National Electrical Installation Standards

Standards as High as Your Own

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Tuesday, January 11, 2022

Question:

Hello CQD,

Are enclosures of equipment installed for and supplied by ungrounded A/C systems required to be marked to indicate that? What NEC rule applies.

Thanks for any help you can provide.

Bill Cole

A

Answer:

Hi Bill,

Section 250.21(C) indicates that ungrounded systems shall be legibly marked “Caution: Ungrounded System Operating — _____Volts Between Conductors” at the source or first disconnecting means of the system. The marking shall be of sufficient durability to withstand the environment involved.

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