MCC Disconnect

[kriverswaters]

I have an application where we are feeding a Nema 3, (external), 480 Volt, 250 Amp, Motor Control Center from a 600 Amp, 480\277 Volt Panel. The new MCC is going to be physically located external from the warehouse, and not in view, where the existing 480 Volt, 600 Amp panel is located. The new MCC does not have a main breaker or disconnect. Does the NEC require that a main disconnect, (400 Amp), be installed next to the MCC?

 

[augie47]

Is it a free standing MCC or in another building ?

Based on the NEC definition of a structure, I would say the MCC would have to meet the requirements of Art 225 Part II which opens a whole new can of worms.

 

[kriverswaters]

MCC

MCC

The MCC is free standing, exterior of the warheouse where the MCC feed is coming from.

 

[augie47]

Others may look at it differently, but, I would see it as requiring a main per Art 225.32.


(from there you are already posting in the realted thread)

 

[weressl]

Others may look at it differently, but, I would see it as requiring a main per Art 225.32.


(from there you are already posting in the realted thread)

It is not clear from the OP that the equipment that is served by the MCC are part of the same distribution system and whether it serves equipment located inside or outside of the building. Since it appears to be a sub-distribution it does not require a separate breaker and 225.32 is not applicable. Since it appears to be part of a distribution system, not a separate service, 430.95 does not apply.

430.94 Overcurrent Protection.​

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Motor control centers shall be provided with overcurrent protection in accordance withParts I, II, and VIII of Article 240. The ampere rating orsetting of the overcurrent protective device shall not exceedthe rating of the common power bus. This protection shall beprovided by (1) an overcurrent protective device located aheadof the motor control center or (2) a main overcurrent protective​

device located within the motor control center.

430.95 Service Equipment.​

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Where used as service equipment,each motor control center shall be provided with asingle main disconnecting means to disconnect all ungrounded​

service conductors.

 

[augie47]

True. Placement and location of the equipment it supplies would play a key role.
I am drawn back to that dang NEC definitions:

Building. A structure that stands alone or that is cut off from adjoining structures by fire walls with all openings therein protected by approved fire doors.

Structure. That which is built or constructed.

So, if you have an MCC, free standing, exterior of the building where power is obtained, does it not fit the bill for a Art 225 Part II installation ?

 

[don_resqcapt19]

I know that using the NEC definitions, the MCC is a structure, but if the MCC is covered by Article 225, how to you supply the motors in the building from that "second structure"?

225.30 Number of Supplies. A building or other structure that is served by a branch circuit or feeder on the load side of a service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E). ...

 

[augie47]

In my experience, in most of those situations 225.32 Exception covers that.

I do think the whole "structure" situation (definition) and Art 225 clash in real life

 

[don_resqcapt19]

In my experience, in most of those situations 225.32 Exception covers that.

I do think the whole "structure" situation (definition) and Art 225 clash in real life

225.32 only applies to the disconnect, not the number of supplies. Maybe in some cases 225.30(E) would permit the remote MCC, but only if you have the required documentation.

 

[weressl]

True. Placement and location of the equipment it supplies would play a key role.
I am drawn back to that dang NEC definitions:

Building. A structure that stands alone or that is cut off from adjoining structures by fire walls with all openings therein protected by approved fire doors.

Structure. That which is built or constructed.

So, if you have an MCC, free standing, exterior of the building where power is obtained, does it not fit the bill for a Art 225 Part II installation ?

I believe that is neither a structure nor a building. It is a manufactured assembly, a panel. In the 430 para I cited it refers to being used as a service 'equipment'.

Service Equipment.​

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The necessary equipment, usually consistingof a circuit breaker(s) or switch(es) and fuse(s) andtheir accessories, connected to the load end of service conductorsto a building or other structure, or an otherwise designatedarea, and intended to constitute the main control and cutoff of​

the supply.

 

[don_resqcapt19]

I believe that is neither a structure nor a building. It is a manufactured assembly, a panel. In the 430 para I cited it refers to being used as a service 'equipment'.

Service Equipment.​

The necessary equipment, usually consistingof a circuit breaker(s) or switch(es) and fuse(s) andtheir accessories, connected to the load end of service conductorsto a building or other structure, or an otherwise designatedarea, and intended to constitute the main control and cutoff of​

the supply.

This would not be "service equipment" as it is not connected to the load end of the service conductors. It is supplied by a feeder from an existing 600 amp panel in the building.

