Fuse: fast blown vs slow blown

[Man-wai Chang]

** When are you going to stick you fat head up a dead dragon's arse ??

dragon? you meant this one: http://sites.google.com/site/changmw/

Still no idea what Confucius meant by:
" The quick brown fox jumps over the lazy dog"

That's not a chinese idiom as far as I knew.... you have the chinese words?

--
@~@ Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and farces be with you!
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[Smitty Two]

** When are you going to stick you fat head up a dead dragon's arse ??

dragon? you meant this one: http://sites.google.com/site/changmw/

Still no idea what Confucius meant by:
" The quick brown fox jumps over the lazy dog"

That's not a chinese idiom as far as I knew.... you have the chinese words?[/QUOTE]

It's a typing exercise. Contains every letter of the alphabet. Stop
taking Phil seriously.

 

[Man-wai Chang]

It's a typing exercise. Contains every letter of the alphabet. Stop

taking Phil seriously.

Thanks. I wonder whether he/she met a REAL dragon before!

--
@~@ Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and farces be with you!
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[Rich Grise]

don't feel so bad, it used to be an accepted practice to use your index
finger and thumb as a go-no-go voltage test.. I know some one that has
one of the first NEC or what ever they called it back then, books, with
that statement in it.

The way I heard that was that with the one hand in the equipment
manipulating the probe, and the other hand in your pocket or tied behind
your back, that sometimes people will ground their thumb or more likely
little (pinkie) finger, so that when they _do_ get zapped, it only burns
their hand and doesn't go through their heart and cause fibrillation or
cardiac arrest.

Hope This Helps!
Rich

 

[Winston]

(...)


Called arc-flash in US.
Yes.

The hazard isn't always obvious.

I meant 'conceptually speaking'. At higher voltage levels,
a lot more objects look like conductors. At higher current
levels, a lot more objects *continue* to be conductors.
When we combine higher voltage with higher current, it is
amazing that more electricians aren't injured.

I spent my career working on the really low-power
end of the spectrum and never thought about high-power
hazards. I recently helped troubleshoot a 208 V
3 phase system and thought I was in the 'big leagues'!

Um. Turns out I wasn't.

One of the
smartest electricians I have run across wanted to measure the motor
current in a food plant. The motor starters were in a motor control
center, which is a frame with many motor starter modules - busbar feed
in back. He defeated the door interlock, opened the module door and
put a clamp-on ammeter on one of the contactor motor wires - all
absolutely routine. No one knows what happened - the guess was there
was a loose screw. In any case there was an arc-flash. He had bad
burns, some from vaporized copper condensing on his skin. He spent a
lot of time in the hospital with multiple plastic surgeries. But he
survived. You can be killed from burns, concussion from the explosion,
shrapnel.

That's one of those situations where living can be worse
than dying.

These days to be OSHA compliant and make the same measurement you
might have to wear an arc-flash suit. OSHA interest in arc-flash is
relatively recent. Some related equipment issues are now in the US-
NEC.

http://www.texsoinstruments.com/arc-flash-suits

I see that this company makes several suits that apparently
comply to NFPA 70E but only their most expensive is said to
protect against shrapnel and none are said to protect
against plasma (reasonably enough!).
I guess 'something' is better than nothing.

(...)

(Snip fuse 'fault current rating')

A commonly available Bussmann FRN 20A fuse is "current limiting" and
rated for 200,000A available fault current. But much bigger.

Whoa.

--Winston

 

[Man-wai Chang]

The way I heard that was that with the one hand in the equipment

manipulating the probe, and the other hand in your pocket or tied behind
your back, that sometimes people will ground their thumb or more likely
little (pinkie) finger, so that when they _do_ get zapped, it only burns
their hand and doesn't go through their heart and cause fibrillation or
cardiac arrest.

Would it help wearing think leather gloves?

--
@~@ Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and farces be with you!
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[Jamie]

Would it help wearing think leather gloves?

Ah, Gloves that take the guess work out of it!

Jamie

 

[Man-wai Chang]

Would it help wearing think leather gloves?

Ah, Gloves that take the guess work out of it!

I believe those that need to deal with high current have safety
measures.... so the chance of getting hurt should be really low.

--
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[Man-wai Chang]

I believe those that need to deal with high current have safety

If you say so

They are being WELL PAID to do the job!

--
@~@ Might, Courage, Vision, SINCERITY.
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[Jamie]

I believe those that need to deal with high current have safety
measures.... so the chance of getting hurt should be really low.

If you say so

Jamie

 

[Winston]

bud-- wrote:

(...)

