IEC 62368-1: Ask the Engineers, Question-and-Answer Page

More specifically you asked (edited for clarity): I am currently developing a bass reflex subwoofer speaker which is driven by a PS3 amplifier output. The subwoofer shall comply with UL 62368-1. However, because of that, one could think that the driver itself needs to be housed within a fire enclosure against the spread of fire. This would limit the maximum hole size on the front grille to a maximum of 3mm if the speaker is oriented top down and the grille holes become bottom openings. Is there an exception of this rule for loudspeakers?

In response, a fire enclosure is the primary safeguard for protection against fire when relying on the “control fire spread” method covered in sub-clauses 6.4.4, 6.4.5 and 6.4.6 of UL 62368-1:2019. However, there is another method of investigation allowed for by sub-clause 6.4.1 of UL 62368-1:2019, which is the “reduce the likelihood of ignition” method, covered by sub-clauses 6.4.2 and 6.4.3. In the application of the “reduce the likelihood of ignition” method, a fire enclosure, including opening size limitations for different orientations, is not required. However, via performance testing, the equipment needs to demonstrate that no internal parts have sustained flaming. According to Annex B.4.6, loudspeakers shall be short-circuited or disconnected, whichever is more unfavorable. Also noteworthy, per sub-clause 6.4.1, this method only is permitted for circuits in which the available steady state power does not exceed 4,000 W, such as most applications of pluggable equipment type A.

Note too, UL 62368-1 Ed.4 remains under development and likely will be published in the second half of 2024.  It will be based on IEC 62368-1:2023, for which we would like to provide some additional information for your reference. There are many changes related to loudspeaker drivers and assemblies in IEC 62368-1:2023, such as in sub-clauses 3.3.6.11, 6.3.1, 6.4.5.2, 6.4.6, and 6.4.7.1. In fact, it states in sub-clause 6.4.6 that a fire enclosure is not necessary for loudspeaker drivers/assemblies. This change in Edition 4 provides some design relief for manufacturers of loudspeaker drivers and assemblies without compromising safety due to the unique design requirements for such loudspeaker drivers and assemblies and lack of any field incident data, which also is consistent with past practice under IEC 60065. 

As this forum is not intended to analyze and provide guidance on specific designs, we recommend that you contact UL Solutions and request an engineering engagement if you have a specific design or construction that you would like to discuss.

More specifically you asked (edited for clarity): For Class I equipment, Basic Insulation should be applied between AC input (ES3) and Grounded metal enclosure, and Reinforced Insulation should be applied between AC input (ES3) to unearthed ES1 conductors or circuits (e.g., USB port +5Vdc power rail since it cannot meet protective bonding requirements). However, there is a high probability of a failure when you apply the 4000Vdc (Reinforced Insulation) Hi-pot test between AC input and USB port +5Vdc power lead, even though the 2500Vdc (Basic Insulation) Hi-pot already passed between AC input and Enclosure since most designed-in spacings between +5Vdc and GND are very close (5-10mils). (Basic Insulation + Functional Insulation is not equivalent to Reinforced Insulation.) How do I understand and address this requirement? Is there any different assessment/requirement when the USB port is accessible versus inaccessible?

In response, when considering electrical insulation between mains and external circuits (classified per sub-clause 3.3.1.1 of IEC 62368-1:2018), if unknown devices can be connected to the external circuits, the external circuits should be considered accessible because it is assumed that users may access the circuits in the unknown devices. Therefore, all conductive pins of USB connectors should be classified as accessible when applying the electrical insulation requirements in IEC 62368-1.

Regarding electric strength (Hi-pot) testing, we note that generally it is only applied to solid insulation investigated to sub-clause 5.4.4, although it is permitted as an alternative method to also meet some Clearance requirements per sub-clause 5.4.2.  Also, in accordance with sub-clause 5.4.9.1, “For equipment incorporating basic insulation and supplementary insulation in parallel with reinforced insulation, care is taken that the voltage applied to the reinforced insulation does not overstress basic insulation or supplementary insulation.”  Therefore, generally, the electric strength test should not be applied to a complete system of Basic, Supplementary and Reinforced insulation, but should be applied separately to each individual insulation.

If applied to the complete system, and the electric strength tests reveal insulation breakdown, root causes could include insufficient safeguards or overstressed Basic or Supplementary Insulation (breakdown through the parallel path). In this situation, insulation should be individually tested and insulation that is not being specifically tested may be disconnected and separately tested according to sub-clause 5.4.9.1 of IEC 62368-1:2018.  In your case, only insulation defined as Reinforced Insulation should be subjected to the electric strength testing for Reinforced Insulation. 

