Battery-powered self-testing clamps are suitable where they are not expected to be attached to plant items for prolonged periods.  If continuous monitoring is required, such as a drum store where product is regularly tapped-off from the drums, mains Externally Powered self-testing clamps with "remote" indicator LEDs are recommended.

CLC/TR 50404 states that:  cables for earthing movable items should be equipped with a strong clamp capable of penetrating through paint or rust layers (11.4.1).  10 Ohms....... is often specified for convenience in monitoring (11.2.2).

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