The Circuit Detective    -  Signs of Source of Outage

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How to Recognize the Bad Connection
in a Home's Electrical Circuit

What are we looking for? This page is not about Whether you have a bad connection or about Finding which electrical box(es) to look for it in. Here I am talking about what you are looking for in a box -- how to recognize which connection there is poor, so that you can make the right improvement or repair.

What can be bad? At an electrical box, a wire can be loose in, or pulled loose from, its terminal or wirenut. The wire's metal quality can have deteriorated (from heat/corrosion) till it is no longer able to conduct current. Or, not often, a wire can be broken at the terminal or wirenut (usually from being nicked, back when, by the wireman's stripping tool).

Many resources, both online and in books, give the impression that you will find soot, burn marks, or melted wires at the site of an open in the electrical circuit. Actually, it is much more common to see very little obvious difference between a good connection and a bad one. This does not mean we can't find out what is bad, however.

Of course, if you know you are at the right electrical box from testing and deductions, then you could just make all new connections in that box. You don't have to ponder what the exact trouble was. But by the time they have come this close to the culprit, most people want to try to understand what happened.

Obvious Signs of a Bad Connection

Yes, there might be Ugly evidence of the trouble. Often enough an open will have created some heat, because before things stopped operating, this connection was still carrying current, but through an imperfect conductor at this point. Current with unintended resistance typically gives you heat. This isn't something that happens overnight. Overheated connections often take years to reach the point of disrupting the path of current entirely.

Look For:
Don't Pay Much Attention To:

Subtle Signs of a Bad Connection

In my experience, opens on a electrical circuit often give little or no visual evidence of their presence. (Why some do and some don't is a question for people with time on their hands or maybe for nobody). If you look closely, are there particular things to expect to find? Don't look for just anything odd.

Look For:

No Sign of a Bad Connection

This is often the case with push-in-the-hole connections of a receptacle. It is also common enough when one wire in a wirenut didn't stay lined up (slipped a little back) when the wirenut was being twisted on the group of wires. These kinds of connections in the box may all need to be checked, undone, and done over. Then you'll know if you were right about which box had the problem in it!

If you did see evidence of where the problem was, you will likewise usually be replacing at least anything that was affected -- receptacle, wirenut, etc. -- anything that suffered from heat or is felt to be unreliable based on this performance.

Troubleshooting an Open

© 2007 Larry Dimock

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