Application of NEC to Industrial and Campus-Style Complexes

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jtinge

Senior Member
Location
Hampton, VA
Occupation
Sr. Elec. Engr
The following is an example of how one campus-style location applies NEC feeder and service requirements to their system.

1. The service point at which the utility services end and the center?s primary distribution system begin, is defined as the connection between the utility?s overhead conductors and the main bus of the center?s primary substation.

2. The "source ends" (primary substation ends) of the center's primary distribution cables are feeders and shall comply with NEC Article 215, ?Feeders? and Article 225, ?Outside Branch Circuits and Feeders?.

3. The "load ends" (building ends) of the center?s primary distribution cables, however, shall be treated as the utility services to the building. Install service disconnecting means and comply with all of the requirements of NEC Article 230, ?Services?.

4. In a like manner, a secondary-voltage feeder (or feeders) from one building to another building shall be treated as the utility's service to the building. Install service disconnecting means and comply with all of the requirements of NEC Article 230, ?Services?.

Is this a reasonable approach, if not what changes should be made?

Since the equipment supplying building power at the load end of the primary feeder is by definition a separately derived system, is it appropriate to apply service requirements to this equipment?

How should grounding and bonding be addressed?

Does anyone know if there are any proposals to provide service entrance equipment requirements for equipment served by a feeder and separately derived system and not a utility connection?
 

mgookin

Senior Member
Location
Fort Myers, FL
The campus owns that substation, right?

I'm not saying I have your answers, but that's one thing that was just slightly not understood in your post.
 

GoldDigger

Moderator
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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
To me the question of how to treat the incoming power to a building hinges on two points:
1. Are there a separate grounded conductor and an EGC? and
2. Is there upstream overcurrent protection that directly protects the supply conductors at their ampacity?
If both answers are yes, then treating the incoming wires as a service is both overly restrictive and in some cases (e.g. bonding) flat out wrong.

Tapatalk!
 

jtinge

Senior Member
Location
Hampton, VA
Occupation
Sr. Elec. Engr
To me the question of how to treat the incoming power to a building hinges on two points:
1. Are there a separate grounded conductor and an EGC? and
2. Is there upstream overcurrent protection that directly protects the supply conductors at their ampacity?
If both answers are yes, then treating the incoming wires as a service is both overly restrictive and in some cases (e.g. bonding) flat out wrong.

Tapatalk!

Agreed. From a grounding and bonding perspective, 250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s) seems pretty clear on this.

With both a sparate grounded conductor and an EGC, you would also need to maintain an isolated neutral to allow control over the location of the system bonding jumper, which would proclude the use of service ONLY equipment.

This is often a point of contention with my collegues who think that buildings should use service entrance equipment complying with 230 regardless of the source.
 

jtinge

Senior Member
Location
Hampton, VA
Occupation
Sr. Elec. Engr
I think the HDBK commentatary for Part II of Article 225, Buildings or Other Structures Supplied by a Feeder(s) or Branch Circuit(s) provide some perspective regarding the questions in my OP.

Part II of Article 225 covers outside branch circuits and feeders on single managed properties where outside branch circuits and feeders are the source of electrical supply for buildings and structures. Important in the application of the Part II requirements are the Article 100 definitions of service point, service, service equipment, feeder, and branch circuit. Determining what constitutes a set of feeder or branch-circuit conductors versus a set of service conductors depends on a clear understanding of where the service point is located and where the service and service equipment for a premises are located. In some cases, particularly with medium- and high-voltage distribution, the service location of a campus or multi-building facility is a switchyard or substation. With the location of the service point and service equipment established, the requirements for outside branch circuits and feeders from Part II (and Part III if over 1000 volts) can be properly applied.

Included in Part II of Article 225 are the requirements for overhead and underground feeders that supply buildings or structures on college and other institutional campuses, multi-building industrial facilities, multi-building commercial facilities, and other facilities where the electrical supply is an outdoor feeder or branch circuit. The feeders and branch circuits covered in Part II of Article 225 may originate in one building or structure and supply another building or structure, or they may originate in outdoor equipment such as freestanding switchboards, switchgear, transformers, or generators and supply equipment located in buildings or structures. Such distribution is permitted under the condition that the entire premises is under a single management. Many of the requirements in Part II covering the number of feeders or branch circuits and the location and type of disconnecting means are similar to the requirements for services in Article 230.
 

david

Senior Member
Location
Pennsylvania
Agreed. From a grounding and bonding perspective, 250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s) seems pretty clear on this.

With both a separate grounded conductor and an EGC, you would also need to maintain an isolated neutral to allow control over the location of the system bonding jumper, which would preclude the use of service[ ONLY ] equipment.

This is often a point of contention with my colleagues who think that buildings should use [service entrance equipment] complying with 230 regardless of the source
.

are they saying service rated equipment or service only equipment
 

jtinge

Senior Member
Location
Hampton, VA
Occupation
Sr. Elec. Engr
are they saying service rated equipment or service only equipment

"Suitable for Use as Service Equipment" as I understand allows you to install the Main Bonding Jumper at the isolated neutral bar but "Suitable Only for Use as Service Equipment" does not have an isolated neutral bar, so it couldn't be used for SDS's where the system bonding jumper is at the transformer.

230.66 Marking
Service equipment rated at 1000 volts or less shall be marked
to identify it as being suitable for use as service equipment. All
service equipment shall be listed. Individual meter socket enclosures
shall not be considered service equipment.

Service equipment is required to be listed. ?Suitable for Use as Service
Equipment? is a common marking found on equipment that
can be used at the service location. The marking is not a field marking,
but is applied by the equipment manufacturer and indicates the
equipment meets requirements in the applicable product standard
(i.e., panelboard, switchboard, enclosed switch, or other equipment
product standard) that enables it to carry a marking indicating its
suitability as service equipment. ?Suitable Only for Use as Service
Equipment? is a marking that indicates the grounded conductor or
neutral terminal bus is not able to be electrically isolated from the
metal equipment enclosure. This inability precludes most feeder
applications for this equipment where the equipment grounding terminals
and the grounded conductor terminals are required to be
electrically isolated. A similar requirement is contained in 225.36 for
outside feeder and branch-circuit disconnecting means.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Among other things, the "Suitable for Use as Service Equipment" designation will involve design aspects to make it suitable for a power source which is unfused (at least in proportion to the nominal conductor size) and can deliver very large fault currents. It will be support installation of OCPD devices with a high AIC ratings.
 
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