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These Fuses Melt in Water

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TJ McDermott
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Re: We talked about fuse substitution last month
TJ McDermott   10/16/2012 10:10:36 AM
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Now that's a good idea.

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.  

deejayh
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Silver
Re: We talked about fuse substitution last month
deejayh   10/16/2012 10:00:11 AM
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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.

OLD_CURMUDGEON
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Platinum
OOOOPS!!
OLD_CURMUDGEON   10/16/2012 9:47:36 AM
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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!

 

pennyman
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Iron
Melting fuses
pennyman   10/16/2012 9:41:39 AM
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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.

Beth Stackpole
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Re: We talked about fuse substitution last month
Beth Stackpole   10/16/2012 7:07:00 AM
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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.

Beth Stackpole
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Re: We talked about fuse substitution last month
Beth Stackpole   10/16/2012 7:06:14 AM
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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.

Rob Spiegel
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Re: Averting a major problem
Rob Spiegel   10/15/2012 11:40:50 PM
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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. 

Charles Murray
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Re: Averting a major problem
Charles Murray   10/15/2012 10:30:05 PM
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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.   

tekochip
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Platinum
Hot Contacts
tekochip   10/15/2012 4:48:37 PM
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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.


TJ McDermott
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Blogger
We talked about fuse substitution last month
TJ McDermott   10/15/2012 12:58:37 PM
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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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