MCC supplying motor loads in another building

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retire09

Senior Member
I am reviewing a plan that shows motors in a building that is entirely class I division II being fed from an MCC located in another building.
The motor feeders go directly from the MCC to the motors with only a lockable switch at the MCC (nothing insight of the motors) for a disconnect.
In order to kill all power to this building, you would have to turn off the mains in two separate panels in the building and four switches at the MCC in another building.
The engineer tells me that this is a common industry practice for this type of facility.
Is there a code section that would allow this type of design?
This is a compressed natural gas storage facility, is this a common industry design for this type of project?
 

RUWired

Senior Member
Location
Pa.
The engineer tells me that this is a common industry practice for this type of facility.
Is there a code section that would allow this type of design?
This is a compressed natural gas storage facility, is this a common industry design for this type of project?
If the facility meets the requirement of single management, documented safe switching procedures etc. are maintained, article 225.32 exception 1 for the feeder disconnect to the building and 430.102(B) exception 2 for the motor disconnect might apply.

Rick
 
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retire09

Senior Member
I have agreed to the 225.32 exception but would not each of these motor feeders not be considered a supply or service to the building and have to have service rated disconnects for each in the building?
 

retire09

Senior Member
The feeder grounding conductors to the motors will be connected to the electrode system in the building they originate from but not the building housing the motors. Is this not a problem?
 

RUWired

Senior Member
Location
Pa.
The feeder grounding conductors to the motors will be connected to the electrode system in the building they originate from but not the building housing the motors. Is this not a problem?

In this situation, all of the conditions in 250.32(D) must be met.


(D) Disconnecting Means Located in Separate Building or Structure on the Same Premises. Where one or more disconnecting means supply one or more additional buildings or structures under single management, and where these disconnecting means are located remote from those buildings or structures in accordance with the provisions of 225.32, Exception No. 1 and No. 2, 700.12(B)(6), 701.11(B)(5), or 702.11, all of the following conditions shall be met:
(1) The connection of the grounded conductor to the grounding electrode, to normally non?current-carrying metal parts of equipment, or to the equipment grounding conductor at a separate building or structure shall not be made.
(2) An equipment grounding conductor for grounding and bonding any normally non?current-carrying metal parts of equipment, interior metal piping systems, and building or structural metal frames is run with the circuit conductors to a separate building or structure and connected to existing grounding electrode(s) required in Part III of this article, or, where there are no existing electrodes, the grounding electrode(s) required in Part III of this article shall be installed where a separate building or structure is supplied by more than one branch circuit.
(3) The connection between the equipment grounding conductor and the grounding electrode at a separate building or structure shall be made in a junction box, panelboard, or similar enclosure located immediately inside or outside the separate building or structure.

Rick
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I have agreed to the 225.32 exception but would not each of these motor feeders not be considered a supply or service to the building and have to have service rated disconnects for each in the building?
Why would they need to be service rated when they are feeders?
The feeder grounding conductors to the motors will be connected to the electrode system in the building they originate from but not the building housing the motors. Is this not a problem?
As far as code goes it might well be an issue. but one not all that hard to resolve. It seems to me that the EGCs are all bonded together at the MCC so all that might need to be done is to bond one of them in the separate structure to a GE.
Is the non classified building essentially an electrical room or is there more to it than that?
Does it matter any?
 
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Rockyd

Senior Member
Location
Nevada
Occupation
Retired after 40 years as an electrician.
I am reviewing a plan that shows motors in a building that is entirely class I division II being fed from an MCC located in another building.
The motor feeders go directly from the MCC to the motors with only a lockable switch at the MCC (nothing insight of the motors) for a disconnect.

See 430.102 Ex.(b) in particular.


In order to kill all power to this building, you would have to turn off the mains in two separate panels in the building and four switches at the MCC in another building.

? Should be one main...What does the engineer say on this? Sounds like there is more to this.


The engineer tells me that this is a common industry practice for this type of facility.
Is there a code section that would allow this type of design?
This is a compressed natural gas storage facility, is this a common industry design for this type of project?


Take a look at 500.5 and the informational note. Classified equipment prices are astronomical compared to non-classified space equipment. This type of arrangement is pretty typical in oil patch work.
 

kwired

Electron manager
Location
NE Nebraska
Why would they need to be service rated when they are feeders?

As far as code goes it might well be an issue. but one not all that hard to resolve. It seems to me that the EGCs are all bonded together at the MCC so all that might need to be done is to bond one of them in the separate structure to a GE.

