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Fusible resistor characteristics query

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and 5 band colour coding

Markings are to be shown on the resistor body by color coding.

1st, 2nd and 3rd color codes : nominal resistance value. 4th color code: resistance tolerance-J (±5%) - gold color. 5 th color code : fusing characteristics green color -8 times blue color -12 times white color -16 times violet color -32 times

if 1W then white band means subjecting to 16W will fuse in 1 minute

Surely any normal 1W resistor subjected to that sort of overload will have burnt up quicker than in 1 minute or have I misread something ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook
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That's probably worst case.

The biggest advantage of fusible resistors is they burn up gracefully, failing suddenly rather than drifting, and they won't catch fire or pour out nasty smoke.

Reply to
James Sweet

have

Any suggestions what to look for on scrapping off the coating of what maybe a mechanically failed one. Where to find the fusing bit to check for fracture versus fusing ? or any other indications to look for ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook

Removed the grey coating and remnant parts of the metalisation/ MO sum to about 1.5 ohm. The joining section is about 1 x 1 mm with a neat hair-line crack across it and no sign of any heating there. So mechanical breakage, I will dig out my microscope and take a photo of it.

Before removing coating, was definitely 2.2 ohm markings with white band (if) for x16 presumably referring to that 1 x 1 mm section, so x32 violet banded one would have a something like 0.7 x 0.7mm intercept region and a green band x8 would have more like 1.4 x 1.4 mm fusing area.

Anyone care to give a reason for shock induced fracture just at that point?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook

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Is a microscope view of the crack. Now viewing magnified it can now be seen the fault developement. The just left of centre part of the crack must be part of a crack that formed initially but enough current flowed in the other parts making touching contact until there was too much localised fusing.

1 to 1 marks the 1mm or so of conductor between the 2 straight line etching/millings ? into the conductor to form part spiral paths. The C marks the end of one of these formed breaks and there is another one on the other track , off the top left of the image, giving about 1 x 1mm central fusible conductor. Nowhere on the remaining conductor is there any discolouration due to overheating

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook

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