Fuse question

I have a Sony TV that has a blown fuse, 2.5amp, 250V. Can I replace
with a 2.5amp - 125V fuse? I don't know why some TV' s have 250V fuses,
and some have 125V fuses. Thanks group.

 

In an earlier contribution to this discussion,

Probably because a large part of the world uses a supply voltage in the
region of 250v!

 

If you have a 120v mains supply and the fuse is on the AC side of the
rectifier then yes, that should be fine.

 

yes a lot of people don't get Voltage rating on fuses

e.g. It would be pointless to put a 125 Volt fuse in a 3KV microwave line to
the magnetron as when the fuse "fused" the Voltage would jump the gap, so
you would need a 3KV fuse or greater

so another words the Voltage rating is not imported until the fuse blown,
then the fuse must stop the Voltage arcing the gap


I have a Sony TV that has a blown fuse, 2.5amp, 250V. Can I replace
with a 2.5amp - 125V fuse? I don't know why some TV' s have 250V fuses,
and some have 125V fuses. Thanks group.

 

That sounds reasonable, but I'm confused. If I've got two fuses that are
both the same physical size, and one is 125 volts and the other is 250
volts, the gap from end cap to end cap (when the fuse blows) is the
same. (And that gap is far in excess of what either of those voltages
will jump.)

 

But fuses only blow like that when they encounter a severe fault condition,
ie the appliance presenting a short circuit to the mains supply, which
vapourises the entire fuse wire. Sometimes the fuse wire will simply fail at
its weakest point leaving a small gap, which must be wide enough to prevent
an arc.

Dave

 

so another words the Voltage rating is not imported until the fuse blown,

They may just have been through different testing and certification
processes at the manufacturer.

 

Probably, though keep in mind that high current arcs can do jump much larger
gaps than you might think, especially when mixed with a little metal vapor...

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Yes, but first you should find the reason that the fuse blew,
before more damage occurs.

 

Yes, and as someone pointed out, they may behave differently (producing
different size gaps) when they blow gently under minor overload.

 

More on fuse ratings:

http://www.lnl.com/howto/fuse.htm

 

Using "suppose" numbers, are you saying that a fuse manufacturer can
actually make a 250 volt fuse that will burn a 1/4" length of filament
and a 125 volt fuse that will burn a 1/8" length of filament? Reliably
and repeatedly?

If we're talking about standard 1/4" x 1 1/4" or 5 mm x 20 mm fuses, I
say there's no damn difference between a 250 and a 125 with the
exception of the lettering on the cap.

Now, if anyone can give me real information to the contrary, I'll
happily concede, but so far I haven't seen anything that I'd consider
more than speculation.

 

This is the good guts: From http://www.lnl.com/howto/fuse.htm (some
minor editing included.

QUOTE
VOLTAGE RATING: The voltage rating, as marked on a fuse indicates the
fuse can be relied upon to safely interrupt its rated short circuit
current. in a circuit where the voltage is equal to, or less than its
rated voltage.

The standard voltage ratings used by fuse manufacturers for most small
dimension and midget fuses are 32, 125, 250 and 600.

Fuses are sensitive to changes in current, not voltage maintaining
their "status-quo" at any voltage from zero to maximum rating. It is
not until the fuse wire reaches melting temperature and arcing occurs
that the circuit voltage and available power influence the fuse
performance and determine the safe interruption of the circuit.

To summarize, a fuse may be used at any voltage less than its voltage
rating without detriment to its fusing characteristics, but may also
be used at voltages higher than its certified voltage rating if the
maximum power level available at the fuse under a "dead short"
condition can only produce a low energy level non-destructive arc.
ENDQUOTE

Note that any power source supplying the load via the fuse must not be
able to sustain an arc into a short circuit via the blown fuse. As
long as this criteria is observed a low voltage fuse (eg, 125V AC) can
be used in a circuit supplied from 250V AC, or even more.

From page 150 of SWE-CHECK's Fuse Bible
http://www.swecheck.com.au/frames/product_catalogue_index.html

Interrupting Rating (Breaking Capacity)

Also known as the breaking capacity or short circuit
rating - is the maximum approved current which the fuse
can safely interrupt at rated voltage. During a fault or
short circuit condition, a fuse may receive an
instantaneous overload current many times greater
than its normal operating current. Safe operation
requires that the fuse remain intact (No explosion or
body rupture) and clear the circuit.
LBC = Low Breaking Capacity
HRC =High Breaking Capacity
EBC = Enhanced Breaking Capacity.

 

"Smitty Two" bravely wrote to "All" (03 Jan 06 21:10:49)
--- on the heady topic of "Re: Fuse question"

ST> From: Smitty Two <>
ST> Xref: core-easynews sci.electronics.repair:353870

ST> Using "suppose" numbers, are you saying that a fuse manufacturer can
ST> actually make a 250 volt fuse that will burn a 1/4" length of filament
ST> and a 125 volt fuse that will burn a 1/8" length of filament? Reliably
ST> and repeatedly?

ST> If we're talking about standard 1/4" x 1 1/4" or 5 mm x 20 mm fuses, I
ST> say there's no damn difference between a 250 and a 125 with the
ST> exception of the lettering on the cap.

ST> Now, if anyone can give me real information to the contrary, I'll
ST> happily concede, but so far I haven't seen anything that I'd consider
ST> more than speculation.

Perhaps a 125 volt fuse is made with the same wire as the 250 volt
fuse. However the 250 has been approved at 250 and the 125 passed the
125 testing. So if there is an economy in making a 125 rated fuse over
a 250 rated one then I wouldn't risk using a 125 fuse in a 250 spec'd
circuit. (if made from the same spool of wire, we don't know for sure)
However, the wire may not be the only story. Remember that the package
is part of the fuse. Thus perhaps the thickness of the glass tube
also is a function of the safety rating for the 250 and 125 spec too.
Recall there is 4 times more energy involved between 125 and 250!

A*s*i*m*o*v

.... Thomas Edison invented the "Light Emitting Resistor"

 

Read Ross Herbert's post, that's all I need to say on the subject. Perhaps
next time you might keep it civil rather than jumping on people and making a
dick of yourself.

Dave

 

Wow dude, I'm being as civil as possible, don't know what you read into
my post that isn't there. Or do you consider skepticism rude? Sorry I
hate the smily emoticons and stupid <g> things, but I'm not jumping on
anyone, including you.

Now, Ross Herbert's post SUBSTANTIATES my contention. Have you actually
read and comprehended this entire thread, or did you just take offense
to my use of the word "damn.?"

 

I did read the post as being rather hostile TBH. However, I withdraw my
comments and offer my apologies, you say there was no intended hostility and
I accept that.

No hard feelings I hope!

Dave

 

No sweat Dave, thank you. I do understand that the tone of written words
can be easily misconstrued. I'm as irritated by uncouth behavior on
usenet as you are.

Jon

 

Maybe the confusion here is that the OP was talking about AC fuses. DC
is a whole different story esp. in free air. The physics lab where I
worked for a while had a 100 VDC supply 100 amps available. I was
designing a reversing switch for an inductive load and drew an arc that
completely ate the relay in the test cell. Turned it into a puddle of
molten metal and plastic, walked out the power leads and snapped off.
Talking to engineers at the local transit system they were very
familiar with this. "We just walk away".
Richard