Does it matter any?

225.36 says the disconnecting means for a separate building or structure shall be suitable for use as service equipment.


A separate building or structure supplied by another can not have more than 1 feeder supplying it. (some exceptions)

In the case of hazarous environment the AHJ may allow the separate 'electrcal room' if its only purpose is to serve the hazardous environment that is otherwise a separate building or structure.
 

Smart $

Esteemed Member
Location
Ohio
I have agreed to the 225.32 exception but would not each of these motor feeders not be considered a supply or service to the building and have to have service rated disconnects for each in the building?
Yes.

225.36 Suitable for Service Equipment. The disconnecting
means specified in 225.31 shall be suitable for use as
service equipment
. (Exception irrelevant to this issue)

225.31 Disconnecting Means. Means shall be provided
for disconnecting all ungrounded conductors that supply or
pass through the building or structure.​

250.32 exceptions only permit the disconnecting means to be located elsewhere on the premises. It does not provide exception to the 225.36 requirement.
 

rsorrells

Member
Location
alabama
rsorrells

rsorrells

225.36 says the disconnecting means for a separate building or structure shall be suitable for use as service equipment.


A separate building or structure supplied by another can not have more than 1 feeder supplying it. (some exceptions)

In the case of hazarous environment the AHJ may allow the separate 'electrcal room' if its only purpose is to serve the hazardous environment that is otherwise a separate building or structure.
rsorrells here speaking Those are not feeders going to the other building they are motor branch circuits. The disconnnect,controllers, and overload protection is in the mcc in the other building.They probably want to reduce a fire hazard,so they are putting all the electrical equipment they can in a seperate building.
 
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kwired

Electron manager
Location
NE Nebraska
225.36 says the disconnecting means for a separate building or structure shall be suitable for use as service equipment.


A separate building or structure supplied by another can not have more than 1 feeder supplying it. (some exceptions)

In the case of hazarous environment the AHJ may allow the separate 'electrcal room' if its only purpose is to serve the hazardous environment that is otherwise a separate building or structure.

rsorrells here speaking Those are not feeders going to the other building they are motor branch circuits. The disconnnect,controllers, and overload protection is in the mcc in the other building

I knew I should have mentioned the rest.

A separate building or structure supplied by another can not have more than 1 feeder or branch circuit supplying it. (some exceptions)

see 225.30
 

kwired

Electron manager
Location
NE Nebraska
What about 225.30(E)?

Still has to comply with 225.31 and 32 also.

.30(E) doesn't mention supervision by qualified individuals but exception 1 to .32 does.

Not saying this can't be used but supervision by qualified individuals rules out quite a few installations from using these type of exceptions.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Given that this is pretty common, I am guessing people are relying on 225.30E.

I don't know if the disconnecting means in the MCC are service rated or not. That would seem to be the only issue here given 225.30E.
 

kwired

Electron manager
Location
NE Nebraska
Given that this is pretty common, I am guessing people are relying on 225.30E.

I don't know if the disconnecting means in the MCC are service rated or not. That would seem to be the only issue here given 225.30E.

How does the MCC in another building comply with 225.32? Exception 1 may be the only way. This exception requires qualified individuals to monitor the installation. I don't think disconnect needs service rated or not if doing it this way.

The only way an MCC is service rated is if it has a service disconnect within the MCC but the branch units are not service equipment.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
I have avoided this thread because no amount of interpretation of the current text or potential wordsmithing of a ton of text in the future (which would probably screw something else up) short of a special and specific recognition of the installation described, would make it Code compliant - but it should be accepted anyway; the engineer is correct.
 

Smart $

Esteemed Member
Location
Ohio
...

The only way an MCC is service rated is if it has a service disconnect within the MCC but the branch units are not service equipment.
The MCC can be service equipment rated without containing a service disconnect (not to be confused with a main which is service rated). Under documented safe switching procedures, the MCC main can be the disconnecting means for the motor circuits under specified circumstances.
 

retire09

Senior Member
Should I require that the MCC supplying these loads be service rated and bonding in the class I Div II building be per 250.32(b) and call it good?
 

retire09

Senior Member
What is a reasonable definition of "Documented Safe Switching Procedure"?
I would think it is a facility that is monitored 24 hours a day by qualified persons on site who are trained to execute the switching procedure.
Am I close?
 
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