External Lightning Protection System Design and Air Termination Selection
The external lightning protection system is the first line of defense for building lightning protection. Its function is to safely conduct lightning current into the ground and prevent damage caused by direct lightning strikes on the building. According to Section 4.2 of GB 50057 "Code for Design Protection of Structures Against Lightning," the lightning protection classification, air termination layout, and down conductor arrangement of Class II lightning protection buildings shall meet the corresponding requirements. Lightning protection classification assessment for five-star hotels: according to Article 3.0.3 of GB 50057, residential and office buildings and general industrial buildings with an expected lightning strike frequency N≥0.05 strikes/year shall be classified as Class II lightning protection buildings. Five-star hotels are typically high-rise buildings with a height ≥50m and are places with dense personnel; comprehensive assessment of lightning strike risk is generally 0.05-0.25 strikes/year, and they are usually classified as Class II lightning protection buildings. However, super high-rise hotels (height ≥100m) or hotels located in strong lightning areas shall be classified as Class I lightning protection buildings. Air termination selection and layout: (1) Air termination rods: air termination rods or air termination strips shall be installed on the roof. Air termination rods shall use hot-dip galvanized round steel (diameter ≥12mm) or hot-dip galvanized steel pipe (wall thickness ≥3mm, diameter ≥20mm), with height determined by rolling sphere method calculation (Class II lightning protection rolling sphere radius 45m). (2) Air termination strips: laid along protruding parts such as roof parapets, eaves, and ridges, using hot-dip galvanized round steel with diameter ≥10mm, support spacing ≤1.0m, and 0.3-0.5m from corners at corner locations. Air termination strips shall form a closed loop and be reliably welded to down conductors. (3) Air termination mesh: air termination mesh shall be laid on the roof with mesh size ≤10m×10m or 12m×8m (Class II lightning protection). Metal components on the roof (cooling towers, smoke exhaust fans, outdoor air conditioning units, billboards, antennas, etc.) shall be reliably connected to the air termination mesh. (4) Side flash protection: for buildings with height ≥30m, air termination strips or metal curtain walls shall be installed along the building perimeter on each floor above 30m as side flash protection measures. When height ≥60m, they shall be installed on each floor above 60m. Five-star hotels typically install roof cooling towers, satellite antennas, photovoltaic panels, billboards, and other equipment; these metal equipment protruding from the roof must be reliably connected to air terminations with no fewer than 2 connection points (Article 4.5.7 of GB 50057). Down conductor design: down conductor spacing for Class II lightning protection buildings ≤18m. Dedicated down conductors shall use hot-dip galvanized round steel (diameter ≥10mm) or flat steel (cross-section ≥80mm²), laid along the building exterior wall. When using main reinforcement in structural columns (≥Φ16mm, 2 or more bars) as natural down conductors, the main reinforcement in each column shall be continuously welded from bottom to top. Test points shall be provided on down conductors at 0.3-1.0m above ground. Article 4.3.6 of GB 50057 stipulates that the number of down conductors for Class II lightning protection buildings shall not be less than 2 and shall be evenly arranged around the building perimeter. In the glass curtain wall system of five-star hotels, the metal frame of the curtain wall should be used as auxiliary air termination devices, but electrical continuity between curtain wall frames and reliable connection to down conductors (no fewer than 2 locations per floor) must be ensured.
Grounding System Design and Grounding Resistance Control
The grounding system is the foundation of lightning protection and electrical safety. Its design quality and grounding resistance indicators directly relate to the effectiveness of the entire lightning protection system and the level of electrical safety. According to Section 4.5 of GB 50057 "Code for Design Protection of Structures Against Lightning" and Chapter 12 of JGJ 16 "Code for Electrical Design of Civil Buildings," five-star hotels shall adopt a common grounding system, integrating lightning protection grounding, electrical safety grounding, weak current system grounding, anti-static grounding, and other types of grounding into a single common grounding device through an equipotential bonding network. The grounding resistance of the common grounding device shall meet the minimum value requirement among all types of grounding (≤1Ω). Grounding device type selection: (1) Foundation grounding: using the reinforcement mesh in the reinforced concrete foundation of the building as a natural grounding electrode. When the foundation area is sufficient (≥100m²) and the contact area between concrete and soil is sufficient, the grounding resistance of foundation grounding can typically reach 0.5-2Ω. The main reinforcement in the foundation shall be welded into a grid pattern (mesh size ≤20m×20m). (2) Artificial grounding electrodes: when foundation grounding resistance does not meet requirements, artificial grounding electrodes shall be added. Artificial grounding electrodes may use horizontally laid grounding strips (hot-dip galvanized flat steel, cross-section ≥160mm², thickness ≥4mm) or vertical grounding electrodes (hot-dip galvanized steel pipe, diameter ≥50mm, wall thickness ≥3.5mm, length 2.5-3m). Vertical grounding electrode spacing ≥5m, with the top of the grounding electrode ≥0.8m below ground surface. (3) Deep well grounding: in areas with high soil resistivity (such as rocky geology), deep wells (depth 30-100m) may be drilled to install deep well grounding electrodes. Grounding resistance targets: grounding resistance requirements for common grounding devices of five-star hotels (Article 4.5.2 of GB 50057): (1) Lightning protection grounding ≤10Ω (Class II lightning protection buildings), but