I have a job that I set up (2) 400A panelboards from an 800A Main. I wasn't given accurate information at the onset and have since learned that my Main Panelboard is 800A that no longer has 400A breakers available for it. Possibly 200A Breakers but I am still awaiting information. My question is this....I can feed a 400A Panelboard with parrallel wiring sized for 200A, am I allowed to use (2) 200A breakers each running 200A sized (#3/0) wiring to a 400A panelboard?
Sub-Feeding Panelboards
- Thread starter Pietenpol
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hurk27
Senior Member
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- Portage, Indiana NEC: 2008
If you can change out the 400 amp panels to 200 and have the space to install 4 200 panels, you will have more breaker spaces, but watch the AIC rating, I have done a few jobs with out a 800 amp main but grouping 4 200 amp MB panels next to each other with troughs above and below them much lower in cost, as long as you can meet the AIC requirment, and it allowed more breaker spaces back when we had the 42 space limit.
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- Chapel Hill, NC
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- Retired Electrical Contractor
Do what Wayne said or buy a panelboard that can handle 400 amp breakers. I am surprised that the 800 amp panel can't handle a 400 amp breaker.
I won't know till tomorrow if I can even get 200A breakers....My 2 paths without knowing were to Feed (2) 200A and spread the rest of the 400A onto the 800A main but I doubt I can cram it in given the breaker space. So (4) 200A was the other idea and is looking like the way to go.
The situation is arising from an old panelboard from what I understand. If I can find a company that still sells 200A breakers for that board and have them provide the breakers connected (factory-assembled) to work as a 400A breaker then would it get me around 240.8? At this point I'm going with (4) 200A panels but would like to know if this could be an option in the future if such an issue arises again.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
4 200 amp panels is always an option if you can maintain the required AIC rating needed for the service, I have installed 6 200 amp main breaker panelbords before on a 1200 amp service without a main, the inspector was confused by it, but had to let it go as they were grouped and all landed in a large junction cabnet from the transformer each 3/0 landing in its own lug, the main bonding jumper was in this cabnet as well as the GEC's the metering was done at the transformer with CT's.
This was of course on a 208/120 volt system so GFP wasn't required, but if doing a 480/277 volt system exceeding 1000 amps would require GFP's
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
can you post the info on the breaker needed, maybe we can help?
Where are the two 400A panelboards located with respect to each other and the 800A Main?
The reason I ask is to see whether you can use tapping as a viable means to your end. The difference would basically be just shifting your 400A breakers from the main enclosure to the individual panelboards (i.e. MCB panelboards instead of MLO).
So (If I remember correctly) If I have the panels within 25 feet I can tap into the 800A panel and use 400A mains in the new panels? As to the previous question regarding more info on the panel I don't know when or if I will get that.
Yes. But the 25' limitation is on the tap conductors. The feeder conductor can be any length.
Say your subpanels are within 50' wire length of each other but 300' from the main panel. You could run a 400A set ? 2 feeder (which you would anyway for two 400A panels) to the center point between panels, combine the sets (e.g. a two in, two out terminal blocks per parallel conductor), then take one out from each block to each panel not more than 25' away. It would technically work without the terminal blocks (i.e. unspliced) but you would not be code compliant :roll:.
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