[chbot] Robotics Group meeting, Monday 19 Nov 2018, 630pm, 5 Idris Road
list57 at top.geek.nz
Tue Nov 20 06:41:16 GMT 2018
On Tue 20 Nov 2018 01:45:08 NZDT +1300, Trevor Wignall wrote:
> It is a common practice to route a slot in the PCB underneath the opto so
> there is some air gap providing isolation between the copper pads. I have a
> distant recollection that for 230V AC, you need 8mm creapage distance, not
> 4mm, hence the slot. However I will happily accept corrections on this. In
> any case, the more separation, the safer the design.
Basic EN60950, IEC60950 (or worldwide variations, they're all basically
the same) is about IT equipment safety, and the local UL lab
accepted/passed 4mm without slot on standard FR4 with sodler stop some
years back and I doubt it has changed.
DIP6 case opto-couplers have pin centres at 7.62mm, they are used all
the time in 240Vac circuits, and after you take away copper ring (pad)
widths there's no way you get near 8mm. All that equipment gets passed
by the test labs.
Where you might be right with 8mm is in dusty or otherwise dirty
environments. Sure the more the better, slot is better than not, but it
can't be required for something like household appliances, your
computer modem (yes PSTN has mains voltage isolation requirements!!), or
encapsulated plug packs.
If one could just read the standards, but they cost more than one arm
and one leg...
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