Discussion on issues easily overlooked in the design of building electrical construction drawings

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By identifying the issues that are often overlooked in the design of building electrical construction drawings, Changhui Instruments outlines the problems present in six areas: design specifications, the representation of diagram symbols, power supply and distribution system diagrams as well as main circuit diagrams, electrical layout plans, substation and diesel generator rooms, and floor plans. It also provides solutions for reference by those working in the electrical field. Original text: yunrun.com.cn/tech/2976.html I. Relevant issues in the design description 1. The description of the building’s general characteristics in this project is incomplete. Information such as building type, nature, structural type, area, number of floors, and height should be provided. 2. The cited design criteria are incomplete and inaccurate. ① The design criteria should include the relevant ** laws, regulations, and relevant standards applicable to this project ； ②Engineering design materials provided by related fields for this specialty ； ③The design assignment letter provided by the project owner, along with relevant design requirements, etc. The laws, regulations, and standards to be used shall be the latest versions available (the number, year, and version number should be indicated). 3. Unclear scope of design: ① It should be specified what tasks need to be completed in this design ； ②The design responsibilities and the interface between them should be specified. Furthermore, issues such as those parts of the design that need to be completed by specialists in this field but were not finished in this design phase, and who will be responsible for completing them later on, should all be clearly specified. 4. The description of the main parameters of the building electrical system is incomplete. ① The installed capacity and calculated capacity of the electrical loads at various levels for this project should be listed ； ②It should describe the layout of the substation(s), including the number of substation(s), the configuration of transformers, and the setup of emergency power supplies. 5. Unclear measurement method: The measurement method for this project, as well as the locations where the measurement points will be installed, should be specified in the documentation in accordance with the requirements of the local power supply authority. 6. The requirements regarding the selection and installation of equipment and cables are not fully specified. ① In this project, the selection of equipment and cables must comply with relevant codes and standards. For example, the specifications clearly stipulate the protection levels required for equipment such as transformers and control cabinets for fire pumps ； ②There are also clear requirements regarding the material, fire resistance, and installation methods of fire protection power cables. Furthermore, all relevant requirements for the seismic design of mechanical and electrical engineering should be specified in the instructions. 7. Regarding lightning protection, grounding, and safety, the content is incomplete. ① The lightning protection level for this project should be determined through calculations, and the results must be specified in the description ； ②To protect against direct lightning strikes, side lightning strikes, lightning induction, and the intrusion of lightning waves, the measures taken must meet the requirements of relevant standards and be reflected in the drawings ； ③The overvoltage protection measures should meet the requirements of this project (it is necessary to specify clearly how many levels of surge protectors are required and how they should be installed) ； ④When setting up equipotential bonding, equipment rooms should not be overlooked (such as motor rooms for strong and weak current systems, pump rooms, and air conditioning rooms). 8. Some versions of the ** or local standard atlas sheets have become obsolete. ① Designers should keep an eye on the updates to relevant standard atlas sheets and avoid using outdated versions ； ②Where the drawings require a secondary schematic diagram, standard atlas sheets may be used, but it is necessary to list the number of the standard atlas sheet selected (in some cases, the page number of the atlas sheet as well must be indicated). 9. The detailed explanations regarding the electrical design aspects of the building are missing or incomplete. ① These detailed explanations should be based on the specific conditions of this project; common categories include those related to electrical energy efficiency, environmental protection, civil defense, seismic resistance of building mechanical and electrical systems, and electrical fire protection (including automatic fire alarm systems, fire control systems, emergency evacuation lighting systems, or intelligent emergency evacuation lighting systems). ②The Provincial Department of Housing and Urban-Rural Development has stipulated that, in order to address common quality issues in residential buildings, design documents for residences must include a dedicated section outlining measures to prevent such quality problems. II. Issues regarding the representation of legend symbols 1. The legend symbols used in engineering design are not listed in a tabular form, or not all of them are included. 