For DC powered products with internal PS2 circuits and containing only resistive PIS, does this construction require a Fire Enclosure?
All references are to IEC 62368-1:2018.
In case of the “Reduce the likelihood of ignition” method, including application of 6.4.3, a fire enclosure normally is not required. However, if separation from PIS requirements are not met per the first dash of 18.104.22.168, then a suitably rated fire barrier would be required. Therefore, this method may not be the best method for the type of application you describe. (The first dash paragraph of 22.214.171.124 states, “- an arcing PIS or a resistive PIS shall be separated as specified in 6.4.7 with the accessible outer surface of the equipment considered to be covered with a combustible material.”)
In case of the “Control fire spread” method, for a product only having PS2 circuits inside the product complying with 6.4.5, a PS2 circuit does not require a fire enclosure, regardless of whether PIS also is available. However, note the component requirements in 126.96.36.199, in which one option is adequate separation from a PIS, although it is not the only option.
Please also note that if the DC powered product also has a secondary lithium battery inside, M.4.3, Fire enclosure, of Annex M also is required. Unless the cell is PS1, a fire enclosure, V-1 or better, is required for the cell or combination of cells. The product enclosure also can serve as the fire enclosure required by M.4.3. Currently, IEC TC108 is collaborating on a formal Interpretation for M.4.3 that PIS considerations and separation from combustible parts need not be considered inside batteries. Therefore, in such batteries, even for PIS in very close proximity to the enclosure, a V-0 material would not be required even when normally required by 188.8.131.52.