be used to ensure that the bearing surfaces of the nuts and bolt heads are perpendicular to the screw shaft. Classification requirements for bolt usage locations: Based on the location and function of bolts in distribution lines, bolts can be classified into three categories: those used for electrical connections, those used to fix electrical equipment, and those used to fix metal accessories. The details are as follows: 1. Electrical connections: Outdoor primary wiring should be connected using hot-dip galvanized bolts; these bolts must be equipped with flat washers and spring washers. After the bolts are tightened, they should protrude by 2–3 threads. One bolt is equipped with two flat washers, one spring washer, and one nut. During installation, place a flat washer on the side of the bolt head, and a flat washer along with a spring washer on the side of the nut, with the spring washer positioned next to the nut. 2. Electrical equipment fixation: When connecting the base of transformers and distribution boxes to iron fittings using bolts on the inclined surface of channel steel, one bolt should be paired with one nut, one inclined washer (for use on the inclined surface of the channel steel), and one flat washer (for use on both flat surfaces). When using channel steel and flat bolts for fixation, one bolt requires two flat washers, one spring washer, and one nut. During installation, place a flat washer on the side of the bolt head, and a flat washer along with a spring washer on the side of the nut, with the spring washer positioned next to the nut. For the connection of isolating switches, drop fuses, arresters, and iron accessories, the installation bolts provided by the equipment manufacturer should be used in principle. 3. Iron accessory fixation type: When the bolt holes for connecting iron accessories are round, one bolt is paired with one nut and two flat washers; when the bolt holes are rectangular, one bolt is paired with one nut and two square washers. During installation, one flat washer (or square washer) is placed on each side of the bolt head and the nut. When double-headed bolts are used for connecting iron fittings, each end of the bolt is equipped with a nut and a flat washer (square washer). For bolted connections on the inclined surfaces of the flanges of channel steel and I-beams, inclined washers should be used as much as possible, so that the bearing surfaces of the nut and bolt head are perpendicular to the shank. Requirements for the direction of bolt insertion: 1. For three-dimensional structures: horizontally, from the inside outward ； Vertically, from bottom to top. 2. For planar structures: along the direction of the line, for double-sided components, from the inside outward; for single-sided components, from the power supply side or in a unified direction ； In the transverse direction: from inside to outside on both sides, from left to right in the middle (facing the power reception side), or in a unified direction ； Vertically, from bottom to top. 3. Planar structure of the transformer test bench: Using the high-voltage and low-voltage terminals of the transformer as reference directions, it extends from the low-voltage terminal side toward the high-voltage terminal side ； Using the transformer and the electric pole as reference directions, pass from the transformer side toward the electric pole side (from inside to outside). Requirements for bolt tightening: The connecting bolts shall be tightened one by one. The torque applied to the bolts shall not be less than the values specified in Table 4. If it is found that the threads of the screw and nut are stripped, or that the edges of the nut are worn to the point where the wrench slips, the bolt and nut should be replaced. Table 4: Bolt Tightening Torque Standards – Bolt Assembly 1. Before assembly, visually inspect the bolts, nuts, or the threaded holes of the components to be connected; there should be no dents or scratches, and they must meet the requirements specified in the drawings or the standards referenced in this specification. 2. During assembly, do not damage the threaded portion of the bolt. 3. The washer on the head of the bolt and on the nut’s end face should make even contact with the surface of the part being fastened; it should not be tilted, and hammers must not be used to force these two surfaces into contact. The screw shaft should not be bent or deformed. 4. The connected parts should be subjected to even pressure, fit tightly together, and be firmly connected. 5. When tightening bolts and nuts, it is strictly prohibited to use inappropriate wrenches. 6. When assembling bolts and screws, they should be hand-tightened for more than 2–3 threads, and then tightened using a wrench or power tool. 7. When assembling bolts and nuts, be careful to protect the paint coating and plating of the components being connected, as well as the heads of the bolts and nuts, to avoid any damage. 8. After the nut is tightened, the head of the bolt should protrude 2–3 pitches beyond the end face of the nut. Both the nut and the washer should have their opposite sides facing the components being connected (the side with inscriptions on the nut is the front side, while the smooth side of the washer is also considered the front side). 9. After the bolts are tightened, apply paint markings; these markings are usually made using red paint at the point where the bolt meets the nut. The color can be changed depending on the location of use, but it must be clearly distinguishable.