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

Get the facts about successful IEC 62368-1 compliance from UL Solutions experts.

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The IEC 62368-1 service page covers an exceptionally wide range of topics, which we believe can be helpful to manufacturers and distributors of audio/visual (A/V) and information and communication technology (ICT) equipment.    

The question-and-answer feature allows visitors to our site to ask questions directly to UL Solutions experts. Previously answered questions are arranged by topic and searchable for your convenience.  

As this is an open forum, submitted questions should be of general applicability and reasonable complexity – UL Solutions has the right to edit submitted questions for clarity or brevity or redirect the submitter for more detailed discussion outside this forum.  Please provide your business email address with your questions to ensure a response.    

Questions and answers to IEC 62368-1

For UL 62368-1 certification, if a PE symbol (per IEC 60417-5019) is marked next to the protective earthing terminal of a terminal block used for a permanent connection, does the PE terminal screw or nut additionally need to be green in color?

More specifically you asked (edited for clarity): We design networking routers meeting UL 62368-1. We have a permanently connected equipment (supply type) using a terminal block which has three terminals Line, Neutral and Protective Earth. The supply is DC MAINS. The protective EARTH or ground terminal is marked with PE Symbol as per IEC 60417. If this symbol is there, do we also need a green color nut or screw? (This PE terminal is covered by a cover, so is not visible and only the PE mark per IEC 60417 can be seen.)

In response, the protective earth terminal screw or nut does not need to be additionally green in color if the IEC 60417-5019 symbol is provided next to the PE terminal. The IEC 60417-5019 PE symbol marking next to the earthing terminal is sufficient to indicate that the terminal is intended for the protective earthing conductor.

In UL 62368-1, these considerations, including use of green color for PE, are based on the requirements in the National Electrical Code (NEC). For details, and additional considerations on visibility, please see Annex DVH (normative) – Permanently connected equipment – mains connections, and its requirements in DVH.5.1, Identification of protective earthing terminal, which states, “If the terminal is not visible, the conductor entrance hole shall be marked with the word “green” or “ground,” the letters “G” or “GR,” or the grounding symbol (IEC 60417, No. 5019), or otherwise identified by a distinctive green colour.” Therefore, the described construction appears to meet the intent of this NEC-driven requirement in UL 62368-1.

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

How to determine PS classification for a passive loudspeaker with no power source (power amplifier) provided, just a rated maximum power handling capacity?

More specifically you asked (modified for clarity): Regarding Power Source (PS) classification, how are you supposed to perform measurements on equipment that does not contain a defined power circuit and is delivered without one, such as a passive speaker? The speaker may have a rated power handling capacity, but the actual details of the power circuit (amplifier) are unknown and will most probably vary in later use. For a worst-case fault in the load, the maximum delivered power is dependent on the specifications and behavior of the power amp.

In response, to assess a passive loudspeaker that does not have a specific power source, reliance is placed on the information, including recommendations and ratings, provided by the manufacturer.

Although sub-clause F.3.3.2, Equipment without direct connection to mains, of IEC 62368-1 does not require equipment without direct connection to mains to have an electrical rating, it is standard industry practice for passive loudspeakers to have information or a rating related to power handling capacity. For lack of other details, this information can be used to establish a PS level classification for a passive loudspeaker, along with any other relevant information provided by the manufacturer.

For classifying part of an overall system for PS, although imperfect, this approach is relatively consistent with the general information in sub-clause of IEC 62368-1:2018.

However, it should be noted that IEC 62368-1:2023 includes numerous changes related to loudspeaker drivers and loudspeaker driver assemblies that were incorporated, in part, due to some of the challenges classifying loudspeaker drivers and assemblies that your question introduces. In fact, most of the safeguards against risk of electrical fire in Clause 6 of the latest edition have exceptions for loudspeaker drivers and loudspeaker driver assemblies due to their unique design requirements and the lack of adverse field incident data, which also is consistent with past practice under IEC 60065. Therefore, PS classification of loudspeaker drivers and assemblies is less important under IEC 62368-1:2023.

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

For a product evaluation to one edition of IEC 62368-1, is it acceptable to use a power supply in the product to an earlier edition?

More specifically you asked (edited for clarity): For a product evaluation and an IECEE CB Test Report/Certificate to IEC 62368-1 3rd edition, is it acceptable to use a power supply only evaluated to and having an IECEE CB Test Report/Certificate to IEC 62368-1 2nd edition? How about for the US, UL 62368-1, and European, EN 62368-1 3rd edition? Is it acceptable to use a power supply evaluated to UL 62368-1 2nd edition and EN 62368-1 2nd edition?

