I've been working with my team on the secondary side of power distribution for a data center. Yesterday, the contractor responsible for working on the HV/primary side of things finished up his work and I noticed that they connected all of their grounds to the same grounding electrode conductor used for the LV/secondary while bonding the utility provided neutral via one of the transformer's casing. I've been trying to understand the reasoning behind their wiring and since I can't seem to get a hold of them I thought I'd reach out to you guys (the gurus).
This is a 3 phase transformer bank made up of three 167kVA single-phase dual-voltage transformers in a Delta-Delta configuration. The figure below is an exact replica of the current wiring of the system. The utility provided neutral comes straight from the pole while the primary lines consist of 15kV shielded cable with terminations that are grounded as per the diagram as well as at the primary fused disconnect (some 250' away with its own GEC) and again at the pole terminations to a ground rod at the base of the pole.
My main question is regarding the use of the utility supplied neutral. It's connected to a single transformer grounding lug. That same transformer also has an additional EGC attached to a different grounding lug, which is connected in series to grounding lugs on the other two transformers and on to the same grounding point as HV cable shield grounds and the secondary center tap ground. I'd yet to come across this configuration and would appreciate any comments as to if this seems correct or not or, better yet, what logic, if any, would be behind this.
Thanks in advance for your input!
This is a 3 phase transformer bank made up of three 167kVA single-phase dual-voltage transformers in a Delta-Delta configuration. The figure below is an exact replica of the current wiring of the system. The utility provided neutral comes straight from the pole while the primary lines consist of 15kV shielded cable with terminations that are grounded as per the diagram as well as at the primary fused disconnect (some 250' away with its own GEC) and again at the pole terminations to a ground rod at the base of the pole.
My main question is regarding the use of the utility supplied neutral. It's connected to a single transformer grounding lug. That same transformer also has an additional EGC attached to a different grounding lug, which is connected in series to grounding lugs on the other two transformers and on to the same grounding point as HV cable shield grounds and the secondary center tap ground. I'd yet to come across this configuration and would appreciate any comments as to if this seems correct or not or, better yet, what logic, if any, would be behind this.
Thanks in advance for your input!
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