I have a question on a GDT connected in series with an MOV in Type A pluggable equipment and how this construction impacts application of 5.5.7, G.8.1 in the context of post production Hi-Pot testing at 1.5 kv.
More specifically you asked:
IEC 62368-1 requires a GDT to be connected in series with any MOV used in a L-PE and N-PE protection for the usual Type A pluggable equipment (5.5.7) and the GDT used must withstand the Basic Insulation voltage withstand requirement (126.96.36.199, 2.5 kV for 230 V a.c.).
Given the GDT requirement, was it the intention of IEC 62368-1 to render the tests of G.8.1, G.8.2 and G.8.3 benign, so that no testing is necessary, and the post production Hi-Pot test of 1.5 kV a.c. can be passed with ease?
In response, the submitted question on SPD requirements per 5.5.7 and Varistor requirements per Annex G.8 of IEC 62368-1 appears to be combining or confusing considerations for Type investigation/test requirements and Routine electrical safety testing in production. This is not the intent of IEC TC108.
Since the focus seems to be with the GDT, specifically per 5.5.7, the GDT is required to comply with the electric strength test of 188.8.131.52 for basic insulation; and the external clearance and creepage distance requirements of 5.4.2 and 5.4.3 respectively for basic insulation.
For a Type investigation/test, this testing on the GDT is performed on the GDT and not the entire product. Therefore, compliance with the GDT with 5.5.7 can be wholly determined during the Type investigation.
Similarly, compliance with Annex G.8 for the Varistors can be determined during the Type investigation.
Regarding Routine testing, generally this testing is conducted to detect manufacturing failures (e.g., miswiring in product) and unacceptable tolerances in manufacturing and materials. In fact this is stated in the Scope of IEC 62911, Audio, video and information technology equipment – Routine electrical safety testing in production,also produced by IEC TC108.
The intent of Routine testing is not to attempt to reconfirm compliance of the equipment with every requirement considered during the Type investigation/testing.
IEC 62911 also states in Clause 4, Conformance, “Practical measures can be used to conduct the test, such as finding an appropriate way to make the connections necessary to perform the relevant test.” This principle often has to be applied during Routine testing due to the variety of equipment and constructions subjected to the limited routine tests (typically limited to resistance of protective bonding and electric strength).
However, in the case of a GDT & Varistor in series, during Routine testing on a product level there would be nothing gained from a safety perspective attempting to conduct a mains to protective earth electric strength test under special conditions, so typically the GDT & Varistor are tested in the product without modification even if it means that part of the circuit, including MOV, may not experience the full 1.5 kV electric strength test during routine test.
If there are concern with the current set of requirements in either IEC 62368-1 or IEC 62911, it is recommended that IEC TC108 be engaged via participation in your national committee.