240.21(C)(1) secondary feeder protection and autotransformers

[DW98]

I have a shop drawing showing an elevator disconnect feeding a 208V to 480V transformer but doesn't show secondary conductor protection. Transformer is provided by elevator equipment supplier. I've contacted supplier for cut sheet of transformer to see if they were simply wiring a stock 480D-208/120Y backwards or using a delta-delta transformer. We went and took pictures of installation and it turns out xfmr is an auto-xfmr. I'm not too familiar with auto-transformers and want to confirm that the secondary conductors need overcurrent protection. Does NEC 2008 240.21(C)(1) apply?

 

[rlundsrud]

So I am shooting from the hip on this as I haven't had a chance to work on a 3 phase auto transformer. An auto transformer doesn't have a secondary coil, it uses the same coil with taps to create the step up or down. This means there isn't any electrical isolation in the way that a standard transformer operates. Since there isn't isolation, a fault on the output side would operate the OCP on the input side. It is for this reason that I would surmise it doesn't require secondary OCP. I am certain that others can wade in and give you something more concrete than my somewhat anecdotal answer.