when shared with electrical safety grounding, the minimum value ≤1Ω shall be adopted. (2) Electrical safety grounding ≤4Ω (Article 5.4.2 of GB 50054). (3) Weak current system grounding (computer rooms) ≤4Ω (Section 4.2 of GB 50343). (4) Anti-static grounding ≤100Ω (Article 4.5.3 of GB 50057). In actual five-star hotel projects, after adopting a common grounding system, measured grounding resistance values are typically between 0.2-0.8Ω, far superior to code limits. Grounding resistance measurement: grounding resistance measurement shall be conducted after construction completion and before each thunderstorm season. The three-electrode method shall be used for measurement (using a grounding resistance tester), with test electrode layout: voltage electrode at ≥20m from the grounding device, current electrode at ≥40m from the grounding device. Measured values shall consider seasonal coefficients (1.0 for dry soil season, 1.2-1.5 for rainy season). Equipotential bonding requirements: (1) Main equipotential bonding (MEB): main equipotential bonding terminal boxes (MEB boards) shall be installed at substations, distribution rooms, weak current equipment rooms, and other locations, connecting metal pipes entering and exiting the building (water supply pipes, drainage pipes, gas pipes, fire protection pipes, etc.), building metal structures, grounding main lines, PE main lines, etc. to the MEB board. (2) Supplementary equipotential bonding (SEB): supplementary equipotential bonding terminal boxes (SEB boards) shall be installed in floor distribution rooms and weak current rooms, connecting metal pipes and metal components on the floor to the SEB, which is then routed to the MEB through grounding main lines. (3) Local equipotential bonding (LEB): LEB terminal boxes shall be installed in wet locations such as bathrooms, swimming pools, SPA areas, and kitchens. Article 8.0.5 of GB 50054 mandates the installation of LEB in wet locations such as bathrooms. Marriott MIDS standards require five-star hotels to install at least 1 SEB terminal box per floor, and LEB must be installed in bathrooms, kitchens, swimming pools, and other areas.
Surge protective device (SPD) graded configuration scheme
Surge protective devices (SPDs) are important devices for preventing lightning electromagnetic impulse (LEMP) and switching overvoltage from damaging electrical equipment and electronic information systems. According to the requirements of Section 5.4 of GB 50343 "Technical Code for Protection of Electronic Information System against Lightning" and Section 6.4 of GB 50057 "Code for Design Protection of Structures against Lightning," a five-star hotel should install SPDs in graded configurations in the power system, signal system, and antenna and feeder system. Graded configuration of SPDs in the power system (three-stage protection): (1) First stage (LPZ0 zone → LPZ1 zone): Class I test SPDs are installed at the main distribution cabinet (substation low-voltage outgoing cabinet). Nominal discharge current In ≥50 kA (10/350 μs waveform), voltage protection level Up ≤2.5 kV. Gap-type or combined-type SPDs are recommended (such as the OBO V50 series). (2) Second stage (LPZ1 zone → LPZ2 zone): Class II test SPDs are installed at distribution cabinets (floor distribution rooms). In ≥20 kA (8/20 μs waveform), Up ≤1.8 kV. Metal-oxide varistor-type SPDs are recommended (such as the OBO V20 series). (3) Third stage (LPZ2 zone → LPZ3 zone): Class III test SPDs are installed at terminal equipment (precision equipment distribution boxes, RCU distribution boxes, front end of weak-current equipment). In ≥10 kA (8/20 μs waveform), Up ≤1.2 kV. Combined-type fine-protection SPDs are recommended (such as the OBO F series). Technical parameters for SPD selection: (1) Maximum continuous operating voltage Uc: For a TN-S system, Uc ≥1.15×U0 (phase voltage), i.e., Uc ≥253 V (U0=220 V). Uc ≥275 V or 320 V is recommended. (2) Voltage protection level Up: The Up value of the SPD should be lower than the withstand voltage level of the protected equipment. Generally, the withstand voltage of electronic equipment is ≤1.5 kV, and that of switching power supplies is ≤2.0 kV. The Up value of the SPD should be ≤80% of the withstand voltage of the protected equipment. (3) Discharge current Iimp/Imax: Determined according to lightning risk assessment. Because a five-star hotel has a large amount of precision electronic equipment (computer networks, security systems, guest room control systems, etc.), higher discharge current ratings are recommended: first stage Iimp ≥50 kA, second stage Imax ≥40 kA, third stage Imax ≥20 kA. (4) Backup protection: A dedicated fuse or circuit breaker should be provided at the front end of the SPD for short-circuit protection, with the rated current determined according to the Imax value of the SPD (generally 32–125 A). Signal system SPD configuration: Computer network interface (RJ45) SPDs: used for connecting guest room network switches, RCU network interfaces, and surveillance camera network interfaces. Transmission rate ≥1,000 Mbps. Telephone interface SPDs (RJ11): used for telephone exchange ports and guest room telephone interfaces. Coaxial cable SPDs: used for the cable television system (CATV) and satellite television receiving system. Control signal SPDs: used for signal lines of the BAS system, fire alarm system, and security system (RS485, 4–20 mA, etc.). SPD installation requirements: (1) SPDs should be installed inside the distribution box or immediately adjacent to the distribution box, with connecting conductor length ≤0.5 m (total length); when exceeding 0.5 m, the Kelvin connection method (V-shaped connection) should be used. (2) Cross-sectional area of SPD connecting conductors: first stage ≥16 mm², second stage ≥10 mm², third stage ≥6 mm². (3) The SPD PE connecting conductor should use a conductor of the same material and cross-section as the phase conductor. The Marriott MIDS standard requires that SPDs be installed at the power supply inlet of all electrical and electronic equipment in the hotel, and that SPDs for important equipment (such as data center equipment and fire control equipment) have degradation indication and remote monitoring functions.
