Bonding of covers 1

[richerdick32]

We have some large motors that have covers over the slip rings, the covers are removable using a standard panel key, should the covers have a bonding wire between the covers and the generator? I know electrical panel doors should be bonded?
If a bonding wire is required what size should it be? the main supply earth is 25mm2 are there any regulations I can look at for this?

 

[Skogsgurra]

The generic rule is that "Any conductive part that can get into contact with a lethal voltage during normal operation or any conceivable fault condition shall be permanently and securely connected to a reliable ground".

It is expressed in different ways in different standards. But that is the gist of it. The bonding braid/wire shall have enough capacity to carry the worst case fault current without melting (or getting too hot) until protection trips.

My pet is that a motor shaft needs to be grounded (permanently and securely) if both bearings are insulated or have ceramic balls.



Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[KuanYau]

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.