How good is ETL safety certification?

[Rich Grise]

The interrupting capacity of a typical 1.25" Fast-Acting 3AG fuse at
250V is MUCH lower than at 125VAC. They will interrupt 10kA at 125V,
but only more like THIRTY-FIVE amps at 250V. Check out the data
sheets.

Put them in a situation where they can see thousands of amperes fault
current @240V and they can and often do EXPLODE, rupturing the glass
and sending fragments everywhere.

Of course the 20mm types are worse again.

That's why Fluke multimeters use a much larger fuse.

During failure of the 3AG type fuses, the melted metal ionizes inside
the fuse and allows an arc to form directly from one end cap to the
other, which has very low impedance (low voltage drop, but lots of
watts for such a small enclosed space).

I have a couple of fuse stories.

One is, I've seen 32V fuses used in a 240V circuit explode and blow
the cap off the holder, half-way across the factory floor.

One time, in the USAF, some guy in the shop ordered a 15A fuse, but
somebody made a typo in the stock number or something, because they
sent a 15A, 15,000V fuse. It was just like a standard 3AG, but it
was about 3" in diameter and about 12" long. The ends were copper,
and it was filled with sand. Nobody knew what to do with it, so we
took it apart. Inside, down the middle of the sand, was a ceramic
rod which looked like it had been extruded through an asterisk-
shaped die. Wrapped in a very loose helix around this (like,
looser than one turn per diameter) were five very fine silvery-
colored wires, the fuse element itself. The glass tube had about
about a 3/8" wall. It was quite fascinating. The sand, I guess,
was just plain old ordinary sand.

It was kinda kewl.

Cheers!
Rich

 

[Michael A. Terrell]

Really? Even an 1 1/4" 'automotive' fuse?

--
*Why is it considered necessary to screw down the lid of a coffin?

Dave Plowman [email protected] London SW
To e-mail, change noise into sound.

http://www.bussmann.com/ & http://www.littelfuse.com/ have a lot of
information on the proper use of fuses.

 

[Pooh Bear]

The interrupting capacity of a typical 1.25" Fast-Acting 3AG fuse at
250V is MUCH lower than at 125VAC. They will interrupt 10kA at 125V,
but only more like THIRTY-FIVE amps at 250V. Check out the data
sheets.

Put them in a situation where they can see thousands of amperes fault
current @240V and they can and often do EXPLODE, rupturing the glass
and sending fragments everywhere.

Of course the 20mm types are worse again.

That's why Fluke multimeters use a much larger fuse.

During failure of the 3AG type fuses, the melted metal ionizes inside
the fuse and allows an arc to form directly from one end cap to the
other, which has very low impedance (low voltage drop, but lots of
watts for such a small enclosed space).

Fuses to the IEC specs have a rupture current rating.

L = low breaking capacity.
H= high breaking capacity.

E.g T300mAL meaning T = time delay ( 'slo blo' )300mA - Low breaking
capacity.

Graham

 

[Pooh Bear]

I have a couple of fuse stories.

One is, I've seen 32V fuses used in a 240V circuit explode and blow
the cap off the holder, half-way across the factory floor.

One time, in the USAF, some guy in the shop ordered a 15A fuse, but
somebody made a typo in the stock number or something, because they
sent a 15A, 15,000V fuse. It was just like a standard 3AG, but it
was about 3" in diameter and about 12" long. The ends were copper,
and it was filled with sand. Nobody knew what to do with it, so we
took it apart. Inside, down the middle of the sand, was a ceramic
rod which looked like it had been extruded through an asterisk-
shaped die. Wrapped in a very loose helix around this (like,
looser than one turn per diameter) were five very fine silvery-
colored wires, the fuse element itself. The glass tube had about
about a 3/8" wall. It was quite fascinating. The sand, I guess,
was just plain old ordinary sand.

It was kinda kewl.

A lot of those measures are about arc extinguishing.

Must be tricky @ 15kV though !

Graham

 

[Rich Grise]

Rich Grise wrote: ....

A lot of those measures are about arc extinguishing.

Must be tricky @ 15kV though !

Graham

I think it'd be fun to blow one and watch! To see if it actually
melts the sand, and how that ceramic form would stand up, and stuff
like that.

Unfortunately, this is the sport of the kind of kings who have a
15 KV 20A power supply lying around in the junque box. ;-P

Cheers!
Rich

 

[Jasen Betts]

How do you rate a fuse for voltage? It would be a peculiar design that

would flash over between terminals even at 500 volts.

when the little cylinder is full of metal vapor it takes less than 500 volts
to maintain the arc for a few seconds especially if that voltage is DC.

