National Electrical Installation Standards

Standards as High as Your Own

Tuesday, March 12, 2019


Re: CQD answer published February 21 & March 1, 2019 -Isolated Phase Conductors

Charlie, Most code experts say that the only time you can use an isolated phase installation is per the Exception to 300.3(B)(1). This installation does not appear to be an underground installation. Note, that I don't agree with those experts that say you can only install an isophase installation underground. It appears to me that the language in 300.3(B)(3) would permit it anywhere you want to use it.

Don Ganiere



Hey Don thanks for your comment, you make a good point and it's good to hear from you. The exception to 300.3(B) is limited to underground installations but the wording in 300.3(B)3 has different conditions and is not limited to underground installations.

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