Tap rule for additional "house panel" off existing 200A subpanel feeder?

[mpoulton]

A commercial building has a 600A 120/240V 1ph single-meter service with four 200A fused pull-out disconnects, each of which feeds a 200A panel in each of four separate suites. As part of a remodel, the owner wants to install a "house panel" for site lighting, irrigation control, etc. The electrical contractor proposed placing a new 150A panel adjacent to the SES and feeding it from a tap on the least-loaded existing feeder. The tap would be protected with the 150A main breaker in the new panel. The total calculated load on that feeder (with the existing panel plus the new panel) is well under 200A. The electrical engineer says "no" to this arrangement because "I don't think you can do it like that." I don't see anything wrong with it. Thoughts?

 

[Smart $]

Not a violation as long as tap rules of 240.21(B) are met.