Does Article 250 permit a solid corner ground on a 480 Volt Delta secondary transformer winding? In this application a 750kVA, 208V Delta to 480V Delta step-up transformer is used in a high-rise commercial office building. Its purpose is to step up the system voltage to more efficiently carry power a long distance up the high-rise building, where it is then stepped back down through a 480V Delta to 208Y/120 step-down transformer. I'm having difficulty determining whether such an application is code compliant. Should the 480V system be grounded, ungrounded or impedance grounded? All opinions are welcome. Thanks.
Art. 250 - Corner Grounded Delta
- Thread starter bigapple
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Re: Art. 250 - Corner Grounded Delta
There is no code requirement that this system be grounded. This system can be ungrounded, soldily grounded or impedance grounded. It is a design choice. See 250.20(B), 250.21(4) & (5), and 250.36.
Don
There is no code requirement that this system be grounded. This system can be ungrounded, soldily grounded or impedance grounded. It is a design choice. See 250.20(B), 250.21(4) & (5), and 250.36.
Don
Re: Art. 250 - Corner Grounded Delta
This building is in Manhattan, where the service voltage is dictated by the utility (Con Edison). In some areas of Manhattan Con Ed only provides 208Y/120V. It is not unusual to see large 208-480V step-up transformers specified when buildings undergo electrical renovations. Typically, however, the transformers are 208 Delta to 480Y/277V and the 480V secondary is solidly grounded.
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