As this forum is not intended to analyze and provide guidance on specific designs, we suggest that you contact UL Solutions requesting an engineering engagement if you have a specific design or construction that you would like to discuss.

In response, the tests in Annex G.13.6 of UL 62368-1 are not applicable for coated printed boards with a UL recognized conformal coating (CCN:QMJU2) applied in accordance with the coating’s ratings and Conditions of Acceptability. In Annex DVF (G.13.6) of UL 62368-1,  conformal coatings complying with UL746C (which refers to UL746E) are identified as an acceptable alternative to G.13.6 and IEC 60664-3. Thus, no additional tests from Annex G.13.6 are required for coated printed boards with such a UL recognized conformal coating being used. However, please note, the allowances covered in Annex DVF, UL and CSA component requirements (alternative to IEC standards), only apply for certifications associated with Canada and the U.S. If the same product would be covered by an IECEE CB Report investigated to IEC 62368-1, testing per Annex G.13.6 would be required.

More specifically you asked (Edited): In Edition 3, for determining a clearance, Table 10 should be used for the switching frequencies not exceeding 30 kHz and Table 11 for those exceeding 30 kHz. Since most power supplies would generate switching frequencies greater than 30 kHz, Table 11 is necessary to follow. For an overvoltage category II, PD 2, Material Group III, this value jumps from 1.27 mm in Table 10 and to 13.2 mm in Table 11 for > 30kHz. Please let me know if my understanding is correct. Also please confirm, whether these "switching frequencies" are of the "mains voltage" or of the "working voltage" of the power supply? Primary? Secondary?

In response, for determining Clearances per 5.4.2, the highest value of two procedures is used. Your question is specifically related to Procedure 1, determining Clearances according to 5.4.2.2, which considers the highest voltage of either the Working Voltage (across the Clearance), Recurring Peak Voltages, and the Temporary Overvoltage.

More specifically, the highest voltage is used to determine the Clearance, using Table 10 for circuits with fundamental frequencies up to 30 kHz, Table 11 for circuits with fundamental frequencies higher than 30 kHz, and both Tables 10 and 11 for circuits where both frequencies lower and higher than 30 kHz are present.

When Table 10 applies, the temporary overvoltage 2000V should be considered, and for the conditions you stipulated, we confirm a 1.27 mm Clearance would be the resulting minimum Clerance for basic or supplementary insulation.

When Table 11 applies, which is only applicable for those voltages with working frequencies higher than 30 kHz, the voltage associated with the switching frequency generated from pulse-width modulation (PWM) in the primary circuit of the power supply should be applied rather than a temporary overvoltage, which does not have a frequency higher than 30 kHz.

Therefore, the clearance result you indicated of 13.2 mm (based on a temporary overvoltage value of 2000V used in Table 11) would be incorrect. Generally, most applications of switch mode power supplies would result in a peak working voltage in the primary circuit not exceeding 1000 V, resulting in a Clearance from Table 11 of 0.6 mm for basic or supplementary insulation.

However, the highest clearance values of Table 10 and Table 11 should be chosen for circuits where both frequencies lower than 30 kHz and higher than 30 kHz are present in Procedure 1. Therefore, the result from Table 10, 1.27 mm Clearance would be the highest for the Procedure 1. However, values per Procedure 2 also need to be considered as part of the final determination.

We expect you would find very helpful subclause 5.4.2 of IEC TR 62368-2:2019, which is the Technical Report (TR) containing explanatory information on IEC 62368-1 and is often known as the ‘Rationale Document.’ This sub-clause 5.4.2 contains a very good flowchart / worked example on the application of the Clearance requirements.

More specifically you asked: UL 62368-1 F.3.3.9DV.1 requires that output terminals provided for supply of other equipment except mains supply shall be marked with the nominal output voltage and frequency and, in addition, the maximum output current or power, unless the terminals are marked with the type references of the equipment which are permitted to be connected. If this requirement is applied to standardized computer interfaces / connectors such as a USB-C PD port, what voltage and frequency shall be marked on the product given the range of DC (0 Hz) voltages that might produce based on negotiation with an attached device?

