RE: Re: Quick blow fuse

["Keith Doxey" <ukha.diyha@xxxxxxx>]

Ian,

You are almost right....

Different alloys have different melting points which is what determins the
speed of the fuse blowing. All fuses *should* be able to carry their
maximum
rating forever, but in reality metal fatigue causes time related failure.
The alloy is chosen to blow at the required time interval, for instance....

Anti Surge (aka Slow Blow) PSU INPUT PROTECTION
- will take longer to fail and will withstand a current several times its
rating for a short time after which it would still fail. This allows surges
but cuts the power in the event of a prolonged overload. Toroidal
transformers MUST have Anti Surge fuses fitted to the primary due to the
extremely high inrush current. Ordinary fuses die.....quickly! The spring
ensures that when the fuse fails the two ends of the wire are rapidly
pulled
apart to extinguish any arcing that may take place.

Quick Blow (Clear Glass) GENERAL PURPOSE and PSU OUTPUT PROTECTION
- fail *fairly quickly* and will not withstand high switch on surges. Can
shatter when they fail.

Hi Speed Ceramic (Buff coloured and filled with sand) TRIAC PROTECTION
- These are designed for protecting semiconductors like triacs. When lamps
fail you can get extremely high currents flowing as the filament in the
lamp
drops off and shorts out the lamp stem. Quick blow will shatter under these
conditions and will also not fail quick enough to protect the triac. HSC
fuses (aka HRC High Rupture Capacity) blow almost instantly and protect the
triac. The fuse wire effectively vapourises in a mini explosion which is
contained by the sand in the fuse.

Hope that helps

Keith

> -----Original Message-----
> From: Ian Lowe [mailto:ian@xxxxxxx]
> Sent: 18 May 2001 16:51
> To: ukha_d@xxxxxxx
> Subject: Re: [ukha_d] Re: Quick blow fuse
>
>
> Keith,
>
> As an aside, how does that work? I thought those were quick blow
> fuses too,
> with the thought that the spring coil placed the filament under
> tension such
> that it was always under slight stress and would (physically) come
apart
> faster when loaded to failure...
>
> if it's an Anti-surge (and I am sure you are right) what's the
> spring do???
>
> Ian.
>




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