There was a building downtown, maybe 8 stories, that burned down. Just
the 1st floor and basement were left, and they were used as a parking
lot. The existing service remained - a mere 208/120V, but fed by 4 or
6 parallel conductors. They cleverly stored ice melting salt on top of
the service. It burned down. The utility guys said some of the
conductors burned back into the supply conduits and remained hot. Some
others burned back and welded to the conduit. (They were fed at the
utility end with "cable limiters", which are lugs combined with fuses.
Limiters on the welded cables opened.)

'Cable limiters'. That's a new one on me.
If it weren't for the guys that insist on 'belt, suspenders *and* rope,
we'd be caught with out pants down much more often.


(...)

Plasma is at the arc, and you should get blown away from it, an
advantage of the explosion.

"It's A Feature!" we explained, as the electrician (slumped against the
wall on the other side of the garage) finally opened his eyes.

This'll be my entry! http://www.bulwer-lytton.com/

The emphasis is to work on dead circuits. I am not sure how you do
useful work in an arc flash suit. Can't remember - the protection may
be so you 'only' get 2nd degree burns, but a lot better than
"nothing". One of the things you don't want to wear is polyester - it
melts.

Which wouldnt be too bad, except that it *sticks* too. Ouch.

(...)

It is a commonly used garden variety 2" x 0.5"d "time delay" cartridge
fuse. It is safe on 200kA available by clearing long before the
current through it reaches 200kA.

I use my arc welder at ~120A (~30 V) for my hobby projects.
I'm trying unsuccessfully to get a visceral understanding of 200kA
at 220 V.

--Winston <-- Nope. Still don't get it.

 

[Winston]

Robert Macy wrote:

(...)

It turned out the BEST fuse for this test equipment
was a small 3AG 1A FB, went off like a flash bulb, and created the 'in-
spec' waveforms.

I wonder what those waveforms looked like?

I *guess* that there was a >> 1 A current spike as the surge power
ionized the fuse element, then down to zero.
Or did the current peak at just over 1.0 A?

While visiting an Alcoa plant (in Iowa?), I saw a large casting of
aluminum, approx 18 feet long, 14 to 18 inches tall and 10 inches
wide, of a very strange shape. I was told that that was ordered by a
utility company. It is a FUSE and they had just blown one on one of
their high tension distribution lines and this was the replacement!
Now you want shrapnel and melted metal. Blowing that kind of fuse
must be awesome to behold.

The installation manual for that fuse must be a work of art.
Imagine trying to keep the oxide off of the contact surfaces!

--Winston

 

[William Sommerwerck]

The installation manual for that fuse must be a work of art.
Imagine trying to keep the oxide off of the contact surfaces!

All you need is a gallon jug of Cramolin!

 

[Winston]

All you need is a gallon jug of Cramolin!

Interesting!

http://store.caig.com/s.nl/sc.2/.f

--Winston

 

[Rich Grise]

I use my arc welder at ~120A (~30 V) for my hobby projects.
I'm trying unsuccessfully to get a visceral understanding of 200kA
at 220 V.

The arc is pretty much the same, but 1,667 times as fat. ;-)

Cheers!
Rich

 

[Rich Grise]

I believe those that need to deal with high current have safety
measures.... so the chance of getting hurt should be really low.

The most important piece of safety equipment anybody has is a
fully functional brain. ;-)

Cheers!
Rich

 

[Rich Grise]

Would it help wearing think leather gloves?

Personally, I wouldn't depend on them, but I don't know what industry
guidelines are. Leather is only animal skin, after all.

Cheers!
Rich

 

[Jamie]

Man-wai Chang wrote:



The most important piece of safety equipment anybody has is a
fully functional brain. ;-)

Cheers!
Rich

Well, then I guess a lot of people are in a world of shit!

Jamie

 

[Man-wai Chang]

The most important piece of safety equipment anybody has is a

Well, then I guess a lot of people are in a world of shit!

If they slept well.. Some jobs demand shift duties, affecting your sleep
and hence your safety.

--
@~@ Might, Courage, Vision, SINCERITY.
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[Winston]

Robert Macy wrote:

(Snip installation details of stunningly huge over-current
protection device)

From Alcoa employee: the utility breaker was mounted on top the towers
and simply bolts in place with the surface the contact. Once bolted,
no oxide can form.

Sounds like the geometry and pressure used for the contact surfaces
was such that it broke through existing aluminum oxides and created
a gas - tight seal in the connector area. Sounds simple if you don't
have to actually design to achieve that effect.

(Snip effect of shorting huge batteries through an inductor)

Thanks! Very interesting!

--Winston