Hi Susan:
> to my products. Is there a general guideline for separating traces to meet
> isolation requirements and survive a 2000 VDC (input to chassis) hi-pot
> requirement?
There are regs and there are rules of thumb and there are
physics...
...that govern the distance at which air is an acceptable
insulator (nee isolator or separator).
There is no relationship between regs, rules of thumb, and
physics (for the separation distance).
Physics...
The withstand voltages and breakdown voltages for air as
a function of distance are published in IEC 60664.
Unfortunately, the voltages are for ac, not dc.
For 2000 volts peak:
inhomogeneous homogeneous
field field
------------- -----------
withstand: 1.6 mm 0.45 mm
breakdown: 1.2 0.35
(I'll leave it to you to convert these to mils.)
(The curves published in IEC 60664 are not linear. I
would be wary of a rule-of-thumb that was a constant!)
For dc, the distances are smaller, but I cannot make an
estimate.
More physics...
Since you mentioned a 2000 V dc hi-pot test, and since
such a test is typical for a mains input (primary) circuit...
The purpose of the hi-pot test is to determine that the
primary circuit can withstand the normally-occuring power
line transient voltages that can be as high as 1500 volts
peak. The breakdown of insulation, both solid and air, is
directly related to both voltage and distance. When
dealing with distances close to the transient voltage, it
is imperative to have close manufacturing control of those
distances. The hi-pot test verifies that the manufacturing
process has maintained the minimum distance. Failure of a
primary insulation can lead to electric shock conditions.
No matter what distance you choose, I suggest you run up
the hi-pot voltage until you experience a breakdown. Then,
determine exactly where the breakdown occured, and then
determine if you have adequate production control over
that construction. Then, interpose a solid insulation at
that breakdown point and repeat the test to determine the
next weakest spot. Again, make a judgement as to whether
you have manufacturing control. If the two weakest spots
are under control, then you probably have an acceptable
design.
Best regards,
Rich
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