Module 1 · Lesson 2

Three-phase power, protection and earthing

Understand three-phase voltage, current, power, power factor, protection and industrial earthing arrangements.

Learning outcomes

Explain the key principles of three-phase power, protection and earthing.
Carry out a structured practical check or configuration task.
Recognise common faults, risks and evidence needed for diagnosis.

Before you begin

A safe training board or approved drawings and calculation examples.

Safety: Use site procedures, approved test equipment and competent supervision. Never bypass a protection or interlock without formal control.

Step-by-step learning

Trace line, neutral and protective-earth conductors on a single-line diagram.
Calculate approximate three-phase power using voltage, current and power factor.
Match overload, short-circuit and earth-fault protection to the load and cable.
Check that protective-earth continuity and bonding are shown on the design.

Ian's practical tips:

Protection must coordinate so the device nearest the fault trips first where practicable.
Treat measured earth continuity and insulation resistance as commissioning records, not casual notes.

Fault-finding questions

What should be happening, and what evidence proves it?
Where is the last known correct signal, voltage, state or process condition?
What changed immediately before the fault?
Can the system be divided into smaller testable sections?

Practical activity

Create a one-page test record for this lesson. Include expected values, measured results, equipment used, risks controlled, defects found and the final proven condition.

I completed the lesson activity. I checked the result safely. I can explain the fault-finding approach.