2. In the electrical system design diagram, the component symbols used are inaccurate. For example: circuit breakers, fuses, load switches, isolating switches, etc., do not meet the requirements of the \"Common Graphic and Alphabetic Symbols for Building Electrical Engineering Design\". 3. The legends used in this project have not been assigned any relevant meanings. The legends appearing in the diagram should have their respective meanings defined in advance, including the names of the devices they represent, their specifications, installation locations, and installation methods. In the drawings of this project design, the equipment represented by each legend should be of the same type and specifications. III. Electrical General Plan 1. Relevant architectural elements should be retained. ① The names of all buildings and structures shown in the general plan of this project should be kept ； ②Information such as the number of floors of the building, elevations, main road elevations, and topographic contour lines should all be retained. These architectural elements can be softened and have their grayscale adjusted in electrical drawings, but they should still remain clearly distinguishable. 2. Missing or omitted items in the electrical design: ① The location of the substation, as well as the number and capacity of transformers and diesel generators are not specified ； ②The numbers and models of the outdoor distribution boxes/cabinets are missing ； ③Parameters such as specifications, models, and capacity of outdoor lighting fixtures are missing ； ④The cable routing, circuit numbering, and installation method are not clearly specified ； Lack of relevant detailed drawings (such as detailed drawings of cable manholes or access shafts, cross-sectional views of cable trenches or buried cable conduits, etc.) ； ⑤When it is not convenient to express something in the diagram and additional explanation is needed, the details are insufficient and the explanation is unclear. 3. The entry and exit points of various electrical cables do not match those in the individual units. The locations and directions of the cables reserved for entry and exit in the individual buildings differ from those indicated in the overall plan; in some cases, they are even completely opposite ； The way cables enter and exit various buildings is not consistent. IV. Problems in power supply and distribution system diagrams and main circuit diagrams
1. High- and low-voltage power distribution system diagrams (single-line diagrams)
① The model and specifications of busbars are not indicated, or the specifications do not meet the requirements (they are too small or too large, without any calculations or verifications) ； ②The operating voltage of the DC operating mechanism does not match that of the selected DC power supply (DC110V or DC220V) ； ③When using dual power supply feeds, the operating status requirements for the two feed switches and the bus coupler switch are not clear ； ④The current setting value of the circuit breaker in the outgoing circuit does not match the cable specifications; the ratio between the circuit breaker and the current transformer is also mismatched ； ⑤The breaking capacity, protection methods, tripping mechanisms, and other specifications of the outgoing circuit breakers in the low-voltage cabinet do not meet the requirements ； ⑥The reactive power compensation capacity is either too large or too small; the automatic reactive power compensation controller does not match the capacitor bank ； ⑦The power supply circuits for equipment such as the transformer temperature control box, the DC panel charging circuit, and the high-voltage panel are missing ； ⑧The low-voltage outgoing circuit has not undergone dynamic and thermal stability testing, and some wire diameters do not meet the requirements. 2. Low-voltage vertical main electrical conductors: ① The main conductors are not numbered, or the numbers do not match those in the system diagram ； ②When there are multiple electrical shafts, the main wiring diagram is not drawn separately for each shaft ； ③The main diagram does not show the numbers and capacities of the transformers or diesel generator sets connected to each main line ； ④When there are multiple substations, the codes or numbers of the substations should be indicated on the main line diagram. 3. System diagram of the distribution box: ① No numbers are marked on the outgoing circuits of the distribution box ； ②The circuit breaker current setting values for the protection of each circuit do not match the current-carrying capacity of the cables ； ③The parameters of various components are not fully specified; necessary parameters are missing ； ④The user name was not indicated for important load circuits ； ⑤The phase sequence (phase difference) of the single-phase load circuit is not indicated ； The distribution box does not have a design for phase sequence balance. 4. Schematic diagram of the power distribution control box: ① For the outlet circuits that require control, the specific control requirements are not clearly specified ； ②For circuits that require connection to external control devices, the number and specifications of control wires are omitted or indicated incorrectly ； ③When referencing a standard diagram in a secondary schematic, the atlas number is not indicated. 