The resistance of the connection between the protective earthing terminal or earthing contact and parts required to be earthed shall not exceed 0.1 ohm.

For Canada, the capacity of connection between earthing terminal and parts required are to be earthed, is evaluated according to CSA C22.2 No.0.4, Bonding and Grounding of Electrical Equipment.

An AC or DC test current is passed between the protective earthing terminal and parts required to be earthed. The voltage drop is measured and the resistance calculated. The resistance of the earthing conductor of the power supply cord is not included.

If the current rating of the circuit under test is 16 A or less, the test current, test voltage and duration of the test are determined as follows:

• the test current is 1.5 times the current rating of the circuit under test; and
• the test voltage is not to exceed 12 V; and
• the duration of the test is 60 seconds;

and the resistance of the potential bonding conductor, calculated from the voltage drop, shall not exceed 0.1 ohm.

If the current rating of the circuit under test exceeds 16 A, the test current and duration of the test are as follows:

• twice the current rating of the circuit for two minutes; or
• as specified by the manufacturer for dc powered equipment;

and the voltage drop across the protective bonding conductor shall not exceed 2.5 V.

Note the this test is carried out under high current conditions, simulating a fault to earth. Measuring the resistance using a DVM is not considered sufficient, as 'hot spots' may appear under high current conditions.