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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Coating versus Noncoating
In IEC 60950-1 (first edition), there is a useful table called Table 2N, meant for coated PCBs. This coating is the usual PCB “green-masking.” The table seems to say to some engineers out there that we can use PCB coating to minimize distances dramatically, even with high-voltage differentials between them. Quite obviously, since the board is separated from the elements, the recommended separations in the table no longer depend on pollution degree or material group. The coating, is supposed to “kill” tracking altogether, and no current conduction can occur along the PCB surface.
Further, the IEC standard, and also ECMA-287, imply that if either one of the two conductive surfaces is coated, even the possibility of flashover ...

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