Regulatory considerations for 500W, 400V DC power tether
You need to comply with the safety codes where the equipment will be used. That means the state, county and perhaps city electrical code. Those codes are based on the National Electrical Code (NEC) but contain some additions and may contain some exceptions. You need to study the codes carefully for industrial use exemptions. NEC requires equipment to be acceptable to the authority having jurisdiction(AHJ). The NEC has provisions calling for listing and labeling by a nationally recognized testing laboratory (NRTL). The Occupational Safety and Health Administration (OSHA) maintains a list of NRTL's. UL and ETL are the most well known electrical NRTL's on that list. Although there may be several NRTL'S to choose from, most of the applicable standards are published by UL. Regardless of which NRTL you may want to use, you probably need to get advice from someone who is familiar with UL standards. You can probably find a consultant to advise you. It is best to get advice during design rather than after the design is substantially complete. For an industrial establishment, OSHA requirements may be the primary concern. The local AHJ may defer to OSHA. You may also want to talk to your insurance underwriter.