ITI Electrician Important SI Units depend of “International Conference Of Weight and Measure”
| Sr. No | Quantity | Measuring Unit | Symbol |
|---|---|---|---|
| 1 | Force | Newton | N |
| 2 | Area | Square Meter | m2 |
| 3 | Resistance | Ohm | Ω |
| 4 | Power | Watt | W |
| 5 | Density | Kg per cubic meter | kg/m3 |
| 6 | Velocity | Meter Per Second | m/s |
| 7 | Capacitance | Farad | F |
| 8 | Magnetic Flux | Weber | Wb |
| 9 | Inductance | Henry | H |
| 10 | Pressure | Newton per square meter | N/m2 |
| 11 | Magnetic Flux Density | Tesla | T or Wb/m2 |
| 12 | Angular Velocity | Radian per second | rad/s |
| 13 | Work, Energy, Heat | Joule | J or N-m |
| 14 | Frequency | Hertz | Hz |
| 15 | Magnetic Field Strenght | Ampere Per meter | A/m |
| 16 | Magnetic Motive Force | Ampere turn | AT |
| 17 | Electric Field Strength | Volt Per meter | V/m |
| 18 | Electric Charge | Coulomb | C |
| 19 | Potential , Potential Difference | Volt | V |
| 20 | Luminous Flux | Lumen | lm |
| 21 | Illumination | Lux | lx |
| 22 | Admittance | Siemens | S |
| 23 | Conductance | Siemens | S |
| 24 | Conductivity | Siemens per meter | S/m |
| 25 | Current Density | Ampere Per Square Meter | A/m2 |
| 26 | Electric Flux | Coulomb | C |
| 27 | Electric Flux Density | Coulomb per Square Meter | C/m2 |
| 28 | Impedance | Ohm | Ω |
| 29 | Self Inductance | Henry | H |
| 30 | Mutual Inductance | Henry | H |
| 31 | Change on Quantity of electricity | Coulomb | C |
| 32 | Magnetic Constant or Permeability of free space | Henry per meter | H/m |
| 33 | Reactance | Ohm | Ω |
| 34 | Reluctance | Ampere per Weber | A/Wb |
| 35 | Resistivity | Ohm meter | Ωm |
| 36 | Susceptance | Siemens | S |
| 37 | Torque | Newton meter | Nm |
| 38 | Current | Ampere | A |
| 39 | Voltage | Volt | V |
| 40 | Heat Energy | Joule | J |
For students in the ITI Electrician trade, mastering SI units is more than just passing the exam; it is a fundamental skill for workplace safety and technical accuracy. Below is a comprehensive guide to the essential SI units every electrician must know.
1. Fundamental Electrical Units
These are the “Big Four” of electricity. Understanding the relationship between these units is the cornerstone of Ohm’s Law.
| Quantity | Unit | Symbol | Description |
| Electric Current | Ampere | A | The flow of electric charge per second. |
| Potential Difference | Volt | V | The electrical pressure or electromotive force (EMF). |
| Resistance | Ohm | Ω | The opposition to the flow of current. |
| Electric Power | Watt | W | The rate at which electrical energy is consumed. |
2. Electromagnetism & Inductance
Since ITI Electricians work extensively with motors, transformers, and chokes, these units are critical for understanding magnetic circuits.
- Magnetic Flux: Measured in Weber (Wb). It represents the total magnetic field lines.
- Magnetic Flux Density: Measured in Tesla (T) or Wb/m2
- Inductance: Measured in Henry (H). This is the property of a coil to oppose changes in current.
- Magnetomotive Force (MMF): Measured in Ampere-turns (AT).
3. Capacitance & Frequency
In AC circuits and panel wiring, you will frequently encounter capacitors and frequency ratings.
- Capacitance: Measured in Farad (F). (Note: In the workshop, you will usually see Microfarads (mu $) or Picofarads (pF)).
- Frequency: Measured in Hertz (Hz). In India, the standard power supply frequency is 50 Hz.
- Electric Charge: Measured in Coulomb (C).
4. Energy and Work
When dealing with billing or battery capacities, these units are used:
- Electrical Energy: The SI unit is the Joule (J), but for commercial purposes, we use Kilowatt-hour (kWh), also known as “1 Unit” of electricity.
- Apparent Power: Measured in Volt-Ampere (VA) or kVA (commonly used for transformer and UPS ratings).
- Reactive Power: Measured in Volt-Ampere Reactive (VAR).
5. Illumination Units
For electricians involved in house wiring and lighting design, these units are essential:
- Luminous Intensity: Candela (cd).
- Luminous Flux: Lumen (lm).
- Illuminance: Lux (lx) or $lm/m^2$.
Important Conversion Factors for Exams
- 1hp (British) = 746 Watts
- 1hp (Metric) = 735.5 Watts
- 1kWh = 3.6 x 106 Joules
- 1 Megaohm = 106 Ohms
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