What Are SI Units? (Standard Units Explained for Electricians)
When you start learning electrical theory, one of the first things you’ll notice is that everything is measured. Voltage, current, resistance, power — none of it makes sense unless everyone is using the same units, defined in the same way. That’s where SI units come in.
SI units form the foundation of electrical theory, testing, and installation work, and they are a core part of Level 2 electrical training.
What Does SI Stand For?
SI stands for Système International d’Unités, which translates to International System of Units.
It is the globally agreed system of measurement used in science, engineering, and electrical installation. SI units ensure that measurements are:
Accurate
Consistent
Universally understood
Suitable for safety-critical work like electrical installations
In short: SI units make sure everyone is speaking the same technical language.
Why SI Units Matter to Electricians
Electrical work relies on precise measurements. Using standard units ensures:
Safe design and installation of circuits
Accurate inspection and testing results
Compliance with regulations and standards
Clear communication between electricians, engineers, manufacturers, and inspectors
From calculating cable sizes to verifying test results, SI units appear everywhere in electrical work.
At Level 2, learners begin applying SI units practically — not just memorising them, but using them to understand how electricity behaves in real installations.
The Core SI Base Units Used in Electrical Work
The SI system is built on seven base units. Electricians don’t use all of them daily, but several are fundamental:
Metre (m) – length (e.g. cable runs, containment)
Kilogram (kg) – mass (e.g. equipment handling)
Second (s) – time (used in calculations and waveforms)
Ampere (A) – electric current (critical for circuit design)
Kelvin (K) – temperature (relevant for derating and thermal effects)
These base units combine to form the electrical units used every day on site.
SI Prefixes Every Electrician Must Know
SI units often use prefixes to represent very large or very small values — essential when dealing with electrical measurements.
PrefixSymbolMultiplierExamplemillim0.001mA (milliamps)kilok1,000kW (kilowatts)megaM1,000,000MΩ (megaohms)microμ0.000001μF (microfarads)
Understanding prefixes prevents common mistakes — especially when reading test instruments.
How SI Units Are Used in Level 2 Electrical Training
On a Level 2 Electrical Installation Course, SI units are applied practically through:
Basic electrical calculations
Understanding Ohm’s Law
Measuring voltage, current, and resistance
Interpreting test results correctly
Safe installation and verification practices
This is where theory starts to make sense — and where learners build confidence using real measurements in real scenarios.
👉 Level 2 Electrical Installation Course – link here
👉 Level 3 Electrical Installation Course – link here
Both courses use SI units extensively across electrical science, system design, installation, inspection and testing, ensuring learners understand not just how to install, but why systems behave the way they do.
Question of the Week – WC 19.01.2026
As part of our ongoing learner support, this topic also links directly to our Question of the Week for week commencing 19.01.2026, where we explore key electrical terms and concepts used throughout Level 2 and Level 3 training.
👉 Link to Question of the Week (WC 19.01.2026) here
Please ensure you review the terms and conditions associated with weekly questions and learning resources.
👉 Link to Terms & Conditions here
Final Thoughts
SI units aren’t just something to memorise for exams — they are the language of electricity. Every safe installation, accurate test, and compliant job depends on using standard units correctly.
By mastering SI units at Level 2, electricians build a strong foundation for future qualifications, testing courses, and real-world work on site.
Ready to Take the Next Step?
Whether you’re starting out at Level 2, progressing to Level 3, or just want to strengthen your understanding of electrical science, we’re here to help.
👉 Contact us to discuss the right course for you, upcoming start dates, or any questions about electrical training.