anyone know a part type designation for this fuse (?) breaker (?) alarm (?)

Old-timer's test:  This a close-up of a master power panel from a late 1930's radio station rack installation.  The 3 terminal parts below the cartridge fuses, with the spring coil and green bead.  They are not wired in series with the fuses above.  I can't find any references as to what this part is, exactly.  There was  a relay activated blown fuse alarm, maybe they are part of that system?

"Indicating fuse".

Modern versions:
https://www.fusesunlimited.com/products/alarmindicatingfuse
http://www.littelfuse.com/products/fuses/specialty-power-fuses/telcom-alarm-indicating-fuses.aspx
http://www.littelfuse.com/~/media/electronics/datasheets/fuses/littelfuse_fuse_481_datasheet.pdf.pdf

Be glad you do not have to replace this:
https://www.reddit.com/r/Skookum/comments/6jxt3a/giant_old_fuse_that_my_friend_found_while/

Interesting, thanks.  Have never encountered such. 

I see two terminal components under the common cartridge fuses.  The panel labels them RECT which logically sounds like rectifier diodes. These may be very early use of solid state rectifiers, making them field replaceable , perhaps like tube rectifiers were  replaceable.

If the lamps above the fuses are wired in parallel to the fuses they will light when the fuses fail open. I did a similar trick in a console PS last century, but with LEDs instead of incandescent lamps.

JR

John, there are 3 wired terminals on the rear, and you can see them on the unloaded slots.  The center pin touches the bolt head which is wired on the other side.  The 'rectifier' mentioned is a regulated rack mount supply.  The shot is at an angle to show the dimensions more clearly, other slots are labeled things like 'studio A' 'studio B' 'master channel' 'ring down'  etc.  There is a separate relay activated PSU behind the panel with related panel switches labeled 'relay supply loss alarm' which appears to have been connected to a buzzer system, I think because of the on/off switches for 'buzzer', also indicator light for 'blown fuse' and 'emergency PSU'.    The upper group with cartridge fuses and lamps are labeled  things like 'rack 1'  'rack 2'  'rack 3' 'studio A' 'studio B' , and the two 'studio' slots are the only things duplicated between the layers. 

They measure a fraction of an ohm, end to end.    All the center terminals are bussed together, as are some of one side, depending on relationship.  I wonder when this package went out of style. 

emrr said:

They measure a fraction of an ohm, end to end.    All the center terminals are bussed together, as are some of one side, depending on relationship.  I wonder when this package went out of style. 

Click to expand...

Nice pic's, those are new to me, fascinating.

Single pole, double throw, one shot fuses, not suitable for hazardous locations.

Gene

wow... I have no idea... maybe the coiled wire unwinds with heating, but not sure what happens, maybe the solder melts and opens the circuit?

JR

The coiled wire is a spring. When the link or solder melts, the spring pops up (down?). In this rig, it hits that buzzer buss to wake-up the attendant and he knows to look at the fuses first.

This type, smaller size, was in use into the 2000s on a 1950s telco PBX in a school I knew. (How do I know? Well, I was drilling a wall for network wires, cleverly drilled 47 of a 50-pair telco cable hiding on the other side...)

> not suitable for hazardous locations.

Radio station? School? Not NEC-Hazardous. Generally arc-resistant. (That PBX had a fiberglass cover so workers or kiddies couldn't get zapped, though it was in a closet and the cover was usually off.)

Thanks PRR.  This bakelite panel was mounted in a rack shelf with a fold down front panel, away from random hands.  I'm not sure the purpose of the green bead in all this.  Just a more obvious visual indicator I'd guess. 

emrr said:

  I'm not sure the purpose of the green bead in all this.  Just a more obvious visual indicator I'd guess.

Click to expand...

Yes. Since the alarm buss doesn't tell you which fuse blew, the green flag sticking out make it obvious to quickly locate it. The color green likely indicates the amp rating, it does on some other fuses like this.

Once the tension is released, that shiny piece of spring steel on the bottom side springs down onto the alarm contact, note that it has a bent tip for a contact. At least that's what it looks like from here.

@PRR re 50 pair. Yeah, automotive brake and fuel lines also have a way of being in exactly the wrong place when you have a drill in hand. And it only takes a bit of carelessness to turn a non-hazardous location into a hazardous one. Ask a friend of mine who sent a guy to do a power tie in for live sound, and only after the guy managed to get a screwdriver across two legs of a 400A panel, did he notice the open bucket of paint thinner right under the panel.

Gene