Guess this is as good a time as ever to raise
this question ...
First in regards to IPC-D-275, Table 3-1...
Be sure to calculate with respect to *peak* AC voltage
as required by the header of the left-hand column of 3-1.
That means 115vac rms is approx. 163 volts PEAK or the
values must be drawn from the 151 - 170 row. For uncoated
external conductors up to 10,000 ft (B2), that's 1.27mm.
230vac rms is approx. 325 volts PEAK or the values must
be drawn from the 301- 500 row. For uncoated external
conductors up to 10,000 ft (B2), that's 2.54mm.
Second ...
Now, if say you're designing boards for
UL Standard 1950, 3rd Edition approval
in the US and Canada, then you must use
Table 6, page 77.
This requires knowing CTI ratings, whether a trace is
"PRIMARY" trace next to a "GROUND" trace,
"PRIMARY" trace next to a "SECONDARY" trace.
and Pollution Degrees 1 (clean room), 2 (office),
and 3 (outside).
So say for instance, I have a primary trace carrying
up to 230vac next to secondary +5vdc trace. If I worse
case the CTI and say Pollution Degree 2 (office),
table 6 page 77 of UL1950 requires a spacing of 5 mm.
(Note 1 says to multiply by 2).
Why the 2.54mm with IPC 275 and 5mm with UL?
Hate to raise the muck, but really need to
know what I'm doing wrong here...
Regards, Doug
----------
> From: [log in to unmask]
> To: [log in to unmask]
> Subject: [TN] 110v air gap
> Date: Tuesday, November 25, 1997 11:37 AM
>
> can you please tell me how to figure the minimum allowable air gap on a
PCB
> for any given voltage?
>
> thanks
>
> Howard Kaminsky
>
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