Wires/Cables

1. Cable Types Based on Function

1.1 Power Cables:

These are used to supply electrical power to equipment and assets. Power cables need to handle higher currents and are typically designed with higher voltage ratings and thicker conductors.

• Common Types:

  • Single-core cables: Often used for simple, low-power applications.

  • Multi-core cables: Consist of multiple insulated conductors and are used for higher loads.

  • Armoured cables (e.g., SWA – Steel Wire Armoured cables): Provide mechanical protection, typically used for underground and outdoor applications.

• Size:

  • Power cables are sized based on the current-carrying capacity (ampacity) and the voltage drop across the cable.

  • Typical Sizes:

    • 4 mm² to 6 mm²: Lighting circuits or small load circuits.

    • 10 mm² to 25 mm²: Domestic supply cables or small power circuits (e.g., air conditioning).

    • 35 mm² to 300 mm²: Industrial equipment such as motors, generators, or transformers.

• Voltage Drop:

  • Voltage drop is the reduction in voltage as electrical current flows through the cable due to resistance. It’s important to minimize voltage drop to maintain efficiency and performance.

  • The permissible voltage drop in most installations is between 2-5%.

  • Thicker cables (larger cross-sectional area) reduce resistance and thus minimize voltage drop, which is crucial for long cable runs or high-power applications.

1.2 Control Cables:

Used for the interconnection of electrical control equipment, such as motors, relays, and panels. These are typically low voltage and designed for control signals.

• Common Types:

  • PVC-insulated control cables: Used for general control wiring.

  • XLPE-insulated control cables (Cross-linked polyethylene): Offer higher temperature resistance and better performance in harsh environments.

• Size:

  • Control cables are generally smaller in size because they carry low currents.

  • Typical Sizes:

    • 0.75 mm² to 2.5 mm²: Common for panel wiring, relay controls, and signal transmission.

• Voltage Rating:

  • Typically rated for 300V to 600V, depending on the control equipment being used.

1.3 Instrumentation and Signal Cables (CY, SY, YY):

Used for transmitting data, signals, and control information between different equipment. These cables are designed to minimize electrical noise and interference (EMI).

• Common Types:

  • CY Cable (Screened Flexible Cable): Used for low-frequency instrumentation and control signals where EMI shielding is necessary. The copper braid shield helps reduce interference.

  • SY Cable (Steel Braided Control Cable): Offers mechanical protection and is used in control circuits for industrial machinery.

  • YY Cable (Unscreened Flexible Cable): Used where no EMI shielding is required, typically in light control or communication tasks.

• Size:

  • These cables are smaller as they carry signals rather than power.

  • Typical Sizes:

    • 0.5 mm² to 1.5 mm²: For signaling and low-power instrumentation connections.

• Applications:

  • CY and SY cables are often used in industrial automation, PLC (Programmable Logic Controllers) systems, and for linking sensors, actuators, and instrumentation devices to control panels.

1.4 Data Cables (CAT5e, CAT6, Fibre Optics):

Used for communication and data transmission in automation, networking, and control systems.

• Common Types:

  • CAT5e/CAT6 Ethernet cables: Used for networking and communication in modern electrical systems.

  • Fibre Optic Cables: Used in applications where data transmission over long distances without interference is needed (such as in high-speed internet or industrial automation networks).

• Size:

  • Ethernet cables don’t have significant ampacity, but the gauge is typically between 24 AWG to 26 AWG.

  • Fibre optics transmit light instead of electricity and thus have no wire gauge in the traditional sense.

2. Voltage Drop Considerations

Voltage drop occurs when there is a loss of voltage in a circuit as electricity travels through the wiring. Factors such as wire size, length of the run, and the current affect voltage drop. Minimizing this drop is critical in both power and control systems to maintain efficiency.

• Cable Sizing for Voltage Drop:

  • The larger the cable’s cross-sectional area (measured in mm²), the lower the resistance, resulting in reduced voltage drop.

  • For long distances or higher loads, cables with larger cross-sectional areas (like 35 mm² to 300 mm²) are often required to ensure voltage drop remains within acceptable limits.

3. Application of Cables for Different Electrical Assets

3.1 Lighting Circuits:

• Cable Size: Typically 1.5 mm² to 2.5 mm².

• Type: PVC-insulated cables (non-armoured) are sufficient as the current demands are relatively low.

• Voltage Rating: 230V (for general household or commercial lighting circuits).

3.2 Power Circuits (Motors, Generators):

• Cable Size: Ranges from 4 mm² to 25 mm² depending on the load.

• Type: XLPE-insulated cables are often used for higher current demands and better heat dissipation.

• Voltage Rating: Typically rated for 415V three-phase systems or higher, depending on the industrial requirement.

3.3 Control Panel Wiring:

• Cable Size: 0.75 mm² to 2.5 mm².

• Type: Flexible, multi-core PVC or XLPE-insulated cables.

• Voltage Rating: 300V or higher, depending on the control system’s needs.

3.4 Instrumentation and Sensors:

• Cable Size: 0.5 mm² to 1.5 mm².

• Type: CY cables for EMI-sensitive environments, SY cables for robust mechanical protection.

• Voltage Rating: Generally low voltage (<100V), focused on accurate signal transmission rather than power.

3.5 Data and Communication Systems:

• Cable Type: CAT6 or fibre optics, depending on data transmission speed and distance requirements.

