I want to know more about creepage and clearance distance measurement, as here they are given for the peak voltages above 330V - what actually would the limits be for psu with 240 Vrms and also for 48V Dc powered?
Your question is related to the fundamental application of IEC 62368-1’s Clearance and Creepage Distance requirements, which would be challenging to fully answer / explain in this sort of Q&A forum. Therefore, we recommend that you contact UL offline ( https://62368-ul-solutions.com/contact-ul.html ) for a more detailed engineering engagement. Also, please take a look at our Knowledge Solutions offerings ( https://www.ul.com/offerings/designing-compliance-iec-62368-1-3rd-edition ), and/or please consider whether our 62368-1 UL Transition Guide ( https://62368-ul-solutions.com/toolkit.html ) may be of value to you since it has close to 80 pages of details on the use of the Standard.
However, in general, subclauses 5.4.2 and 5.4.3 in IEC 62368-1:2014, or the same subclauses in IEC 62368-1:2018, are used to determine the required minimum clearances and creepage distances. Moreover, new for the application of IEC 62368-1:2018, for overvoltage category II, clearances in circuits connected to an AC mains not exceeding 420V peak (300V rms) may be determined per Annex X as an alternative. Annex X is similar to subclause 220.127.116.11 in IEC 60950-1:2009+A2:2013.
Using a switch mode power supply as an example, for IEC 62368-1:2018 to determine the required minimum clearance and creepage distance for basic and reinforced (insulation) safeguard, the following parameters need to be taken into account: overvoltage category, pollution degree, material group, declared operational altitude, and working voltage frequency, in addition to the peak and r.m.s working voltages.
(Although your product may be rated 240 Vrms, that is not the voltage typically used to investigate the significant insulation safeguards in SMPSs. Please see 18.104.22.168 for some of the details why.)
Also, although the procedures in subclause 5.4.2 are somewhat complex, it in many cases they allow for smaller clearances than permitted by Annex X.
We expect you would find very helpful subclause 5.4.2 of IEC TR 62368-2:2019, which is Technical Report containing explanatory information on IEC 62368-1, 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, which many new users of IEC 62368-1 find very helpful.