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I am trying to determine how to determine compliance of a construction to the requirements in sub-clause 5.6.5 and Table 32 involving a 3.5mm sheet metal (spaced thread) screw or smaller, with a 1mm2 protective earthing conductor or smaller?

More specifically you asked: In sub-clause, Table 32,  shall protective earthing terminals be over or equal 3.5mm for screw types when a protective earthing conductor is less than 1mm2?  Additionally, in UL 62368-1, Annex DVA (5.6) ND requires that sheet metal (spaced thread) screws shall not be used. How to understand spaced thread screws? I also check the definition in NEC.250.8 - "Spaced thread "means thread over two. I would like to understand whether only screw types with min two thread and 3.5mm dimension may be used with protective earthing conductors less than 1mm2?


In response, clause 5.6.5 includes requirements for terminals connecting PROTECTIVE EARTHING CONDUCTORS and PROTECTIVE BONDING CONDUCTORS.


Terminals for PROTECTIVE EARTHING CONDUCTORS shall meet the requirements in Table 32.  Terminals for PROTECTIVE BONDING CONDUCTORS can comply with more options and are not discussed here since they were not mentioned in your question.


You asked the min. terminal size in Table 32 for protective earthing conductors under 1 mm2.  As you noted, there are no smaller terminals than 3.5 mm thread diameter considered for such protective earthing conductors. Therefore, a screw terminal for protective earthing conductor smaller than 1 mm2 is required to have min. 3.5 mm thread diameter.  This is because, if we look at, the PROTECTIVE CURRENT RATING of the equipment almost always has to be factored into the determination, regardless of the RATED CURRENT of the equipment. For equipment with a small RATED CURRENT, in almost all cases the PROTECTIVE CURRENT RATING of the equipment will not allow less than a 1 mm2 conductor size for the PROTECTIVE EARTHING CONDUCTOR.


Regarding the National Difference in DVA (5.6), the key conclusion is that ‘sheet metal screws’ are not permitted for the termination of the PROTECTIVE EARTHING (and BONDING) CONDUCTORS, regardless of the number of threads engaging the metal.  The discussion of the different screws types asked about in your inquiry, because of the detail involved, is beyond what can be discussed in this sort of forum.  


For a detailed analysis of your construction, 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.

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