Electrical Load Calculation and Wiring Types

Posted on Feb 25, 2026 in Technology

UNIT-5

1.3. Problems on Energy Consumption Calculation

A house has the following electrical load for January (31 days):

• (a) Lamps: 5 lamps of 60 W each, working 8 hours per day.
• (b) Lamps: 4 lamps of 100 W each, working 8 hours per day.
• (c) Heaters: 2 heaters of 1000 W each, working 3 hours per day.
• (d) Fans: 5 fans of 80 W each, working 12 hours per day.

Calculate the January month energy bill if the rate of charge is Rs. 0.50 per unit (kWh) and add Rs. 10 as meter rent per month.

Solution:

Given Data:

• (a) Lamps (60W): Number=5, Power=60 W, Time=8 h/day
• (b) Lamps (100W): Number=4, Power=100 W, Time=8 h/day
• (c) Heaters: Number=2, Power=1000 W, Time=3 h/day
• (d) Fans: Number=5, Power=80 W, Time=12 h/day
• January Days: 31
• Rate of Charge: Rs. 0.50 per unit (kWh)
• Meter Rent: Rs. 10 per month

Step 1: Daily Energy Consumption Calculation

(a) 5 lamps of 60 W:

• Total Power: 5 × 60 W = 300 W = 0.3 kW
• Daily Consumption: 0.3 kW × 8 h = 2.4 kWh/day

(b) 4 lamps of 100 W:

• Total Power: 4 × 100 W = 400 W = 0.4 kW
• Daily Consumption: 0.4 kW × 8 h = 3.2 kWh/day

(c) 2 heaters of 1000 W:

• Total Power: 2 × 1000 W = 2000 W = 2 kW
• Daily Consumption: 2 kW × 3 h = 6 kWh/day

(d) 5 fans of 80 W:

• Total Power: 5 × 80 W = 400 W = 0.4 kW
• Daily Consumption: 0.4 kW × 12 h = 4.8 kWh/day

Step 2: Total Daily Energy Consumption

Total Daily Consumption = 2.4 + 3.2 + 6 + 4.8 = 16.4 kWh/day

Step 3: Monthly Energy Consumption (January)

Monthly Consumption = 16.4 kWh/day × 31 days = 508.4 units (kWh)

Step 4: Energy Charges

Energy Charges = 508.4 units × Rs. 0.50/unit = Rs. 254.20

Step 5: Total Monthly Bill

Total Bill = Energy Charges + Meter Rent = 254.20 + 10 = Rs. 264.20

Final Answer:

January month energy bill = ₹ 264.20

2. Types of Wires and Cables for Electrical Installations

This section explains various types of wires and cables utilized in electrical installations:

1. VIR (Vulcanised India Rubber) Wires

• Construction: Copper conductor insulated with vulcanised rubber, covered with cotton braiding for mechanical protection.
• Pros: Flexible and easy to install.
• Cons: Rubber deteriorates due to heat, moisture, and age.
• Use: Primarily in older domestic installations (now largely obsolete).

2. PVC (Polyvinyl Chloride) Insulated Wires

• Construction: Copper or aluminium conductor insulated with PVC. Available in single-core or multi-core configurations.
• Pros: Moisture-resistant, durable, low cost, and long life.
• Use: Most common wiring for homes, offices, and industries today.

3. TRS / CTS (Tough Rubber Sheathed / Cab Tyre Sheathed) Cables

• Construction: Rubber-insulated conductors covered with an outer tough rubber sheath.
• Pros: Strong, moisture-proof, and abrasion-resistant.
• Use: Workshops, damp locations, and outdoor wiring where robustness is needed.

4. Lead Sheathed Cables

• Construction: VIR insulated conductors covered with a lead alloy sheath.
• Pros: Offers excellent protection against moisture and chemicals.
• Cons: Heavy, costly, and requires proper earthing.
• Use: Underground wiring and installations in chemical plants.

5. Weatherproof Cables

• Construction: PVC or rubber insulated with a protective outer covering designed for external exposure.
• Pros: Withstands sunlight, rain, and general atmospheric effects.
• Use: Overhead service connections and outdoor installations.