Bye.
Jasen

 

[Don Klipstein]

What I see as the main problem at the moment is fake and counterfeited UL
(and other) marks placed on products, mostly imported, that haven't been
inspected or built to standards. Major manufacturers are paying extra to
CSA, for example, to do "dock" inspections overseas to ensure that
what's in the container is what they ordered including proper standards
marking.

But where does the fake stuff end up -- on the internet, in "dollar"
stores? I don't know.

I have been gaining this impression that dollar stores get a lot of
stuff that is fake in one way or another.
I have had a dollar store compact fluorescent lamps burn out in an
uncomfortably spectacular manner a few minutes after I started running it.
Also I have heard of others having spectacular failures of dollar store
compact fluorescent lamps, including one that went "pop" 3 times
in the process of burning out.

And also fakes in matters other than safety - how about those
flashlights that say they never need batteries - shake to recharge? In my
expereince, the $2 dollar-store version (in 2 different packages now yet!)
has a fake magnet, a shorted coil, and non-rechargeable "coin style"
batteries.

Maybe I will send the FTC a dollar store compact fluorescent lamp that
produces somewhere around 30% of its claimed light output, in its package
that claims 1580 lumens and "light of a 100 watt bulb". I have yet to see
a dollar store compact fluorescent lamp meet a light output claim. Some
dollar store compact fluorescent lamps also claim "soft warm white light"
but actually glow a bluish "daylight" color.

- Don Klipstein ([email protected])

 

[Don Klipstein]

How do you rate a fuse for voltage? It would be a peculiar design that
would flash over between terminals even at 500 volts.

Vaporized metal can sustain an arc that long (I am assuming length
of an AGC style fuse) with even less voltage than that. Try seeing how
long an arc you can draw with an arc welder at merely 30-40 volts or so,
and then imagine what 500 or even 250 volts can do. I once had an arc
almost an inch long between 12 AWG copper wires with only 2-3 amps at 120
volts during an experiment trying to see the spectrum of a copper vapor
arc.

Also, fuses often have a lower voltage rating for DC than for AC.

- Don Klipstein ([email protected])

 

[Don Klipstein]

Really? Even an 1 1/4" 'automotive' fuse?

May work OK with AC voltage that high, especially if it is a lower
current fuse - but it has not been tested and certified to be reliably
safe/effective in such use. May even usually work OK. May work OK when
you try it, and then your luck may run out sometime later if that fuse is
somewhere other than under your eyes or sometime when you (or worse still
others) don't know where the power disconnect and the fire extinguisher are.

- Don Klipstein ([email protected])

 

[Joerg]

Hello Don,

Maybe I will send the FTC a dollar store compact fluorescent lamp that
produces somewhere around 30% of its claimed light output, in its package
that claims 1580 lumens and "light of a 100 watt bulb". I have yet to see
a dollar store compact fluorescent lamp meet a light output claim. Some
dollar store compact fluorescent lamps also claim "soft warm white light"
but actually glow a bluish "daylight" color.

I don't buy at Dollar stores but I did buy a six-pack of CFL for under
$6 at Home Depot. So that's under a dollar a pop. They work great,
unlike many of the more expensive ones I had. The light is spectrally
more filament-like and they start instantly, just like a bulb.

Merry Christmas, Joerg

 

[Joerg]

Hello Don,

Vaporized metal can sustain an arc that long (I am assuming length
of an AGC style fuse) with even less voltage than that. Try seeing how
long an arc you can draw with an arc welder at merely 30-40 volts or so,
and then imagine what 500 or even 250 volts can do. I once had an arc
almost an inch long between 12 AWG copper wires with only 2-3 amps at 120
volts during an experiment trying to see the spectrum of a copper vapor
arc.

Also, fuses often have a lower voltage rating for DC than for AC.

It is also a matter of energy to be absorbed. A 1A fuse blowing in a 24V
circuit because the current gradually sauntered towards 2A is one thing,
the same fuse in a 240V mains circuit experiencing a sudden dead short
on the other side is quite another. The breaker for such circuits can be
designed for 16A or more depending on where you are in Europe.

I've had fuses spewing their glass and sand all over the place and
leaving nasty scorch marks. I don't think running fuses above their
maximum voltage rating is a good idea. If a manufacturer does it anyway
and something happens the lawyers will be all over them.

Regards, Joerg