Construction and testing of local equipotential bonding (LEB) in bathrooms
Local equipotential bonding (LEB) in bathrooms is a key safety measure to prevent electric shock accidents, and is particularly important in damp locations such as guest bathroom, SPA areas and swimming pools in five-star hotels. According to the mandatory provisions of GB 50054 Code for Design of Low Voltage Electrical Installations, Clause 5.4.3, and GB 16895.13 Electrical Installations of Buildings - Part 7-701: Requirements for Special Installations or Locations - Locations Containing a Bath or Shower, locations containing a bath or shower must be provided with local equipotential bonding. Mechanism of LEB: when a potential difference exists between different metal parts in a bathroom, once an earth fault occurs (e.g., damaged equipment insulation causing the equipment enclosure to become live), a person may suffer electric shock by touching metal parts at different potentials. LEB connects all accessible metal parts to the same potential via conductors, eliminating potential differences and fundamentally preventing electric shock accidents. Installation of the LEB terminal box: (1) Location: the LEB terminal box should be installed inside the bathroom (usually in the cabinet under the washbasin or at the side of the toilet), with the bottom edge 300-500 mm above the floor. The box size is recommended to be >=240×160×100 mm, made of stainless steel or PVC. (2) Internal configuration: copper busbar (cross-sectional area >=120 mm²), with no fewer than 10 terminals. The LEB terminal box should have pre-embedded φ20 mm or φ25 mm PVC conduits connecting to each metal part. LEB bonding scope: the metal parts that need to be connected to the LEB terminal box include: (1) All metal pipes in the bathroom: water supply pipes (including hot water pipes and cold water pipes), drainage pipes (cast iron pipes), floor drains, bathtub drain pipes, etc. If PPR pipes are used for hot and cold water pipes, they may not be connected (non-conductive), but metal valves and faucets must be connected (when the metal parts are exposed and accessible). (2) Metal components of bathtubs/shower trays: metal frames of bathtubs, metal rails and frames of shower enclosures. (3) Fixed metal components in the bathroom such as metal grab bars, towel racks, and coat hooks. (4) PE conductor (protective earth conductor) of bathroom sockets: connect the LEB terminal box to the PE terminal of the socket. (5) Other metal parts in the bathroom: metal heating radiators (if any), metal door frames (if any). (6) Reinforcement mesh in the floor (bathroom area); when the bathroom has underfloor heating, the metal shielding mesh of the underfloor heating should be connected. Technical requirements for LEB connecting conductors: (1) Conductor specification: single-core or multi-core copper conductor, cross-section >=4 mm² (6 mm² recommended), color yellow-green bicolor (PE conductor identification). (2) Connection method: mechanical crimping (cable lug) or welding. The connection of conductors to metal pipes should use dedicated grounding clamps (copper or stainless steel), clamped firmly. (3) Anti-corrosion treatment: all connection points in damp environments must be treated for corrosion protection (apply conductive paste and then seal). Testing standards: (1) Continuity test: use a DC micro-ohmmeter (accuracy 1 mΩ); the resistance between the LEB terminal and each metal part should be <=0.05 Ω. (2) Potential difference test: under normal power supply conditions, the potential difference measured between the LEB terminal and each metal part should be <=0.2 V. (3) Earthing resistance test: the LEB system should not affect the earthing resistance value of the main earthing system. Marriott MIDS requirements for LEB: (1) All guest bathrooms (including accessible bathrooms) must be provided with LEB. (2) The LEB terminal box should be clearly marked (yellow-green bicolor earth symbol + number). (3) After LEB construction is completed, a continuity test must be carried out, and the test records shall form part of the completion acceptance documents.