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Typically the AHJ will prefer the use of listed materials and equipment, because listing means they have been evaluated by an independent agency. If material or equipment used in an installation is not listed Perhaps because it may not be available as a listed product or because there may not be a product standard for evaluation of that particular item., Section 110.3(A) provides a list of eight considerations that should be used in judging equipment.
The AHJ can use this list of eight criteria in Section 110.3(A) to determine whether or not materials or equipment should be approved. Someone who is seeking approval from the authority having jurisdiction might also use this list to provide information to the AHJ to show that the issues in the list are all addressed somehow with regard to safe application and use of that particular item of equipment.
The NEC requires that some equipment be listed, such as Type NM Cable (Section 334.6), flexible metal conduit (Section 348.6), electrical metallic tubing (Section 358.6), and all luminaires (Section 410.6). Some things like conduit straps or staples for cables may not be available as listed products. AHJs will require many items to be listed because they cannot properly evaluate the equipment in the field.
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