Spacing Between Power and Low-Voltage Cabling and Restrictions on Shared Conduits and Cable Trays
Spacing control and shared conduit/tray restrictions between low-voltage and power cabling are the primary measures to prevent electromagnetic interference. Basic spacing requirements: Parallel routing spacing — when low-voltage cables (unshielded) are routed parallel to power cables (voltage greater than 380V), the minimum clear distance shall not be less than 300mm (this may be reduced to 150mm when metal conduit or metal trunking shielding is used). When low-voltage cables (shielded type) are routed parallel to power cables, the minimum clear distance shall not be less than 100mm. When the parallel routing length exceeds 10m, the spacing shall be increased to 500mm (cumulative interference effect of long-distance parallel routing). Crossing spacing — when low-voltage cables cross power cables, the minimum clear distance shall not be less than 100mm (at the crossing, power and low-voltage cables shall cross perpendicularly at 90 degrees to reduce interference coupling), and at the crossing the power cable shall be below (to prevent the electromagnetic field generated by the power cable from radiating upward and affecting the low-voltage cable). Vertical spacing — when low-voltage cable trays and power cable trays are routed parallel in the vertical direction (stacked one above the other), the spacing shall not be less than 300mm (low-voltage tray on top, power tray below). Shared conduit/tray restrictions: Absolute prohibition — power and low-voltage cables shall not be run in the same protective conduit (power and low-voltage cables shall not be installed simultaneously in the same PVC or steel conduit), and power and low-voltage cables shall not be installed in the same channel of the same cable tray (even with a divider, they shall be routed in separate channels). Separate-channel routing requirements — when power and low-voltage cable trays are installed on the same combined support, tiered cable trays shall be used (low-voltage tray on the upper tier, power tray on the lower tier), with tier spacing not less than 300mm (a metal isolation plate between tiers is preferable). When power and low-voltage cable trays are routed parallel on the same horizontal plane, a metal divider shall be installed between them (divider height not less than 1/2 of the tray height, divider thickness not less than 1.5mm galvanized steel sheet). Handling of insufficient spacing under special circumstances: When actual space cannot satisfy the 300mm spacing, the following measures may be adopted — use shielded cable for the entire low-voltage run (shield grounded to suppress electromagnetic interference), change the low-voltage tray to fully enclosed metal trunking (metal enclosure grounded for good shielding effect), add a metal shielding plate between the power and low-voltage trays (1.5mm galvanized steel sheet, height exceeding the tray height by 100mm), and use armored cable for both power and low-voltage cables (metal armor layer grounded to enhance shielding effect). Shielding effectiveness verification — after the shielding measures are installed, an electromagnetic field tester (such as TES-1390) shall be used to measure the electromagnetic field strength near the low-voltage cable tray (measured under normal operating conditions); the electromagnetic field strength shall not exceed 10V/m (power frequency 50Hz), and if exceeded, enhanced shielding measures shall be taken.
Shielding and Grounding of Low-Voltage and Power Systems
Shielding and grounding of low-voltage systems are key measures to ensure signal quality and system stability. Shielding measures: Low-voltage cable shielding — the structured cabling system (network cables) shall use shielded cables (FTP or STP type, aluminum foil shield + copper braid shield), with the shield continuous throughout (from the patch panel in the low-voltage room to the guest room information outlet) and grounded at both ends (grounded at the patch panel end and the information outlet end). The measured shielding effectiveness (S-parameter) of shielded network cables at 100MHz shall not be less than 50dB. Low-voltage cable tray shielding — low-voltage cable trays shall use metal trays (hot-dip galvanized steel sheet or aluminum alloy profiles), with tray covers fully covering (not missing), reliable electrical connection between the cover and the tray body (stainless steel spring clips or bonding jumpers), and the tray grounded throughout (repeated grounding every 20m). Low-voltage equipment enclosure shielding — the metal enclosures of low-voltage equipment (switches, servers, monitoring hosts, etc.) shall be reliably grounded (grounding resistance not greater than 1Ω), with the equipment enclosure connected to the grounding bar using 6mm2 yellow-green two-color copper-core wire. Grounding system requirements: Independent grounding for the low-voltage equipment room — the low-voltage equipment room (low-voltage room, network equipment room, fire control room, etc.) shall be provided with an independent grounding busbar (30*3mm copper bar or 6mm2 copper wire), and the grounding resistance of the low-voltage equipment room shall not be greater than 1Ω (required by GB 50174-2017 Code for Design of Data Centers). Equipotential bonding — all metal components in the low-voltage equipment room (equipment enclosures, cable trays, conduits, doors and windows, etc.) shall be equipotentially bonded (connected to the grounding busbar through the equipotential bonding terminal box using BVR-6mm2 yellow-green two-color wire). Separate grounding for power and low-voltage — the functional grounding (signal ground) of the low-voltage system shall be set up separately from the protective grounding (PE line) of the power system (independent grounding electrodes spaced not less than 20m apart), but the two shall be equipotentially bonded at the building's main equipotential terminal box (to prevent potential difference during lightning strikes from damaging low-voltage equipment). Selection of grounding conductor cross-section — the low-voltage system grounding main conductor shall use copper-core wire not less than 16mm2 (BVR-16mm2), branch grounding conductors shall use copper-core wire not less than 6mm2 (BVR-6mm2), and the grounding conductor color shall be yellow-green two-color.
