BC rewirable fuses

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davetheglitz

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Correct me if I'm wrong but I believe that the Breaking Capacity of semi enclosed rewirable fuses is 1kA. Why? Surely the wire melts on overcurrent and the higher the overcurrent the quicker it melts. Given the thickness of the ceramic enclosing the fuse I can't see how it could crack or cause any hazard - and it must break the current regardless. Surely this is a case of 'you cannie change the laws of physics captain'! Any thoughts would be appreciated!

 

kme

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You are correct in the 1KA short circuit breaking capacity. The issue arises due to the extreme current which could be passing through the fuse wire, in the instant immediately preceeding it`s rupture.

If this current was to be in the magnitude of, say 3KA; the wire will not simply melt, it will, to all intents and purposes, vaporise. The spot heat therein; and the flashover plasma, will serve to explode the fuse carrier.

I have seen a board which suffered an estimated 6KA SCC. Or, to be more precise, what was left of it!

There is a board in the NICEIC "black museum"; which is in a similar state.

Hope that`s what you were after m8.

KME

 

davetheglitz

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Just a note for anyone else - I missed this on a recent inspection - Ipf of 1.3kA with rewirable fuses. I believe this should have been scored as a 2 - needs improvement.

 

kme

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Thanks kme! Ideal! You wouldn't credit the forces involved would you!
It can be a bit "wow" sometimes mate. Remember being shown a H&S dvd, where a 315A switchfuse was operated on a 3ph circuit with a phase/phase short.

I expected BANG

What actually happened was a ball of plasma was created inside the S/F, and exploded it`s was out of the front of the box.

It looked like a bomb had gone off inside the casing!

Therefore, I ALWAYS remember to check. Otherwise, I`d be standing in front of it, switching on, when engulfed.

Don`t think a pair of safety goggles and a leather gauntlet will help much? :|

 

kme

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Just a note for anyone else - I missed this on a recent inspection - Ipf of 1.3kA with rewirable fuses. I believe this should have been scored as a 2 - needs improvement.
If it was that close, yes.

If I was reading 3KA or greater; OR the cover for the fuse carriers was absent (as when one circuit has been replaced with a plug-in MCB) I`d mark it as a "1"

Just my opinion!!

 

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You are correct in the 1KA short circuit breaking capacity. The issue arises due to the extreme current which could be passing through the fuse wire, in the instant immediately preceeding it`s rupture.If this current was to be in the magnitude of, say 3KA; the wire will not simply melt, it will, to all intents and purposes, vaporise. The spot heat therein; and the flashover plasma, will serve to explode the fuse carrier.

I have seen a board which suffered an estimated 6KA SCC. Or, to be more precise, what was left of it!

There is a board in the NICEIC "black museum"; which is in a similar state.Hope that`s what you were after m8.

KME
But surely....

wont the fuse blow when it reaches 5x its rated value... :p :p

and most of the voltage will have been dissipated across a spark at the fault.. :p :p:p

so it will NEVER reach 1k??? ?:| :(

Thats wot I lurned on a 4frum somwhere??? cant remember where???? ?:| ? :|

 

kme

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But surely....wont the fuse blow when it reaches 5x its rated value... :p :p

and most of the voltage will have been dissipated across a spark at the fault.. :p :p:p

so it will NEVER reach 1k??? ?:| :(

Thats wot I lurned on a 4frum somwhere??? cant remember where???? ?:| ? :|
You bar steward.

Where`s my manners? Evenin` mate.

I`ve been trying to calm that down - AND I think I`ve upset uncle Albert in the process:_| :_|

Then you come in like yourself, and next thing we know there`ll be a war, and I`ll have to hide in me bunker again.

 

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You bar steward.Where`s my manners? Evenin` mate.

I`ve been trying to calm that down - AND I think I`ve upset uncle Albert in the process:_| :_|

Then you come in like yourself, and next thing we know there`ll be a war, and I`ll have to hide in me bunker again.
Evenin!!!!!!!!!!!!!!!!!!!!!!X( X(

well according to your post time...

its very nearly tomorrow!!!! ]:) ] :)

so I shall say..

Good Morning Mr KME...

hows ya hangin m8...

I hope you aint been pokin them sleepin dogs???

Mr WW will not be happy if you have!:(B)

 

kme

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They`re still hangin bud:)

pokin` `em? Nah.

I tried to "defuse" things, after a couple of posts got a tad vitriolic! Think Steppie thought I was having a go at him, and went off for a ride on `is donkey.

You been a busy boy today?

 

Mr Sworld

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As cack as rewirables are they do have one handy feature when you have to investigate faults.

You can tell by the remains of the fuse wire if the fault is overload (wire melted but still present) or short-circuit (no wire left at all!)

Just the extra sod with these is when you find the old boards still with the asbestos liner in the back of the carrier! :(

 

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Correct me if I'm wrong but I believe that the Breaking Capacity of semi enclosed rewirable fuses is 1kA.
Just a quick additional point for the benefit of others reading this thread..

If you were wondering were to find the short circuit breaking capacity of fuses/MCBs? :|

A useful reference list can be found on

Table 7.2A Page 50 of the On-Site-Guide (16th edition, 17th not yet published... last dates I read were September 08)

:) :D

 

welshwizard

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Just a quick additional point for the benefit of others reading this thread..If you were wondering were to find the short circuit breaking capacity of fuses/MCBs? :|

A useful reference list can be found on

Table 7.2A Page 50 of the On-Site-Guide (16th edition, 17th not yet published... last dates I read were September 08)

:) :D
That's Jolly decent of you, Young Man. :)

 

Nicky Tesla

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As i can remember, there are different categories of fuse, giving different Ka ratings. How do you know what category the wylex domestic fuse is.

 

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