The production floor supervisor calls maintenance to say the equipment is down. A competent engineer quickly diagnoses the problem: A loosened terminal screw caused the circuit to heat enough to blow the fuse. He tells maintenance to replace the fuse. Uh, oh, no more fast-acting KTKR fuses. Maintenance thinks, "We're out of KTKR fast-acting fuses, but I've got a bunch of KTDR fuses in the same current rating. They'll be fine."
In our example, if a time-delay fuse gets put where a fast-acting fuse should be, the fuse will allow 20 more amps through before melting. Improper substitution, even though the fuses are identical in shape and current rating (and the part numbers differ by only one letter), can cause machine damage, fire, and possibly human injury.
Who becomes liable? Is this foreseeable misuse? The codes governing electrical panel safety require panel manufacturers to have fuse replacement schedules prominently placed on the panel (along with terminal screw torque requirements). The trick is following them. This is something that concerns every machinery manufacturer.
This makes me think of the Darwin Award given to the gentleman who removed himself from the gene pool without actually killing himself. OK, it was just an urban legend. But improper substitution does happen. If we think Thurston Poole of the bullet fuse urban legend is an idiot, shouldn't we think the same of the maintenance technician who replaces a fast-acting fuse with a time-delay one? Or should we be looking at the machinery manufacturer and the fuse manufacturer as the dummies for designing circuit protection where fast-acting and time-delay fuses can be mixed and matched interchangeably?
CC is just one class. We also have classes J, T, L, and H, to name a few -- not to mention inverse time circuit breakers. The subject of circuit protection is not a simple one.
TJ, while there are always potential problems on the maintenance end where there can be a substitution, I don't believe that this is the manufacturer's fault. Back when we had fuses at home (sometime in the third quarter of the last century of the last millenium) we made sure we had a full set of the correct fuses on hand. We also made sure we put the correct fuse in as a replacement. Now, my father worked in an place where precision was paramount, so it was in his nature that we did so.
Now, the situation you describe is probably all too common these days. I think it becomes a management issue to ensure that you are properly equipped with spares.
I agree with all that you say, Naperlou, but I also believe that short-sighted management decisions lead to litigation for assigning blame when something goes wrong.
I've watched the quality of maintenance departments decline over the years - pick your reason why: lower pay offered, staff cuts leading to overwork, running equipment longer without commesurate maintenance. All reasons point to maximizing profit.
When a manufacturer names three similar but functionally very different items with very similar part numbers, ANYONE can make a mistake.
The varying character should either be first, or last, plain and simple.
I've seen a number of maintenance departments run on a shoe-string budget (penny-wise, pound foolish) and am amazed at what the technicians can do with almost nothing. That environment is ripe for misusing a same-sized but differently rated fuse.
One alternative is to use a resettable polymer PTC (PolySwitch Device) instead of a fuse. That way, after the fault condition is cleared and the power is removed, it will reset itself to the low resistance condition, and the sytsem will work again. This eliminates the possibility of someone useing the wrong fuse. I should point out that these devices are not designed for large power systems, but in lower votlage applicatoins and circuit board level applications, they are very useful.
I perfer ciruit breakers in the applications I'm involved. And the same or similar information applies.
Some of my motorcycle ciruits were over loaded. The solder holding the fuse element melted but the element and fuse was still "good".
We had a coffee vender that had a problem with a 50 amp CB kicking out. Well it was very hot inside the coffe shack and the thermal CB was only working as design. You have to get the heat out of the environment not replace the CB.
We were challenged for 60 Hz ciruit protection for a flying test bed that used much GPTE intended for ground use. The only manufacturer Cultler - Hammer with some slight derating. Typical 400 Hz CBs do not open wide enought to quelch the 60 Hz arc.
I agree wholeheartedly with your statement, "That environment is ripe for misusing a same-sized but differently rated fuse." Maintenance personnel are also not necessarily conversant with subtle nuances like time-delay versus fast blowing fuses...I had a friend that used to work on control boxes for door openers and I would shudder to see what he would pull out of a fuse holder in place of the correct fuse - tin foil, screws and pennies were popular choices.
The nature of electronics demands that folks may need to substitute parts but to do so without proper cross-referencing them is to me, very shabby work. Unforeseen problems may or may not develop with parts that are not OEM or are comparable but specs aren't exactly the same and these problems are hard to predict.
While I see your concern and the reality is, people will often make assumptions without further verification, I think having the responsibility of replacing a part should require the person doing it to make sure the part is adequate for the task. So if we are speaking about the ideal - the fuses would always be verified. But companies have to deal with reality. A smart manager would make sure there is a ready supply of the correct fuses available!
At some point the owners of equipment must assume responsibility for not behaving in a stupid manner! This is particularly applicable to fuses, and the replacement of fuses. When we mark a fuse holder with a particular fuse type and rating that is what should be used as a replacement. It is the users responsibility to install the correct fuse type and size. An individual who does not understand that is fundaamentally unqualified to do the job. It is that simple. Unfortunately the courts are choosing to reward stupidity at the expense of the rest of us.
William K, I'm sure you're happy to hear that you'd make a bad lawyer. You're thinking too sensibly.
I agree with you, and I bet most readers do too. That doesn't change the fact that improper fuse use happens, doesn't change the fact that product misuse happens all the time. As the link I gave stated, a screwdriver used to open a paint can is a misuse of the tool which should be expected.
The woman who initially won her civil suit against McDonalds for their too-hot coffee should have been sensible enough to expect a burn with hot liquid near her lap. A jury disagreed and gave her a substantial award for her utter stupidity.
Luckily, an appeals judge had more sense and drastically slashed the award.
What you said is what SHOULD happen, but is not what DOES happen.
Just once, I'd like to see a news story about a judge who told the plaintiff "Are you a complete idiot? Are you unable to pour water from a boot even when the instructions are printed on the heel? Case dismissed for utter lack of common sense".
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When a crane doesn't have a monitoring system, crane owners schedule service every six months and simply scrap the parts they replace, even if a part has had little use and doesn't need replacing. This can cost thousands.
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