control transformer secondary

[mvbub]

Article 270.170 states that secondary circuits have to be grounded when primary is 300 volts to ground.
Is there anywhere else in code that requires a 480 volt primary 120 volt secondary 50 va transformer to have a secondary conductor grounded???
I typically ground for troubleshooting purpose, but can not find an article that requires it in a control panel.
any assistance would be appreciated
mvbub

 

[don_resqcapt19]

Re: control transformer secondary

250.170 is for instrument transformers and not control transformers. It appears that 250.20(B)(1) requires a grounded conductor on the secondary side of the transformer. Look at the definiton of "premises wiring" includes control and signaling circuits. 250.21(3) would permit the secondary to be ungrounded if all of the conditions in that section are met.
Don