You are here:

Electrical Wiring in the Home/voltage detected when OFF, none when ON


Mr. Lutz,

I have an old house with some old (2 black hot wires only, K&T) and some newer wiring. I noticed the other day that some of the lights and a ceiling fan (w/ rheostat) cause my non-contact electrical tester to beep strongly even about a foot away when turned off. In the case of the lights there is no beep when the lights are turned on although they light up. I have not tested the fan yet but I think it is connected to the old wiring and the kitchen should be hooked up to Romex. Another ceiling fan I have does not cause the beep when turned off. I used two different testers and also tested "normal" conditions as well. To my knowledge there is only one circuit in each box.

I do not think any of this is new; I just think I never noticed it before but now that I know it concerns me. Any ideas?

Thank you,

Hi Paul,

There is nothing wrong with your tester or wiring. The test you are using get triggered by electrical fields. It is a handy toy but not trusted as a true tester because it give false reading often. That being said I keep one in my pocket and use it all the time because it is quick. If I really need to know if a wire is live I check with a contact tester.

The bigger problem is the K&T. You need to start to plan on when to replace it.  
About Electrical Wiring in the Home
This site answers questions related to home electrical wiring, home wiring, general electrical help,and other electrical questions related to aleternating current (AC). You can find help on the National Electical Code, home electrical issues, wiring electrical outlets, installing lighting, electrical grounding, and general electrical help for do-it-yourself projects not require an electrician. If you do not see your home electrical wiring question answered in this area then please ask your electrical wiring question here

Electrical Wiring in the Home

All Answers

Answers by Expert:

Ask Experts


Bill Lutz


Any questions about being an electrician or doing electrical work. I can help advise people on their wiring needs, what kind of outlets and switcher to use, explain what an electrical service is and how their breakers work. I can also help them with their lighting needs. . I CAN HELP YOU UNDERSTAND WHAT YOUR LOOKING AT.


My Father apprenticed to his Father-and I apprenticed to mine, repeating an invaluable tradition of child labor and a great place to learn a trade. Beginning at the age of 13, I worked with my dad every weekend and summer vacation in homes throughout Philadelphia repairing and rewiring all levels of residential electrical systems. Studying electrical engineering and earning a degree in architecture has given me a solid advantage in solving the myriad of residential electrical problems. Generation 3 Electrical, Inc. takes pride in every job - building confidence by how we do things - by being prompt, thorough and leaving every job site finished and clean.

©2017 All rights reserved.