Color Code for Fusible or Flame Retardant Resistors: Data Sheets, Standards?

Question

In the context of the repair of European audio and video gear, made by companies like Grundig or Philips, I come across "safety" resistors every once in a while, i.e. flameproof or fusible resistors. They are often marked in the schematic like this:

The actual components are often in the range of 1...10 Ohms, size 0207 (like your good ol' 1/4 Watt through-hole resistor) and they have a fifth ring that's often yellow, orange or violet.

Examples:

Note: This is just a temporary fix. The replacement part I used to bridge the defective resistor will likely fail prematurely. On the other hand, using a large 1...4 Watt resistor will last forever, but it will fail to protect the unit and I might create a fire hazard. This is just a temporary fix to check if the rest of this particular CD player still works (it does).

I would like to replace the resistors with the closest possible match. However, the service manuals often don't say what exact manufacturer or type they used, and I had no success finding data sheets by some of the companies that come to mind (Vishay, Beyschlag, BC components, ...)

White or black rings on more modern and often larger fusible resistors are common in today's switching power supplies etc., but any sources with data for safety resistors with yellow, orange or violet rings would be greatly appreciated.

Answer 1

Overview (details and sources follow below)

Body Color	Fifth Band	Manufacturer	Type	Material	Fusing	Non-Flammable
Grey	Violet	Vishay BC	NFR25	Metal Film	Yes	Yes
Grey	White	Vishay BC	NFR25H	Metal Film	Yes	Yes
Dark Brown (Bakelite)	Blue	Yageo / Vitrohm	BWF	Wirewound	Yes	Yes
Grey	Blue	Yageo / Vitrohm	RFS	Wirewound	Yes	Yes
Green	Brown, Black, Red or Orange	Yageo / Vitrohm	CRT	Wirewound	Yes	Yes
Grey	Black	Yageo	FCR	Carbon Film	No	Yes
Green	White	Yageo	FKN	Wire Wound	Yes	Yes
Grey	Yellow	TT electronics / Welwyn	FC4	Carbon Film	Yes	Yes
Grey	Yellow	TT electronics / Welwyn	FA8225, FA8325, FA8425	Metal Film	Yes	Yes
Blue	Yellow	Firstohm	FGE	Not stated in data sheet, maybe metal film?	Yes	Yes
Pink	Black	Firstohm	SCP	Not stated in data sheet, maybe wirewound?	Yes	Yes
Blue	Green	KOA Speer	RF25CC	Likely metal film?	Yes	Yes

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For resistors with a grey body and a violet 5th ring, the answer is Vishay, NFR25. Grey body with white band: NFR25H

Data Sheet: https://www.vishay.com/doc/?28737

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Bakelite case with blue band: Vitrohm/Yageo BWF (data sheet)

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Grey body with blue band: Vitrohm/Yageo RFS The picture does not show the blue band, but it is mentioned in the data sheet.

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Green Body with fifth band in brown, black, red or orange: Yageo / Vitrohm CRT (data sheet):

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Grey body, black fifth band: Yageo FCR carbon film resistor, flame-proof, non-fusible. 2021 (current) data sheet, no marking specification. 2020 (previous) data sheet, "gray color lacquer", "5th color code: black"

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Green body, white fifth band: Yageo FKN wirewound resistor, fusible, flame-proof. 2022 (current) data sheet, no marking specification. 2020 (previous) data sheet, "green color [...] lacquer", "5th color code: white"

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Grey body with fifth yellow band: TT electronics / Welwyn type FC4 (data sheet).

... or FA8025 series (FA8225, FA8325, FA8425)

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Blue body, yellow fifth band: Firstohm FGE. Link to distributor for the catalog, because the individual data sheet from the manufacturer is only available upon request. The data sheet does not state the marking code, so we have to rely on the picture for the type/series on their website.

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Pink body, black fifth band: Firstohm SCP. Link to distributor for the catalog, because the individual data sheet from the manufacturer is only available upon request. The data sheet does not state the marking code, so we have to rely on the picture for the type/series on their website.

Note (1): Firstohm uses a blue fifth band to mark high voltage resistors. For small types like 0207 especially, high voltage resistors will have high resistance values (above 100 kOhm, mostly above 1 MOhm) while fusible resistors will have low values (below 1 kOhm, mostly below 100 Ohm).

Note (2): The data sheets are not easily available for download from their website, there are no specifications for the marking codes, but hey - if you enjoy fancy artwork instead, they certainly have some on-topic stuff in their catalog, boom!

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Blue body, green fifth stripe: Fusible resistors, series RF25CC

KOA: Their marking specification is exceptionally valuable. Thank you, KOA Speer.

Also, I do wish that all manufacturers had charts like this one:

Note: KOA also has surge-rated resistors, they have a blue/grey body with a fifth band in black, green or white. Another example why one must check the footnotes and think about the application when replacing a special-purpose resistor. My favorite chemistry teacher once taught me that "one can do anything if one knows what they're doing". In the context of repair work: Fix anything, but know what you're doing. (And you won't cause someone's house to burn down.)