Please forgive me but I have no intention to analyse the Minnesota OSHA laws. This is extracted from the current FedOSHA Regulations:
1910.303(a)
Approval. The conductors and equipment required or permitted by this subpart shall be acceptable only if approved, as defined in Sec. 1910.399.
1910.399 (Definitions)
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Approved. Acceptable to the authority enforcing this subpart. The authority enforcing this subpart is the Assistant Secretary of Labor for Occupational Safety and Health. The definition of "acceptable" indicates what is acceptable to the Assistant Secretary of Labor, and therefore approved within the meaning of this subpart.
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Acceptable. An installation or equipment is acceptable to the Assistant Secretary of Labor, and approved within the meaning of this Subpart S:
(1) If it is accepted, or certified, or listed, or labeled, or otherwise determined to be safe by a nationally recognized testing laboratory recognized pursuant to ? 1910.7; or
(2) With respect to an installation or equipment of a kind that no nationally recognized testing laboratory accepts, certifies, lists, labels, or determines to be safe, if it is inspected or tested by another Federal agency, or by a State, municipal, or other local authority responsible for enforcing occupational safety provisions of the National Electrical Code, and found in compliance with the provisions of the National Electrical Code as applied in this subpart; or
(3) With respect to custom-made equipment or related installations that are designed, fabricated for, and intended for use by a particular customer, if it is determined to be safe for its intended use by its manufacturer on the basis of test data which the employer keeps and makes available for inspection to the Assistant Secretary and his authorized representatives.
The definitions (1910.399) are not actually ?in order.? I underlined a few things to put them in relevant order though. (The installation must be ?approved? ? ?approved? must be ?acceptable? ? the ?acceptable? laundry list)
If you can demonstrate that there is no equivalent listed product that meets your needs, the Minnesota equivalent to ?Acceptable (3)? may indeed be appropriate.