Grounding

[thinker]

Please advise: We have a single phase 120 VAC power feeder
in the control cabinet. This is the voltage between phase
and a grounded neutral. One of the units in the cabinet
requires power 230 VAC, so we install a single phase
step-up transformer 120/230. Now the question: do we need
to ground a secondary of this transformer?

 

[Newton1Law]

I believe NEC code 250-5 (b), Exception #3 applies. You do not need a ground. The exception is, "spparately derived systems supplied by transformers that have primary voltage rating less than 1000 volts, providing that all of teh following conditions are met:
a) System is used for control circuits only
b) Only qualified persons shall service the installation
c) continuity of power is required
d) ground detectors are installed on the control system.

Hope this helps.