What are the requirements for internal and external wiring acc. IEC 62368-1 3ed. and UL 62368-1 3ed.?
More specifically you asked: I am seeking product certification to IEC 62368 and have come up against the wire flammability issue - I note the existing answer regarding equivalence with VW-1, but what about superior standards - such as CL2? Is there a means by which CL2 being superior (i.e. NEC allows substitution) to VW-1 allows me to demonstrate compliance with 62368?
In response, as you inferred the note under sub-clause 6.5, Internal and external wiring, in the IEC 62368-1 3ed., as well in the UL 62368-1 3ed., accepts UL 2556 rated VW-1 wires to demonstrate compliance with 6.5.1 as an alternative method.
In addition, for external wiring according to the US / CAN Deviations under 4.1.17DV.1, External interconnecting cable and wiring, it is to be investigated to the requirements of sub-cl. 6.5 and either 4.1.17DV.1.2 or 4.1.17DV.1.3, depending on the cable length.
External interconnecting cable and wiring 3.05m or less may be investigated as part of the equipment (system) to the requirements of this standard, depending on the PS circuits involved:
- external interconnecting cable and wiring connected to PS2 or PS3 circuits, the flammability requirement of 6.5 applies;
- there are no flammability requirements for external interconnecting cable and wiring in PS1 circuits.
Other external interconnecting cable and wiring exceeding 3.05m in length are required to comply with 4.1.17DV.1.3, including the references to the Canadian Electrical Code, Part I, CSA C22.1, and the National Electrical Code, NFPA 70 under Annex DVA (Annex Q), where CL2 Listed Cables are allowed to be used in Class 2 and LPS circuits.
Such CL2 cables are UL Listed as Power Limited Circuit Cable (QPTZ), information for which can be found in the UL Product iQ - https://iq.ulprospector.com/en/profile?e=210650 .
Please note, CL2 cables are subjected to a Vertical-Tray Flame Test in UL 1685, "Vertical-Tray Fire-Propagation and Smoke-Release Test for Electrical and Optical-Fiber Cables," which is a more onerous test than VW-1. Therefore, if a manufacturer wanted to also substitute Listed CL2 cables for internal wiring or external cabling not exceeding 3.05m in length, that would be considered acceptable too, as long as the circuit were Class 2 or LPS. However, most manufacturers choose not to do so due to cost considerations.
The complete answer to this topic is complex, and there appears to be a specific, detailed construction that needs review/analysis. Therefore, you are encouraged to contact UL for an in-depth consultation, either via your local account executive or via https://62368-ul-solutions.com/contact-ul.html