4 Core Cables for Motor Feeders..

[alanElec]

Hi..

1. Is it recommended to use 4 Core Cables for '3 phase applications without neutral'? Then the neutral will have to be left unterminated at either ends right..? Also would it lead to any induced currents in the neutral Core..?

 

[7anoter4]

NEC Art. 250.4 General Requirements for Grounding and Bonding. (B) Ungrounded Systems. (2) Bonding of Electrical Equipment.:
"...shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it."
Art. 250.24 Grounding Service-Supplied Alternating-Current Systems. (C) Grounded Conductor Brought to Service Equipment. (3) Delta Connected Service.: “The grounded conductor of a 3-phase, 3-wire delta service shall have an ampacity not less than that of the ungrounded conductors.”
That means-in my opinion- in any case the 4th conductor could be the grounding bonding wire. It has to be the same cross section area as live conductors and has to be grounded both ends.

 

[waross]

The usage of "core" as I understand it refers to insulated similar conductors. A three core cable may have a grounding conductor in addition to the three main conductors. The grounding conductor may be bare and is often smaller than the phase or main conductors.
If you mean four core plus ground cable, then the unused conductor should be insulated to the same standard as the splices on the energized conductors. With the conductor insulated at each end there is not a complete circuit so that no current may flow. There may be an induced voltage which may approach the voltage on the other conductors. That is why the unused conductor should be insulated for the same voltage as the energized conductors.

Bill
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"Why not the best?"
Jimmy Carter

 

[alanElec]

The Four Core Cable as I mentioned above refers to 4 insulated similar conductors.It is usually used for 3ph Neutral Applications.An Yellow Green Earth Cable is run separate for the purpose of earthing.

My only doubt is whether it I can I Leave one core(meant for neutral) unused when im feeding a motor which does not need a neutral.in short I will be actually using only 3 out of 4 available cores since I require only 3 ph..and not 3 phase Neutral.For earthing always a separate conductor is run..that is the standard here..

 

[waross]

Just insulate both ends for the highest voltage found in the enclosure.
I suspect that you have surplus four core cable on hand.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[alanElec]

No I don't have surplus cable..But out of ignorance we usually order four core cables for Motors as well.I wanted to confirm whether its right technically..Commercially speaking its a waste of money.