Technical standards for temporary power safety at construction sites of buildings and municipal engineering projects
1Key Takeaways
Now approved, the "Safety Technical Standard for Temporary Electrical Use at Construction and Municipal Engineering Sites" is established as an industry standard, numbered JGJ/T46-2024, to be implemented starting January 1, 2025. The original industry standard "Technical Specifications for Safety of Temporary Electrica…
2Expert Interpretation
Comprehensively analyze the core contents of "Technical Standard for Temporary Electricity Safety at Construction Sites of Buildings and Municipal Engineering" JGJ/T46-2024, covering TN-S system configuration, residual current protection settings, three-level distribution specifications and distribution device selection requirements, and provide implementation points and typical application scenario analysis.
Standard Revision Background and Technical Evolution
This standard replaces the JGJ46-2005 version. The main revisions include: expanding the "grounding and lightning protection" chapter to "distribution system", adding special provisions for residual current protection, refining the technical requirements for wire rope wiring, and supplementing the requirements for tower crane power cable laying. The revision reflects three major trends: strengthening system protection, refining equipment specifications, and improving management requirements.
Core safety technology system
| System type | Configuration requirements | Key parameters |
|---|---|---|
| TN-S system | When a dedicated transformer is used for power supply, the PE line is drawn from the N line on the power supply side | PE line cross section ≥ 50% of the phase line |
| Secondary residual current protection | Main distribution box＞30mA/0.1s, switch box ≤30mA/0.1s | Product ≤30mA·s |
| Three-level distribution | Main distribution box→distribution box→switch box, spacing ≤30m | Switch box is ≤3m away from equipment |
Key technical requirements for distribution devices
Typical violation case: A construction site used aluminum core wire as PE wire, resulting in grounding failure. According to the standard, the following should be selected:
- Distribution device PE wire: ≥2.5mm² insulated multi-strand soft copper wire
- Handheld tool PE wire: ≥1.5mm² insulated multi-strand soft copper wire
- It is prohibited to install switches/fuses on PE wire
Distribution box steel plate thickness requirements: switch box ≥1.2mm, distribution box ≥1.5mm, fixed installation height 1.4-1.6m.
Protection measures for special places
| Type of place | Voltage limit | Protection requirements |
|---|---|---|
| Tunnel/civil air defense project | ≤36V | Dual-winding safety isolation transformer |
| Inside metal container | ≤12V | Class III tools + residual current protection |
| Tower crane | 380V | Repeated grounding + lightning protection grounding (R≤10Ω) |
Implementation suggestions and common problems
Main points for cable laying: Direct burial depth ≥ 0.7m, 50mm fine sand + protective plate on the top and bottom of the cable, parallel distance with the pipe network ≥ 2m. Overhead line spacing ≤ 35m, number of joints ≤ 50%.
Typical problem handling: When the distance to the external power line does not meet the requirements of Table 8.1.2, insulation isolation protection (reaching IP30 level) or negotiated power outage migration should be adopted.