Tap off the bus in a switchboard

[dabatman]

I have a switchboard that has an 800A main in it and nothing else. My problem is that I need 800A OCPD to feed an MLO panel sitting right next to it (less than 10ft). Can I use that 800A main and tap off the bus of the switchboard to feed my MLO 800A panel?

I believe 240.21(B) somewhat states I can from a tap rule standpoint. I was supposed to be supplied with an 800A disconnect and I was given a 800A switchboard to feed my panel with. It seems like this should be okay though since this is the only device that the switchboard will feed.

 

[charlie b]

You are not within the scope of the tap rules, and you don't want to be. If you use a set of conductors that have an ampacity of 800 amps (and by the way, a pair of 500 MCM's won't suffice), then you can use the main breaker on the switchboard to protect the conductors and the MLO panel.

The tap rules are all about using a smaller conductor to go from the tap point to the downstream panel or load. They require you to land on an overcurrent device, so you can't land on an MLO panel. That is what I mean by saying you don't want to be in the tap rules.

 

[augie47]

I agree with charlie that you don't need to worry about the tap rules as long as you use 800 amp conductors.
"Field tapping" the buss is often viewed as altering a piece of listed equipment. It would be a good idea to contact the gear manufacturer and see what instructions, etc they provide about tapping their buss.