Few Q's on 400A/480V entrance, and busway setup.

[fastline]

1. An entrance to building being designed. Will have an outdoor disconnect, then to "something", whether that is a pair, or just a single panel board. Thoughts on one better than the other? If we use Aluminum conductors, would like to use 2 sets for the service. How can the tandem set be terminated in the disconnect and panel board?

2. Our area requires that any "conductor" rated over 100A (odd way to say in our code), must be Copper so intent is the stay above that to stick with Al. For that reason, a sort of "busway" type setup is being discussed, in which a larger branch will take off from the main, then pull various terminations to protected disconnects for pieces of equipment. For clarity, consider a 125A branch feeding 3 machines, each their their own disconnect off that branch. It's not ideal, and if any combination of equipment exceeds the need, they all go down, but the bean counting department has determined it will be cheaper to run one branch rather than several. Any thoughts to advice to this? I am wondering about how we will "daisy chain" to these disconnects with only one lug. I don't really like the insulated lug thing unless I have to. Seems there should be a better way.

Also, no way budget will allow for a real busway here. Any branch distance would not exceed about 75ft. I think the general idea was to pepper the walls with disconnects that could be fused to serve different loads as time went on, with little disruption to the system, and keep it cleaner.

 

[electrofelon]

1. An entrance to building being designed. Will have an outdoor disconnect, then to "something", whether that is a pair, or just a single panel board. Thoughts on one better than the other? If we use Aluminum conductors, would like to use 2 sets for the service. How can the tandem set be terminated in the disconnect and panel board?

IF a single 400A panelbaord was used, you would not need a main breaker. IF 2 200A PB's were used you would need main breakers in them and need to comply with a tap rule. The other things that comes to mind is if fault current is high and you want to use series ratings, then it is possible you would need a 200A frame to get the series rating for your branches, making the 2 200s with MB a better option.

400A equipment should have two port lugs, so I dont see an issue there.

2. Our area requires that any "conductor" rated over 100A (odd way to say in our code), must be Copper so intent is the stay above that to stick with Al. For that reason, a sort of "busway" type setup is being discussed, in which a larger branch will take off from the main, then pull various terminations to protected disconnects for pieces of equipment. For clarity, consider a 125A branch feeding 3 machines, each their their own disconnect off that branch. It's not ideal, and if any combination of equipment exceeds the need, they all go down, but the bean counting department has determined it will be cheaper to run one branch rather than several. Any thoughts to advice to this? I am wondering about how we will "daisy chain" to these disconnects with only one lug. I don't really like the insulated lug thing unless I have to. Seems there should be a better way.

Also, no way budget will allow for a real busway here. Any branch distance would not exceed about 75ft. I think the general idea was to pepper the walls with disconnects that could be fused to serve different loads as time went on, with little disruption to the system, and keep it cleaner.

You could use the tap rules to tap a feeder multiple times for each piece of equipment (I think that is what you are proposing). Another option that might be better depending on proximity of everything is run multiple feeders to strategic locations and mount a panelboard there and serve each piece of equipment from that with branch circuits. Would need more specifics on everything to know which is more economical. IF you want or need fuses, then maybe the former would be better.

 

[fastline]

Thanks. Yes, I mean feeders. Sort of vague on terms of the "bus" relative to second disconnect. Never seen one done to know how the intersect splice would be made. In this case, it would be basically done in the disconnect. As an example, 150A feeder leaving panel, drops into first disconnect fused at 100A, next one is the same 100A, next one is say 50A.

As for main panels, I guess what you are saying is exploit the tap rules to space them out of desired? However, I need to check codes here because they have a "15ft rule" for extension inside a building before a disconnect, but I can't recall if that is null if there is an outside disconnect. There has also been odd findings locally if these panels are treated as subs because I've seen a few that were not, even with outside disconnect. I know a couple had a steel nipple connection though. I just want to comply.