240V Mains polarity testing

An example of a continuity tester being used for a polarity check

This is a DEAD test, it must be conducted WITHOUT the power connected to the vehicle. Before the test is done, you MUST verify that the installation is NOT LIVE. This includes if you have an inverter fitted, this must be isolated.

One of the tests you will need to complete before you can certify and use your new electrical installation will be a mains polarity test. 

These tests should be carried out by a competent person with the relevant experience.

This test should be carried out on all mains terminations, so that's all of the 3 pin plugs, hard-wired items, the inlet socket and the hookup lead. 

For this test, you will need a multimeter, ideally with a socket testing adaptor. 

A basic multimeter can be used for this test. As long as it's verified as accurate.

A Kewtech socket testing plug can speed the process up.

Before you begin the testing on the vehicle, you should first test your meter. Turn it on, set it to the audible resistance test or the continuity buzzer. Check that with the probes apart, that it is giving you a reading of no continuity, usually "OL" or "1", then touch the probes together, this should give you a reading of continuity, 0 ohms

Hook up lead

The first part of this is to test your hook up lead, as we're going to use this as a "wander lead" (meaning we can wander about the van with it) when we're testing the sockets in the van shortly.

  1. Test the polarity of your hook up lead using your multimeter, set your meter to the audible resistance test, often denoted by a musical note symbol.
  2. Place one probe into the live terminal of each end of the hookup lead, you should get an audible buzz and the screen should read around 0 ohms.  
  3. Keeping one probe on the live terminal in one end of the hookup lead, now touch the neutral and earth terminal in the other end of the hookup lead, these should not give you an audible sound and the resistance should indicate overload or no continuity, usually denoted by a "1" on the screen or "OL".
  4. In the first plug, move your multimeter probe onto the neutral terminal of the plug and repeat the check on all 3 terminals in the other end of the hookup plug, again you're looking for continuity to the neutral and no continuity to the live and earth.
  5. Finally, in the first plug, move your multimeter probe onto the earth terminal of the plug and repeat all 3 checks, you're looking for continuity between the two earth connections and no continuity to the live and neutral. 

You should get the following readings;

Male Plug Female Plug or OutletContinuity?
Live terminalLive terminalYes
Live terminalNeutral terminalNo
Live terminalEarth terminalNo
Neutral terminalNeutral terminalYes
Neutral terminalLive terminalNo
Neutral terminalEarth terminalNo
Earth terminalEarth terminalYes
Earth terminalNeutral terminalNo
Earth terminalLive terminalNo

If you get any results except these, you should check your method, restest and if you repeatedly are getting incorrect results, it's possible that you have a faulty hookup lead. Swap for a known good replacement.

Once you have the correct results here, plug the FEMALE end of the hookup lead into your van's hook up socket and wander into the van, 

By plugging the wander lead into the inlet socket and moving the opposite end around the van with you, you're able to conduct the tests in a simple way having both connections within reach of the multimeter.

If your multimeter has crocodile clip connectors, it can be very handy to use these on the terminals in the wander/hookup lead to make the testing as easy as possible. 

240V Outlets

Ensure that the main switch (RCD) and all circuit breakers and socket switches are in the ON position for this test.

The same process is used for the rest of the 240v installation, at each 240V outlet the same 9 check tests as above should be performed and the results should be the same. For the 3 pin plugs, you could do this with a multimeter probe before the back boxes are attached to the socket, or it's often a lot easier to use a socket adaptor as pictured above if you have one.

For any hardwired connections, such as a fused spur etc. the test should be carried out with your multimeter probes. 

Once you have tested and verified the polarity is correct on all of the 240V terminations, you can fill out the polarity section on your installation certificate and move onto the next test.

This polarity testing should be repeated at your period inspections also.

This is intended as a guide only and should not be substituted for the proper knowledge and experience.