On Wed, 2006-08-30 at 10:32 -0400, john.brewer@us.schneider-electric.com
wrote:
> Due to some creative wiring while redoing the shack, I tested (inadvertently)
> the "which is
> faster, fuse or breaker" question....twice.
>
> This particular bench has a Astron 20A supply fed into a TenTec breaker (I
> forget the number,
> but the one spec'd for an Omni VI). On the downside of the breaker is a
> small terminal strip
> branch, for small accessories (keyers, LED lighting, etc.) which is fused at
> 3A.
>
> I inadvertently shorted the 3A strip (twice!) and the breaker opened twice,
> protecting the gear
> AND the 3 amp fuse installed in the low-current 12V branch.
>
> Those magnetic breakers are fast and reliable. They open up fast enough to
> protect a 3A 3AG
> fuse from the available current of a crowbarred 20A supply.
>
> John
>
The crowbar has no effect on the short circuit capability of the power
supply. It only comes into effect when the output voltage rises beyond a
reasonable level, probably about 15 volts. Then the crowbar circuit
drops a crowbar across the supply and shuts it down rapidly letting the
supply's internal current protection protect the rectifiers and
transformer.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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