Installing a transformer load greater than its rating?

[sbyrne]

Would it be a code violation to install a load on a transformer that exceeds the nameplate rating of the transformer? Here is my scenario:

Installing multiple large pump motors fed from a single transformer, roughly 50kva total load. Only one pump will ever operate, lets say it is 15kva. Can I install a 25kva transformer to feed all motors and still be within code? I would size the secondary OCPD for the single motor, not the entire connected load.

 

[augie47]

If you system OCPD and is designed to protect the transformer then I see no real problem. If the system has the circuitry interlocked to prevent both motors from operating at the same time, then 430.24 allows you to size your motor conductors based on the one motor with the highest current.
If the design is such that there is no circuit interlock, just an operational procedure, I think you would need to take that into consideration in sizing the components, but as long as the transformer has proper protection per 450.3, you should be o.k. with it.
It is not uncommon to find a transformer with OCPD devices on the secondary side that exceed the transformer rating and load diversity prevents a problem. However, in these cases, 450.3 requires proper primary protection.