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The definition of weak current cable and examples of its selection
Wire and cable are materials used in power, communication, and related transmission applications. There is no strict boundary between "wires" and "cables." Generally, a product with fewer cores, smaller diameter, and simpler structure is called a wire. A non-insulated wire is referred to as a bare wire, while the rest are called cables. A conductor with a large cross-sectional area (greater than 6 square millimeters) is considered a large wire, while one with a small cross-section (less than or equal to 6 square millimeters) is called a small wire. Insulated wires are also classified as wires. Wire and cable include bare wires, electromagnetic wires, insulated wires for electrical appliances, power cables, communication cables, and optical cables.
The naming principle of weak current cables follows specific rules. First, the product name usually includes its application, size class, structural materials, or types. It may also highlight important features. These elements are typically listed in order, but sometimes features are mentioned first if they are critical.
The structure of a cable is described from the inside out: conductor → insulation → inner sheath → outer sheath. Some structural descriptions can be simplified without causing confusion.
For example:
- **SYV 75-5-1**: S = RF, Y = Polyethylene insulation, V = PVC sheath, 75 = 75 ohms, 5 = 5mm diameter, 1 = single core.
- **SYWV 75-5-1**: S = RF, Y = Polyethylene insulation, W = Physical foaming, V = PVC sheath, 75 = 75 ohms, 5 = 5mm outer diameter, 1 = single core.
- **RVVP 2*32/0.2**: R = Flexible wire, VV = Double sheathed, P = Shielded, 2 = 2-core, 32 = 32 copper wires per core, 0.2 = 0.2mm diameter.
- **ZR-RVS 2*24/0.12**: ZR = Flame retardant, R = Flexible wire, S = Twisted pair, 2 = 2-core, 24 = 24 copper wires per core, 0.12 = 0.12mm diameter.
A weak electric cable consists of an inner conductor, insulation, outer conductor, and sheath. The inner conductor significantly affects signal transmission due to resistance. Insulation influences attenuation, resistance, and return loss. The outer conductor serves as a return path and provides shielding.
Cable codes have specific meanings:
- **RVVP**: Copper core, PVC insulated and sheathed flexible cable, 300V/300V, 2–24 cores. Used for instruments, intercoms, monitoring, and control systems.
- **KVVP**: PVC sheathed braided shielded cable. Used for signal transmission, control, and measurement in electrical and instrumentation equipment.
- **SYWV (Y), SYKV**: TV and broadband network dedicated coaxial cables. Structure: single oxygen-free copper + physical foamed polyethylene insulation + (tin wire + aluminum) + PVC.
- **RVV**: PVC insulated flexible cable. Used for household appliances, small power tools, and lighting.
- **AVVR**: PVC sheathed flexible cable.
- **RV, RVP**: PVC insulated cable.
- **RVS and RVB**: Suitable for home appliances, small tools, meters, and lighting connections.
- **BV, BVR**: PVC insulated cable. Ideal for fixed wiring in electrical and instrumentation equipment.
**Weak cable selection examples:**
1. For video lines within 200 meters, use **SYV75-3**. For distances over 200 meters, use **SYV75-5**.
2. For PTZ control lines under 100 meters, use **RVV6 × 0.5**. For distances over 100 meters, use **RVV6 × 0.75**.
3. Use **RVV4 × 0.5** for lens control lines.
4. Use **RVV2 × 1** shielded twisted pair for decoder communication lines.
**Selection of weak current cables:**
Video signals are typically transmitted using baseband frequency (around 8MHz). Coaxial cables are the most common medium due to their low loss and good image quality. The commonly used model is **SYV75-5**, which can transmit video signals up to 300–500 meters. For longer distances, **SYV75-7** or **SYV75-9** is recommended.
Communication cables are used for remote control decoders in cameras with pan/tilt heads and motorized lenses. They are generally 2-core shielded cables like **RVVP** or Category 3 UTP. Each core has a cross-section of 0.3–0.5 mm². For long distances, thicker cables like **RVV2-1.5** can extend the communication range beyond 2000 meters.
Control cables are multi-core cables used to control pan/tilts and motorized lenses. They are short, so shielding is not always necessary. Common models include **RVV6-0.2** and **RVV10-0.12**.
Audio monitoring cables are usually 4-core shielded cables like **RVVP** or Category 3 UTP with 0.5 mm² cross-section.
In monitoring systems, audio signals are transmitted via point-to-point wiring with high voltage and low current, so unshielded 2-core cables like **RVV2-0.5** can be used.
Signal and power supply cables between front-end detectors and alarm controllers often use **RVV2*0.3** or **RVV4*0.3**. The choice depends on the brand and distance.
In building intercom systems, cables such as **RVV**, **RVVP**, and **SYV** are commonly used. They must support voice, data, and video transmission, with high-quality performance.
**Difference between weak electric cables:**
- **SYV vs. SYWV**: SYV is used for video transmission with polyethylene insulation, while SYWV uses physical foam insulation for RF transmission in cable TV.
- **RVS vs. RVV 2-core**: RVS is a twisted pair of two RV wires for broadcast, while RVV 2-core has an outer jacket for power and control.
- **RVV vs. KVV / RVVP vs. KVVP**: RVV and RVVP use flexible multi-strand copper wires, while KVV and KVVP use rigid single-strand copper wires.
- **AVVR vs. RVVP**: AVVR is unshielded with small diameter, while RVVP is shielded with larger diameter.
- **RVS vs. RVV 2-core**: RVS is a twisted pair for broadcast, while RVV 2-core is for power and control.