Must external protective earthing conductors be provided with a Class I permanently connected equipment powered by DC mains, or may use of such PE conductors be indicated in user documentation?
More specifically you asked: For permanently connected equipment powered by DC mains, using an external protective earthing conductor: Is the manufacturer expected to provide this protective earthing conductor as part of the equipment or can the specifications and/or use of such a conductor be stated in the user documentation?
There is a variety of equipment types powered by DC mains, so we cannot answer your question in great specificity in this public Q&A platform. Therefore, we recommend you contact UL for an in-depth engineering consultation based on specific product details and information.
However, in general, yes, permanently connected equipment may have a protective earthing conductor that is installed in the field by skilled persons (electricians).
Such field wiring can consist of both line conductors and PE conductor(s). Electricians who install the equipment will provide suitable wiring materials necessary for the supply and PE connections in accordance with the installation instruction associated with the equipment (and in accordance with national/local electrical codes). However, proper interface with the electrical system (mains) is required as part of the equipment, including not only the instructions, but also proper terminal sizes, etc.
In IEC 62368-1:2018, appropriate requirements primarily are in 5.6, Protective Conductor. Equipment can either be shipped with the appropriate PE conductor(s) complying with the relevant requirements in 5.6, or be provided with installation instructions so that the installers can select proper wiring material for the field installation.
In CSA/UL 62368-1, appropriate National Differences that reflect the US and Canadian electrical codes are in Regulatory Annex DVA, 5.6, including the provision that “Equipment intended to be connected to a nominal 48 V d.c. (or higher) power supply source, or systems rated less than 48 V d.c. that have one point directly earthed (grounded), shall have provision for the earthing (grounding) of all exposed dead metal parts that might become energized from the power supply source or from circuits involving a risk of electric shock.” Additional National Differences are in Annex DVH, Requirements for permanent connection, and associated Marking and Instruction requirements in Annex DVK.