⚡ SANS 10142 Testing Principles Series

Test 7: Elevated Voltage on Supply Neutral

Introduction

Up to now, we’ve verified:

Test 1: Bonding
Test 2: Earth continuity
Test 3: Ring circuit continuity
Test 4 & 5: Loop impedance
Test 6: Prospective short-circuit current

Now we move to a test that checks for a dangerous condition that may exist before the installation is even switched on:

👉 Elevated voltage on the supply neutral

According to SANS 10142-1 clause 8.6.6, with the main switch off, the voltage must be measured between the supply neutral and an earth external to the installation. If the reading exceeds 25 V, the supplier must be notified. If it exceeds 50 V, the installation must be disconnected and the supplier notified.

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

This test checks whether the incoming neutral is sitting at an unsafe voltage compared to true external earth.

In simple terms:

👉 The neutral should not be dangerously “raised” above earth.

A raised neutral can indicate supply-side problems, poor neutral integrity, or dangerous conditions outside the installation.

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

Correct method:

1. Switch the main switch OFF.
2. Measure voltage between the supply neutral and an external earth.
3. Where practical, use an auxiliary earth spike driven into wet ground as the reference earth.
4. Record the voltage on the test report. The CoC test report specifically includes “Elevated voltage between incoming neutral and external earth” as Test 7.

Pass / action levels:

👉 ≤ 25 V: acceptable
👉 > 25 V: notify supplier
👉 > 50 V: disconnect installation and notify supplier via Annex H

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

This test is not about fixing the client’s DB.

It is often about identifying a supply-side danger.

The professional asks:

👉 Is my reference earth truly external to the installation?
👉 Is the main switch off?
👉 Is the reading stable?
👉 Could load or supply conditions be affecting the result?
👉 Have I recorded and notified correctly?

💡 Final Thought

Test 7 is simple, but it can reveal a serious danger.

At TDMI Training, we teach electricians not only to take readings — but to understand when a reading means:

👉 Stop.
👉 Record.
👉 Notify.
👉 Do not ignore.

Because a raised neutral is not just a number on a tester.

It can be a warning sign.