A specific IEC 62368-1 edition has published requirements to demonstrate compliance with that specific edition. There are no provisions in the Standard itself for considering earlier editions, unless stated as a specific requirement. In general, the way these situations are usually handled is, if a manufacturer wants to use a power supply to a previous edition of the Standard other than the edition being used for the end product, then there will need to be a determination (investigation) made as part of the end product investigation to determine that the power supply investigated (certified) to the earlier edition can be shown to comply with the latter edition. This can be relatively straightforward, or complex, depending on the specific power supply and end product. (Often it is easier to change the power supply and use one that complies with the latest edition, thus the component power supply industry often is the first sector to update their component certifications to the latest edition.) This approach is used for EN 62368-1 and CSA UL 62368-1, and the IECEE CB Scheme. To help with these challenges UL Solutions has published Certification Impact Analyses for IEC 62368-1 (and previously IEC 60950-1) for over 20 years to assist understanding what specific changes have been made from one edition to the next, which help aid determine what additionally might need to be considered.

The complete answer to this topic can be complex, and there appears to be a specific, detailed construction that needs review/analysis. Therefore, you are encouraged to contact UL Solutions for an in-depth engineering engagement.

If our server comes with slide-rails in the box, but can be fitted to any rack, do I have to perform slide-rail mounted equipment testing?

Yes, if the server is provided with slide rails as a possible mounting means, regardless of whether the slide rails are attached at the manufacturing facility, or they are provided in the box for shipment, IEC 62368-1, Sub-Clause 8.11 testing of the mounting rails for slide-rail mounted equipment (SRME) is applicable, unless the product is an MS1 energy source as defined in Table 35 of IEC 62368-1. The Mounting means for rack mounted equipment testing is intended to evaluate the suitability of the mounting hardware, regardless of what rack it is installed in. If a rack is not part of the supplied system, then testing of the SRME with slide-rails is conducted on a representative rack/system.

What is defined as a 'suitable coating' in IEC 62368-1? Is a standard solder mask considered to be a suitable coating?

More specifically your asked:  I can't find a proper definition of a 'coated board' in the 62368-1 standard. What is defined as a 'suitable coating'? Is a standard solder mask considered to be a suitable coating?

In response, there is no definition of a “coated board” or “suitable coating” in Clause 3 of IEC 62368-1:2023, the latest edition, or earlier editions.  However, in relation to ‘suitable coating’, sub-clause G.13.3 of Annex G of IEC 62368-1 states the following:

“For printed boards whose outer surfaces are to be coated with a suitable coating material, the minimum separation distances of Table G.13 apply to conductive parts before they are coated.”

For application purposes, it is generally understood in IEC 62368-1 that a coated printed board that meets tests of G.13.6 of IEC 62368-1 is considered a printed board coated with a suitable coating material covered in G.13.3.  Generally, a standard solder mask would not be considered a suitable coating material unless it complied with the test specified in G.13.6.  However, even if a solder mask complies with G.13.6, it only would allow for reduction of Clearances and Creepage distances across the conductor pattern, which is different than a traditional conformal coating, which also may cover component leads, etc.

Also note that an alternative method to qualify coated printed boards is given in IEC 60664-3, which IEC 62368-1 permits per G.13.3.

Additionally, in the U.S. and Canada, compliance of a conformal coating with the UL 746 series is considered as an acceptable alternative to IEC 60664-3 according to Annex DVF (G.13.6) of CSA UL 62368-1.

Information on ULS Recognized Component Conformal Coatings can be located in the UL category, QMJU2,  Coatings for Use on Recognized Printed Wiring Boards – Component.  Please see UL Product iQ for additional information. Use of a conformal coating in accordance with QMJU2 needs to be utilized in accordance with its conditions of acceptability and ratings.

Note too, QMJU2 has additional information on the difference between a Resist coating (solder mask) and Conformal coating. Please see below. Under QMJU2, a Resist coating is only tested for flammability, not as insulation, so it would not fulfill the requirements in G.13.3 of CSA UL IEC 62368-1.

“Resist coating, also known as solder resist or solder mask, is a material supplied in liquid or film form used to mask or to protect selected areas of a conductor pattern from the action of an etchant, solder, or plating, and remains on the printed wiring board after processing.  Resist coatings have been tested for flammability with regards to the specific laminate and/or UL/ANSI type material indicated in the individual Recognition.

