‘PAT Testing’ Basic Information is a vital foundation for carrying out the role to the required industry standard.  This page gives a brief overview of some of the terminology we use every day.

Environment Check

This piece of ‘PAT Testing’ Basic Information is to do with the safety of everyone.  Whether you are the ‘PAT Tester’ or the equipment user.  Upon entering the room, a ‘PAT Tester’ should have a good look around at the overall safety of the environment.  

For example, is the equipment being used for its designed purpose?  A good example of this is a domestic kettle being used in a busy workplace. Is the user using it safely? Are there trip hazards? Is there a moisture problem (dry appliances being used in a wet environment)? Does the ‘PAT Tester’ have sufficient space to carry out their role safely? What about excessive use of trailing sockets and extension leads? Is there a high concentration of people? Are there any potential hot spots or fire hazards? ……I’m sure you get the point.

It is good practice for the ‘PAT Tester’ to carry out a Risk Assessment before they start work.  Their findings should be reported to the Responsible Person or Duty Holder of the site.  

User Check

Whilst many employers think that their responsibility towards the ‘PAT Testing’ is to bring in a ‘PAT Testing’ company, they fail to realise that they and their employees have an additional role – the User Check.

The ‘PAT Testing’ Contractor may visit the site every year or so to formally inspect and test the appliances, but who should determine whether the appliances are safe to use between scheduled ‘PAT Testing’ visits?  The ‘PAT Tester’ won’t be on hand 24 hours a day, 7 days a week to keep an eye on the appliances, so the job falls to the appliance user.

A User Check is designed to help identify any external damage or abnormalities on an appliance prior to it being used.  The user should be trained to carry out a basic external inspection of the appliance, with it switched off, and to report any issues to the Responsible Person e.g. Line Manager.  If no issues are found, no record of the user check needs to be made.

Formal Visual Inspection

The full name for ‘PAT Testing’ is In-service Inspection and Testing of Electrical Equipment.  The ‘PAT Test’ equipment we use these days is very good, but it has its limitations.  The tests we perform are designed to look for faults.  They are very specific.  For example, the Earth Continuity Test will establish the presence and quality of the earth path.  It won’t, however, let us know if one of the controls has broken off the appliance.

The Formal Visual Inspection is designed to identify many things, including:

    • any external damage or abnormalities;
    • the correct fuse is being used
    • the appliance has been made to the correct UK / European Standard
    • the Class of the appliance
    • whether the plug and fuse carry the correct BS numbers
    • the suitability of the appliance for the environment
    • ingress protection rating (where necessary)
    • …and many more.  


The Formal Visual Inspection is quite technical.  Therefore, it is carried out by a suitably trained member of staff or ‘PAT Testing’ contractor.  The results of a Formal Visual Inspection are typically recorded.  This includes whether the appliance has passed or failed.

If carried out correctly, the Formal Visual Inspection will identify up to 95% of appliance failures.  However, the electrical tests will only find around 5% of appliance problems.

Earth Continuity

The electrical tests we carry out are designed to measure the quality of the safety devices built into the appliance. Firstly, there is the earth path.  If the appliance develops a fault, the casing could become ‘live’.  Most importantly, the user could get a shock if they touch these parts.  To help prevent this, an earth wire is connected between the appliance casing and the socket.  In other words, if the appliance develops a fault and the metal parts become live, the user is protected.  In conclusion, the fault current should pass from down the earth wire into the earthing provision of the building.

An appliance with a protective earthing conductor (earth wire) is known as Class I.

The Earth Continuity Test uses a test current of 20 Amps or 200mA.  This is applied to exposed metal parts of the appliance – thus simulating a fault in the appliance.  After that, the test current should find the earth path and return to the test device.  The test result is a measure of the resistance of the earth path, measured in Ohms (Ω).  A perfect result would be 0.00Ω.  Above all we should use our skills and known values to determine whether the test result is acceptable.

Typical results are between 0.01Ω and 0.10Ω for an appliance with a short lead. Items with a longer lead will naturally have greater resistance.  Values in excess of 0.30Ω for longer extension leads are quite normal  Maximum values do apply and must be observed at all times.

Insulation Resistance

Insulation is described as any non-conductive material.  In appliances it is used to keep the appliance user away from live parts within the appliance.  Also it keeps live parts away from other conductive parts.  In other words, the insulation reduces the risk of electric shock and fires.  It can be anything from modern materials such as plastic or silicone, although air is also used.  Most importantly, the material being used needs to be very high resistance to act as a ‘barrier’.  However, it will deteriorate with age and use.

