1. Electrical Units
| Name | Symbol | Unit |
|---|---|---|
| Voltage | V | Volt |
| Current | I | Ampere (A) |
| Power | P | Watt (W) |
| Resistance | R | Ohm (Ω) |
| Frequency | f | Hertz (Hz) |
| Energy | E | kWh |
2. Main Formulas
- Voltage:
V = I × R - Current:
I = V ÷ R - Resistance:
R = V ÷ I - Power:
P = V × I - Current from power:
I = P ÷ V - Resistance from power:
R = V² ÷ P
3. Common 230 V Examples
| Appliance | Voltage | Watt | Approx. Current |
|---|---|---|---|
| LED light | 230 V | 9 W | 0.04 A |
| LED light | 230 V | 12 W | 0.05 A |
| Fan | 230 V | 60 W | 0.26 A* |
| Heater | 230 V | 1000 W | 4.35 A |
| Heater | 230 V | 2000 W | 8.70 A |
*Actual motor current can differ.
Switches
One-Way Switch
Purpose: Control one light from one location.
Terminals:
- COM
- L1
Basic circuit:
Phase → Switch → Light → Neutral
Two-Way Switch
Purpose: Control one light from two locations.
Terminals:
- COM
- L1
- L2
Common use:
- Stair light
- Corridor light
- Two-door room
Stair Light
Uses two two-way switches.
- One switch at bottom
- One switch at top
- One lamp
- Either switch can turn the lamp ON/OFF.
MCB
MCB = Miniature Circuit Breaker
Purpose:
- Short-circuit protection
- Overcurrent protection
Common ratings:
6A | 10A | 16A | 20A | 25A | 32A | 40A | 63A
Important: MCB size must be selected according to the circuit wiring, cable capacity, load and applicable electrical standards.
Busbar
Busbar = Metal conductor used to distribute electrical power.
Usually made from:
- Copper
- Aluminium
Example:
Main Supply → Main Switch → Busbar → MCBs → Different Circuits
Clamp Meter
Purpose: Measures current without normally disconnecting the conductor.
It may also measure:
- Voltage
- Resistance
- Continuity
- Current
When measuring current with a clamp meter, clamp around one conductor, not phase and neutral together.
