MOOP between Mains Part and Earth/Ground

[eldercosta]

My understanding of the Standard is 1xMOOP is required between Mains Part (e.g., L/N or L1/L2) and Earth (PE).Though 2xMOOP is required between Mains Part and protectively earthed accessible parts, my understanding is one is provided by that Basic Insulation (that 1xMOOP) and the other by PE itself (1xMOOP).

I am reviewing a test report I just received from the test lab and in the section regarding Air Clearances/Creepage distances they considered the distances corresponding to 2xMOOP between MP and PE. Though the device (specifically the power supply) passed on both requirements with wide margin, I am considering the same PS for another design whose spec include 5000m instead of 3000m altitude, in which case Air Clearance would fail by a narrow margin if 2xMOOP is required.

Thanks in advance for your insights.

 

[Peter Selvey]

For a part that is genuinely protectively earthed (0.1Ω etc.) then only 1MOOP is required. This is only for solid metal parts (e.g. a metal case, metal frame), and the green/yellow wiring that is used to earth them. There are also many other parts that are earthed, such as a secondary of a power supply, but they are usually not "protectively earthed", because it's not practical to maintain all the PE requirements to all relevant parts. Such parts usually need 2MOOP. However, the distances only need to be checked where the part (e.g. the secondary) is close to the mains parts.

 

[eldercosta]

Hello, Peter, thank you very much.