MCC Main Breaker vs MLO

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dcheser

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Is there anything in the code the defines when you have to have a Main Breaker in an MCC? I have always added a main unless the MCC was in the same room as the Power Distribution Panel/Switchgear or was within a short distance (i.e. 50-75 Feet). I have an issue where a client wants to put an MLO MCC 400 Feet from his power distribution panel/Switchgear and a need something in the code to back it up.

Thanks for any input
David C.
 
Have done it all the time. Waste of much $$$ to repeat the feeder breaker function in the MCC. Could cause confusion if both trip under a fault.

The one time you might need one is if the MCC is in a different building.

RC
 
MCC will be in a different building......sorry! Left that part out and there is approximately 400-Feet between the buildings
 
225.31 Disconnecting Means. Means shall be provided
for disconnecting all ungrounded conductors that supply or
pass through the building or structure.

225.32 Location. The disconnecting means shall be installed
either inside or outside of the building or structure
served or where the conductors pass through the building or
structure. The disconnecting means shall be at a readily
accessible location nearest the point of entrance of the conductors.
For the purposes of this section, the requirements
in 230.6 shall be utilized.

Exception No. 1: For installations under single management,
where documented safe switching procedures are established
and maintained for disconnection, and where the
installation is monitored by qualified individuals, the disconnecting
means shall be permitted to be located elsewhere
on the premises.

225.33 Maximum Number of Disconnects.
(A) General. The disconnecting means for each supply
permitted by 225.30 shall consist of not more than six
switches or six circuit breakers mounted in a single enclosure,
in a group of separate enclosures, or in or on a switchboard.
There shall be no more than six disconnects per
supply grouped in any one location
 
All industrial facilities should have sufficient documentation and labeling to meet 225.32 Exception 1, so this is not a code issue, it is an operational issue that is up to the facility. Having a main breaker at the MCC may serve some useful operational purpose depending on the type of facility. In a continuous process plant we shut down MCCs every 5 years, so for us it is not worth the cost and the additional device to maintain, whether the MCC is 5 feet from the switchgear that feeds it or 800 feet away in another building.

From the client's perspective, main breakers cost money and serve no power system protection purpose*, so why would the client want to pay for one? Whatever protection is provided by the main can be provided instead by the upstream device, which can be 400 feet away in a different building.

I'm assuming from the OP that the "power distribution panel/Switchgear" that is feeding the MCC is the same voltage as the MCC and therefore will have a branch circuit device that can provide the equivalent protection that a main breaker in the MCC would provide. If you have your heart set on a local disconnect device you can use a metal enclosed switch, but that's just as pointless as a main breaker.



*A main breaker on the secondary side of a unit substation transformer with a 15 kV or 5 kV feed to a 480V step down transformer is an exception. Some facilities use MCCs coupled to transformers like this without switchgear/switchboards/panelboards in between, and in this case a main should definately be provided. A lower cost solution is a "virtual main" that uses CTs on the secondary side that feed a protective relay on the primary, but there are some downsides to this scheme:
- It will clear slower than a MCCB or ICCB on the secondary
- this involves additional transformer switching that will reduce the life of the transformer
- many facilities do not have the sophistication to understand and maintain this scheme - it is bringing elements of MV relaying down into the 480V world, which may not be acceptable at some locations
 
jdsmith said:
All industrial facilities should have sufficient documentation and labeling to meet 225.32 Exception 1, so this is not a code issue, it is an operational issue that is up to the facility. Having a main breaker at the MCC may serve some useful operational purpose depending on the type of facility. In a continuous process plant we shut down MCCs every 5 years, so for us it is not worth the cost and the additional device to maintain, whether the MCC is 5 feet from the switchgear that feeds it or 800 feet away in another building.

From the client's perspective, main breakers cost money and serve no power system protection purpose*, so why would the client want to pay for one? Whatever protection is provided by the main can be provided instead by the upstream device, which can be 400 feet away in a different building.

I'm assuming from the OP that the "power distribution panel/Switchgear" that is feeding the MCC is the same voltage as the MCC and therefore will have a branch circuit device that can provide the equivalent protection that a main breaker in the MCC would provide. If you have your heart set on a local disconnect device you can use a metal enclosed switch, but that's just as pointless as a main breaker.



*A main breaker on the secondary side of a unit substation transformer with a 15 kV or 5 kV feed to a 480V step down transformer is an exception. Some facilities use MCCs coupled to transformers like this without switchgear/switchboards/panelboards in between, and in this case a main should definately be provided. A lower cost solution is a "virtual main" that uses CTs on the secondary side that feed a protective relay on the primary, but there are some downsides to this scheme:
- It will clear slower than a MCCB or ICCB on the secondary
- this involves additional transformer switching that will reduce the life of the transformer
- many facilities do not have the sophistication to understand and maintain this scheme - it is bringing elements of MV relaying down into the 480V world, which may not be acceptable at some locations
Click to expand...

Who said it was supervised and industrial?
 
There is a good IEEE paper called arc flash mitigation with no main breaker that pertains to this situation. I tried to post but too large.
 
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