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How to use an insulation tester to verify the integrity of the electrical insulation in an evse unit

smart charger

EVSE (Electric Vehicle Supply Equipment) is now a standard feature in UK homes and workplaces as well as public areas such as residential streets, service stations and retail and leisure car parks. Type 2 electric chargers (7-holes) are the European standard and as they are required to conform to BS 7671 they need to comply with all the standard installation tests for electrical equipment, such as continuity, insulation, RCD and earth loop impedance.


The importance of Insulation Testing in EVSE

Insulation does not carry electric current, and therefore it is used to protect wires and cables and other conductors so that they are safe to handle and safe in the environment. However, no type of insulation is 100% reliable. Insulation often cannot be seen because it is submerged below ground or inside panels, and here it is subjected to possible water damage, mechanical damage and general wear and tear from electrical stresses.

When insulation loses its reliability it can start to allow electrical current to travel through it, and this is where hazards exist. Resistance is the measure of how electric current is opposed in a circuit. Good insulation has a high resistance because it doesn’t allow current to travel through it, while poor insulation has low resistance, because it has deteriorated in quality and now allows electric current to escape, which is called current leakage.

Insulation resistance testing determines how much current leakage is occurring through insulation, and is measured in ohms. A drop in insulation resistance can be quite sudden, but it normally occurs gradually over time, so it is important to monitor this regularly. A gradual increase in current leakage – through a loss of resistance – can result in short circuits or leakage to earth. This can result in a loss of power and a safety risk for the user.

EVSE is being used frequently and involves high levels of charge, particularly public charging units which are more likely to be rapid or ultra-rapid chargers. So it is essential that we monitor these and all other EVSE and test them upon installation and periodically afterwards. Carrying out regular insulation tests will highlight trends over time, so that if we see a gradual reduction in resistance it suggests there will be an impending problem, and so we can take the appropriate corrective action.


Carrying out an Insulation Test on EVSEhow to use an insulation tester to verify the integrity of the electrical insulation in an evse unit

The insulation integrity of your EVSE can be continuously monitored or you can carry out simple tests as and when required. You can use a multi-function tester such as the TIS MFTPRO for this, or a stand-alone Insulation Resistance Tester such as the TIS 1835 in conjunction with the TIS EV-TEST100 adapter.  In particular it is a good idea to check EVSEs with tethered lead connections as these are the systems which are most likely to suffer higher levels of wear & tear.

  • Connect the Insulation Tester between the L1 & N sockets of the EV-TEST100 using the test leads
  • Connect the TIS EV-TEST100 to the charging unit
  • Set-up the dials on the TIS EV-TEST100 for the Insulation Test, so this should be:

Set PP State to NC, set CP State to A and set Fault to OK. This set up configuration will make sure that the charger is de-energised.

  • Carry out the Insulation Test checking the integrity between L1 (also L2 & L3 for 3 Phase), N & PE
  • Make a note of the readings in Ohms on the LCD display.

Please note that this section is for information purposes only. Anyone using equipment referred to in this section must be suitably qualified and/or experienced within the respective field. If in doubt before use, please consult a qualified electrician or engineer & thoroughly read all instruction booklets.

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