6. Flexible Cables

• Construction: Fine stranded copper conductors insulated with rubber or PVC.
• Pros: High flexibility and easy bending capabilities.
• Use: Portable appliances such as irons, mixers, heaters, and lamps.

3. Methods for Power Factor Improvement

Power factor improvement involves reducing the phase difference between voltage and current to ensure electrical power is used more effectively. A low power factor leads to higher current draw, increased losses, poor voltage regulation, and higher electricity bills.

The main methods used in practice are:

1. Static Capacitor Method

• Capacitors draw a leading current, which compensates for the lagging current drawn by inductive loads.
• They are connected in parallel with inductive loads (motors, transformers, fluorescent lamps).
• Types of Compensation: Individual, Group, or Centralized capacitor banks.
• Advantages: Simple, economical, low maintenance, and improves voltage level while reducing line losses.

2. Synchronous Condenser Method

• This involves running an over-excited synchronous motor without any mechanical load.
• It draws leading current, supplying reactive power (VARs) to the system.
• The power factor can be smoothly adjusted by changing the field excitation.
• Advantages: Stepless and smooth power factor control; improves system stability.
• Disadvantages: High initial and maintenance cost; requires skilled supervision.

3. Phase Advancer Method

• This method is specifically used with slip-ring induction motors.
• It supplies exciting current to the rotor circuit at slip frequency, reducing the magnetizing current drawn from the supply.
• Advantages: Improves power factor without significantly affecting the stator current; useful for large slip-ring motors.
• Disadvantages: Not suitable for squirrel-cage motors; limited industrial application.

4. Automatic Power Factor Correction (APFC)

• APFC systems use sensors and controllers to automatically switch capacitor banks ON or OFF.
• This maintains the power factor near unity under constantly varying load conditions.
• Advantages: Fully automatic operation; avoids both over- and under-compensation; widely used in modern facilities.

4. Various Battery Backup Concepts

Battery backup concepts detail how stored electrical energy in batteries supplies power when the main grid supply fails or becomes unstable. These are crucial in data centers, hospitals, and renewable energy systems.

1. Standby Battery Backup

• The battery remains idle during normal operation.
• It automatically supplies power upon mains failure, usually with a small switching delay (a few milliseconds).
• Applications: Emergency lighting, alarms, small UPS systems.

2. Online Battery Backup (Double Conversion)

• The load is always powered through the battery and inverter path (AC → DC → Battery → DC → AC).
• This provides zero switching delay during power failure.
• Advantages: Zero interruption; excellent voltage & frequency regulation.
• Applications: Servers, critical data centers, medical equipment.

3. Offline / Standby UPS

• The load runs directly from the mains during normal operation.
• The battery and inverter activate only when the supply fails, causing a small switching delay (2–10 ms).
• Applications: Personal computers, home electronics.

4. Line-Interactive Battery Backup

• An improvement over offline UPS, utilizing an Automatic Voltage Regulator (AVR) to correct minor voltage fluctuations without engaging the battery.
• The battery is only used during a complete power failure.
• Applications: Office systems, network devices.

5. Inverter-Based Battery Backup

• The battery stores DC energy, and an inverter converts this DC to AC power during an outage.
• Changeover can be manual or automatic.
• Applications: Homes, shops, small offices (common residential backup systems).

6. Hybrid Battery Backup (Solar + Battery)

• Combines solar panels, batteries, and grid supply, managed by intelligent energy controllers.
• Batteries charge from solar generation and/or the grid.
• Advantages: Reduced electricity bills; eco-friendly operation.
• Applications: Solar homes, telecom towers, microgrids.

7. Centralized Battery Backup

• Large battery banks supply power to multiple loads, often sharing a common DC bus or AC distribution network.
• Requires a sophisticated Battery Management System (BMS).
• Applications: Substations, large industries, hospitals.

8. Distributed Battery Backup

• Individual battery backup units are installed for each critical load.
• This configuration offers higher reliability, as the failure of one unit does not affect others.
• Applications: Data centers, communication systems requiring high redundancy.

5. Comparison between Primary and Secondary Cells/Batteries

Comparison Table: Primary vs. Secondary Cells