Code Change Summary: New code language provides clarity on transformers and enclosures used at Marinas, Boatyards, Floating Buildings, and Commercial and Noncommercial Docking Facilities.

In the 2017 NEC^®, transformers used in the areas covered within the scope of Article 555 were only required to be approved for the intended location, with the bottom of the transformer enclosure installed not below the electrical datum plane.

In the 2020 NEC^®, transformers and enclosures shall be identified for wet locations. The bottom of transformer enclosures shall not be located below the electrical datum plane.

According to Article 100 definitions, the electrical datum plane is a specified distance above a water level above which electrical equipment can be installed and electrical connections can be made. In 555.3, the actual distances required for the electrical datum plane are specified as follows:

555.3 Electrical Datum Plane Distances.

(A) Floating Piers. The electrical datum plane for floating piers and boat landing stages that are (1) installed to permit rise and fall response to water level, without lateral movement, and (2) that are so equipped that piers and landing stages can rise to the datum plane established for 555.3(B) or (C), shall be a horizontal plane 762 mm (30 in.) above the water level at the floating pier or boat landing stage and a minimum of 305 mm (12 in.) above the level of the deck.

(B) Areas Subject to Tidal Fluctuations. In land areas subject to tidal fluctuation, the electrical datum plane shall be a horizontal plane that is 606 mm (2 ft) above the highest tide level for the area occurring under normal circumstances, based on the highest high tide.

(C) Areas Not Subject to Tidal Fluctuations. In land areas not subject to tidal fluctuation, the electrical datum plane shall be a horizontal plane that is 606 mm (2 ft) above the highest water level for the area occurring under normal circumstances.

Below is a preview of the NEC^®. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC^® edition of NFPA 70.