Transformer Secondary Protection (3-Ph, D-W, >600V, Industrial)

[VxA]

Hi,

This application is a 13.2/4.16kV 3-Phase Delta-Wye transformer feeding a Medium Voltage MCC line-up in an industrial (supervised) facility. The transformer is oil filled (outdoor).

The location of the transformer is such that I would need to run the secondary conductors outside for 50' or so (they will be physically protected as per NEC). Then I would like to enter the electrical room and run for 25ft or less to the proposed location of the Medium Voltage MCC.

The primary protection (which is tied into secondary side ground fault detection to allow for quicker reaction in event of secondary ground fault) keep the Arc Flash levels quite low (Cat 1). As a result, I would like to not have incoming protection on the MV MCC and simply let the individual cubicle fused disconnects do the job. There are 5 such fused disconnect switches.

Questions;

1) because the overall secondary run is > 25ft, am I able to avoid having secondary protection installed outdoors (or at nearest indoor location to the conductor entrance)? Sections 240.21(C) (3) & (4) talk about this. It is an industrial application.

2) if questions (1)'s answer is yes, can I avoid having incomng protection on the MV MCC so long as I use 6 or less individual OCPDs in the MCC, and I size the secondary conductors such that they are protected by the OCPDs? Section 450.3(A) discusses this.

Your help would be appreciated.

Thanks,

 

[RUWired]

Questions;

1) because the overall secondary run is > 25ft, am I able to avoid having secondary protection installed outdoors (or at nearest indoor location to the conductor entrance)? Sections 240.21(C) (3) & (4) talk about this. It is an industrial application.

Article 240 1 through 8 is for 600 volt or less conductors. See article 240.100 and 101 in section 9 for your application.

2) if questions (1)'s answer is yes, can I avoid having incomng protection on the MV MCC so long as I use 6 or less individual OCPDs in the MCC, and I size the secondary conductors such that they are protected by the OCPDs? Section 450.3(A) discusses this.

See table 450.3A note # 2. The total of all your secondary OCPD cannot exceed 300% of the secondary current.

Thats about all the help i can lend.Rick

 

[VxA]

Thanks Rick,

I appreciate the feedback. I didn't realize 240.1-8 was for 600V or less.

 

[charlie]

Article 240 1 through 8 is for 600 volt or less conductors. . .

240.90 General. Overcurrent protection in areas of supervised industrial installations shall comply with all of the other applicable provisions of this article, except as provided in Part VIII. The provisions of Part VIII shall be permitted only to apply to those portions of the electrical system in the supervised industrial installation used exclusively for manufacturing or process control activities.

Part VIII is to provide relief from many of the restrictions in the first parts of Article 240 because of the physical size of industrial equipment and the expertise that is on hand to take care of the electrical installation and maintenance. :smile:

 

[charlie]

. . . It is an industrial application. . .

Since the outside feeder tap is feeding a building, I believe 240.92(D) applies to your installation. This section requires you to provide overcurrent protection and disconnecting means in accordance with 240.92(D).

This is all assuming you meet the definition of supervised industrial installations.

 

[RUWired]

240.90 General. Overcurrent protection in areas of supervised industrial installations shall comply with all of the other applicable provisions of this article, except as provided in Part VIII. The provisions of Part VIII shall be permitted only to apply to those portions of the electrical system in the supervised industrial installation used exclusively for manufacturing or process control activities.

Part VIII is to provide relief from many of the restrictions in the first parts of Article 240 because of the physical size of industrial equipment and the expertise that is on hand to take care of the electrical installation and maintenance. :smile:

Charlie, article 240.1 explains that part VIII covers those portions of supervised installations operating at voltages of not more than 600 volts nominal. Part IX covers over 600 volt nominal.


Rick

 

[charlie]

. . . part VIII covers those portions of supervised installations operating at voltages of not more than 600 volts . . .

OOOPS

That is a direct result of not paying attention and snapping off an answer. You are absolutely correct.