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Thursday, January 26, 2017
Question:
Charlie,
My question is two part:
1) What is considered “Effectively Guarded by Insulating Materials”?
2) What would have to be done to a Concrete Wall to permit it to go from a Condition 2 to a Condition 1 rating according to Table 110.26 (A)(1)?
Thanks, Richard
A
Answer:
Hey Richard thanks for your question.
The word "guarded" is defined in Article 100 and in part means that something is "protected in a way that removes the likelihood of approach or contact". The word effectively is not defined in the NEC so we can use a standard dictionary definition such as "to achieve a result" or "accomplish a purpose". The words "wood or other" [before insulating materials] was removed during the 2005 NEC process based on substantiation that it was redundant and an old practice that wasn't still necessary. See 1-208 in the Report on Proposals (ROP) for the 2005 NEC for more information. Notice 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.