Appliances Safety Glossary - Testing the safety of electrical appliances


PAT testing “PAT” is an abbreviation for Port- able Appliance Testing. This refers to the formal inspection and testing of portable appliances to ensure that they are safe to use.


Class I appliance


Equipment in which protection from electric shock is provided by both basic insulation and connection of exposed metal parts to the protec- tive conductor and onto the earthing of the plug.


Class II appliance


Equipment in which protection against electric shock is provided by basic insulation and an additional safety precaution (e.g. supplementa- ry insulation) or via reinforced insula- tion. Class II appliances usually have the following symbol on them:


 Visual check


This is a visual test of the equipment to confi rm that there are no visible signs of damage or defects. This can be recorded on most of Metrel’s PAT testers for future reference.


Earth Bond/Continuity test Test to ensure that the earth cable has the ability to withstand a fault current should a problem occur in the appliance. IT equipment can have problems with high current Earth Bond tests, in which case a soft curent test (20 mA - 200 mA)


4. 2 Differential Leakage


If an appliance has more than one connection to ground (e.g. the met- al housing of the appliance sits on the ground or is screwed down). A measure of the current passing through the cable may not be a true indication of the full leakage current supplied by the appliance. Differ- ential leakage measures the differ- ence in current between the live and neutral cable which provides a true value of how much current a appli- ance leaks to ground.


continuity test can be performed to simply check an earth path exists (for Class I appliances only).


Insulation test


A high DC voltage test to ensure that the resistance between the phases (i.e. live and neutral) and earth is suf- fi ciently highenough to guarantee that equipment is safe to use.


Leakage test


The amount of current that fi nds an alternative path back to the supply, other than through the neutral con- ductor.


v


High leakage currents can cause both operation problems (e.g. tripping RCDs) and health and safety issues (e.g. cause voltages to appear on pipe-work which can cause in- jury). This test powers up the equip- ment with 230 V a.c. and measures the amount of leakage current the equipment produces.


A v


A Touch leakage test


This test measures the amount of current that would pass through the human body if a person was to touch the appliance while it was in operation. The PAT tester powers up the appliance and via a probe which the user connects to the appliance, simulates the average resistance of the Human body and measures how much current would pass through a person if he touched the appliance.


Polarity test


A polarity test checks that all the con- nections in an IEC cable or extension cable are correctly fi tted. Results in- clude L-open, N-open, PE-open, L-PE shorted, L-N shorted, N-PE shorted, L-N crossed, L-PE crossed, N-PE crossed and multiple faults.


Flash test


Also referred to as Hi-Pot or Dielec- tric strength test. The test is a high a.c. voltage test which checks the dielectric strength of the insulation in a piece of equipment. This can


Accessories: page 4.24 Substitute leakage


In this test the Live and Neutral con- ductors of the appliance are shorted together and a voltage of 40V a.c. is applied between this point and ei- ther the earth conductor (class I) or the probe connected to any exposed conductive parts (class I and class II). The test measures how much current passes from the live conduc- tors into the test points.


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