Wavecom TnP-500 - Class 2 Double Insulated Construction; Testing Electrical Equipment Safely

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TnP-500 User Manual Wavecom
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 TnP-500 these
concerns are alleviated.
The TnP-500 can safely test electronic equipment as the tests are carried from Active-Neutral (shorted by a
relay inside the tester) to Earth. In this mode no dangerous voltages pass through to the internal components
of the appliance, or Device Under Test (‘DUT’). If these tests are done using an Insulation Tester and the user
tests Active to Neutral, this could potentially cause damage.
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 the DUT should be retested. If the 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 TnP-500.