• Size: Not measured in mm², but 24 AWG is common for copper Ethernet cables.

• Application: Networking, communication between PLCs, or linking remote assets to control systems.

4. Cable Protection and Armouring

4.1 Armoured Cables (SWA, AWA):

• Steel Wire Armoured (SWA): Typically used for underground, outdoor, or high-impact applications to protect against mechanical damage.

• Aluminium Wire Armoured (AWA): Used in single-core cables to avoid magnetic interference.

Size Range:

• 1.5 mm² to 400 mm² depending on the application.

4.2 Shielded Cables (CY, SY):

• Provide protection from EMI, important for control and instrumentation cables.

Key Notes:

• Power Cables: Larger cross-sectional area (mm²) cables are used to handle higher currents and reduce voltage drop, essential for long cable runs and heavy electrical loads.

• Control Cables: Often smaller, flexible, and multi-core, these cables are designed for handling control signals, typically for panel wiring or connecting control circuits in industrial settings.

• Instrumentation Cables: Signal transmission cables are generally shielded to prevent EMI, especially in sensitive environments like industrial control systems.

• Data Cables: Ethernet cables (CAT5e/CAT6) and fibre optics are essential for high-speed communication and data transfer in industrial automation and control systems.

• Armouring and Screening: SWA provides mechanical protection for power cables, while CY/SY cables offer protection from EMI in control and instrumentation environments.

 

Wiring in Parallel:

Cabling in parallel is used in electrical systems for several key reasons, mainly to improve performance and safety, especially in high-power applications. Below are the main reasons for using parallel cabling:

1. Increased Current-Carrying Capacity

• Single cables have current limits: Every cable has a maximum current-carrying capacity (ampacity) based on its size, insulation type, and environmental conditions. If a single cable cannot carry the required current without overheating, parallel cables are used to share the current load.

• Multiple smaller cables instead of one large cable: By running cables in parallel, the total cross-sectional area increases, allowing the circuit to carry more current without the need for a single, excessively large cable.

Example: For a high-power application, instead of using one large 300 mm² cable, you could use two or more 150 mm² cables in parallel, which would be more practical to install and handle.

2. Reduction in Voltage Drop

• Long cable runs cause voltage drop: Voltage drop occurs when electrical current travels through a conductor and encounters resistance. This becomes more significant with long distances or high current loads.

• Parallel cables reduce resistance: Running cables in parallel reduces the overall resistance of the circuit, as the current is shared between the cables. With lower resistance, there is less voltage drop, making the system more efficient.

Example: If a single cable over a long distance leads to significant voltage drop, running cables in parallel helps maintain the required voltage at the load end by reducing the overall resistance.

3. Improved Heat Dissipation

• Single cables can overheat: High currents in a single cable can generate excessive heat, leading to insulation breakdown, fire hazards, and equipment damage.

• Parallel cabling improves heat management: By dividing the current across multiple cables, the heat generated in each cable is reduced. This ensures better temperature control and prevents the cables from overheating.

Example: If one cable were carrying the full load, it could overheat and fail. By running two or more cables in parallel, the heat generated is spread out, reducing the temperature rise in each cable.

4. Practical Installation and Flexibility

• Easier handling and installation: Large cables are often bulky, rigid, and difficult to handle during installation. Running several smaller cables in parallel is often more practical, as they are easier to route, bend, and connect, especially in confined spaces.

• Maintenance and redundancy: Using parallel cables also provides flexibility for future maintenance. If one cable fails, the system may still operate, albeit at reduced capacity, until the issue is resolved.

Example: In a power distribution system, running multiple 95 mm² cables in parallel might be easier to manage than using a single, much larger cable.

5. Fault Tolerance and Redundancy

• Improved reliability: In critical applications, parallel cabling can provide redundancy. If one of the parallel cables develops a fault, the others can still carry part of the load, reducing the likelihood of a total system failure.

• Easier fault isolation: When a fault occurs, it is often easier to isolate and repair one cable in a parallel setup rather than a single, heavily loaded cable.

6. Compliance with Electrical Codes

• Regulatory requirements: In some situations, electrical codes or standards may require parallel cabling for certain installations to meet safety, efficiency, or reliability requirements. For example, large industrial installations or high-power equipment often mandate parallel cabling to prevent overheating or excessive voltage drop.

Key Considerations for Using Parallel Cabling

1. Balanced Load Sharing: All cables running in parallel must be of the same type, length, and size to ensure equal current distribution. If the cables are not identical, one cable may carry more current than the others, potentially leading to overheating and failure.

2. Correct Termination: Each cable must be properly terminated at both ends to ensure balanced current distribution. Faulty or poor connections can lead to unbalanced loads and increased resistance.

3. Conductor Sizing: The total cross-sectional area of the parallel cables combined should meet or exceed the current-carrying capacity required for the system.

Example of Parallel Cabling in Practice

In industrial electrical systems, especially for large motors or transformers, cabling in parallel is common practice. For instance:

• A large motor rated at 500A may use two 240 mm² cables in parallel rather than a single larger cable, allowing the motor to draw the necessary current without overloading a single conductor.

Conclusion

Selecting the right cable for the job is vital in electrical engineering. The cable type, size, and insulation must match the application’s voltage, current, and environmental conditions. Power cables typically require larger sizes for high-current applications, while control and signal cables focus on minimizing interference. Proper sizing helps minimize voltage drop, ensuring efficiency and safety.