DC fuses and arcs

George Herold · 2009-12-03T21:20:48+00:00

I pulled Bob Pease's book of the shelf last night, "TroubleshootingAnalog Circuits". In chapter 3 he makes the following statement aboutfuses,"Most fuses are fully rated for 115 or 230 VAC, but no more than 32VDC. That's because the alternating current flow gives time for an arcto be extinguished, which would not happen with DC."I was confused by this, where is the arc? Across the fuse itself?George H.

Dec 03, 2009 41 Replies

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Robert Baer 16 years ago

This is correct...as long as the AC current is not "excessive". One time, in an Army barracks, someone tired of someone else not limiting radio volume, gave the abuser a "grid leak detector" (was a gimmicked short circuit in a plug). Well, a fire shot out of the wall outlet, and the idiot kicked it, trying to put it out. The flame increased to about a foot or so and nobody seemed to know how to stop it. I flipped the 15 amp circuit breaker off; my guess is that arc was running at ten amps. Melted half of the outlet as well as the copper of the outlet and started on the wiring..

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christofire 16 years ago

This must also affect the choice of materials for mains-voltage incandescent light bulbs, and high-power valves. Perhaps one of the reasons for the quartz in 'quartz halogen' (another being that the envelope shouldn't collapse!).

I could have mentioned earlier that a proportion of HV distribution insulators (in the UK at least) have their axis horizontal, particularly at corners in the route. Those with their axis vertical might not be expected to provide so much of a current path in the rain, particularly 'mushroom'-shaped ones.

Chris

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