Cabling and coordination requirements for typical ELV subsystems
The cabling requirements of each ELV subsystem in a hotel have their own characteristics and must separately meet their specific technical specifications. Structured cabling system (information points): Cabling grade — each hotel guest room is provided with 2 information points (1 network data point + 1 telephone voice point, 86-type AP panel); public areas are provided with wireless AP points (spacing 15–20 m to cover the entire area); meeting rooms are provided with floor-mounted information outlets (quantity determined by the number of seats). Cabling requirements — the horizontal subsystem uses Category 6 (or Category 6A) shielded network cables (FTP/STP), with a maximum length not exceeding 90 m (from the patch panel to the information faceplate); network cables must not have intermediate joints (continuous single run); the bending radius of network cables shall not be less than 4 times the cable outer diameter. Cable binding — cables in ELV cable trays shall be bound by category (binding spacing 1.5 m for horizontal installation and 1.0 m for vertical installation); the tension of the binding ties shall be moderate (not too tight to cause cable deformation); the cable fill ratio in the cable tray shall not exceed 50%. Security surveillance system: Cabling requirements — video cables (SYV-75-5 coaxial cable + RVVP-2*1.0 power cable for analog cameras; Category 6 network cables for network cameras); maximum transmission distance: coaxial cable not exceeding 300 m (extendable with amplifiers), network cable not exceeding 100 m (extendable through switch cascading). Camera installation height — indoor cameras 2.5–3.5 m above the floor (lens tilted downward 30–45 degrees), outdoor cameras 3–5 m above the ground. Access control system: Cabling requirements — RVVP-4*0.5 mm2 cable between the controller and the card reader (maximum distance not exceeding 100 m); RVV-2*1.0 mm2 cable between the controller and the electric lock (maximum distance not exceeding 50 m); RVV-2*0.5 mm2 cable between the controller and the door release button. All access control cables shall be installed in conduits (steel conduits or flame-retardant PVC conduits). BA building control system: Cabling requirements — RS485 communication cable (RVSP-2*1.0 mm2 shielded twisted pair) between DDC controllers, with a maximum communication distance of 1,200 m (extendable with repeaters); RVVP-2*0.75 mm2 or RVV-2*1.0 mm2 cable between DDC controllers and sensors/actuators. Coordination of ELV systems with other systems: Cables of all ELV systems shall maintain spacing from strong current systems (not less than 300 mm parallel, not less than 100 mm crossing); ELV system cables must not share conduits or trunking with fire alarm cables (the fire alarm system has independent cable trays and trunking).
Key points of acceptance inspection and testing requirements
The acceptance inspection of coordinated wiring between extra-low voltage (ELV) and low voltage (LV) systems is a key step in ensuring system functionality and engineering quality. Key points of the acceptance inspection: Spacing inspection — randomly spot-check no less than 20% of parallel and crossing sections of ELV/LV wiring (measure actual spacing); parallel section spacing shall be no less than 300mm (or effective shielding measures in place), crossing section spacing shall be no less than 100mm with LV cables positioned below. Shared conduit/shared tray inspection — inspect floor by floor and section by section whether ELV and LV conduits share the same conduit or tray (open all cable tray covers and trunking covers for visual inspection); a single violation shall be judged as non-compliant (full rectification required). Shielding effectiveness inspection — ELV cable tray covers fully in place (no missing covers), reliable electrical connection between covers and tray body (spring clips or jumpers), reliable tray grounding (no fewer than 2 grounding connection points per floor). Grounding system inspection — ELV equipment room grounding resistance no greater than 1Ω (measured with a grounding resistance tester), spacing between ELV and LV grounding electrodes no less than 20m, reliable equipotential bonding connections (bolts tightened). Wiring quality inspection — no intermediate joints in ELV cables (continuous single runs), cable binding spacing compliant (1.0–1.5m), moderate binding tie tension (not over-tightened), cable bend radius no less than 4D. Functional testing requirements: Structured cabling testing — 100% of information outlets performance-tested (using Fluke DSX-8000 or equivalent tester); test items include wiring map, length, attenuation, near-end crosstalk (NEXT), return loss (RL), etc.; test results shall comply with Category 6 cabling standards (250MHz). Security system testing — 100% of cameras checked for image quality and field of view (clear image without snow or distortion, complete field-of-view coverage), camera PTZ functions normal. Access control system testing — 100% of access control points tested for card swipe opening, button opening, and fire linkage opening (functions normal, response time no more than 2s). BA (building automation) testing — no less than 30% of DDC points spot-tested (sensor data read correctly, actuators operate normally), communication delay no more than 2s. All test data shall be recorded and archived (retained for no less than 5 years).