For AV/ICT equipment intended to be installed outdoors, is the 30Vdc limit for accessible parts from 60950-22 applicable, or do we apply touch current requirements as in IEC 62368-1 table 4?
More specifically you asked: I have a question regarding interpretation of touch current requirements for outdoor equipment per IEC 60950-22. Per clause 6.1 of 60950-22 the requirements are based on voltage limits only for example 30Vdc max under normal conditions. There seems to be no touch current requirements specified here. Now in IEC 62368-1 Ed 3, with IEC 60950-22 requirements now included the standard basically does not specify any touch current requirements specific to wet locations but applies only the table 4 in 62368-1 from my understanding. Looking further, in IEC TR 62368-2:2019 the following statement exists on voltage limits with no limits indicated:" For outdoor equipment, lower voltage limits apply because the body impedance is reduced to half the value when subjected to wet conditions as described in IEC TS 60479-1 and IEC TS 61201." Question : Do we have to still follow the 30Vdc requirements as in 60950-22 or stick to the hazard based approach & apply touch current requirements as in IEC 62368-1 table 4? I saw a 60950-22 to 62368-1 Ed 3 clause mapping document made by UL but it seems to be unclear on this topic.
In response, we would like to first make note that IEC 60950-22, and it’s requirements for outdoor equipment, have been incorporated directly into IEC 62368-1 as of IEC 62368-1:2018 (Edition No. 3). Specifically, related to accessible circuits, see sub-clause 220.127.116.11, Accessibility to electrical energy sources and safeguards – Requirements, which states,
“For bare parts of outdoor equipment that are accessible to an ordinary person in their intended outdoor location, the following shall not be accessible:
– bare parts exceeding 0,5 times ES1 voltage limits under normal operating conditions and abnormal operating conditions and single fault conditions of a component, device
or insulation not serving as a safeguard; and
– bare parts exceeding ES1 voltage limits under single fault conditions of a basic safeguard or of a supplementary safeguard (see 18.104.22.168).”
Therefore, for accessible circuits of outdoor equipment that do not exceed 0.5 ES1 voltage limits, such as 30Vdc for dc circuits, there is no need to take additional current measurements. For such accessible circuits that exceed 0.5 ES1 voltage limits, then the normal current limits for ES1 cannot be exceeded, but they are not halved. They are not halved because, while in the case of voltage the voltage limits need to consider reduced body impedance due to the wet conditions as part of the process of deriving effect of actual current, in the case of current, the measured current itself is the energy source directly associated with the physiological risk of electric shock, so it is not halved. (The same was true for the application of IEC 60950-22: the SELV voltage limits were halved for outdoor applications, but if these were exceeded, the LCC (Limited Current Circuit) limits were not halved.)
This subject was discussed at a past IEC TC08 meeting and its our understanding further explanation about not halving current will be provided in the next edition of IEC TR 62368-2.