National Electrical Installation Standards

Standards as High as Your Own

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Monday, November 11, 2019

Question:

I have a stepdown transformer 480V-120V. Usually for single phase, 120 Volts is line to neutral, is there any code violation per NEC 250.26 if the connection is 120 Volts line to line, both conductors are ungrounded?  

Jesus Santos
A

Answer:

Hey Jesus thanks for your question. A Neutral Conductor only exists if it is connected to a Neutral Point as those terms are defined in Article 100. If the transformer secondary (120 volt) only has two termination points there is no neutral point therefore no neutral conductor.

If the transformer is used to supply Premises Wiring, as that term is defined in Article 100, the 120 volt secondary must be grounded as stated in 250.20(B)(1). The conductor you ground becomes the Grounded Conductor also as it is defined in Article 100. There are special conditions for systems to not be grounded such as in 250.21 and 250. 22.

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