[Abstract] In view of the obvious characteristics of temporary electricity consumption in the construction site, in order to ensure the safety of people's lives, equipment and property in the construction site, according to the relevant norms and standards, this paper expounds the specific problems existing in temporary electricity consumption in the construction site and their solutions, hoping to provide reference for everyone.

[Keywords:] construction site temporary electricity problem solution

First, power management.

1. There is a problem. (1) There is no professional electrician on site, but people who know a little about electricity use are allowed to do electrician work. (2) The electrician failed to set the power supply circuit and protection measures according to the specifications. (3) No special construction organization design has been prepared for the temporary electricity utilization project, and no necessary safety protection measures have been taken. (4) The compiled electricity construction organization design has no load calculation, no circuit diagram, and some of them are out of touch with the actual situation of the construction site, which cannot play a role in guiding electricity construction.

2. Solutions. (1) The installation, inspection, maintenance or removal of temporary electricity works must be completed by electricians. (2) Electrician work is a special operation, which is very harmful to the safety of the operator, others and surrounding facilities. Therefore, it is necessary to conduct safety training for special operators organized by relevant departments in accordance with state regulations, and only after obtaining the operation certificate can they operate. (3) Electricians should wear corresponding labor protection articles correctly when working. (4) When there are more than five electrical equipment on the construction site or the total capacity of the equipment is 50KW or above, the electrical construction organization design shall be prepared.

Two-level and three-level distribution system

1. There is a problem. (1) The distribution system is not set in the way of "main distribution box (or distribution cabinet)-distribution box-switch box", resulting in three-level distribution. (2) Distribution boxes at all levels failed to implement classified protection as required, which expanded the scope of accident power failure.

2. Solutions. (1) The main distribution box is located near the power supply, the distance between the distribution boxes shall not exceed 30m, and the horizontal distance between the switch box and the fixed electrical equipment it controls shall not exceed 3m. (2) The construction site shall be set according to the principle of "one machine, one box, one brake and one leakage". (3) The protection parameters (delay time and action current) of the general distribution box (or distribution box), distribution box and switch box should be longer than the general distribution box and distribution box according to the delay time of overload protection; The rated action current of overload protection is greater than the distribution box, and the distribution box is greater than the switch box. So as to achieve the purpose of hierarchical protection.

Third, secondary leakage protection system

1. There is a problem. (1) The setting of power system leakage protection is less than level 2. (2) The leakage protector is installed near the power supply. (3) The parameters of the leakage protector do not match or the action fails.

2. Solutions. (1) Secondary leakage protection system means that the power consumption system should at least be provided with secondary leakage protection of the main distribution box and switch box, and the rated leakage action current and rated leakage action time of the secondary leakage protector in the main distribution box and switch box should be reasonably matched to form hierarchical and segmented protection. (2) The leakage protector should be installed on the side of the main distribution box and switch box near the load, that is, the power cord should go through the power switch of the knife and then to the leakage protector, and it cannot be reversed; The leakage protector used in wet places has leakage action current ≤30mA, rated leakage action time ≤0. 1s, rated leakage action current ≤ 15mA and rated leakage action time ≤ 0.1s. (3) The rated leakage action current and rated leakage action time of the leakage protector in the main distribution box should be greater than 30mA and 0. 1s, but the product of the rated leakage action current and rated leakage action time should not be greater than 30mA.s. (4) The leakage protector should be sensitive, and there should be no inaction or misoperation. It should be installed and used according to the product manual, and its characteristics should be tested month by month.

Four, protection by zero

1. There is a problem. (1) The lead-out of the protection zero line is not in conformity with the specifications, and the repeated grounding point is insufficient. (2) The protective zero line is not laid with all lines from beginning to end, nor is it connected with the shell of electrical equipment, so it can't play a protective role. 930 doesn't use special color coded wires as protective zero line, and the wire diameter is too small.

