Continuity Testing - The Illustrated Guide |

Continuity Testing

What is continuity testing?

An electrical continuity test is the checking of an electric circuit to see if the current flows throughout the circuit. Continuity test is performed by applying a small voltage to one end of the circuit and measuring on the other end.

How to do a continuity test?

The most common and basic way of performing a continuity test is with the help of a resistance tester (any simple Multimeter with this function will do). This is because the resistance of conductors between the two ends is usually very small (less then 100 ohm).
As a handy feature, continuity testers usually have a little piezo buzzer built in, which beeps when something is continuous between the two test leads.

When we talk about Continuity Testing within the Inspection and Testing Procedure then we apply the same principle, but with a bit more detail.

The Continuity Test sequence:

hintBefore everything, a safe isolation procedure must be carried out.

Step 1. Select the circuit to be tested in the distribution board and remove the Line conductor from the MCB

Continuity Test Step 1

Step 2. Connect the Line conductor to the Earth conductor (for simplicity, connect it to one of the spare terminals on the Earth bar). This way you will form a circuit which is half made up of the Line conductor and half made of the Earth conductor (provided that the terminations within the electrical accessories such as wall sockets are correct).

Continuity Test Step 2

Step 3. Select the correct test function on the test equipment, which is the low reading ohm meter function (Megger 1553).

Continuity Test Step 3

Step 4. Do not forget to null the test instrument if required (you can do this by connecting the two test leads together and pressing the TEST button until the measured value on the display becomes zero ohm`s)

Continuity Test Step 4

Step 5. Measure between Line and Earth terminals at each outlet in the circuit. The highest reading should be recorded on the Schedule Of Test Results as the value of (R1+R2).

Continuity Test Step 5

Step 6. Return the Line conductor back in to the MCB

Repeat these steps for every circuit except for the ring main circuit.

Test method for the continuity of bonding conductors and the earthing conductor (long lead method):

hintBefore everything, a safe isolation procedure must be carried out.

It is allowed to use any of the correct testing methods. For simplicity we will focus on the most commonly used method.

Step 1. Select a long lead (or long wire) and connect it between the two test leads of the resistance tester (low reading ohm meter). You must null the instrument at this point in order to ignore the resistance of the long lead (press the TEST button until it displays zero ohm`s).

Step 2. Connect one lead of the low reading ohm meter to the bonding conductor inside the distribution board

Bonding Test Step 2

Step 3. Connect the long lead to the other end of the bonding conductor

Bonding Test Step 3

Step 4. Measure to confirm the continuity of the bonding conductor
Repeat these steps for every bonding conductor and for the earthing conductor.

The Inspection and Testing C&G 2391 practical exams

Regulation 411.3.1.1 of BS7671 requires that installations which provide protection against electric shock using automatic disconnection of supply must have a circuit protective conductor run to and terminated at each point in the wiring and at each accessory. Double insulated accessories make an exemption from this rule.

You will be expected to test for continuity every CPC and bonding conductor as well as the earthing conductor.

Next we move on to Ring Circuit testing.

Important things to remember:

AM2 tippDo not forget that with the lighting circuits the intermediate switch should be switched to all available positions so that all the conductors could be tested for continuity.

AM2 tippDo not forget to link out the dimmer switch on the other lighting circuit, otherwise you will get wrong test results.

AM2 tippRemember, that by doing these steps you will also confirm the correct polarity of the conductors, so there is no need to do polarity dead tests again.

AM2 tippRemember to constantly inspect the installation for faults and signs of damages.


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