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Sherlock Ohms

These Fuses Melt in Water

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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.

TJ McDermott
User Rank
Blogger
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.  

bob from maine
User Rank
Platinum
Troubleshooting AC
bob from maine   10/16/2012 10:36:11 AM
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The replacement of the fuse with one of a higher rating while going to the parts room for the correct value makes sense. The clamp-on ammeter showed much less current flow than the fuse rating. It is a military installation so the presumption is it MUST stay operational and it will be staffed while the electrician is en-route. No equipment had malfunctioned, so it could be assumed (love that word!) that the problem was in the wiring. Blowing a 40A fuse on one leg of a 208 3PH line implies a heck of a lot of heat being dissipated somewhere. All these being considered, upping the fuse and going for more fuses seemed the reasonable thing. Picking up the blown fuse was pure luck. Understanding what the temperature of the fuse implied was the stroke of genius. Those fuses are removed using pullers and there would normally be no reason to handle the fuse with your bare hands. Good story and a good lesson for the rest of us: be curious, observe, think.

Jon Titus
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Blogger
Similar problem
Jon Titus   10/16/2012 12:51:56 PM
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We had a similar problem in our first house--water in the circuit-breaker box.  I looked for a leaking water line but found none.  Then during a rain storm I noticed water dripping from the breaker box.  Apparently water got into the outdoor service cable, ran into the meter box, and then the water flowed into the service cable and into the breaker box.  The local power company came and wrapped their part of the cable in waterproof tape.  Then I thoroughly caulked the meter box with silicone sealant.  No more water problems.  The circuit-breaker box was about 20 feet from the entrance of the service cable into the house, so a lot of water had to accumulate to push through to the circuit breakers. No permanent damage, thankfully.

daveladd
User Rank
Iron
Re: Averting a major problem
daveladd   10/22/2012 3:27:44 PM
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Every electrical shop ought to have an infrared camera.  You can get a reasonably good basic model these days for 6-800$  When you have unexplained fuse and circuit issues, scan the panel, the receptacles, starters, etc.  For troubleshooting, where you have quirkly stuff going on, it's much safer to start with the IR scan than to go poking around on fuse clips with meter probes, looking for voltage drop, or manipulating conductors to get a clamp-on ammeter attached.  You're liable to poke a connection that's loose and start an arc that results in an arcing fault ... in your face. 

Larry M
User Rank
Platinum
Re: Averting a major problem
Larry M   10/22/2012 3:36:40 PM
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Daveladd wrote "Every electrical shop ought to have an infrared camera.  You can get a reasonably good basic model these days for 6-800$."

You don't even need to buy a special infrared camera. The image sensors in inexpensive point-and-shoot cameras and even cellphone cameras are sensitive to infrared and the cameras have no filters. You can quickly find a hotspot just by waving the camera around. (The camera is also a good tool to check your TV or DVD player remote. Watch the camera screen while pressing buttons on the remote.)

You can measure the hotspot temperature with one of these inexpensive non-contact devices" http://www.harborfreight.com/catalogsearch/result?q=thermometer . They are also useful for measuring duct outlet temperatures when you suspect heating or air-conditioning problems.

 

 

Larry M
User Rank
Platinum
Re: Hot Contacts
Larry M   10/22/2012 3:41:56 PM
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My dishwasher has a small circuit board with user option switches on it, connected with a Molex connector. One of the switches is directly in series with the heating element used for drying. The Molex connector also caused a circuit board fire.

I suppose I could submit this as another Made by Monkeys article but I've just told the complete story (except for the repair).

warren@fourward.com
User Rank
Platinum
Re: Averting a major problem
warren@fourward.com   10/22/2012 3:42:41 PM
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It is amazing how often the simple things are often overlooked. Fuses aren't as complex as the equipment they are protecting, so we find it easy to dismiss them. The same way with plugs, knobs, pots, switches, and other interim devices.  We forget they are there until we have problems we cannot explain.  He did a good job finding the problem!

rkinner
User Rank
Iron
Re: OOOOPS!!
rkinner   10/22/2012 5:27:24 PM
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I also had an "issue" with a new construction house I moved into 10 years ago. First, I had my own inspector do an onceover on the house and found that the range wiring had a high impedance to ground on one phase. The problem was that the drywall had been installed with a nail that was put entirely through the phase wire. The builder was not happy but replaced the entire feed and redid the drywall.

About 6 months later i installed a ceiling fan in our dining room and tried to control it from the switch that had been prewired by the builder. No power anywhere downstream of the switch (but the switch had 120 VAC on it)! After much up and down on the ladder, I pulled the wiring out of the box at the switch and found that the wire I used had some electrical tape wrapped around it. It ended up that the wire had been cut and since it was not immediately put in use the electrician simply hid it by wrapping tape around it.  It did pass inspection but wasn't usable.  I did get enough wire freed up to make the connection and got the switch operational but not before a few choice words about a fellow in my profession.

 

tekochip
User Rank
Platinum
Re: Averting a major problem
tekochip   10/22/2012 6:47:26 PM
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$30 for an ir thermometer? Crazy, but I have to try that camera trick. I've used cameras to pick up remote signals before and is helpful when focusing IR sensors.

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