Main Circuit Breaker Requirement for Like-Voltage Equipment

[EBSoares]

Hi, all.

Trying to determine the need for MCBs for downstream panels of the same voltage as their parent panel (say, a 480V panel feeding another 480V panel). From my understanding, the NEC does not require an MCB on the child panel in this scenario, if it has a circuit breaker in the parent panel, so I do one of the two below:

• If the child panel is in the same room, I make it MLO (main lug only).
• If the child panel is in another room (specially if it’s a room far from the parent panel), I provide an MCB, so they don’t need to go hunting for the parent panel to turn off power (I guess this could be considered "safer")

Generally speaking, is the above a good design to follow?

As a specific example, we have a 480V, 2000A switchboard being fed from a 480V, 4000A switchboard, both really far from each other (around 1,000 feet) – should the 2000A switchboard have an MCB? This MCB might add a huge cost to the project...

Thanks in advance,

Edgar

 

[ron]

Your proposed direction is often the way it is done, although it is also code compliant to remove the downstream MCB as long as the upstream protection is present for the feeder and panelboard

 

[don_resqcapt19]

As a specific example, we have a 480V, 2000A switchboard being fed from a 480V, 4000A switchboard, both really far from each other (around 1,000 feet) – should the 2000A switchboard have an MCB? This MCB might add a huge cost to the project...

Is there a 2000 amp OCPD in the supplying switchboard? Will 225.31 apply and required a disconnect at the load end?

 

[augie47]

I would think the determining factor would be if the 2nd (child) panel is in the same "building"
(Taking into account the definition of a building)
Same building = no main required at 2nd panel
Separate building = main required.

 

[suemarkp]

Not sure how much it helps if it is in the same building, because you still can't work in the panel with the just the main flipped off if its LINE lugs are live. It is safer to have a local main when you just want to change out a branch breaker, but not good enough for OSHA. So you either don PPE or go find the parent panel and shut down the feeder. So the important thing is to have good labeling and location information as to what feeds what.

 

[EBSoares]

Thanks for quick replies, everyone! I think they are all super helpful!
For those asking, this is all the same, single building, so it seems an MCB is really not required, and not really helpful either, per Mark.
Don, thanks for providing the code reference. Based on that, even if the equipment are in the same building, but if for some reason the feeders are routed in such as way that they leave the building outline and return back into it (such as when the building has an odd shape - like a "U" shape), then a disconnecting means would be required. In this specific scenario I presented above the building does have an odd shape and we were indeed thinking the most "straight" path would have the feeders outside the building for a portion of the route - so I need to make sure I apply this code properly.
Thanks again, y'all

 

[don_resqcapt19]

Don, thanks for providing the code reference. Based on that, even if the equipment are in the same building, but if for some reason the feeders are routed in such as way that they leave the building outline and return back into it (such as when the building has an odd shape - like a "U" shape), then a disconnecting means would be required.

I don't think a disconnect at the load end would be required under those conditions. It is not a second building being fed from the building that has the service equipment.

 

[EBSoares]

I don't think a disconnect at the load end would be required under those conditions. It is not a second building being fed from the building that has the service equipment.

Thanks again, Don. The "pass through the building" portion of the code makes it a bit tough... are you sure that it wouldn't be required?

 

[don_resqcapt19]

Thanks again, Don. The "pass through the building" portion of the code makes it a bit tough... are you sure that it wouldn't be required?

225.30 is not as clear as I thought it was...I could see an AHJ saying the rules in Article 225 Part II apply. I have always read that Part as only applying where the feeder or branch circuit originates in a separate building.

 

[augie47]

I agree with don that Art 225 does muddy the waters a bit but if Art 225 is applicable, 225.31(B) Exception 1 might still allow a MLO at the subpanel.

 

[YouConduit!]

Helpful thread! What if you have the same situation outdoors?

480V panel feeding a smaller 480V subpanel through a correctly sized feeder circuit breaker (OCPD). Does the subpanel require a MCB/disconnect or can it be MLO? Also curious if the answer has changed over time.

I recently came across an installation like this where an outdoor main panel feeds multiple outdoor subpanels and all of them are MLO.

 

[augie47]

Helpful thread! What if you have the same situation outdoors?

480V panel feeding a smaller 480V subpanel through a correctly sized feeder circuit breaker (OCPD). Does the subpanel require a MCB/disconnect or can it be MLO? Also curious if the answer has changed over time.

I recently came across an installation like this where an outdoor main panel feeds multiple outdoor subpanels and all of them are MLO.

The two most applicable Sections that would apply would be 408.36 which requires a main OCPD rated for the panel and conductors either in the panel ot ahead of the panel and 225.31 (& .32) which give the requirements if the supply is for a building ot structure.