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Old 11-27-2019, 03:17 AM   #1
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Default 480/12kv ungrounded delta

Taking on a barn rewire, property has an interesting service. Utility provided 600a 480 service at road. MDP feeds a 480vΔ-12kvΔ 500kva xfmr. Feeds a 225kva 12kvΔ-480vΔ transformer about 1/4 mile away. Distribution from the padmount is 480Δ splitting out to 75kva 480Δ-208Y transformers at each building. All 480 and 12kv is ungrounded delta.

At the barn location there are three spare 1/0 thhns already pulled in a handhole, no egc. Wanting to install a 75kva 480Δ-208Y xfmr there. I would think an EGC would be needed to be pulled back to the 480v panel? No ground fault alarm is installed, and no EGCs are present other than the concentric neutrals on the 15kv URD which are tied together to the ufer and transfomer frames at both ends.

Pull a ground and install a ground fault detector?
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Old 12-03-2019, 04:33 PM   #2
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There is a lot of waste in those transformer sizes...

You are not running any 480V, other than the transformer connections, right? Your service from the utility is their problem, not yours, so if it is 480V corner grounded delta, you are fine. If it is ungrounded delta, you will need to either corner ground it or add the GF monitoring in order to feed the transformer. The 12kV circuit does not need grounding. Your barn would then be an SDS, so you would have a GEC there for making that 480V a corner grounded delta too, or put in a GF monitor there (too). Why all the delta stuff? makes it harder to deal with IMHO.
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