Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old July 10th 19, 12:32 AM posted to sci.electronics.repair
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Default Is this a fuse?

It was in a variac, connecting the wiper to its terminal. It had a
connector tab on each end & was inside the sleeve. It's lead colored,
but much stiffer than lead - zinc?. The variac is 20A resistive, 14A
otherwise. It failed with a pop when an end connector came off.

I dunno what else it might be, but it was really inaccessible,
underneath the terminal block - a terrible location for a fuse. And
where would you get a replacement?

https://i.imgur.com/y0RREz0.jpg

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Old July 10th 19, 12:30 PM posted to sci.electronics.repair
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Default Is this a fuse?

On 10/07/2019 00:32, Bob Engelhardt wrote:
It was in a variac, connecting the wiper to its terminal. It had a
connector tab on each end & was inside the sleeve. It's lead colored,
but much stiffer than lead - zinc?. The variac is 20A resistive, 14A
otherwise. It failed with a pop when an end connector came off.

I dunno what else it might be, but it was really inaccessible,
underneath the terminal block - a terrible location for a fuse. And
where would you get a replacement?

https://i.imgur.com/y0RREz0.jpg


looks like termination/weld failed at say 15 amp , rather than the
"fuse-link" which is intact, otherwise looks like automotive blade fuse
in construction.

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Old July 11th 19, 03:06 AM posted to sci.electronics.repair
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Default Is this a fuse?

On Tue, 9 Jul 2019 19:32:42 -0400, Bob Engelhardt
wrote:

It was in a variac, connecting the wiper to its terminal. It had a
connector tab on each end & was inside the sleeve. It's lead colored,
but much stiffer than lead - zinc?. The variac is 20A resistive, 14A
otherwise. It failed with a pop when an end connector came off.

I dunno what else it might be, but it was really inaccessible,
underneath the terminal block - a terrible location for a fuse. And
where would you get a replacement?

https://i.imgur.com/y0RREz0.jpg


I couldn't find anything similar, partly because you didn't supply the
maker and model number of the variac.

The lead colored material is probably zinc steel. Try checking with a
magnet.

Thanks for including a ruler in the photo. However, the photo is too
small and fuzzy to use it to make measurements. My guess(tm) is that
the fuse width is 1/16th inch. Since push on tab connectors were
used, I measured a handy large tab connector at 0.033" thickness.
Therefore, the cross sectional area is:
0.063 * 0.033 = 0.0021 sq-in = 2700 circular-mils
http://www.kylesconverter.com/area/square-inches-to-circular-mils
Looking at a handy wire table:
https://www.engineeringtoolbox.com/awg-wire-gauge-circular-mils-d_819.html
2700 circular-mils is approximately the area of #16 AWG wire. Checking
a fusing current table at:
https://www.powerstream.com/wire-fusing-currents.htm
shows that #16 AWG will fuse at:
Copper 117 Amps
Aluminum 86.7 Amps
Iron 36.0 Amps
Tin 18.8 Amps
My guess(tm) is iron at about 36A.

I doubt that you're going to find a replacement fuse. Find a piece of
similar thickness tin plated steel at the local hobby shop. Something
like this, but either thicker, or use 3 layers:
https://www.acehardware.com/departments/hardware/metal-sheets-and-rods/sheet-metal/5611660
If you can't find any, just take some sheet steel and solder plate it.
For 0.033" 20 or 22 gauge looks about right:
https://www.law.cornell.edu/uscode/text/15/206

Be sure to adjust the numbers for the actual measured dimensions.

Or, you could just replace it with an external 35A cartridge fuse.


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http://www.LearnByDestroying.com
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Old July 11th 19, 03:43 PM posted to sci.electronics.repair
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Default Is this a fuse?

On 7/10/2019 10:06 PM, Jeff Liebermann wrote:
I couldn't find anything similar, partly because you didn't supply the
maker and model number of the variac.


It's a Ward Leonard (no model number) - yeah, I never heard of them
either and I didn't find anything on the web. They did make variacs for
theatrical lighting, so that's probably where this came from.

The lead colored material is probably zinc steel. Try checking with a
magnet.


It's non magnetic. Following your powerstream lead, I'm guessing it's
tin, or lead-tin.

...
Therefore, the cross sectional area is:
0.063 * 0.033 = 0.0021 sq-in = 2700 circular-mils


The bridge measures .017 x .068 in; 1472 circ mils (.038 equiv diam)

....
https://www.powerstream.com/wire-fusing-currents.htm
shows that #16 AWG will fuse at: ...


AWG 18 is .0403 diam & tin fusing current is 13A. Which is considerably
less than the 20A that the variac is rated for resistive.

