Motor Control Center Disconnect

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vanagsys

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Ohio, US
Hello,
I am building a motor control center for a facility remodel and have a question about disconnect means. This MCC will be fed from an 800 Amp 240volt 3ph breaker in an MDP which is located on the outside of the building that will house the MCC. Does my MCC need a disconnect means inside for the entire panel, with a handle through the door? I am using a 3 door enclosure so the door interlock poses some obvious problems and I also do not want to have to shut the entire MCC down just to reset one starter. Inside the enclosure each motor starter or drive has its own breaker. The panel will have to pass a county electrical inspection. I am trying to avoid using a main breaker inside due to cost.
Thanks
 
Having the disconnect on the outside of the building meets the NEC rules for the MCC disconnect.

That being said, you are not permitted to open the enclosure door to reset an overload while the panel is energized.
 
I am curious as to what you mean in building a MCC? Are you designing one for a manufacturer, are you a manufacturer, or are you physically building one?
 
I agree with the other poster that said you can't open the door with the power on for the purposes of resetting an overload.

There are ways to reset a tripped overload that would not require you to open an energized cabinet.
 
Thanks for the reply--
I am assembling the panel myself for this job.
My VFD's will be reset through Modbus should they trip but some of the starters don't have automatic reset OLs.
 
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vanagsys said:
Thanks for the reply--
I am assembling the panel myself for this job.
My VFD's will be reset through Modbus should they trip but some of the starters don't have automatic reset OLs.
Click to expand...
You need to find a way to have a remote reset. You cannot open the door of the enclosure to do a reset unless all of the power inside the enclosure is off. Many overload relay manufacturers have a solenoid reset option. You use a push button in the door to operate the solenoid reset so you can do a reset without opening the door.

Also if this is going into an industrial plant, you can have OSHA issues unless you are going to get the panel you are building UL listed. In general the OSHA rules require all equipment in the workplace to be listed equipment.
 
vanagsys said:
Thanks for the reply--
I am assembling the panel myself for this job.
My VFD's will be reset through Modbus should they trip but some of the starters don't have automatic reset OLs.
Click to expand...

Most motor starters are available with solenoid (sometimes motor) operated resets as another poster mentioned.

Another option is a remote PB with a rod the engages the reset mechanically.
Check out AB

800FP-R611
800F-ATR08

Most motor starters are available with similar accessories.
 
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vanagsys said:
Thanks for the reply--
I am assembling the panel myself for this job.
My VFD's will be reset through Modbus should they trip but some of the starters don't have automatic reset OLs.[/QUOTE

The reason I ask is there is a definition of MCC and specific UL listing requirements.
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Yes I realize there are a UL issues to work with. I am putting all UL listed components into a UL listed enclosure to control motors in a facility.
 
vanagsys said:
Yes I realize there are a UL issues to work with. I am putting all UL listed components into a UL listed enclosure to control motors in a facility.
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Guess I might as well be the one to throw a flag here. Use of UL listed components alone does not create an approved piece of equipment in many jurisdictions. Best to check with your AHJ.
 
So far, what you have described is, at best, an industrial control panel [Art 409], not an MCC. Even then "... putting all UL listed components into a UL listed enclosure ..." isn't enough.
 
rbalex said:
So far, what you have described is, at best, an industrial control panel [Art 409], not an MCC. Even then "... putting all UL listed components into a UL listed enclosure ..." isn't enough.
Click to expand...

IIRC, the NEC definition of MCC is pretty explicit as to what constitutes an MCC.

I don't think what he is doing qualifies, although I also think it does not matter all that much what he calls it. It probably is still an industrial control panel as defined by the code.

We usually call such things MCPs (motor control panels). We make a lot of them. Some are UL listed as industrial control panels, some not. Some of our customers are unwilling to pay the small incremental expense to get it UL listed, and to date we have not had a single case where not being UL listed mattered any in the field. It just has not come up. It does not appear to me that all localities really care if such things are listed or not.

One of the issues we run into is that many times existing designs are quite adequate but not UL508a compliant, usually for minor reasons. Customers are unwilling to spend the resources to redesign their panels to meet UL requirements. Most of the industrial control panels we design are more or less UL508a compliant even if it ends up not being listed.
 
Isn't the equipment that is generally marketed as a MCC more less a switchboard by basic design?

There is gear out there that have mostly feeders supplied from them but maybe a limited number of sub units that contain the needed motor circuit components - disconnecting means, short circuit/ground fault protection, motor controller, motor overload protection. If the majority of sub units are for motor control - we usually call it a MCC, if the majority are other then motor circuits we usually call it a switchboard, but either one is built with similar methods and maybe even have components that interchange relatively easily.

I do agree the OP is describing an industrial control panel more then a MCC.
 
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