Hi all, I read something about an avionics power connection arcing upon contact during troubleshooting.
Most electronics products, like radios, transponders, electronic digital devices all have input power filters designed to limit input power voltage variations. Sometimes we ET's call the undesirable voltage variations "noise" or "AC riding on DC". The voltage variations, which one could plot on a graph, or even view that graph in realtime live on an oscilloscope, are intended, at least to a useful extent, to be filtered out of the inbound DC power by filter circuits inside the electronic device (radio, etc). Those power filter circuits all include capacitors, which charge up in a way like a small battery except because no chemical reaction is necessary, the charging is MUCH faster. To the extent it may as well go zero to full charge in the blink of an eye. Thus there will almost always be an arc upon closing (Making) the power connection due to the very high initial charge current for those capacitors. This would be normal contact switch behaviour when initially energizing electronic devices. Traditional motors, solenoids, and other inductive loads are not electronics and have different characteristics, with a motor the normal switch arc happens upon de-energizing the device (opening the switch) or disconnecting the wire. I point this out because the wording of the report I read did not clarify if the suspected faulty switch was in the on or off position during testing, which matters alot. The position of the switch would have been critical in the troubleshoot and analyzing the cause of the arc, due to the effects of power supply filters described above. had the switch contacts been open (switch in the off position) at the time and the connection closing would draw an arc, then I'd agree: a bad switch is suspect, however switches almost never pass current or potential to their cases when they fail. If it was an LED lighted switch, with a lighting circuit malfunction (shorted led), those have a current limiting resistor inside that would limit the 12vdc current to around 0.020 amperes, even with a shorted led which would not have sufficient current to draw an arc, or even be noticeable on the rest of the system. If the switch alone drew sufficient current to draw an arc on account of an internal defect, with the switch in the off position, and it's contacts open, the switch would generate heat and would at least be warm or hot to the touch. So anyway, what I read was missing some info and as an ET, the thoughts above are what flashed through my mind. Just thought I'd share that. cheers! ps. My ten ET employees and myself together, in 1998 at my Audio/Video repair business performed well over 17,000 component level electronic chassis repairs. We were in there as deep as it gets.
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