Back in 80s I was a calibration technician in the US Air Force, working in an Electronic Warfare shop. We had a major expansion that doubled the size of the facility. After the normal new building problems (leaky roof, phones not working, etc.), we had a new, shiny building with plenty of workspace, storage space, a break room, and even a shower.
After about six months, however, some strange electrical problems started showing up. Because this was Florida during the summer, we normally had to shut down for afternoon thunderstorms and lightening advisories to protect the tens of millions of dollars of test stations, avionics, and other systems. It took a while for the patterns to emerge from the normal glitch noise level.
First, my test station started blowing 45A fuses in the disconnect box mounted on the wall. This wasn’t too uncommon, but one of the station power supplies would usually go first. We would replace the fuse and bring the station back up, stage-by-stage, until we found the fault. Sometimes the fuse would just blow -- or so it seemed. The pattern started to emerge when a fuse blew about once a week. We would troubleshoot each time, but couldn't seem to find the problem.
The frequency increased until we were blowing a fuse a day. We then realized that we were only blowing the B phase fuse. At this point, we called in the electrician from base Civil Engineering. His clamp-on ammeter indicated we were only drawing about 17 amps per phase and the phases were fairly well balanced. The CE electrician had run out of 4517A fuses and only had 60A fuses in his kit, so he installed one.
After some lively discussion, we noted the station was on a 50A circuit, and we needed to get back up and running while the electrician ran across base to get the correct fuse. In the meantime, the 60A fuse blew and the 50A breaker didn’t. This time, instead of sending it straight to the trash, I picked up the fuse from the fuse puller to check the rating and burned my fingers.
That was the aha moment. We weren’t blowing the fuses, we were melting them! After shutting the main breaker off, I started probing and prodding the disconnect box, and I found some discoloration on one fuse holder clip and the terminal lug underneath it. The ohmmeter indicated more than 1 ohm on this heavy gauge connection. P= I˛R. The 17A draw was enough to cook the fuse until it melted. A closer look revealed water marks inside the disconnect box. The box was mounted on what was the outside wall before the expansion.
The new roof had overlapped the old one, resulting in numerous leaks when we moved in. Water had gotten into the box and corroded the contact. The leaks had been fixed and the damage done before we even moved in.
The electrician returned about an hour later with the new fuses. I explained my findings and indicated that the box needed to be replaced, even after cleaning up the contacts. After three more electricians were called out to view the problem, the senior CE electrician finally agreed and the box was replaced about a week later.
On a recent troubleshooting call, the fuses in question were rated for 650 amps. The customer had a "water event" through their motor control center. After replacing the fuses and powering up, they blew a second time. Since these 650A fuses cost $350 a piece, blowing 3 of them a second time was expensive enough to justify calling in some expert help.
Still, to justify the very high cost you propose, some bells and whistles would be appropriate.
Just raise the price of the fuses to something intolerable. Management won't tolerate that too long. When the box costs less than the fuses they'll agree more quickly to replacing it.
I see several comments here which are worthy of my 2 cents.
It was interesting to read the part about this fellow having to "consult" with three or more "CE" personnel BEFORE getting the requisite repair. Sounds like TYPICAL gov't operation, OR maybe a CYA move!
My uncle was an electrical contractor with many certified electricians & helpers running large & small jobs. When in college I also worked for him during the summers & other times off. Furthermore, I have had close friends who are or were in the commercial/industrial/residential electrical contracting field. It has been the topic of conversation MORE than once over the years as to the "effectiveness" of the local Bldg. Dept. inspector. The runningjoke is whether the inspector actually gets out of his vehicle or not, before, during and/or after his report is filed. So, while the purist may call for more diligent authenticating processes, in the real world this ain't never gonna happen!!!! People are people, and soon learn how to flim-flam their jobs, especially in local gov't services.
So, while it may be altruistic to assume that a licensed contractor WILL do the proper thing in a project, there's MORE evidence to substantiate the fact that either the foreman or the laborers will take steps to short circuit (no pun intended!) that effort.
