Back to Engineering After A Year

[mkmorris]

So I got back into engineering again and brushing off and digging into design at an old chemical plant. They have a few MCCs with 600A Horizonal, 300 Amp Vertical Bus and 1200A Horizontal, 300 Amp Vertical Bus. The only thing on the single vertical sections appears to be loaded with either 350hp or 400hp motors for pumps. The FLA of the motors exceeds the rating of the vertical section, but cumulatively they are theoretically under the 600A or 1200A horizontal rating and have not blown the MCC out yet.

To me, I would think that motor needs to be swapped out with a 300hp for a vertical MCC section rated for 300A, but they have not had any issues from what I have heard and have been running 350hp motors for some time off of Delta-Wye starters coming off that bus. Curious what other's thoughts are.

 

[jim dungar]

In many cases MCC buckets with 400A frame switches/breakers are cabled directly to the cross bus and are not connected to the vertical bus at all.

 

[Jraef]

The vertical bus is for plug-in units, nobody has breakers larger than 400A for plug-in units, so for 350-400HP starters, those would definitely be connected direct to the horizontal bus. In fact there is likely no vertical bus in those sections..