 

[augie47]

I believe that is neither a structure nor a building. It is a manufactured assembly, a panel. ......................

I would agree you have the best approach, albeit debatable.
As stated earlier, these NEC definitions leave a lot to be desired IMHO.
(I don't propose that I can do better)

 

[weressl]

This would not be "service equipment" as it is not connected to the load end of the service conductors. It is supplied by a feeder from an existing 600 amp panel in the building.

I was not implying that the MCC in the OP was a 'service equipment'. I was using the reference from the 430 MCC section to counter the assertion that the MCC is a 'structure' or a 'building'. The OP question morphed into of trying to define what category AN MCC can be slotted and what Articles would be applicable to it.

 

[don_resqcapt19]

I was not implying that the MCC in the OP was a 'service equipment'. I was using the reference from the 430 MCC section to counter the assertion that the MCC is a 'structure' or a 'building'. The OP question morphed into of trying to define what category AN MCC can be slotted and what Articles would be applicable to it.

Sorry, I did not read your post that way.

I think equipment is covered under the very broad definition of structure that is in Article 100. There are a number of issues with the use of the definition, especially in industrial applications, where is it not uncommon to have outside disconnects feeding equipment in buildings.

 

[weressl]

Sorry, I did not read your post that way.

No problem, written exchanges often fall victim to misunderstanding.

I think equipment is covered under the very broad definition of structure that is in Article 100. There are a number of issues with the use of the definition, especially in industrial applications, where is it not uncommon to have outside disconnects feeding equipment in buildings.

True, but I think that in electrical lingo we would find a fairly high percentage of professionals agreeing that the main categories of objects in our field would be

• enclosures,
• equipment,
• devices and
• materials.

 

[don_resqcapt19]

No problem, written exchanges often fall victim to misunderstanding.

True, but I think that in electrical lingo we would find a fairly high percentage of professionals agreeing that the main categories of objects in our field would be

• enclosures,
• equipment,
• devices and
• materials.

But at some point, I think enclosures and equipment become structures. I just don't know where that point is.

If some one could come up with some good wording the proposals for the 2014 code are due in about a month.

 

[weressl]

But at some point, I think enclosures and equipment become structures. I just don't know where that point is.

If some one could come up with some good wording the proposals for the 2014 code are due in about a month.

I think that is incorecct.

Definition of a structure:

In engineering and architecture, a structure is a body or assemblage of bodies in space to form a system capable of supporting loads. Physical structures include man-made and natural arrangements. Buildings, aircraft, soap films, skeletons, anthills, beaver dams and salt domes are all examples of physical structures. The effects of loads on physical structures are determined through structural analysis. Structural engineering refers to engineering of physical structures.

Built structures are a subset of physical structures resulting from construction. These are divided into buildings and nonbuilding structures, and make up the infrastructure of a human society. Built structures are composed of structural elements such as columns, beams and trusses. Built structures are broadly divided by their varying design approaches and standards, into categories including Building structures, Architectural structures, Civil engineering structures and Mechanical structures.

 

[pete m.]

It would seem (according to the author of the '08 handbook commentary) that the definition of Structure is meant to be vague.

Structure. That which is built or constructed.

Commentary: The definition of structure allows architects, electrical engineers, general contractors, electrical contractors, and all building officials to use the same definition.

Pete

 

[don_resqcapt19]

I think that is incorecct.

Definition of a structure:

In engineering and architecture, a structure is a body or assemblage of bodies in space to form a system capable of supporting loads. Physical structures include man-made and natural arrangements. Buildings, aircraft, soap films, skeletons, anthills, beaver dams and salt domes are all examples of physical structures. The effects of loads on physical structures are determined through structural analysis. Structural engineering refers to engineering of physical structures.

Built structures are a subset of physical structures resulting from construction. These are divided into buildings and nonbuilding structures, and make up the infrastructure of a human society. Built structures are composed of structural elements such as columns, beams and trusses. Built structures are broadly divided by their varying design approaches and standards, into categories including Building structures, Architectural structures, Civil engineering structures and Mechanical structures.

When a term in defined in the NEC, that is the only defintion that can be used for the application of the NEC. I see a MCC as a structure and see it as triggering the rules in Article 225 if it is installed outside of a building.

 

[petersonra]

When a term in defined in the NEC, that is the only defintion that can be used for the application of the NEC. I see a MCC as a structure and see it as triggering the rules in Article 225 if it is installed outside of a building.

By that definition just about anything that is manufactured would be considered a structure.