In response, National Difference F3.3.9DV.1 has been in CSA UL 62368-1 since its Edition 1 (F.3.3.8DV.1) and is intended to apply to equipment with ‘terminals’ (e.g., Field Wiring Terminals) that need to be hard-wired to supply power to other equipment. Therefore, this requirement does not apply to standardized computer interfaces / connectors supplying power to other AV/ICT equipment, such as a USB PD port, which supplies power to other AV/ICT equipment in close proximity.  For a USB PD port, which is a standardized interface, the importance of communicating the information required for terminals that is in F.3.3.9DV.1 is less important.

However, we make note, for interfaces connected to “building wiring”, including PoE, there are requirements in Article 725, Class 2 and Class 3 Power-limited Circuits, that would apply to these standardized interfaces / connectors, such a PoE. In the 2023 NFPA 70, National Electrical Code (NEC), its Section 725.60(C), Power Sources for Class 2 and Class 3 Circuits - Marking (Section 725.121(C) of the 2020 NEC) contains a marking requirement that includes information similar to F3.3.9DV.1. In CSA UL 62368-1, see Annex DVA (Q), Power sources for Class 2 circuits, for more details on the marking as it applies to AV/ICT equipment with PoE.

More specifically you asked: For an EPS (i.e., External Power Supply/Adapter) with no charging control circuit (i.e., has no way to monitor the temperature of the battery to stop the charging if the battery exceeds its maximum charge temperature) that is used to charge external Lithium-Ion batteries directly, when such EPS submitted for IEC 62368-1 evaluations, does Annex M.4 of IEC 62368-1 apply?

In response, we believe an important clarification may be in order. The question mentions the EPS charges “external Lithium-Ion batteries directly.” IEC 62368-1 applies to AV/ICT systems and components. It would not apply to an EPS within a larger system submitted for certification intended to charge generic Lithium-Ion batteries (e.g., 18650) for general applications, such as a system consisting of an EPS and battery cradle/charger for external batteries. While the EPS may be submitted for certification to an IEC 62368-based standard (which at the time of the submittal the intended system may be unknown), there are other IEC and UL standards (e.g., UL 1310, UL 1012) that would be used for such general Lithium-Ion battery charging applications.

For Annex M.4 of IEC 62368-1, it is applicable to those EPSs so designed for charging specific Lithium-Ion batteries used together with specific AV/ICT equipment and that can be evaluated (tested) as a system.

As this forum is not intended to analyze and provide guidance on specific designs, we suggest that you contact the UL Solutions office you work with and send in a request for an engineering engagement if you have a specific design or construction that you would like to discuss.

More specifically, you asked (edited for clarity): Can you advise if batteries under the new version of UL 62368-1 are required to have a UL 94 V-2 or higher flammability rating to comply with the latest regulations for the NA market? Also, are legacy compliant end product systems required to have a metal housing to comply with the LVD / IEC / UL changes when the battery has a rating of UL 94 HB? It would be helpful if a document was released to share with installers. Also, as the January 2024 deadline approaches, will there be audits (recertification) required to determine compliance with the latest requirements, or in doubt, is it best to use of a flame-retardant batteries with a UL 94 V-2 rating or higher to ensure it meets the regulations?

In response, both the battery and product details in your question are not descriptive enough to be able to provide a precise response.  However, we will assume that the batteries being asked about are secondary (rechargeable) lithium batteries used in Class III AV/ICT equipment.

First, let’s clarify, the effective date of UL 62368-1 Edition 3 (based on IEC 62368-1:2018) has been postponed to July 6, 2024 (18 months after the originally announced date - January 6, 2023, not January 2024).  Detailed information related to the UL 62368-1 Effective Date is available via UL.com at: https://www.ul.com/resources/ul-62368-1-effective-date-information.

Related to fire enclosures for secondary lithium batteries, per Annex M.4.3 in UL IEC 62368-1 Edition 3, secondary lithium batteries should be provided with a fire enclosure according to Clause 6.4.8,  which may be that of the secondary lithium battery itself, or of the cell, or a combination of cells, or may be that of the equipment containing the secondary lithium battery.

Note, the latest version of the standard, IEC 62368-1:2023 (Ed 4), has more details in Annex M.4.3 on battery fire enclosures.  More specifically, the fire enclosure, in the case where it is part of the battery itself, should either comply with Annex S.1 (flammability testing on the battery), or be made of V-1 class material (via preselection), or be made of non-combustible materials (e.g., metal). In the case where the fire enclosure is established by the end product enclosure, the cells are considered a resistive PIS and the material of the fire enclosure should comply with Clause 6.4.8, which may result in a higher flammable class V-0 for combustible materials if the spacing from the resistive PIS is less than 5 mm. However, there remains an exemption from the fire enclosure requirement for secondary lithium batteries if the cell or a combination of cells comply with PS1.

