Class 1 (Earthed Appliance) Construction

(Single basic insulated and protectively earth equipment)

This type of product design provides two safety barriers between all live conductors at dangerous voltages and the equipment user.

The provision of basic insulation between exposed metal parts and live parts is the first barrier to provide basic protection against electric shock.

The second safety barrier is by the connection of exposed (accessible) conductive (metal) parts to the protective earthing conductor (earth wire) in the fixed wiring of the device/Installation.

The protective earthing terminal of the equipment must be marked with the word "earth" or the symbol "E" or the symbol for Earth Terminal or Protective.

To perform this test a continuous earth loop must be made between the exposed conductive material (metal) and the TnT appliance tester.  This is done by means of connecting the earth lead with the crocodile clip/probe attached to a GOOD earth point (paint & coatings will not provide effective connections) and the DUT (Device Under Test) plugged into the TnT appliance testers’ DUT socket. The Maximum allowable limit is less than1.0 (ohm).

Class 2 (Double Insulated) Construction

(Double insulated equipment)

This method of construction employs two safety barriers comprising two layers of insulation between dangerous voltages and the user of the equipment.

The first layer of insulation is formed around the live conductor and is termed ‘the Functional Insulation’.

The second layer of insulation is termed ‘the Supplementary Insulation’. In Class II equipment, protection against electric shock does not rely on basic insulation only, but has additional supplementary insulation such as double insulation or reinforced insulation provided, there being no reliance on precautions in the fixed wiring of installation.

Class II equipment is marked with the words "DOUBLE INSULATION" or the symbol

For double insulated under Safety Symbols:

Note 1 – Double Insulation is insulation comprising both basic and supplementary insulation.

Note 2 – Reinforced Insulation is a single insulation system with a degree of protection against electric shock, which is equivalent to double insulation.

Testing of Electrical Equipment

Many testing personnel have some reservations in testing sensitive, electronic equipment using a 500V DC insulation test. There is a perceived fear of causing internal damage from over voltage. With the introduction on the TnT Range of appliance testers, these concerns are alleviated.

The TnT Range of electrical portable appliance testers is safe to test electronic equipment as the tests are carried from Active-Neutral (shorted by a relay inside the tester) to Earth. No dangerous voltages pass through in this mode to the internal components of the DUT (Device Under Test).  If these tests are done using an Insulation Tester only and the user tests Active to Neutral, this would be a cause of potential damage, this is why the TnT product range is far safer to use.

Some changes may be required in certain configurations where fitted surge protection devices (MOV's) in the DUT may cause a failed test result.  Applying 500V in this these situations can cause the surge protection devices to trip, therefore conducting the applied voltage to earth, thus showing a failure of insulation. In these instances the test voltage should be changed to 250V then retest. If DUT still fails, check with the DUT Operators Manual or an electrician. [for details see - ‘Double Insulation Test’ 250/500VDC to change test voltage]. 

Under these circumstances, it would be difficult for any damage to occur to either the surge protection device or the DUT, as there is insufficient current generated by the TnT-el appliance tester. 

Leakage Test:

If there are any doubts with insulation testing of the equipment, the standard
(AS/NZ3760 since 2001) allows for an alternative test method. A Leakage Test can be performed instead. (The TnT – Series are designed to perform these tests).

NOTE: 10Amps MAXIMUM Resistive Load only (Standard TNT - Series units).

A Leakage Test applies power to the Device Under Test (DUT) and measures the imbalance of leakage current from the DUT between the active and neutral conductors.  The leakage is tested to the limits specified in the standard and a Pass/Fail result as well as a digital reading is provided to ensure that the user gains as much information as necessary.

Earth Continuity Test:

The TnT-el conducts earth continuity tests at Approx. 200mA. Continuity tests at higher currents are not required and are not recommended on certain equipment as this can cause severe damage or premature failure to the DUT under test (as per AS/NZ3760).

3 Phase Testing: *Optional

3 Phase appliances can be tested by the TnT series appliance testers.  This test is carried out by using the adaptor connection socket. As the insulation tests are from Phase to Earth, only a 500V insulation test is required. These adaptors can be made by your electrician or purchased as an accessory. [See ‘Optional Accessories’ for details - when ordering please state plug configuration of 3 phase plug.] 

Please note: (The TnT cannot perform 3 Phase Leakage test. Contact Wavecom Instruments Pty Ltd for the appropriate tester).