IEC - Ground Conductors for Low Voltage Motors

Question

IEC - Ground Conductors for Low Voltage Motors

NickParker (Electrical)

(OP)

20 Jun 18 11:52

thread741-115728: IEC-Armour as grounding conductor?

Reference to the above old thread, I have the same questions,

1. 4 Core Cables (All the 4 cores enclosed in the same cables), Can the 4th core be used as a grounding conductor?
2. Does IEC permit the laying of cables without ground conductor? If so, are there any conditions?
3. If the armor of the 3 Core cable can treated as ground conductor, What if the CSA of the cable is not sufficient to carry the fault current?
4. Does NEC permits the laying of phase cables without ground conductor at Medium voltages?

ScottyUK (Electrical) · Answer 1 · 2018-06-20 20:28:26

In principle yes. It depends if you can find somewhere to connect the earth conductor: many motors don't have a large internal earth stud or boss within the terminal box.
In the UK it would be acceptable (i.e. not a code violation) to provide a local earth electrode without a metallic return path, but there are specific requirements imposed on TT systems, including provision of an RCD at the source. I don't recall actually seeing a motor installed this way though.
Either use an internal conductor (but see 1 above) or run an external CPC alongside the armoured cable if the armour CSA is insufficient on its own. If the circuit conductors aren't adequate to handle the fault current then use a larger cable. If it is a marginal fail then going up to the next size of power cable (with a larger armour CSA) may be a more economical solution than running the separate CPC.
No idea. The NEC belongs in the USA; us Europeans are vaguely aware of it.

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IEC - Ground Conductors for Low Voltage Motors