92. An employer shall ensure that, wherever any transformer or switchgear in which higher voltage is used is installed otherwise than in a building, the transformer or switchgear is adequately protected either by—

(a) suitable fencing not less than 2.4 m high, or

(b) some other effective means for preventing any unauthorised person gaining access to the equipment or to anything connected thereto which is used as a conductor

unless it is completely enclosed by—

(i) a metal casing which is connected to earth, or

(ii) some other equally suitable non-metal casing.