Conformal coating is an insulating protective coating that conforms to the configuration of the object coated, is applied on the completed board assembly to increase the dielectric voltage withstand capability between conductors and protects against environmental conditions. Conformal coatings are used on printed wiring boards in electrical equipment where electrical spacings are insufficient between uninsulated live parts of opposite polarity or between such parts and accessible dead-metal parts.  Conformal coatings have been tested for flammability and dielectric properties (with regard to the effect of environmental, humidity and thermal conditions) for the specific laminate and/or UL/ANSI type material indicated in the individual Recognition.  The environmental, humidity and thermal conditions are intended to emulate the end-use application.”

How is ES class evaluated for a DC to DC switching power supply? Can a measured voltage determine ES class when DC is supplied?

More specifically you asked (edited for clarity): How to evaluate ES class associated with a DC to DC switching power supply? It seems not suitable to test its touch current because, according to 5.7.2, it is based on IEC 60990, which mainly covers AC distributed power. if DC supplied, do we only measure voltage to determine ES class?

In response, electrical energy source (ES) classifications are determined by voltage or current according to sub-clause 5.2. Table 4 defines the ES limits for steady state voltage and current. It’s applied for both AC and DC.  Also, footnote “c” states, “For sinusoidal waveforms and DC, the current may be measured using a 2 000 Ω resistor.” 

If DC output voltage exceeds ES1 limit (60V), then current should be measured using a 2 k Ω resistor, but compliance with both voltage limits and current limits is not required. Note also that ES1 is defined when the measured value does not exceed ES1 limits under normal,  abnormal operating and single fault conditions (or when not exceeding ES2 limits under single fault conditions of a Basic or Supplementary Safeguard).

Related to applicability of IEC 60990 to DC, although most of the example supply circuits in IEC 60990 are AC, the Scope (1) of IEC 60990 covers, “…measurement methods for - d.c. or a.c. current of sinusoidal or non-sinusoidal waveform, which could flow through the human body…,” and “…is applicable to all classes of EQUIPMENT, according to IEC 61140.”  IEC 61140 covers both AC and DC systems. However, as stated above, IEC 62368-1, Table 4, footnote “c”  allows use of a 2 000 Ω resistor rather than an IEC 60990 network for DC and sinusoidal AC. For simplicity, a 2 000 Ω resistor typically is used for DC touch current measurements.

When DC-DC converters are involved, the evaluation and classification is not limited to the voltage levels of the circuit supplying the converter -  the working voltages and frequency generated within the converter also need to be considered. For example, when accessible circuits are required to be ES1 due to some accessibility requirements in the final application, the entire system and its circuits must be analyzed by construction review and, when required, by measurement and tests, such as Working Voltage Measurement and Single Fault Condition (SFC), to demonstrate that the ES1 circuits are not compromised by higher ES2 or ES3 voltages generated within the converter. Investigation and test may show that additional Safeguards are required.

With reference to sub-clauses 4.2.3 and 4.2.4, it also is important to note that the standard allows manufacturers to declare higher class than there is in the product. (For example, if an energy source class 3 is declared by the manufacturer, there is no need to conduct any ES1 or ES2 measurements, assuming ES1 is not required because of accessibility.)

Also, specifically related to switch-mode power supplies, as an ES classification is based on working voltage and/or touch current, it is worth noting that voltages (due to switch-mode conversion) may be generated that exceed the ES1 limit even if the input to the supply is ES1. Therefore, detailed evaluation and tests typically are needed for such switch-mode conversion circuits, even for DC-DC converters. However, for most converters, such as 5V input to 3.3V or 1 Vdc output, typical switching voltages are not expected to exceed ES1 limits under normal, anormal or single fault conditions.

How to address challenges complying with the Y.4.3 tensile strength and elongation tests for gaskets?

More specifically you asked (edited for clarity): IEC 62368-1 Annex Y defines construction requirements for outdoor enclosures. The ongoing problem we have is that gaskets meeting the test requirement of Y.4.3 are virtually non-existent and the actual gasket samples can be difficult to impossible to test due to dimensions. Additionally, Y.4.3 states, regarding the test, “As an alternative, the tensile strength and elongation tests as given in ISO 37, ISO 1798, ASTN D412 or ASTM D3574 may be used.” Is this saying that a gasket which simply has an ASTM D412 test specification can be accepted in place of the heat aging test of Y.4.3?  For the above-mentioned difficulties that make it impossible to test due to dimensions, is there any activity in the standards committee to address this requirement? I will point out that even equipment designed for Hazardous Locations and Explosive Environments does not have such a challenging requirement. I also point out that there is a much more common standard for elastomeric materials (than UL 50E), which is UL 746C, where an f1 rating ensures 50% tensile strength and 50% elongation remaining after 168 h in 70 °C water immersion, which compares reasonably closely to the clause Y.4.3 requirement of 75% tensile strength and 60% elongation remaining after 168 h in 70 °C circulating air. It would be very helpful if UL 746C f1 was also acceptable alongside UL 50E under the sub-clause Y.4.1 national deviation.

