A disintegrating panel-mount fuse hoder: how to avoid a catastrophe? - Page 1
Forum section: electronics / beginners

author: golden_labels
author_rank: Super Contributor
timestamp: November 13, 2019, 01:30:16 pm
content: A few days ago I’ve discovered that my hot air station, the famous 858D, is not powering on. Upon opening it I found out that the fuse holder (panel-mount style) has its butt broken off. The remaining wire was happily flapping in a breeze inside the metal case. No burn marks, not melting signs, no fuse explosion — in fact the fuse is perfectly good. I was never touching the holder before, except for an attempt to open it after the device was no longer powering up. And that attempt was stopped as soon as I’ve noticed that the whole holder is rotating — it literally received a wiggle, like 1/8 turns, so not enough to damage anything. Since I was going to open the station anyway, I decided I can as well check that later. The photo shows the holder after I removed the second wire too, but you can get the idea. Now I have two questions.What could’ve caused the damage? A random manufacturing failure? The factory used some weak plastic that degraded over a course of just a few years so much that it disintegrated by itself? Thermal stress? Phase of the moon?The failure made one of the wires attached to the holder flying freely in the metal case. This was not the one of the power cord side — but we may safely assume this was just a coincidence. How can one design their device to account for that type of a failure? My first guess would be to always attach live wire to the side connector of the holder and putting shrink tube or glue on it. But what is the best practice in this case?

author: Ian.M
author_rank: Super Contributor
timestamp: November 13, 2019, 01:47:20 pm
content: Sh-t happens. The plastic was under tension due to the internal spring in the holder, and as it ages, looses plasticisers by outgassing, leaving it brittle. Then any small crack can rapidly propagate and the whole end pops off the holder.The only answer is a better quality fuseholder made from something like glass filled Nylon that doesn't rely on plasticisers to meet its required toughness spec, and engineered to avoid stress concentrations where the contacts penetrate the body.Putting the line in on the front contact is undesirable as that presents a shock risk if any idiot inserts or removes a fuse with the power on. It should always be on the rear contact.Cable-tying the two wires together immediately behind it is advisable to constrain the wiring if a contact comes loose. Whether or not heatshrink over the whole rear of the holder is advisable depends on proximity of other parts and wiring, as it makes it harder to inspect.

author: madires
author_rank: Super Contributor
timestamp: November 13, 2019, 02:26:33 pm
content: Yep, most likely cheap plastic. I have some audio jacks with a similar issue. After two or three years the plastic became so brittle that the plastic covers crumble between your fingers.

author: ender4171
author_rank: Contributor
timestamp: November 15, 2019, 07:54:44 pm
content: The crappy solder they use often has nasty flux in it and they never clean it. That could easily have contributed to the premature failure.

author: Gyro
author_rank: Super Contributor
timestamp: November 15, 2019, 08:04:26 pm
content: In terms of "how to avoid a catastrophe", I agree that the answer is decent heatshrink and maybe a cable tie.Heatshrink the whole body of the fuseholder and ensure that the end of the shrink extends far enough and is narrow enough to retain the end contact and wire, using a cable tie if necessary.The end contactshouldbe the live feed, so it is doubly important that it is safely retained within the sleeving, even if it does break loose. I'm not sure that cable tying the wires alone would be enough to safely restrain it.P.S. It's possible to get ready made push-on fuseholder boots to achieve the same function and make inspection easier. eg.https://uk.rs-online.com/web/p/fuse-holder-accessories/8527433/