2. Solutions. (1) TN-S zero protection system must be adopted for the power line directly grounded to the neutral point of the special power supply on the construction site. The protection zero line should be led out from the working ground line, the power supply side zero line of the distribution room (main distribution box) or the power supply side zero line of the total leakage protector, and laid separately, and shall not be used for other purposes. (2) In TN neutral protection system, the working zero line and the protection zero line should not be electrically connected through the total leakage protector. (3) The protective zero line in TN system must be repeatedly grounded in the distribution room or the main distribution box, and also in the middle and end of the distribution system, and the repeated grounding resistance should not be greater than10Ω. (4) Protect the zero line with green and yellow double-color lines, and under no circumstances shall green and yellow double-color lines be used as load lines. (5) The cross section of protective zero line of three-phase four-wire overhead line should not be less than 50% of that of phase line, the cross section of protective zero line of single-phase line should be the same as that of phase line, and the minimum cross section of protective zero line in power line should be 5mm2. The "protective zero line" connected with power distribution equipment and electric machinery shall be insulated multi-strand copper wire with a cross section of not less than 2.5mm2. The protective zero line should be set from the starting point to the end point of the line, and can be exposed without electricity together with the electrical equipment (including the electrical box).

Five, the electric box Settings

1. There is a problem. (1) There is no disconnector in the electric box or the setting is not standardized. Use wooden electric box, without marking. (2) Wires enter and exit from the side, top, back or door of the electrical box. Electrical appliances are mounted on wooden boards. (3) The installation position of the electric box is unreasonable.

2. Solutions. (1) The distribution box and switch box shall be made of cold-rolled steel plates or flame-retardant insulating materials, and the thickness of steel plates shall be 1.2-2.0mm, in which the thickness of switch box steel plates shall be no less than 1.2mm, and the thickness of distribution box steel plates shall be no less than 1.5mm, and the surface of the box shall be treated with anti-corrosion. The external structure of distribution box and switch box shall be waterproof and dustproof. The distribution box and switch box shall be numbered and marked with the name and purpose, and the multi-channel distribution in the distribution box shall be marked. (2) The total power distribution should be at the incoming terminal of ground power supply in Gao Qian, which is the first electrical appliance after the wire enters the electrical box. The isolating switch shall be an isolating appliance with visible breaking point when breaking, which can disconnect all poles of the power supply at the same time. Do not use air switch or leakage protector as isolating switch, and do not use slate switch. (3) Wires should enter and exit from the bottom of the electrical box, and the inlet and outlet of the electrical box should be protected by sleeves. (4) The installation of the electrical box shall meet the following requirements: First, the distribution box and switch box shall be installed correctly and firmly, and the vertical distance between the center of the fixed electrical box and the ground shall be 1.4- 1.6m, and the vertical distance between the center of the mobile electrical box and the ground shall be 0.8-1.6m. Second, the distribution box and switch box shall not be stacked in front of them to hinder the operation. The installation position of the electric box should be dry, ventilated, at room temperature, free from vibration and impact.

Six, line laying

1. There is a problem. (1) Overhead power lines are erected on scaffolding, or introduced into projects under construction through scaffolding. (2) Use wooden poles or steel pipes as telephone poles. (3) The height of overhead lines and lamps is too low. (4) The wire sheath is aged and damaged, and the insulation is poor.

2. Solutions. (1) The power lines on the construction site shall be laid overhead or buried. (2) The maximum sag of outdoor overhead lines is 4m from the ground to the construction site, 6m from the motorway and 1m from the building (including external scaffolding). (3) The height of indoor wiring from the ground shall not be less than 2.5m When cables are laid along the wall, the maximum sag distance shall not be less than 2m. (4) Bamboo poles shall not be used for poles, and reinforced concrete poles or wooden poles shall be used. The top diameter of the wooden pole should not be less than 140mm. (5) Cable lines are strictly prohibited to be introduced through scaffolding, and cables must be introduced underground for projects under construction. (6) Five-core cable (TN-S) must be used for the cable connected to the zero protection system.

References:

[1] Technical Specification for Safety of Temporary Electricity Use in Construction Site JGJ46-2005.

[2] Construction site safety manual. Economic science press.

[3] Building safety inspection standard JGJ59-99.

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