Since you mentioned V-2 material, we would like to make special note that batteries using combustible materials with a V-2 class casing generally are not acceptable when a fire enclosure is required for secondary lithium batteries. Typically, a material of V-1 class or better would be required (per 6.4.8).

As battery fire enclosure requirements in UL IEC 62368-1 can be complex, and there appears to be a specific, detailed construction that needs review / analysis, we encourage you to contact UL Solutions for an in-depth engineering consultation.

Class X capacitors are suitable for use in designs where failure of the capacitor would not lead to increased risk of electric shock. If a capacitor is connected between line and neutral of the primary circuit connected to the mains supply, the failure, e.g., short-circuit, of the capacitor would not be expected to increase the risk of electric shock because the insulation bridged by the capacitor is considered functional insulation, even in this case if it is located upstream of the line fuse in the power supply unit.  Therefore, a Class X capacitor can be used for this construction and a Class Y capacitor should not be required at the location in question.  See Sub-clauses 5.5.2 and G.11 in IEC 62368-1:2018 for more details.

In response, since there are no product details provided with your question, including what type of lead-acid batteries (e.g., VRLA, flooded, etc.) are used and what type of AV/ICT equipment will the batteries be installed within, the response to your inquiry will rely mainly on quoting the requirements in IEC 62368-1:2018 that address AV/ICT equipment with lead-acid batteries.

However, first, the simple answer to your question is, yes, IEC 62368-1:2018 (and IEC 62368-1:2023) covers AV/ICT equipment containing lead-acid batteries.

On the component level, lead-acid batteries used in AV/ICT equipment should comply with the applicable component standards noted in Annex M.2, such as IEC 60896-11 (Stationary Lead Acid Batteries – Part 11 – Vented type); IEC 60896-21 (Stationary Lead Acid Batteries – Part 21 – Valve regulated type – method of test); IEC 61056-1(General purpose lead-acid batteries (valve-regulated types) – Part 1: General requirements, functional characteristics – Methods of test); and IEC 61056-2 (General purpose lead-acid batteries (valve-regulated types) – Part 2: Dimensions, terminals and marking).

Table 17, Safety of batteries and their cells - requirements (expanded information on documents and scope), of IEC TR 62368-2, Audio/video, information and communication technology equipment – Part 2: Explanatory information related to IEC 62368-1:2018, provides a good overview of the standards in Annex M.2 that cover lead-acid batteries.

On the equipment level, the requirements for equipment with lead-acid batteries are included in the following Annex M sub-clauses: (a) Annex M.3 - protection circuits for batteries provided within the equipment; (b) Annex M.5 – risk of burn due to short-circuit during carrying; (c) Annex M.6 – safeguard against short-circuits; (d) Annex M.7 – risk of explosion from lead acid and NiCd batteries; (e) Annex M.8 – protection against internal ignition from external spark sources of rechargeable batteries with aqueous electrolyte; (f) Annex M.9 – preventing electrolyte spillage; and (g) Annex M.10 – instructions to prevent reasonably foreseeable misuse.

Due to the limited information in your question, only a general response has been able to be provided to your inquiry.  However, we encourage you to contact UL Solutions for an in-depth consultation related to specific applications that involve use of lead-acid batteries in AV/ICT equipment.

More specifically, you asked: A PSU certified to IEC 60950-1 passes the HIPOT test at 2121 V DC between primary and earth. When it is used in an end product to be certified to IEC 62368-1, does it need to withstand the end product HIPOT test that could be more than 2121 V DC, e.g., 2500 V DC?

Generally, no, as a type test. Per Subclause 4.1.1 of IEC 62368-1, components complying with IEC 60950-1 are acceptable without further evaluation other than to consider the appropriate use of the component in the end product.

Therefore, while there is the need to determine the necessity of an electric strength (HIPOT) test as a type test per 5.4.9.1 on the end product if the end product contains any solid insulation designated basic, supplementary or reinforced insulation, solid insulation in the PSU complying with the relevant requirements of IEC 60950-1 is not required to be reassessed via type test and brought into compliance with IEC 62368-1.

