Solid insulation and air insulation (clearance) are (everywhere) in
parallel. They cannot be separated and tested separately. As in the song,
"You can't have one without the other."
And, the dielectric strength of air is greater when tested with 1.2/50 us
waveform than when tested with a sinusoid waveform (because it takes time to
break down air).
Rich
From: Ralph McDiarmid <rmm.priv...@gmail.com>
Sent: Wednesday, February 26, 2025 10:13 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] major safety issue possibly affecting 20% of the
electronic devices in use
I think it's worth bearing in mind that hipot tests, both routine and
prototype, done to verify clearance are to use either the 1,2/50us voltage
impulse or an a.c. steady-state voltage burden. Solid insulation is
verified by application of a.c. steady-state and by the 1.2/50us impulse
voltage test. This is covered well in IEC 60664-1 and the 1.2/50us "surge"
impulse waveform is well defined in ANSI C62.45
To use a different impulse waveform may result in failure or solid
insulation but that doesn't necessarily mean the equipment under test is in
some way faulty or unsafe when used in the overvoltage category for which it
was intended.
Ralph
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