As a current example, the "kids" just bought a new house. It was a pre-owned house about 6 years old. The lending bank required a home inspection by a registered engineer. His report included the fact that in one of the bedrooms the A/C ducts were improperly connected. I asked myself, "how can this be?" So, I set the thermostat to energize the system, scaled a ladder (9 feet ceilings), and felt the air. It was cool to the sense. Additionally, this room has a filtered return duct. I went to it, and felt the return air motion. Where's the problem? I couldn't find one. Additionally, the mandatory line-voltage-powered fire alarms chirped, all of them. Installing new 9-volt batteries did not help. Where was that in his report? It turns out that there was a defective unit causing the others to broadcast a chirp signal. Finally, each bedroom ceiling is equipped w/ a circuit box for mounting a fan and/or fan-light device. The box is wired with a piece of 3-wire Romex (Blk, Wh, R), and there are two wall switches. So, one would expect that one switch controls the Blk circuit, the other switch controls the Red circuit. NO! The Red switch controls one receptacle of a duplex receptacle on one of the bedroom walls. Where is the other end of the Red wire in the ceiling box? Who knows, but it's powerless, and tucked into the box. How did these serious deficiencies pass "inspection"????????? I rest my case!
I used to repair coin operated games for a living - I had several issues with fuses melting instead of blowing. Usually, replacing the fuse holder solved the problem - until I came across Pole Position and Pole Position II. Both these games had a 3ag(agc) fuse rated at 20 amps for the main +5v power supply rectifier. After the games hit the 5 year mark, they started melting fuses. Changing the fuse holder didn't solve it, neither did removing the crimp on connectors to the fuse holder and soldering the wires directly to the holder. The solution was to take 2 AGC fuse holders and wire them in parallel and install 20 amp fuses. The load draw from the game was causing an ultrasonic vibration that was causing the solder to run out the end of the fuse. The telltale signs were the blob of solder out of the end of the fuse, and the fact that when it was running, the fuse was cool to the touch. After the modification, the fuses never failed in that manner.
Interesting point, TJ, that it's the natural inclination to sidestep what the fuse might actually be trying to indicate with its behavior for a fix that is initially finds the fuse at fault and subs it out. As a parallel, I do that repeatedly when my smoke detector shrills--I take out the battery and reset the device and don't give any kind of real consideration to the fact that there might be a problem. Call it the lazy person's guide to troubleshooting.
Interesting point, TJ, that it's the natural inclination to sidestep what the fuse might actually be trying to indicate with its behavior for a fix that is initially finds the fuse at fault and subs it out. As a parallel, I do that repeatedly when my smoke detector shrills--I take out the battery and reset the device and don't give any kind of real consideration to the fact that there might be a problem. Call it the lazy person's guide to troubleshooting.
I agree, Chuck. It's surprising how these Sherlock Ohms bloggers track down their problems. Time after time, they seek out both the obvious and the completely obscure.
I agree, Beth. It's great detective work. I'm repeatedly amazed at how resourceful are Sherlock Ohms authors are when it comes to tracking down very odd problems like this one.
I've seen the problem with overheating fuses before. In my case it was a consumer device with rather cheap fuse clips rather than an actual holder. Contact resistance is something that is frequently overlooked, and it shouldn't be. The worst I had was a coffee maker with a bad Faston crimp. The contact became so hot that it burned a hole in the circuit board and started a small kitchen fire.
In this article, a maintenance technician improperly replaced a 50 amp fuse with a 60 amp fuse. Our discussions last month said this should never happen, and yet it does, time and again in the real world.
Sometimes it's poor design and the rated fuse is truly undersized. Most times, the fuse it telling us there is something abnormal that must be fixed, and yet the single most common troubleshooting procedure is to replace the fuse to see what happens.
Fuses may be doing circuit protection a disservice by looking so innocuous. The fuse manufacturers might consider making them more impressive, more imposing, in order to gain some respect. Maybe the fuses need literal bells and whistles to tell us there is a significant problem.
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