fusing current of wires

To: tesla-at-poodle.pupman-dot-com
Subject: fusing current of wires
From: Tesla List <tesla-at-stic-dot-net>
Date: Tue, 08 Apr 1997 11:52:03 -0500
Approved: tesla-at-stic-dot-net

Subject: 
        fusing current of wires
  Date: 
        Tue, 8 Apr 97 11:05:16 EDT
  From: 
        pierson-at-gone.ENET.dec-dot-com
    To: 
       
mail11:;;;;;-at-us4rmc.pko.dec-dot-com-at-us4rmc.pko.dec-dot-com-at-unknown.pupman-dot-com;;;;;;;;
(-at-teslatech)
    CC: 
        pierson-at-gone.ENET.dec-dot-com


>> > Fr. MaGahee: At one time you mentioned that you thought these
>> > transformers have large wire in the secondaries. Do you know what size
>> > it is?

>> I fried one of my transformers, so I did a dissection.  I estimated the
>> wire at about a #28 gauge.

>I finally got into one of the secondaries. The wire measures 0.010"
>which is #30. According to the ARRL handbook this wire is capable of
>about 140ma using standard design criteria. I am still very afraid of
>drawing 300ma but will go ahead with tests.

>Skip
        Standard Handbook for Electrical Engineers list three different
        formulas for fusing current.  The simplest is

        I=Ad**(3/2)

        d is in inches.
        A is a constant:
                10,244 for Copper.
                7,585 for Aluminum.

        Tho they say it has limitations.

        (the others get seriously complex for typing...)
        (I haven't run any numbers....)

        Eleswhere they have a chart, which shows
                #30 at 10A for 2 seconds
                #28 at 10A for 5 seconds
        Eyballing off the end of the chart #30 might carry an amp
        'indefinitely....'

        (For comparison #14, UL/NFPA fused for 14A for house wiring,
        is 120A, for 10 seconds...   8)>>.  (the chart only extends to
        10 seconds....))
        
        regards
        dwp