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Does a 480D-600/346Y transformer have to be center tapped grounded if not utilizing the lower volt?

Does a 480D-600/346Y transformer have to be center tapped grounded if not utilizing the lower volt?

Does a 480D-600/346Y transformer have to be center tapped grounded if not utilizing the lower volt?

(OP)
We have a 150 kVA dry type transformer that is a part of a bigger packaged unit. That question came up.
The transformer case will be bonded, there will be equipment grounding conductors run between the panel feeding it and the transformer.

Looking at the NEC 250.4 ... it doesn't appear this is required.

RE: Does a 480D-600/346Y transformer have to be center tapped grounded if not utilizing the lower volt?

It doesn't have to be grounded. Marine electrical installations don't typically ground the 480v system. The do however have some sort of fault monitoring such as ground fault indicating lights as well as an engineer on duty monitoring thee system. Marine systems are ungrounded so that a fault does not cause a trip.

RE: Does a 480D-600/346Y transformer have to be center tapped grounded if not utilizing the lower volt?

I think you need to look at the System Grounding section. See 250.20 and 21.

RE: Does a 480D-600/346Y transformer have to be center tapped grounded if not utilizing the lower volt?

"...Does a 480D-600/346Y transformer have to be center tapped grounded if not utilizing the lower volt?..."I have the following opinion for your consideration.
1. Your transformer is Dyn i.e. primary in Delta Line-to-Line =480V. The secondary in Star Line-to-Line = 600V, Line to Neutral = 346V. There is a Neutral terminal, but NOT distributed (i.e. No single-phase load)
2. NEC Art 250 is on Grounding.
Note: 1. Art 250-20 (b) (2) is NOT applicable.
2. Art 250-21 applies, depending on the application ....
3. In general,
a) the trafo core should be bonded to its casing. This casing should be bonded to the Panel. The Panel should be bonded to the Ground bar from the other Panels.
b) The Neutral may/may not be Bonded to the Ground bar. However, for land boards , it is preferred to connect the Neutral to the Ground bar solidly. For marine boards , which NEC does NOT apply, the Neutral is very often left open (i.e. isolated from Ground and NOT distributed/used).
Che Kuan Yau (Singapore)

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