Fusible resistors queries

[N_Cook]

When did they first arrive and do they always have an unusual body colour?
There is a patent reference to 1977 but when would the first appearance in
domestic equipment have been ?.
Resistors that fail open circuit if a designed-in current capacity weak
point is exceeded , fuse-fashion, not just the thermal limit of the body ,
so often no overheating discolouration to the body or surrounding board

 

[Phil Allison]

"N_Cook"

When did they first arrive and do they always have an unusual body colour?
There is a patent reference to 1977 but when would the first appearance in
domestic equipment have been ?.
Resistors that fail open circuit if a designed-in current capacity weak
point is exceeded , fuse-fashion, not just the thermal limit of the body ,
so often no overheating discolouration to the body or surrounding board

** Genuine "fusible "resistors with specific fuse current ratings are rare
beasts - the only ones I know of were used by Yamaha in some of their 70s
and 80s audio amplifiers and were all miniature wire wound types.

OTOH - what are nowadays laughingly referred to as "fusible resistors" are
simply "flame proof" resistors - typically ordinary 0.5W & 1W metal film
types with a high temp, flame proof coating in lieu of the incendiary paint
coatings normally used.




..... Phil

 

[N_Cook]

Way before 1977 !

Take a look at radio and TV sets from the late 50s and 60s.
Big white or beige wirewound resistors in a ceramic housing, one
of the leads spring loaded along the edge, low temp solder blob
on the spring to keep the circuit closed.

Designed to cut open when the resistor's body reaches some 200
degrees Celsius / 400 degrees Fahrenheit.

(I think I can digg up a picture, if you want

Sorry, I should have said fusible resistors otherwise visually
indistinguishable from conventional 1/3 or 1/2W, MO resistors.
Grey bodied 1/3W and 1/2W Philips ones in a 1992 Farnell catalogue

 

[N_Cook]

As far as Philips NFR25 range came in after 1984 and before 1987.
I was trying to gauge what sort of current surge would knock out a standard
MO resistor without leaving any trace of overheating versus a proper 1/3W
fusible resistor if it was likely to be around in 1990.

 

[David Nebenzahl]

Sorry, I should have said fusible resistors otherwise visually
indistinguishable from conventional 1/3 or 1/2W, MO resistors.
Grey bodied 1/3W and 1/2W Philips ones in a 1992 Farnell catalogue

What's "MO"? Never heard this term applied to resistors before.

 

[David Nebenzahl]

What's "MO"? Never heard this term applied to resistors before.

Hmm, let me guess at my own question: metal oxide?

 

[Shaun]

When did they first arrive and do they always have an unusual body colour?
There is a patent reference to 1977 but when would the first appearance in
domestic equipment have been ?.
Resistors that fail open circuit if a designed-in current capacity weak
point is exceeded , fuse-fashion, not just the thermal limit of the body ,
so often no overheating discolouration to the body or surrounding board

Fusistors have been used in test equipment for many years in the input
section. Fluke uses them in all the meters.
I know, I've replaced many in the past.

Shaun