Switch Sizing arrangement

[mstrlucky74]

Set have all the info right now but figured I'd get the ball rolling. Will be in my office shortly.

Have to feed two 1600a 120/208 dist boards from a main 120/208 dist board(not sure size yet..think 4000a).They want to put (2) 1600a disconnects near the main dist board for these feeds. Not sure why if it's being feeds from switch(es) in the main board it's protected already. Does that make sense? Also obviously have to have two separate switches in the main board to feed each disconnect which then feeds the other dist board correct? I only ask because I think they mentioned one 2500a switch in the main board being used for both sets of feeders to each disconnect which I'm sure is not right. How would you go about sizing the switches in the main board that's feeding the two 1600a switches which feed the two 1600a dist boards? Thanks

 

[petersonra]

Sounds like what they have in mind is a perfectly reasonable application of the tap rules.

As for the rating of the switches and presumably the fuses in them that would be based on the load calculations for the two feeders.

 

[mstrlucky74]

Sounds like what they have in mind is a perfectly reasonable application of the tap rules.

As for the rating of the switches and presumably the fuses in them that would be based on the load calculations for the two feeders.

Ok, thanks. So they are looking to tap the main 2500A switch in the main board. Not 100% clear how that's done. How could a 2500a switch be tapped to feed (2) 1600a switches. Switch undersized, no?

 

[petersonra]

Ok, thanks. So they are looking to tap the main 2500A switch in the main board. Not 100% clear how that's done. How could a 2500a switch be tapped to feed (2) 1600a switches. Switch undersized, no?

the rating of the downstream panelboards or switches has nothing to do with the load calculation. the only requirement is that the feeder conductor ampacity be able to accommodate the calculated load. what does the calculation say the load will be on the 2500 Amp switch?

if they are going to use the tap rule to come off a 2500 Amp fused switch, they would need to run conductors with enough ampacity to each of the 1600 A fused switches that they are protected by whatever fuses are put in the 1600 A fused switches.

 

[mstrlucky74]

So if you had to feed (2) 1600a switches from this 2500A switch with feeder MC cable(temp setup) how would this be done? See attached.You would have to tap 2500A feeder? Can't tap in gear correct, it would have to be in box? Guess you would have to run feeders sized for 2500A? Thanks.

 

[mstrlucky74]

Here is actual pic of switch.