5. Issues regarding SPD backup protection: In distribution boxes/cabinets or control boxes/cabinets equipped with surge protectors (SPDs), the backup protection for the SPDs is either not provided at all or is inadequately configured. Therefore, dedicated SPD backup protection devices should be used. V. Issues with substations and diesel generator rooms 1. Unreasonable location selection. ①The substation is located far away from the load center ； ②Located on the lowest level of the basement ； ③The air inlets and outlets of the diesel generator do not avoid entrances/exits where people gather in large numbers ； The exhaust passage of the diesel generator is not unobstructed. 2. Improper layout within the substation: ① The substation is not arranged in a compact or efficient manner, resulting in significant waste of space; this leads to an increased amount of fire extinguishing agent being required when using gas-based extinguishers, thereby causing unnecessary waste ； ②It is inconvenient for cables to enter and exit the substation; the cable routing, tray specifications, installation height, etc. are not indicated in the drawing. ③Within the same substation, the number of transformers should not be excessive; it is recommended not to have more than 4 units, and in special cases no more than 6 units (provided that the convenience of cable installation and removal is fully taken into account). 3. Lack of corresponding sectional views and detail drawings. ① There are no main sectional views showing the installation of high- and low-voltage switchgear in the substation ； ②The main sectional detail drawing of the cable trench in the facility is missing ； ③There is a lack of a schematic cross-section diagram for the generator set installation. 4. Transportation and loading issues related to power distribution and transformation equipment as well as diesel generator equipment: ① The equipment loading conditions were not provided to the civil engineering design team ； ②The transportation routes for power distribution and transformation equipment as well as diesel generators (including the loads on those routes) were not given sufficient consideration. VI. Issues in the floor plans 1. Electrical floor plans ① In the main power distribution floor plan, the routing for cable trays is missing (or incomplete) ； ②The specifications of the cable tray and its installation height are unclear ； ③When the main and backup circuits are shared in the same cable tray, no partition panel is installed to separate them ； ④The numbering on the distribution boxes is unclear, making them difficult to identify and locate ； ⑤The circuit lacks a number; it also lacks specifications and installation methods (these can be indicated in the system diagram, and should also be specified in the floor plan if necessary) ； ⑥When the power equipment and control distribution boxes/cabinets are not located together but are at some distance from each other, the local control devices (buttons) are omitted ； ⑦The routing and installation methods of the power cables for rooftop electrical equipment are unreasonable. 2. Lighting plan: ① In the main power distribution plan, the routing for cable trays is missing (or incomplete) ； ②The specifications of the cable tray and its installation height are unclear ； ③When the main and backup circuits are shared in the same cable tray, no partition panel is installed to separate them ； The numbering on the distribution boxes is unclear, making them difficult to identify and locate ； ④The calculated values of the lighting power density for the main functional areas should be presented in tabular form within the corresponding floor plans, to facilitate review ； The lighting circuits lack numbering; when there are two or more distribution boxes in the same floor plan, the numbering of the lighting circuits for each distribution box should not conflict with one another (no duplicate numbers allowed). 3. Lightning protection and grounding plan: ① The specifications of the lightning receptor grid and the average spacing between lightning protection down conductors do not meet the requirements of the standards ； ②It should be ensured that all metal components on the roof are not connected to the lightning conductor (special attention should be paid to mechanical and electrical equipment as well as airport obstacle lights installed on the roof) ； ③The lightning protection strip was not provided with expansion joints where it passed through the expansion gaps in the building ； The location of the main equipotential box is not indicated in the ground plane diagram ； The positions of the dedicated down conductors in the equipment room, as well as those of the lightning protection down conductors, do not align (or are inconsistent) with those of the down conductors in the superstructure ； ④Special grounding plans should be provided for equipment rooms with specific requirements and areas that have particular grounding needs. ⑤For more complex projects, a schematic diagram of vertical grounding should also be provided. Author: Liang Zhichao