By Mike Sokol
Dear Readers,
Last month I published an article about tracing short circuits in DC wiring without blowing a bunch of fuses. That turned out to be a very popular topic for my RV technician classes, so I’ve posted a 12-minute video here showing how it works.
The basics
If you have a short circuit in a wire, it’s going to blow the fuse every time you turn on the power. That’s because the short circuit allows lots of current to flow, up to 100 amps in a wire designed for maybe 15 amperes. The fuse is protecting the wire from melting, which is why you don’t put in a larger fuse. But how do you find where the problem is if you can’t turn on the power?
What shall we do???
Enter my simple fault-current tester that uses a blown fuse with an incandescent bulb soldered across it. In this graphic I’m using a 12-volt tester, but in the video below you’ll see me use a bulb soldered to a blown fuse to limit the fault current.
However, the really cool trick is to use a DC clamp meter to trace the current in the wires until it stops. And wherever it stops is right where the short circuit has occurred.
Read it, watch it, do it…
So if you’re looking for a short circuit, first read my article from last month on this topic, then watch the video below. In 12 minutes you’ll learn exactly how to perform this neat trick that can save you hours of troubleshooting time.
Reread cheap trick for finding a short circuit
Click on the screen shot below to watch the 12-minute video.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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Good subject! In my career I had to troubleshoot shorts many times. There were almost always two things to consider. What has just happened that caused the short? Examples could be- recent construction and if so, where? Many short circuits are due to shorted appliances, amplifiers and other devices in the circuit. Try eliminating one after another until you find a normal condition once again. Sometimes a helper is good. You can slowly plug the fuse in while reading voltage. If the voltage drops very quickly to nearly 0- pull the fuse quickly before it blows. In my time on the job an old analog meter was good because it reacted immediately, unlike many of the digital v.o.m.’s of today. You can keep repeating this process each time by eliminating another device or maybe a section of circuit. I had to do this many times in outages- during storms and at night when we had many customers affected. It was usually only me out there so I had to use an effective way to find problems.