The grounding resistance testerunder UHV power can help many power workers conduct various power tests more conveniently.

Types of grounding devices and grounding reference resistance values

The electrical installation technical standards specify the following types of grounding installations and grounding resistance values * 1:

Grounding installation grounding resistance value

Class A (formerly Class 1) 10 Ω or less

Class B (formerly Class 2) calculated value * 2

Class C (old level 3) 10 Ω or lower * 3

D-level (old level 3) 100 Ω or lower * 3

*1 lists the values of a certain standard.

Please note that these values vary by country/region.

*2 The ohm value is equal to the ground fault current (ampere) of a wire in the high voltage side or extra high voltage side circuit of a transformer divided by 150 (or, if the voltage of the low voltage circuit exceeds 150 V due to the combination of the low voltage side circuit of the transformer and the high voltage side circuit of the [a] transformer or the extra high voltage side circuit of the [b] transformer, and the voltage used is 35000 V or lower, according to [1] 300, if equipped with a device that automatically shuts down high voltage circuits or special high voltage circuits with a service voltage of 35000 V or lower for more than 1 second but less than 2 seconds, or [2] 600, if equipped with a device that automatically shuts down high voltage circuits or special high voltage circuits with a service voltage of 35000 V in less than 1 second).

*3 If equipped with a device that automatically shuts off the relevant low-voltage circuit within 0.5 seconds in the event of a ground fault, it is 500 Ω.