Basic Electrical Information
| Quantity | Symbol | Unit | Basic formula |
|---|---|---|---|
| Voltage | V | Volt (V) | V = I × R |
| Current | I | Ampere (A) | I = V ÷ R |
| Resistance | R | Ohm (Ω) | R = V ÷ I |
| Power | P | Watt (W) | P = V × I |
| Energy | E | Wh / kWh | E = P × time |
| Frequency | f | Hertz (Hz) | AC supply frequency |
1. Voltage
Voltage is the electrical potential difference that causes current to flow.
- Unit: Volt (V)
- Common domestic supply in India: approximately 230 V AC, 50 Hz
- Higher voltage generally means greater potential to drive current through a given resistance.
2. Current
Current is the flow of electric charge through a circuit.
- Unit: Ampere (A)
- Formula: I = V/R
- Measured using an ammeter
- An ammeter is connected in series with the circuit.
3. Resistance
Resistance opposes the flow of electric current.
- Unit: Ohm (Ω)
- Formula: R = V/I
- Measured using an ohmmeter
- For a simple conductor, resistance depends on its material, length, cross-sectional area, and temperature.
4. Power
Electrical power is the rate at which electrical energy is used.
P = V × I
For example:
If a load operates at 230 V and draws 2 A:
P = 230 × 2 = 460 W
Other useful formulas:
- P = I²R
- P = V²/R
Busbar
A busbar is a thick conductor, usually made of copper or aluminium, used to distribute electrical power to multiple circuits.
A busbar does not have one universal voltage or current rating. Its rating depends on the particular electrical system and its design.
Typical examples in low-voltage distribution can include:
- Voltage: 230 V, 400 V, etc., depending on the system.
- Current: ratings can range from tens of amperes to thousands of amperes.
- Material: copper or aluminium.
- Important ratings: voltage rating, continuous current rating, short-circuit withstand rating, and temperature rise.
For a three-phase low-voltage system, 400 V is commonly the line-to-line voltage, while approximately 230 V is line-to-neutral.
Switches
A switch is used to open or close an electrical circuit.
Common types:
- SPST – Single Pole Single Throw
- SPDT – Single Pole Double Throw
- DPST – Double Pole Single Throw
- DPDT – Double Pole Double Throw
- Push-button switch – operated by pressing
- Toggle switch – operated by a lever
- Rocker switch – operated by rocking action
- Selector switch – used to select between different positions/circuits
A switch should be selected according to its voltage and current rating.
Electric Bell
An electric bell converts electrical energy into mechanical movement and sound.
Basic working principle:
- Current flows through the coil.
- The coil becomes an electromagnet.
- It attracts an iron armature.
- The hammer strikes the bell.
- The contact opens.
- The electromagnet loses magnetism.
- The armature returns and the contact closes.
- This process repeats rapidly.
This repeated make-and-break action produces the ringing sound.
Important Electrical Components
- Fuse: protects a circuit against excessive current.
- MCB: automatically disconnects a circuit during overcurrent/short-circuit conditions.
- RCCB/RCD: provides protection against residual/leakage current.
- Relay: electrically operated switch.
- Contactor: switching device commonly used for higher-power loads.
- Transformer: changes AC voltage from one level to another.
- Motor: converts electrical energy into mechanical energy.
- Generator: converts mechanical energy into electrical energy.
- Capacitor: stores electrical energy in an electric field.
- Inductor: stores energy in a magnetic field.