The Insulation Resistance Test is designed to measure the quality of the insulation surrounding live parts.  A test voltage of between 250Vdc and 500Vdc is used to ‘stress’ the insulation.  The result is we can identify any insulation breakdown in the appliance between the live parts and the appliance body.

The ‘PAT Test’ device displays the insulation resistance test results Megaohms (MΩ).  In reality, test results are generally very high if the appliance is in good condition.  Generally, we see results of between 9.99MΩ and 299.99MΩ (depending upon the test device).  Beware, minimum values do apply and must be observed at all times.


Knowing how electricity is supplied is part of your ‘PAT Testing’ Basic Information.  Alternating current (AC) is supplied to homes and businesses. Alternating current reverses direction in the circuit 50 times a second (50Hz).  As a result, it passes up the live wire into the appliance and returns to the socket.  Then it reverses direction and passes up the neutral wire to the appliance and back down the live.  It continues to do this constantly, changing direction every 50th of a second.

Reverse polarity means that the live wire is where the neutral should be in the socket.  Therefore the neutral wire is where the live wire should be.  As the current changes direction anyway, the appliance will normally be unaffected.  However, we will have reduced the safety of the appliance.  Under normal circumstances, the current will go to the appliance down the live wire first passing through the plug fuse.  If the appliance has a fault and draws too much current, the fuse would detect this and blow.  If the live and neutral wires are crossed over, the current passes down the neutral first.  The result is the equipment user could be at risk if the appliance has a fault.


A polarity test cannot be performed on an appliance (as we need access to both ends of the live wire).  It must, however, be performed on detachable power leads and extension leads.  An incorrectly wire lead passes the problem to the attached appliance.

Current Leakage

When an appliance runs, current flows through the appliance and back into the mains supply.  If there is a fault in the appliance (normally due to insulation breakdown), some of the current could ‘leak’ out.  This current could get to the appliance casing.  Therefore, if the user was to touch the affected area of the appliance, they could get a shock.  Alternatively, the leakage current could pass down the earth path (if Class I) and into the earthing of the building.  Modern mains circuits with RCDs would trip and cut the mains supply.  However, older circuits may allow the fault current to pass into other appliances.  The result is that non-faulty appliances can become ‘live’ to the touch because of a faulty appliance elsewhere.  This is an important piece of PAT Testing Basic Information which can’t be ignored.

Current Leakage Testing comes in 3 forms; the Current Leakage Test; the Substitute Leakage Test; and the Touch Current Test.

Whilst they all measure current, they do it in a slightly different way.  The test used depends upon the appliance being tested.

Results are displayed as milliamps (mA) and typical results are very low if the appliance is in good condition.  Maximum values do apply and must be observed at all times.

Function Check

Before an appliance can pass its ‘PAT Test’, it must pass its Function Check.  This is a vital piece of ‘PAT Testing’ Basic Information and normally involves plugging the appliance into the mains supply.  The appliance has to work as expected and all of the controls must function.

It is very common for an appliance to pass the Formal Visual Inspection and electrical tests.  However, sometimes it doesn’t work due to an internal component problem.  The electrical tests are designed to look at specific parts of the appliance.  Unfortunately they cannot pick up on broken or faulty components, so a simple function check will do the job.

Interpreting, Recording and Labelling

After the inspection and tests, the results need to be interpreted by the Inspector.  It’s important to determine if the appliance has passed or failed.  Although this information doesn’t need to be recorded, this piece of ‘PAT Testing’ Basic Information is important.  It is good practice to record information in case of any future incident and investigation. The appliance can then be labelled.  

Again, it’s not a legal requirement to label the appliance.  However, it is good practice and shows adherence to set routines (if done with care).  

We often see green ‘pass’ labels and red ‘fail’ labels, but in reality you can use any colour labels you choose.  It is advisable to use contrasting colours where possible (hence the green and red)… just to make the problem items more visible.  Common sense would suggest that any items which fail the process, should have been withdrawn from use and put in a quarantine area, but they should still be clearly labelled.

Do items which fail have to be destroyed?  Not necessarily.  The defect may be relatively minor, or could be repaired easily and cheaply.  Failing an item simply removes it from use until a decision has been made what to do with it i.e. will it be repaired or recycled.