National Electrical Installation Standards

Standards as High as Your Own

Tuesday, October 10, 2017


Could you clarify what is meant when Table 110.26(A)(1) refers to "insulating materials". Thanks a whole lot more than you will ever know!

John James



Hey John thanks for your question and the kind words. We published an answer to a similar question on Friday January 27, 2017. The concept of effectively guarded by insulating materials applies to live parts on both sides of the work space as described in Table 110.26 (A)(1) Condition 1 so materials with rated electrical insulating properties would be suitable.

The wording describing Condition 2 in Table 110.26(A)(1) uses the phrase "grounded parts on the other side of the working space". The last sentence indicates that concrete, brick, or tile walls are considered as grounded. If gypsum board (drywall), wood or some other suitable material was used to cover the concrete wall that was on the other side of the working space most AHJ's would probably consider the Condition 1 distances to be acceptable.

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