SANS 10142 Testing Principles Series (8)

⚡ SANS 10142 Testing Principles Series

Test 8: Insulation Resistance — Proving There Are No Leakage Paths

Introduction

Up to now, we’ve confirmed:

• Test 1–3: Installation integrity
• Test 4 & 5: Protection operation
• Test 6: Fault energy (PSC)
• Test 7: Supply condition (neutral voltage)

Now we move to something you cannot see…

👉 The condition of the insulation inside the wiring.

Because even if everything looks perfect…

👉 Damaged insulation can still make the installation unsafe.

According to SANS 10142-1 (Clause 8.6 – Testing):

👉 Insulation resistance must be measured to verify that conductors are properly insulated from each other and from earth.

🧠 1. Foundation (Understanding): What Are We Actually Testing?

This test answers one simple question:

👉 Is current leaking where it shouldn’t?

⚡ What Is Insulation Resistance?

It is the resistance between:

• Live conductors (L–N)
• Live and earth (L–E)
• Neutral and earth (N–E)

🔑 What This Test Proves

👉 No unwanted leakage paths exist
👉 Insulation is intact
👉 Conductors are properly separated

⚠️ Why This Matters

If insulation is compromised:

🚨 Leakage current flows
🚨 Nuisance tripping occurs
🚨 Shock risk increases
🚨 Fire risk increases

🛠️ 2. Application (Doing): How Must the Test Be Done?

⚠️ IMPORTANT

👉 Test must be done with supply OFF
👉 Using an insulation resistance tester (Megger)

🔧 Correct Method

1. Isolate the installation
2. Disconnect or protect sensitive equipment
3. Link conductors where required
4. Apply test voltage
5. Measure insulation resistance

⚡ Test Combinations

👉 L – N
👉 L – E
👉 N – E

⚡ Test Voltage

👉 Typically 500 V DC for standard installations

🎯 PASS REQUIREMENT

👉 Insulation resistance must be:

🔥 ≥ 1 MΩ (Megaohm)

⚠️ If the Reading Is Low

There is a problem.

Possible causes:

• Damaged insulation
• Moisture in conduits
• Dirt or contamination
• Incorrect connections
• Cable deterioration

⚡ 3. Mastery (Owning Responsibility): What Are the Limitations?

This is where professionals stand out.

🔍 The Professional Must Ask:

👉 Are all loads disconnected?
👉 Are electronic devices protected?
👉 Is moisture affecting readings?
👉 Is the cable length influencing results?
👉 Are readings stable or dropping?
👉 Were all combinations tested?

⚠️ Critical Understanding

A good reading does not always mean:

👉 Everything is perfect

And a low reading does not always mean:

👉 Replace everything immediately

👉 It must be diagnosed correctly

⚠️ Common Mistakes

• Testing with equipment still connected
• Not isolating the circuit properly
• Not testing all combinations
• Using incorrect test voltage
• Misinterpreting results

💡 Final Thought

Test 8 is where hidden problems are found.

Because insulation failure doesn’t show itself…

👉 Until it becomes dangerous.

At TDMI Training, we emphasise:

👉 Don’t just test to pass
👉 Test to uncover faults

✅ The Standard

• Isolate properly
• Test all combinations
• Use correct voltage
• Interpret readings
• Investigate failures

👉 Because insulation failure doesn’t warn you…
it fails when it matters most.