The 100 amp fuse

I found this fuse in an old electrical panel that we were removing from the WICC generator shed.  This was the original service entrance for the site as it was built in 1932 or so.  The generator shed had a manual three pole two position transfer switch, which was fine back when a licensed transmitter engineer was on site whenever the station was on the air.  The generator, according to the old records I could find, was an upright 2-cylinder slow-speed engine with a belt-driven generator.  They were mounted on concrete pads about 5 feet apart.  The motor had a big flywheel that was hand-cranked with the compression off.  Once a good head of speed was built up with the hand crank, the compression lever was thrown and the engine would start.  Alternatively, the procedure was tried again.

That was all replaced in 1971 when the transmitter site underwent a major upgrade.  The old electrical service was bypassed and abandoned in place when a new meter and panel were installed in the transmitter building.  The old service seems to have been frozen in time, untouched for forty years.

Kirkman Engineering renewable fuse
Kirkman Engineering renewable fuse

This fuse is a Kirkman Engineering Company and has a manufacture date stamp of January 1945.  It is a replaceable link AKA “renewable” fuse.  It has “peak lag” links, which I think would be called “slow blow” today.  Peak lag may also indicate a large inductive load, which would lower the power factor.  What I find interesting is that someone, once upon a time, placed two 100 amp links in parallel, then crossed the 100 AMP label out and wrote “200” on the fuse body.

Kirkman Engineering fuse links
Kirkman Engineering fuse links

The problem with this setup is that the panel and wiring were all rated for 100 amps.  The wiring is #4 copper, and the transfer panel and switch are clearly labeled “100 amp, 3 pole.”  It would appear that the finger stock holding the upper blade in place was loose, causing the fuse body to overheat.  In fact, it became so heated that the case and the wood fiber holder were charred and missing.

Fortunately, there was never a fire.

The reason why we use properly sized fuses and breakers.

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2 thoughts on “The 100 amp fuse”

  1. In years past when a dollar was worth something, replaceable fusible links in fuses were popular. Federal Pacific made fuses with replaceable links and called them “ECO-FUSE”. They were of course ECOnomical rather than replacing the entire fuse. If the WICC site is wired with #4AWG copper it doesn’t meet the current (or years past) NEC for a 100 Amp service. It would have to be #3 AWG copper to be in compliance with the NEC in a commercial building. Only residential dwellings can use #4AWG for a 100 Amp service. There is a certain beauty of the old electrical power equipment, and AT&T was one to keep fuses feeding all of their microwave equipment. The higher interrupting capacities of fuses means less time lost to reset a breaker that may have unnecessarily tripped.

  2. It could well be #3 wire, it is cloth covered with hard rubber insulation, there is no gauge or temperature rating on it, I assumed #4. Everything is run inside of rigid metal conduit, so no corners where cut as far as I can see.

    The place is sort of like a museum, I wish the old Western Electric transmitter was still there.

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