How to conduct polarity testing?

What is polarity testing?

A test that creates a circuit using the phase conductor and the single pole device in question, breaking the circuit when operating the device, means that the reading on the instrument will change, and thus confirming that that device must be connected in the phase conductor.

This test will verify that all the switches installed in the system are connected in current carrying conductor and not in neutral. For example, if you isolate or switch the neutral of a circuit via a single-pole circuit breaker or switch, it would appear that the circuit is dead where in fact it is still live. 

source: TLC-Direct UK

If polarity is not correctly determined there may be a risk of electric shock during maintenance procedures. 

This would not be the case, as live conductors and connections would be present at fixed equipment, sockets and switches - this would be very dangerous.

There are three recognized methods of evaluation. All three methods have their advantages and possible dangers, if they are not carried out correctly. 

Methods of polarity testing

1. Polarity by visual inspection
By using your knowledge and sight, correct termination of cables relating to core colors can be established. 

Color Coding Sample
Source: IEC 

It is essential that polarity is checked visually during the process of installation, especially in cases where checking by testing is impractical.

2. Polarity by continuity testing

If visual inspection is not possible, you will need to use a low-resistance ohmmeter for this test. When you continuity test radial and ring final circuits, part of the process is to test and visually inspect the polarity of fixed equipment and socket outlets.

Polarity testing using low resistance ohmmeter
Source: City and Guilds

Steps:

1. Switch off the circuit breaker supplying the circuit.
2. From the specific circuit, put a temporary link that will connect the line conductor and the CPC or any equipotential bonding conductors. It will serve as a testing point for convenience
3. Conduct continuity testing by placing the test leads across the line conductor and the nearest  CPC or any exposed conductive parts of the circuit.
4. If the instrument shows zero reading (with continuity sound) then the switch is connected properly to the line conductor.
5. If the instrument shows some significant ohmic value then the switch is not connected to the line conductor. Interchange the connections to fix the problem.

3. Live testing for polarity
If the two methods are not possible due to urgency we can perform live polarity testing by using the approved voltage GS38.


Steps:
1. Test between LINE and NEUTRAL terminals

2. Test between LINE and EARTH terminals.

3. Test between NEUTRAL and EARTH terminals

The test instrument should indicate full voltage (230V) between Line-Neutral and Line-Earth conductors. No voltage should be detected between Neutral-Earth.

Source:

1. City and Guilds
2. BS 7671
3. TLC Direct