Please note that the electric strength test per 5.4.9.1 of 62368-1 is the type test for solid insulation. Therefore, the test requirements do not generally apply to insulation through the air, i.e., gaps complying with clearance and creepage distance requirements. There is no general HIPOT test at 2121 V DC between PRI and earth that is performed as a type test in 62368-1, although there typically is a production line (routine) test (at reduced ES test values) required per (EN) IEC 62911, Audio, Video and Information Technology Equipment – Routine Electrical Safety Testing in Production, and as a certification requirement of individual certifiers, including UL Solutions. These production line tests typically check for gross manufacturing defects, including miswiring errors, rather than rechecking all specific insulation properties originally qualified via type tests.

The IEC TC108 interpretation panel question of 108/698/INF provides guidance for component acceptance per 4.1.1 with some examples in various situations. Although this particular question was not addressed exactly, it will be helpful for further understanding of the application of 4.1.1, and the document is available through the IECEE website.

More specifically, you asked: When demonstrating compliance with IEC 62368 wire flammability by way of the VW-1 equivalence concession, if a manufacturer has a file listing for AWM Style No. 20276 (which conforms to UL 758, the Standard for Appliance Wiring Material, which itself states a number of flammability tests that can be applied), where is the evidence of which flammability test was used? Is it sufficient to rely on the product marking? If a cable is marked “[File Number] [UL logo] AWM Style 20276 80C 30V VW-1,” is that sufficient to state that it meets VW-1 on the basis that UL Solutions controls such markings, or is there a further document or certificate that should be provided to show which flammability test was performed?

In response, we confirm that a VW-1 rating is acceptable based on a National Difference for USA/Canada (in Annex DVF (6.5.1)) with its reference to UL 2556. A reference to UL 2556 VW-1 is also in Subclause 6.5.1 of IEC 62368-1, Ed. 3, which provides this option for wider use under IEC 62368-1, although the acceptance is at the discretion o a National Certification Body(NCB).

For wires recognized by UL Solutions under the AVLV2 category, the markings, including identification, ratings and the UL Mark, provided on a spool (tag, reel or smallest unit container) are considered the evidence of formal compliance and UL Component Recognition. Please see the AVLV2 Guide Information in the Product iQ database for more details. The marking provided on the wire itself is for reference only and, alone, generally is not considered direct evidence of UL Component Recognition during end-product UL Solutions Follow-Up Services.

Please note that there may be a benefit for your wiring and wiring harness suppliers to get covered under one of our traceability programs, like the UL Wiring Harness Program. Then you could trace the certification and ratings of your components to the original certification markings associated with the spool, etc. More than 3,000 wiring harness suppliers are currently certified under the wiring harness program, so some of your suppliers may already be covered.

Some years ago, IEC TC21/SC21A decided to split IEC 62133 into two standards while also incorporating a number of improvements. In 2017, IEC 62133:2013 was replaced by IEC 62133‐1:2017 for alkaline or other non‐acid batteries and IEC 62133‐2:2017 for lithium batteries. However, although IEC 62133-1 and IEC 62133-2 are the current standards for such chemistries, there is also the need for a transition period.

Please note that you reference IEC 62368-1:2014, Ed. 2, but IEC 62368-1:2018, Ed. 3, is also available now. IEC 62133, IEC 62133-1 and IEC 62133-2 are all listed in Annex M.2 of IEC 62368-1:2018 to allow for the transition.

If an AV/ICT product with a battery covered by the IEC 62133-x series is submitted for UL certification to IEC 62368-1:2014, a valid certification to IEC 62133-1 or IEC 62133-2 would be accepted for batteries and cells without also being compliant with the legacy IEC 62133:2013.

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., the NEC^® allows substitution — to VW-1 allows me to demonstrate compliance with UL 62368, the Standard for Audio/Video, Information and Communication Technology Equipment?

In response, as you inferred, the note under Subclause 6.5, “Internal and external wiring” in IEC 62368-1, Ed. 3, as well as UL 62368-1 accepts VW-1 wires rated to UL 2556, the Standard for Wire and Cable Test Methods, to demonstrate compliance with 6.5.1 as an alternative method.

In addition, for external wiring, according to the U.S./CAN deviations under 4.1.17DV.1, “External interconnecting cable and wiring,” such wiring is to be investigated to the requirements of 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 3.05 m 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 cables and wiring exceeding 3.05 m 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^® (NEC^®), 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 UL Product iQ^®.

Please note: CL2 cables are subjected to a vertical-tray flame test in UL 1685, the Standard for 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 was 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, we encourage you to contact UL Solutions for an in-depth consultation.