I doubt that you're going to find a replacement fuse. ...
Or, you could just replace it with an external 35A cartridge fuse.


Yeah, I put in a piece of 14ga copper & will use an external fuse. For
now, I'll just rely on the 15A breaker that it's plugged into.

The confusing thing to me was how inconvenient this fuse's replacement
was. The mounting block had to be removed (2 screws) & the fuse was
held by another 2 screws, each with a sleeve, flat washer, lock washer,
& nut. What were they thinking?

Thanks for your in-depth reply.

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Old July 11th 19, 08:40 PM posted to sci.electronics.repair
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Default Is this a fuse?

On Thursday, 11 July 2019 15:44:25 UTC+1, Bob Engelhardt wrote:
On 7/10/2019 10:06 PM, Jeff Liebermann wrote:


I couldn't find anything similar, partly because you didn't supply the
maker and model number of the variac.


It's a Ward Leonard (no model number) - yeah, I never heard of them
either and I didn't find anything on the web. They did make variacs for
theatrical lighting, so that's probably where this came from.

The lead colored material is probably zinc steel. Try checking with a
magnet.


It's non magnetic. Following your powerstream lead, I'm guessing it's
tin, or lead-tin.

...
Therefore, the cross sectional area is:
0.063 * 0.033 = 0.0021 sq-in = 2700 circular-mils


The bridge measures .017 x .068 in; 1472 circ mils (.038 equiv diam)

...
https://www.powerstream.com/wire-fusing-currents.htm
shows that #16 AWG will fuse at: ...


AWG 18 is .0403 diam & tin fusing current is 13A. Which is considerably
less than the 20A that the variac is rated for resistive.

I doubt that you're going to find a replacement fuse. ...
Or, you could just replace it with an external 35A cartridge fuse.


Yeah, I put in a piece of 14ga copper & will use an external fuse. For
now, I'll just rely on the 15A breaker that it's plugged into.

The confusing thing to me was how inconvenient this fuse's replacement
was. The mounting block had to be removed (2 screws) & the fuse was
held by another 2 screws, each with a sleeve, flat washer, lock washer,
& nut. What were they thinking?

Thanks for your in-depth reply.


Something that shape will fuse at higher i than wire the same width due to heat conduction away from the hotspot. The shape improves the slow to fast fusing current ratio, but worsens the breaking capacity.


NT


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Old July 12th 19, 12:04 AM posted to sci.electronics.repair
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Default Is this a fuse?

On Thu, 11 Jul 2019 10:43:34 -0400, Bob Engelhardt
wrote:

On 7/10/2019 10:06 PM, Jeff Liebermann wrote:
I couldn't find anything similar, partly because you didn't supply the
maker and model number of the variac.


It's a Ward Leonard (no model number) - yeah, I never heard of them
either and I didn't find anything on the web. They did make variacs for
theatrical lighting, so that's probably where this came from.


Google finds plenty of hits on the company name, but none involving a
variac. Probably parts of a system as you suggest.

The lead colored material is probably zinc steel. Try checking with a
magnet.


It's non magnetic. Following your powerstream lead, I'm guessing it's
tin, or lead-tin.


Ok, it's not iron. It's also not 63/37, 60/40 or 50/50 Sn/Pb, also
known as solder. I would guess 100% tin with the dull coloration that
looks like lead be tinning, or some kind of corrosion.

...
Therefore, the cross sectional area is:
0.063 * 0.033 = 0.0021 sq-in = 2700 circular-mils


The bridge measures .017 x .068 in; 1472 circ mils (.038 equiv diam)

...
https://www.powerstream.com/wire-fusing-currents.htm
shows that #16 AWG will fuse at: ...


AWG 18 is .0403 diam & tin fusing current is 13A. Which is considerably
less than the 20A that the variac is rated for resistive.


I would expect the fuse to be rated at MORE than 20A. Also, a 0.017
in thick spade lug is rather flimsy and will probably make a lousy
push on tab terminal. For 20A, it really should be thicker or the tab
terminal will arc, loosen, and/or fall apart. Tin is easily soldered.
I would therefore expect wires to be soldered to the tabs and not use
push on terminals.

I doubt that you're going to find a replacement fuse. ...
Or, you could just replace it with an external 35A cartridge fuse.


Yeah, I put in a piece of 14ga copper & will use an external fuse. For
now, I'll just rely on the 15A breaker that it's plugged into.


