Is installation of NEUTRAL mandatory on MV application?

[sparkyguy545]

Industrial Campus with Owner's MV distribution.
I will have a line-up of 5kv MV Metal-Clad vacuum swgr fed from two sources (Main-Tie-Main). Vacuum Breakers will be fully-interlocked to prevent paralleling sources. All downstream loads are 3-phase. There are no single-phase L-N loads involved, nor will there ever be.

Source #1 is low-resistance grounded at an exterior pad-mount transformer (center of Y connected to ground thru a grounding resistor).
Source #2 is 4160Y/2400, solidly grounded, fed from another exterior transformer.

Source #1 will consist of phase conductors and insulated ground in PVC ductbank. Since Source 31 is resistance-grounded there will be no grounded system conductor (neutral).

My question is in regards to Source #2:
Is it MANDATORY to install a grounded system conductor (neutral) between Source #2 and my Metal-Clad gear?
For installations below 1kv, I understand the general requirements in 250.24(C) which REQUIRES me to install a grounded system conductor (neutral) between source and the downstream gear. However, is there anything which REQUIRES me do do so for MV applications? If there is such a requirement, please clarify where noted in NEC.

Thanks in advance.

 

[Smart $]

You cited the only requirement that I'm aware of... and that is regarding grounded conductor brought to service equipment. You did not actually state where your service equipment is located with respect to the sources. You implied it was the secondary switchgear. In my experience with customer-owned MV-secondary transformers, the service equipment is on the primary side of the transformers.

 

[SG-1]

The gear will probably only have 4 points for connection, unless it was special ordered with an insulated neutral. You have connection points for 3 phase conductors & a ground bus for your EGC, &/or cable shields.

The only reason I can think of to bring a neutral into the gear would be to form the main/system bonding jumper there at the main breaker or the tie breaker.

 

[don_resqcapt19]

A new section, 250.186, in the 2014 code requires that if the system over 1,000 volts has a grounded conductor at the service point, then you must bring a grounded conductor to the service equipment. Not near as strongly worded as 250.24.

 

[sparkyguy545]

Thanks all.
A bit more information and (I hope) a summary:

All the gear is on the Owner's side of the campus distribution system. Their actual Service Entrance is 12.47kV located some distance away from my application. Therefore, by definition, none of my questions are "Service Entrance" related.

Each of my two Sources are exterior liquid-filled transformers with 12.47kv primaries. Transformers are NOT identical. Source #1 has a 4160Y/2400 secondary with the center of the Y (the X0 bushing) connected thru a low-resistance grounding resistor. Source #2 is a traditional 4160Y/2400 V solidly-grounded system.

What prompted me to ask my original question was consideration of fault clearing between each of my two sources and my indoor MV Metal-Clad gear. Both of my "Sources" are served thru PVC raceways out to each transformer. I was looking to ensure I had metallic return paths back to each transformers for fault-clearing purposes. Obviously, I do not want to set up a condition where I am relying on dirt as a sole means to return fault-current to the transformers.

I would prefer to NOT require a neutral-bus in the Metal-Clad Gear (gear is yet to be manufactured or installed) because of the additional Protective-Relaying, complexity, cost, etc. Also, I would prefer to keep cabling and installation of the two sources as similar as possible. This will help the Contractor, Owner and me understand what is actually being installed.

For Source #1 (secondary from low-resistance grounded transformer), I will be installing a 600 V insulated ground conductor in the PVC raceway with phase conductors. Therefore, there is a clear metallic path back to the transformer for fault current.

For Source #2 (secondary from solidly-grounded transformer), my question was if I was permitted to install ONLY the phase conductors and a 600 V insulated ground conductor (again, with NO neutral conductor) because of the similar language which DOES require the neutral if operating below 1kv.

Unless I'm misreading everyone's replies, if I install 600 V insulated ground conductors in both Source PVC raceways, it appears to meet the current NEC requirements (even meeting the 2014 Code language) AND it provides a clear fault-current return path upstream to each source transformer. Therefore, NO additional neutral conductor is mandated in the PVC raceway between my Metal-Clad Gear fed from Source #2 (which is solidly-grounded). Further, there would be no specific requirement to include neutral bus within my Metal-Clad gear.

Am I summarizing replies as intended?

 

[Smart $]

Thanks all.
A bit more information and (I hope) a summary:

...

Am I summarizing replies as intended?

Summarizing replies as intended has no bearing on compliance. Nevertheless, your summation as I understand it, aligns with a compliant installation.

 

[don_resqcapt19]

Once you are past the service disconnect the rules in 250.24 and the new one 250.186 do not apply. These are feeder conductors and you are not required to run the grounded conductor with the feeder ungrounded conductors unless you are supplying line to neutral loads.