Fuse made of 3/4" copper pipe

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Lxnxjxhx

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Someone had a post showing this.
Well, a handbook formula tells me it should melt at less than 500 amps. I guess before I start producing these I should try to get a UL listing. . .
 
langjahr@comcast.net said:
Well, a handbook formula tells me it should melt at less than 500 amps.
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NEC Handbook? Care to share the formula?

I just noticed your location. You live close to me?
 
Type L, from the Grainger catalog.

It should have read greater than 500 amps, because the formula was for round wires, and a pipe dissipates heat much better. As surface area goes ^, heat dissipation goes ^.
I would guess the flattened part of the pipe melts first.

Fusing current for a wire:
I=K x d^(3/2), I is in amps, d is the wire diameter in inches and the constant K for copper is 10,244, aluminum is 7585. There is a wide tolerance on this value.
#8 copper wire melts at 472 amps. I have measured #30 wire melting at about 10 amps.

I'm near Washington, DC. And, NJ wasn't Hell for me, but you could see it from there. Ditto for San Antonio.
I thought Miami was a tropical paradise.
 
I'm near Washington, DC. And, NJ wasn't Hell for me, but you could see it from there. Ditto for San Antonio.
I thought Miami was a tropical paradise.
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And I thought you lived in Michigan. I live not far from the fine metropolis of Hell, MI and thought you might be a neighbor. And yes Hell does freeze over.:grin:
 
I have seen people do that kind of thing when they wanted a NF disconnect and only had the fusible kind and did not have (or were too cheap to acquire) the non-fuse links.
 
dlhoule said:
And I thought you lived in Michigan. I live not far from the fine metropolis of Hell, MI and thought you might be a neighbor. And yes Hell does freeze over.:grin:
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Is that near Climax? I love that sign on the drive from Detroit to Chicago. "Climax - 1 Mile"
 
dlhoule said:
And I thought you lived in Michigan. I live not far from the fine metropolis of Hell, MI and thought you might be a neighbor. And yes Hell does freeze over.:grin:
Click to expand...


And here's the proof:

hellsign-1.jpg
 
1009 amps for 5 seconds to melt a #8 copper conductor.

1009 amps for 5 seconds to melt a #8 copper conductor.

I couldn't open your source; I get messages lately that "a pop-up window was blocked." Dunno' what causes it.

My objection to this formula (from Reference Data for Radio Engineers, 1982, Howard Sams, "fusing current") is that the constant K for copper is given to five significant figures, implying that this value is known to 1 part in 10,244. From your data, the tolerance on this final answer of 500 amps may be
+100%/-0%.

Also, for short pieces of wire like this "fuse" a lot of heat is conducted out of each end. Computer programs might be able to calculate the heat loss due to radiation, conduction and convection for finite lengths of wire. I still have my slide rule.

Have you forgotten that this fuse is versatile? If you want a time delay you fill the pipe with water before you crimp it.
So, I'll hold off on the UL listing until these minor technical issues have been settled. . .?
 
langjahr@comcast.net said:
I couldn't open your source; I get messages lately that "a pop-up window was blocked." Dunno' what causes it.
Click to expand...
Your browser. There should be an options tab you can select 'allow' from.
 
double integral

double integral

I used the OD to figure the area of that circle, then the ID to figure the area of that circle, then subtracted the areas, then figured out what wire diameter would have this area.
A open tube would dissipate heat better than a round wire, but this tube is sealed.
Where IS my book on thermodynamics??
 
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