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Posted for "bill:endevoursystems.net/mail:thinkhost" <bill@endevoursystems.net>:
please keep in mind however that the duration of the induced current is in the nano seconds
Not really, unless you are talking about 100's of thousands of nanoseconds. The half life of the current spike is in the 10's to 100's of microseconds.
I suspect you are thinking of IEC-1000-4-2 ESD tests which many COTS hardware have to pass. That test involves charging a 150 picofarad capacitor to the test voltage (2KV to 8KV for contact discharge, depending upon the test level) and discharginging it into the pin under test through a 330 ohm resistor. The resulting current pulse lasts in the order of a few nanoseconds and is down to 10% of the peak in a matter of a few 10's of nanoseconds. Even assuming a perfect capacitor and ignoring all effects of inductance, the peak instantaneuous current pulse would be under 25 amps for a nanosecond or two. In contrast, the latest revision of the DO-160D Section 22 "Lightning Induced Transient Susceptibility", calls out a number of waveforms with half-lives ranginging from about 70 microseconds to 500 microseconds, currents ranging from 10 to 1,600 amps and voltages ranginging from 50 to 1,600 volts. If you exclude the standards for "unusally harsh" environments, you are still looking at 1,600volts or 300A (whichever limit happens first) with a half life of 70 microseconds. That is several orders of magnitude more energy than the ESD test. In fact, there is more than an order of magnitude difference in the orders of magnitude!
Let me thrown in a final comparison that may put the differences into perspective. The waveforem generator for IEC-1000-4-2 testing is the size of a hair dryer and is usually battery operated. Just the power supply for the DO-160D tester is the size of a 2-drawer filing cabinet and runs off 220V 3-phase mains.
Hamid
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