That will work. I would heavier wire to a fuse socket. However, I'm
at a loss as to how to rate the fuse. My initial guess(tm) would be
20A or slightly larger to correspond to the stated rating. However,
if the fuse were too large, the variac winding would probably blow
before the fuse, which kinda defeats the purpose of having a fuse.
Therefore, I would measure the variac copper wire diameter, calculate
the fusing current from the Powerstream chart, and size the fuse to
blow at LESS than wire fusing current.

The confusing thing to me was how inconvenient this fuse's replacement
was. The mounting block had to be removed (2 screws) & the fuse was
held by another 2 screws, each with a sleeve, flat washer, lock washer,
& nut. What were they thinking?


My guess(tm) is if the fuse blew, the variac would be considered
totalled and require a factory replacement. That fuse was obviously
not intended for customer replacement. My conspiracy theory is that
someone forgot to design a fuse into the original device, and had the
variac winding blow up in the field. UL or the equivalent, probably
wouldn't like Ward Leonard modifying the design without having the
device recertified. Not wanting to go through that ordeal process
again, WL installed a fuse where UL wouldn't see it and said nothing
about the field failures.

Thanks for your in-depth reply.


Y'er welcome.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old July 12th 19, 05:07 AM posted to sci.electronics.repair
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Default Is this a fuse?

On Thursday, July 11, 2019 at 10:44:25 AM UTC-4, Bob Engelhardt wrote:
On 7/10/2019 10:06 PM, Jeff Liebermann wrote:
I couldn't find anything similar, partly because you didn't supply the
maker and model number of the variac.


It's a Ward Leonard (no model number) - yeah, I never heard of them
either and I didn't find anything on the web. They did make variacs for
theatrical lighting, so that's probably where this came from.

The lead colored material is probably zinc steel. Try checking with a
magnet.


It's non magnetic. Following your powerstream lead, I'm guessing it's
tin, or lead-tin.

...
Therefore, the cross sectional area is:
0.063 * 0.033 = 0.0021 sq-in = 2700 circular-mils


The bridge measures .017 x .068 in; 1472 circ mils (.038 equiv diam)

...
https://www.powerstream.com/wire-fusing-currents.htm
shows that #16 AWG will fuse at: ...


AWG 18 is .0403 diam & tin fusing current is 13A. Which is considerably
less than the 20A that the variac is rated for resistive.

I doubt that you're going to find a replacement fuse. ...
Or, you could just replace it with an external 35A cartridge fuse.


Yeah, I put in a piece of 14ga copper & will use an external fuse. For
now, I'll just rely on the 15A breaker that it's plugged into.

The confusing thing to me was how inconvenient this fuse's replacement
was. The mounting block had to be removed (2 screws) & the fuse was
held by another 2 screws, each with a sleeve, flat washer, lock washer,
& nut. What were they thinking?

Thanks for your in-depth reply.


If it was made for stage lighting, the panel would have a fuse per fader (Variac).

Stage crews would replace blown fuses with anything that would restore the lights, so a hidden fuse prevented a fire from an overloaded fader. The early ones I used in high school and working on school equipment used Edison based screw in fuses. You would find 30A in place of 15 or 20A, and dead faders.
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Old July 14th 19, 04:03 PM posted to sci.electronics.repair
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Default Is this a fuse?

On 7/11/2019 3:40 PM, wrote:
Something that shape will fuse at higher i than wire the same width due to heat conduction away from the hotspot. The shape improves the slow to fast fusing current ratio, but worsens the breaking capacity.


Makes sense - thanks
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Old July 14th 19, 04:13 PM posted to sci.electronics.repair
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Default Is this a fuse?

On 7/11/2019 7:04 PM, Jeff Liebermann wrote:
... the 20A that the variac is rated for resistive.


I would expect the fuse to be rated at MORE than 20A. Also, a 0.017
in thick spade lug is rather flimsy and will probably make a lousy
push on tab terminal. For 20A, it really should be thicker or the tab
terminal will arc, loosen, and/or fall apart. Tin is easily soldered.
I would therefore expect wires to be soldered to the tabs and not use
push on terminals. ...


It failed where the tabs were fixed to the body at right angles. It's
hard to tell exactly, but it looks like a spot weld & not much of one at
that. Pretty flakey & I'm glad to have it out of there.

My guess(tm) is if the fuse blew, the variac would be considered
totalled and require a factory replacement. That fuse was obviously
not intended for customer replacement. My conspiracy theory is that
someone forgot to design a fuse into the original device, and had the
variac winding blow up in the field. UL or the equivalent, probably
wouldn't like Ward Leonard modifying the design without having the
device recertified. Not wanting to go through that ordeal process
again, WL installed a fuse where UL wouldn't see it and said nothing
about the field failures.


That makes as much sense as anything.

Thanks again


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