Home » English riddles » Grounding » Grounding Riddle No. 39 – Grounding systems for Instrument Transformers » Reply To: Grounding Riddle No. 39 – Grounding systems for Instrument Transformers Reply To: Grounding Riddle No. 39 – Grounding systems for Instrument Transformers 2021-08-03 at 11:08 am #3261 Hamid Please refer to ANSI/IEEE C57.13.3 (Guide for the grounding of instrument transformer secondary circuits and cases).