In response to your question about the difficulty in performing the tests, as this forum is not intended to analyze and provide guidance on specific designs or tests for specific applications, we suggest that you contact the UL Solutions office you work with and request an engineering consult if you have a specific design or test that you would like to discuss.

For the gasket tests, it was asked, what was the intent of the inclusion of the sub-clause Y.4.3 alternative standards for the tensile strength and elongation tests? We confirm that these alternative standards only are referred to for the test method – the conditioning requirement (samples subjected to a temperature of 69 °C to 70 °C in circulating air for 168 h) and the compliance criteria (tensile strength of not less than 75 % and an elongation of not less than 60 % of values determined for unaged samples) still need to be followed as per Y.4.3.  The intent of referencing these alternative standards is to allow for alternative test samples and the test setup. Also, while existing practice has permitted the test samples for Y.4.3 to be an actual end product sample gasket (although often there are test challenges due to actual gasket size and composition), conducting the testing on sample materials (not the gasket itself), often is a more realistic approach.  Also, the test samples for the alternative standards should be prepared per the criteria in them, such as by punching (via dies), cutting, moulding, or other appropriate methods.  Please see the details in the alternative standards referenced.

Regarding your question about related activity of the involved standards committees, we confirm there is nothing currently being worked on related to this topic within IEC TC108, which has responsibility for IEC 62368-1.  However, if you believe you have insight or a sound proposal for improving the standard, we encourage you to be proactive and make a proposal (with technical rationale) to improve IEC 62368-1 via your National Committee that participates on IEC TC108.

Related to the National Difference for USA and Canada that was mentioned, Y.4DV DC of CSA UL 62368-1 Ed. 3 allows use of, as an alternative, gasket materials tested in accordance with UL 157, or the gasket tests in CSA C22.2 No. 94.2 / UL 50E.  For more information about associated certifications, please refer to the UL Solutions categories (CCNs) JMST2 and JMLU2 in the UL Solutions Product iQ.   However, suitable gaskets complying with these standards only would be acceptable for Canada and the U.S. and not under the IECEE CB Scheme.

Related to your preference for UL 746C, we note that UL 746C does not cover gaskets explicitly under its scope.  If you believe an alternative method for considering gaskets per test protocols in UL 746C should be included in CSA UL 62368-1, we suggest that you should consider making a proposal (with technical rationale) via the UL Standards & Engagement Collaborative Standards Development System (CSDS).

Can a loudspeaker driver in PS3 circuit be exempt from fire enclosure requirements if applying for UL 62368-1?

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, 6.3.1,, 6.4.6, and 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.

What is the appropriate electrical insulation between AC mains circuits and the unearthed parts of USB ports of Class I equipment, and how to identify whether USB ports are accessible or inaccessible?

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 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, “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 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.

If a UL Recognized Conformal coating (per UL CCN QMJU2) is applied on a recognized component printed wiring board, are the tests in UL 62368-1:2019 Ed 3’s Annex G.13.6 required on the coated printed board?

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.

How is a Clearance determined when the working frequency is above 30 kHz for a switch mode power supply according to IEC 62368-1:2018?

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, 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.

In UL 62368-1, Third Edition, Annex F.3.3.9DV.1, do the words "output terminals" apply to standardized computer interfaces / connectors such as a USB-C PD port?

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.

When a power adapter is used as a charger to charge an external Lithium-Ion battery or batteries, does Annex M.4 of IEC 62368-1 apply?

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.

How to determine compliance with the latest flammability requirements in UL 62368-1 for secondary lithium batteries?

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 at:

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.

In a power supply that has a filtering cap between Live (Line) and Neutral, upstream of the fuse on the live line, can that cap be an X cap, or does it have to be a Y cap?

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.

Does the IEC 62368-1 standard cover lead-acid batteries?

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.

What are the differences in application of the electric strength test in power supplies and end products?

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 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 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.

Can the marking on a wire be used as evidence of compliance with VW-1 rating requirements?

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.

Annex M.2 of IEC 62368-1:2014 requires batteries and cells to comply with the relevant IEC standard, such as IEC 62133: 2013. If a battery and/or cell complies with IEC 62133-1:2017 or IEC 62133-2:2017, does it also need to comply with IEC 62133:2013?

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.

What are the requirements for internal and external wiring according to IEC 62368-1, Ed. 3, and UL 62368-1, Ed. 3?

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.

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