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Nick Alexeev
Nick Alexeev
3:53 PM
@ScottSeidman I've found the answer to my clearance question. There's min width for a transverse slot if it's intended to break creepage. This min width is a function of MOOP vs MOPP, and also a function of pollution degree.
Details in IEC 60601-1 section 8.9.4 .
Here’s an example. I require MOPP. The environment is pollution degree 2. That gives me a minimum slot width 1mm. Further, I require clearance/creepage 2.5mm/4mm.
If I have a 1mm gap between the edge of the PCB and the grounded wall of the enclosure, plus 1.5mm between copper on the PCB (outside layers) and the edge of the PCB, that satisfies the 2.5mm clearance.
But if I have 0.5mm gap between the edge of the PCB and the grounded wall of the enclosure, plus 2mm between copper on the PCB and the edge of the PCB, that doesn’t satisfy the 2.5mm clearance.
In other words, if I want to use a slot across a creepage path, the slot can’t be infinitesimally narrow. There’s a minimum required width.
 
 
5 hours later…
Scott Seidman
Scott Seidman
8:50 PM
@NickAlexeev Good to know. How do you deal with wire connectors to the chassis? Do you just need to make sure they're longer than your creepage? Do you also need to make sure any chassis-mounted hardware doesn't shorten your creepage?
 
 
2 hours later…
Nick Alexeev
Nick Alexeev
10:24 PM
@ScottSeidman If I've got a grounded metal panel, then creepage distances along the connector (from the panel to the terminalson the back of the connector) have to be longer than the required creepage distance. If the connector is attached with a metal nut, then the thickness of the nut is subtracted.
 
Nick Alexeev
Nick Alexeev
10:36 PM
Sometimes I’m forced to use a specific connector when I have to use some specific off-the-shelf accessory. What if that connector’s creepage length ends up being too short?
I can replace a panel with a plastic panel.
I can create a plastic patch in the metal panel. It would provide additional creepage distance.
These are my preferred solutions.
 

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