Is this a fuse?

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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

Re: Is this a fuse?
On 10/07/2019 00:32, Bob Engelhardt wrote:
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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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<http://diverse.4mg.com/scicaf.htm

Re: Is this a fuse?
On Tue, 9 Jul 2019 19:32:42 -0400, Bob Engelhardt

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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.


--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Is this a fuse?
On 7/10/2019 10:06 PM, Jeff Liebermann wrote:
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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.

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

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

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

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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.


Re: Is this a fuse?
On Thursday, 11 July 2019 15:44:25 UTC+1, Bob Engelhardt  wrote:
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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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