fuse capacity higher -why?

The interrupting current is not the fusing current.

Fusing current is the current that melts the fuse element. The melted element will then attempt to interrupt the current by producing a break in the continuous metal path through the fuse.

Interrupting current is the highest current, who's arc between the melted blobs of metal the fuse can extinguish within a reasonable period of time (a 1 or 2 half cycles, perhaps). If the supply to the fuse can produce a short circuit current higher than this, the fuse housing will either melt, turn into a plasma ball, explode, or some sequence of these effects. None of those reactions is considered a safe and successful current interruption.

"dew"

** The maximum " interrupting capacity " of a fuse is at least 10 times & can be well over 1000 times its rated (maximum holding) capacity. ** Simply so the fuse will *open* when a short happens - rather than turn into a fire ball. ** The continuous current capacity of an *equipment fuse* should not be greater than the AC line cables that feed it - however AC line cables are always protected by fuses or breakers of their own. ** You have your definitions all screwy.

......... Phil

Yes, fault currents can be many times to thousands of times that normal currents. Interrupting capacity is as described. Also, interrupting current capacity requirements are always based on available fault current calculations. Having done this several times in the course of my work in the past few years has been a real education in protection systems.

--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.  
--Schiller

in NZ, an old house will typically have around 1kA fault current; newer houses are more like 6kA.

Where I used to work designing motor controllers, the fault current was

250,000A - lots of grid-connected SCIMs with inertial loads, and 2m from a 2MVA xfmr.

Cheers Terry

"Terry Given"

** An absolute LIE. ** An even BIGGER LIE.

** Yawn.....

Crap on, crap on, crap on ....

........ Phil

not according to the EWRB (Electrical Workers Registration Board), who probably know what they are doing.

"The Pinball Wizard of Nelson "

** Blah blah blah ......

No info - just asinine Kiwi fuckwittery.

........ Phil

your geography is a bit screwy.... nor have I done much work with pinballs, and nothing since 1990. perhaps one day you'll learn to harness the power of the internet - a quick google search found this:

the data came from an electrical inspector, when I did my ESTB a couple of years ago (yes, I'm a fully qualified appliance serviceman, although the pay is piss poor, who would want to do that shit)

old houses have a lower fault current than new houses, cos the wires are smaller. the 60A pillarbox HRC fuses will actually limit fault current slightly (as do all fuses) to somewhat less than the fault current of the transformer feeding that house (just as well really), but the dangly wires to the house do the bulk of the work - 1kA needs about 0.23 ohm, which is ~ 20m of 4mm^2 (incl. return). 6kA needs about 0.04Ohms.

I recently had the supply to my house re-wired, and as it was 80 metres my sparky used 70mm^2 Al, around 80mOhm for the round trip, so at the switchboard I will only see ~ 3kA.

If your house is a lot closer to the pillarbox (modern in-fill housing is often only a few metres away), impedances go down and fault currents go up. its pretty clear that 1-6kA is quite feasible. Besides, I've repaired many PSUs, appliances etc with 20mm fuses (125A rupture current) that have been utterly destroyed - in some cases not even end caps remained - so clearly the fault current is well above 125A (although some of those may well have come from commercial buildings, where the fault current is even higher).

Cheers Terry

"The Pinball Wizard of Nelson "

** Then you are free to say exactly which Kiwi shithole you ARE the "Pinball Wizard" of - Terry.

We all need to know.

Urgently.

** The cap fits ......

Even if that pointy head of yours is swollen like a toad fish.

( snip puerile tripe about some worthless Kiwi IT degree - peeeeukkeeee )

** Yawn .............

Anyone with a DVM and an 2400 watt electric jug can demonstrate it is totally false in regards to a domestic, 240 volt, power outlet.

Fuck off - IDIOT !!!!

....... Phil