To richerdick32 (Electrical)(OP)
In the IEC world, the general opinion and practices are:
A. For motors
Motor slip rings removable covers, cable-box removable covers and the like; the usual [metal screwed connections or clamping force by the metallic locking mechanisms] are (considered sufficient to ensure earthing continuity) [provided that no electrical equipment is attached to them]. No PE-conductor is required to be attached on them.
Note: For conductive parts where no electrical equipment is attached to them; if preferred but not mandatory:
a) may be earthed by a flexible bare conductor or with (transparent) sleeving, or with an insulated colour-coded PE-conductor with colour-code, see detail C below.
b) the PE-conductor, bare or insulated shall be NOT smaller than 2.5sqmm of copper material. Larger size if aluminium conductor is used.
B. For electrical panels {See IEC 60439)
" For lids, cove plats and the like, the usual screwed connections and metal hingers are considered sufficient to ensure continuity provided that [no electrical equipment is attached to them]"
Note: For conductive parts where electrical equipment [exceeding the limits of extra-low voltage] are attached to them:
a) steps shall be taken to ensure continuity of the protective circuits.
b) the (copper) PE-conductor [shall not be smaller than 2.5sqmm] but [need not be larger than the largest wire size wired on the equipment] attached on them.
C. PE-conductor colour-code per IEC
a) PE-conductor may be
- bare (no painting of colour is required),
- bare with (transparent)sleeving,
- insulated with colour-coded "yellow/green"
Attention:1. Except "yellow/green" coloured-coded insulated conductor, NO other colour-coded conductors shall be used as PE-conductor.
2. "Yellow/green colour-coded insulated conductor shall NOT be used for phases or neutral conductor.