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Does the "any two leads" short exemption in B.4.1 apply to all pins on the current limiter IC complying with Annex G.9 or is only the requirement for shorting input to output waived as is implied in G.9.1?

More specifically, you asked: B.4.1 offers an exemption from short-circuit tests between any two leads for current limiters complying with clause G.9. G.9 states that for PS1 or PS2 IC current limiters input and output will not be shorted if the IC is compliant. Does the "any two leads" short exemption in B.4.1 apply to all pins on the current limiter IC, or is only the requirement for shorting input to output waived as is implied in G.9.1?

 

In response, Clause B.4.1 generally guides the consideration for single fault conditions of components, including component failure simulation by a short-circuit of two leads at a time and open-circuit of one lead at a time.  However, as you note, B.4.1 also has a general exception for integrated circuit current limiters complying with Clause G.9.

 

As you also note, in G.9.1 (IEC 62368-1:2018) it more clearly states, “IC current limiters used for current limiting in power sources so that the available output power becomes PS1 or PS2 are not shorted from input to output if they comply with all of the following…”  

 

Therefore, it appears that the main emphasis of B.4.1 and G.9.1 when considered together in the context of IC current limiters is the consideration of a short-circuit between input and output pins only, which makes sense for an IC current limiter because a short-circuit between input and output leads is considered to be the worst-case component failure condition as it disables the entire protective (safeguard) function of the output current and power control.  Such a safeguard function is required by 6.5.2, Requirements for interconnection to building wire, and 6.6, Safeguards against fire due to connection of additional equipment, via their reference to Annex Q, Circuits intended for interconnection with building wiring, which in turn references G.9 as an option.

 

However, we need to remember, Annex B also is referenced in other parts of IEC 62368-1, including other sub-clauses in Clause 6, such as 6.4, Safeguards against fire under single fault conditions.  Does the IC current limiter exception in B.4.1 apply for these applications too?  

 

In these cases, since the IC current limiter itself could be a potential source of ignition, it would seem that the short-circuit of two pins should be a consideration, even though the IC Current Limiter complies with Clause G.9.  (It is noted that ‘risk of ignition / fire’ is not a compliance criteria in G.9.3, only that “…the device shall limit the current in accordance with its specification as applicable or the device shall become open circuit.”)

 

Your question identifies an area of the 62368-1 standard that may need some further clarification / refinement by IEC TC108.

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