NEC/NFPA Cable Question

[ukgraduate]

Hello,

Does anyone know if the NEC/NFPA allows:

1) The use of a 4 core cable for a 3 phase supply (such as a motor) and use the 4th (unused core) as the earth. (i.e full sized earth). The 4core, which is usually white will be taped green for identification.
2) The use of Steel Wire Armour cable as a means of mechanical protection for installations .i.e Cable is run inside a cable ladder for protection, however when it drop down to the motor the only mechanical protection shall be via the SWA of the cable.

Regards

UkGrad

 

[resqcapt19]

While commonly done, NEC section 200.7(C)(1) does not permit you to re-identify a conductor with white insulation to be used as a grounding conductor. It does permit you to re-identify that white conductor to be used as an ungrounded circuit conductor.

Assuming that the Steel Wire Armour cable is an equivalent of either Armored Cable or Metal Clad Cable in the NEC, it is a judgement call. Those cable types are not permitted to be installed where "subject to physical damage".

 

[7anoter4]

I agree with resqcapt19.
In my opinion SWA [or AWA] it is not recognized by NEC [NFPA 70] but by British Standard BS 7671 The Electricity Wiring Regulation-Requirement for Electrical Installation Regulation 522.6.5 Impact (AG) Cable installed under floors or above ceiling.
“Generally a cable should either be:
II-incorporate an earthed metallic covering [e.g. SWA,MICC etc.]
Regulation 522.6.6 Impact (AG) cable concealed in walls or partitions =< 50 mm from surface:
I- incorporate an earthed metallic covering [e.g. SWA,MICC etc.]
IEC 60364-5-52 522.6 Impact (AG)
Regulation 522.6 A cable concealed in a wall or partition must:
II have earthed armoring or an earthed metal sheath
However, as one can see, it is not allowed to expose cable-armored or not-in open space mainly in a highly impact area. The solution is rigid conduits connected with flexible armored conduits[ liquidtight flexible metal conduit (LFMC) and associated fittings.]
NEC 305(D) (4) Enclosure or Raceway Damage.” Where the enclosure
or raceway is subject to physical damage, the conductors
shall be installed in rigid metal conduit, intermediate metal
conduit, RTRC-XW, Schedule 80 PVC conduit, or equivalent.”
In my opinion cable tray-if it is mounted exposed [not enclosing in like cable spreading room and at less than 2.5 m height from accessible floor it is not a good protection for cables.
NEC 392.12 Uses Not Permitted. Cable tray systems shall not be used in hoistways or where subject to severe physical damage.