[Milsurplus] Re: RE: Status of Fuse count

[WA5CAB@cs.com]

Joe & Group,

First let me remind everyone that fuses do have a voltage as well as a 
current rating.  It has to do with extinguishing the arc rather than 
sustaining it.  For example, a 32 volt fuse may well burn up the fuse holder 
if it blows with 220 volts across it.

I have a stack of Military Standards on fuses here that date from 1953, which 
may be when the standards were set up.  They cover fuse types F01 through 
F71, and still do not cover all of the physical styles that I have seen (no 
pigtail ones, for example).  Fuses marked according to this standard would 
have markings similar to F02G1R50A.  F02 determines the physical dimensions 
(0.25 dia x 1.25 long), ferrule material (nickle or silver-plated brass) and 
gody material (glass).  G is the voltage rating (250V).  1R50 means 1.5 amps 
(the R is the decimal point, so F02GR750A would be 3/4 amp). And A is the 
"blowing" charasteric where A is immediate (it's actually more complicated 
than that) and B is time-lag or slow-blow.  F03 appears to be the same thing 
except plastic (i.e., bakelite) or ceramic body.  

Some of the types appear to be redundant.  F04A (A = 32 volts) would be the 
same as F02A, except that F02A isn't on the list, only F02G.????

3AG, 3AB, 4AG, etc. are generic commercial type numbers.  About all that 3AG 
defined were the dimensions and ferrule and body material (nickle plated 
brass and glass - 3AB is bakelite body).  Time lag was indicated by the 
suffix "SB" or "Slo-Blo".  Pigtail versions might have a "PT" suffix.  
Voltage rating was stamped on the fuse, and they were easy to mix up.  

Each manufacturer had their own part numbers that crossed to these.  
Littlefuse 311 was 3AG 32V, 312 was 3AG 250V except 8 amp which was 125V, 313 
was 3AG-SB 125V through 5 amp and 32V through 30 amp, 314 was 3AB (but with 
steatite body) 250V except 30 amp was 125V, 315 was 3AG Slo-Blo Pigtail 125V, 
318 was 3AG Pigtail 250V.

Sometime (my memory says early 60's but it could have been a decade earlier) 
during the last century, type numbers of the 3AG, 4AG style were redesignated 
with a three-letter type.  3AG became AGC, MTH or GLH, 3AG SB became MDL or 
MDX, 3AG PT became GJV and 3AG SB PT became MDV.  4AG became AGS.  (The 
preceding two paragraphs gleaned from the 1960 Radio-Electronic Master - and 
that ain't all of it).

I don't know what to make of the example that you gave (F02A125V10A).  I've 
seen fuses marked like this, mostly in Navy shipboard sets I think.  But they 
all had ceramic bodies, and by rights, should have been marked F03G, as F02A 
should be glass and 32 volt.  Maybe someone didn't get the word and was 
allowed to get away with it.  But I think that these would equate to a 
Littlefuse 314010 (type 314, 10 amp 250V).

73
Robert Downs
Houston
<WA5CAB@cs.com>


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