3. In the case of workings where powered supports are used—
(a)such supports shall be advanced as soon as practicable after extraction and set so that the maximum distance between the end of the beam closest to the face and the face is 0.5 metres;
(b)during normal production at any place where a machine is used which shears mineral to a depth exceeding 0.4 metres, the machine shall not be permitted to approach within 27 metres of any powered support which has not been advanced from the previous cut; and
(c)where an immediate forward support system is used, the supports shall be advanced—
(i)as close as practicable behind the coal-getting machine, and
(ii)in any event, no more than 10 metres behind the coal-getting machine.