[TenTec] Answer to "which is faster"...fuse or breaker...

[Dr. Gerald N. Johnson]

On Wed, 2006-08-30 at 10:32 -0400, john.brewer at 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