Polarity Checks

Polarity is one of those concepts that everyone thinks they understand, but on closer questioning few do, leading to very few electricians understanding why they are testing for it, the consequences of incorrect polarity and how we check it.

There are three checks of polarity during testing – dead and live testing and visual inspection and while they all confirm correct/incorrect polarity they do not necessarily check for the same thing.

Lets start by look at the definition of polarity as it affects us installation electricians. If you look at the visual inspection schedules for both the EIC and EICR in Appendix 6 of BS7671 the check is for 'single pole devices for switching and protection in line conductors only', which is a shortened explanation of Regulation 132.14.2

'No switch or circuit breaker, except where linked {2ble pole, 3ple pole etc}, or fuse , shall be inserted in an earthed neutral conductor. Any linked switch or linked circuit breaker inserted in an earthed neutral conductor shall be arranged to break all the line conductors {as well}.' The notes in curly brackets are mine

All this means of course is that you cannot switch only the neutral, but you may switch the neutral if it is linked to switches that also switch the line conductor/s.

The reason why is pretty obvious. If you break a circuit after the load i.e. the neutral, then the circuit including the load remains live even though no actual current is flowing, in other words the load is live but not actually 'on'; the circuit is open. This means that any attempt to work on or maintain the load (a ceiling rose) will put that person at risk of electric shock. This is the very heart of the problem because in this scenario while the function of the switch (operating the load e.g. a lamp) is quite normal the actual method of connection is dangerously incorrect. Unless you test for polarity you will never know and neither will the person operating the load.

Now lets look at the methods and what they achieve.

 

Visual inspection


Whereby a visual check is made to ensure all the conductors are in their correct terminations.

 

Live tests

Perhaps the simplest is the live polarity test. This is conducted as the first of our live tests, however in reality this can be done any time. It comprises of testing with an Approved Voltage Indicator across all the conductors in the supply; its the same conductors and method as for the 10 tests to ensure a system/circuit is dead when carrying out safe isolation. This check confirms that the supply conductors are correctly connected.

Another live polarity test is discretely done automatically when carrying out a live Zs test. Your MFT or EFLI tester will give a warning of incorrect polarity.

 

Dead tests

These are conducted while carrying out the continuity tests. There are two tests. The first confirms that all the switched conductors are only line conductors. This can be done with either the R1+R2 test or with the R2 (wander lead test method) whereby the switch in test is operated and the meter observed to change from a reading to showing an open circuit.

The other dead test is to check that in E14 Edison screw lamp fittings only the centre pole of the fitting is connected to the line conductor. This is not required where the fitting meets the standard BSEN 60238 (regulation 612.6) because these have an internal disconnector.

The testing for correct polarity is vital as if connected incorrectly circuits will function entirely satisfactorily but will be in a potentially dangerous state.

If you read the Electricity Safety Council document Best Practice Guide 4, issue 4 it quite clearly states that incorrect polarity is a 'dangerous state' and requires a coding of C1.

Incorrect polarity is the hidden killer.

More in this category: Continuity Measurement »