I recently went to replace a couple 3 way switches and, I am ashamed to admit, did not do my due diligence when wiring up. The new switches were a different style and the wiring configuration was seemingly different, not to mention that this is a 50 year old house without much conduit or even a grounding system. Though there are quite a few gfci's.
I finished installation and as soon as I put the fuse back in, it blew. I put another in, and it was ok. Went and checked and nothing on the circuit worked.
I must have shorted from hot to neutral through the 3 way switch, though after thinking on it, why was there a neutral leg for that switch anyway?
Too late at that point. Now I am trying understand what I did. ..i get 120v from just downstream of the fuse to the neutral bar, but after it leaves the fuse box, I can't find a hint of hotness anywhere on the circuit. I'm worried I burned the line open, especially since it looks like the previous owner had a 20 amp fuse in with all 15 amp circuit components.
I feel pretty dumb for letting this happen. I have two years of electrical and have schooling though it was back in 2009, and I let my confidence get the best of me.
Tomorrow I might look through the basement drop tile ceiling for clues. Any suggestions on troubleshooting this would be greatly appreciated.
Best Answer
The quickest and safest may be to check the resistance of the conductors with the power off, and determine the resistance it should be based on the material, length, and cross sectional area. Testing in various locations. Of course this requires some math, and guessing about the conductor length.
Another quick way is to test for voltages with the power turned on. You may also need to have some sort of dummy load to check for high resistance connections, this could be done with a solenoid type voltage tester.
The easiest is to go based on the assumption that the problem is at the connections. That means that it is likely in a electrical box. Make sure that none of the connections are loose or charred in every one of the boxes. You would have still needed to do this with the other tests, but they would have helped to narrow down the location of the problem.
Actually that still isn't the easiest; which is of course to call an electrician.
I will say that it is very unlikely that you blew open the conductor anywhere else. According to a chart on Wikipedia it would take about 600 amps to melt a 14 gauge wire in one second, which is more time that it would take for a fuse to blow. So unless the cable was severely damaged beforehand somewhere along it's length; the problem is in a box.