Electrical Wiring in the Home/Low Voltage at Light Switch


My Kitchen light switch failed. I replaced it and the light would still not work. I used my voltage meter and it reads closer to 5 volts instead of the 120.


5 volts is likely a 'phantom voltage' and not real.

Check the feed to the switch and any wire nuts in the box.

Is this a single pole single circuit light  or can you tell me more about the entire circuit?

I assume you are fairly experienced with this kind of thing, or you would not have known to check the voltage in the first place,     

Any problems with the lights or ANYTHING else prior to this switch failing?

You understand that a TYPICAL switch leg is nothing more than a hot wire from main to device [load] cut in half by the switch?

Normally when I hear a device failed,  then the voltage is not anywhere near what it should be, then there was something going on prior.

Check your OLD switch [out of wall on work bench] with the resistance mode on your VOM.

Is it truly open in both positions ?

I want you to go here:


Start at step one and follow the drill down chart       this is much easier than me typing it all out,  this is a great site and every situation is covered with a chart of diagnostics,   

You will really like it,    if you are measuring a hot to ground   [typical light switch circuit] are you on the load side or the incoming side?  

Is the breaker in proper working order?

You asked a good question  but I need details,    are we dealing with a three way?   Are we dealing with a single circuit?     How about the load,  is the light in good working order?

Is there a volt drop caused by a possible hundred different things?

You asked a lot in a few words      but well done,   I just need help understanding what you are looking at   how you are measuring     why the old switch failed  [or not]  

How many wires are in the box?

Just assuming we have a light switch leg with 5 volts AC    AC  scale on meter!   Then the feed side is open,  somewhere.

If you tie the two switch wires together manually   do you get a light?

Flip breaker off,  tie the two blacks together that should be the same as a closed switch.

If you get nothing  then start working backwards to the main,     

It could be  something as simple as a bad wire nut        never  NEVER assume the person before you did ANYTHING right  including an "electrician"

I have a feeling whatever is going on was going before you got involved,      

Again never trust what you are looking at was EVER right!

Good job on checking the voltage   most never do that,  they just unscrew the old and screw in the new without double checking,     that was very professional !

You will love the "Circuit Detective"   I have the same diagnostic charts   but that site covers everything     in case you need something else down the road  you have allexperts,  you have my personal email   you have the Circuit detective   site        

Let me know what you see, more details,  and we WILL figure this out,    and again good job of checking before just screwing in a new switch,        

Use my personal email if it is simpler for you  but remember you are teaching others who read this  down the road,        and the best lesson is to check the voltage even when you didn't really  "need"  to,    I like that thinking   good for you!

Unfortunately it is what appears to be a simple question. There is just no simple answer.   I have to know the entire situation to help walk you through this

Start with the Circuit Detective link      and I promise you will love the organizational diagnostic charts       if not   get right back to me  and we WILL find the answer    and maybe other issues?

AGAIN BROKEN RECORD       if you had NOT checked the voltage  we would have never even suspected anything!

So you have taught a bunch of people how to be complete in doing this switch repair,  and OTHER issues       

Light switches should be simple,     it should be  a hot wire headed to load    diverted to the switch

the switch cuts that wire in half and puts it back together

that is the basic basic basic   correct way to wire a single pole single circuit switch,  

and even if there are 40 other  circuits     it should still boil down to that  

   now there are three ways  four ways, and gfci devices that can make diagnostics a bit more complex  but we WIll find the problem

 and then the unknown of whomever was there before you

That is why I want you to check the old switch   even if the spring, or the knob or whatever is flopping in the breeze          

I want to know if the old switch  opens and closes          

Start with the Circuit Detective link.

Another thing that is maybe strange   5 volts     double check that for AC make sure it is 5 volts AC   and your scales on your meter are not off the scale you need to be dialed into

       there are so many USB sub circuits anymore

   that would be 5 volts AC before it is rectified to DC

        so the number 5 [in volts]   as opposed to 80 or 90 volts  is right on the money for USB     maybe it is just phantom induced voltage which is fairly normal

 but lets make damn sure        

Again great job on checking and doing the RIGHT thing   instead of blindly just replacing a switch         we appreciate that kind of effort          

Also feel free to let me know if anything    ANYTHING at all bothers you,    light bulbs burning out, stuff not acting right,   happy to go over all or any of that if it exists  

Talk soon,

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


Will Babbitt


Electrical issues of all types, wiring, control, appliances, components, specialty in Electric MOTOR or APPARATUS trouble shooting, electric motors, electrical problems, single phase, three phase, DC, capacitors, elevator MG-Sets, modifications, reverse engineering, VFD Drives, single to three phase convertors. Repair of most any electrical/mechanical/electronic apparatus, OEM, AC, DC, Industrial Applications, Three phase, single phase failure mode, determining the root cause of the equipment failure BEFORE failure repeats, Antique appliances, electric motors, fans, ceiling fans, base mount fans, poor equipment performance, Modifications, habitual failures, vibration, redesign, obsolete issues, collectible items restored, rewinding. Owner of EMR Repair Inc www.emrrepair.com More information on electric motors, under Engineering/Motors Ask about any electrical or mechanical problems in the home, office, or even at your work. B2B or business to business CONSULTING I can do but it would be a much more complex issue, that would require a significant amount of time. repair@mearservice.com from there we can discuss and begin work on about anything. Industrial electric motors, controls, troubleshooting, vibration, alignment, any type of industrial or commercial electric/electrcical equipment For the home owner, renter, apartment if you have odd things going on, describe to me, photos are normally very helpful, appliances, heating and air conditioning issues, light switches, installation, DIY PROJECTS FOR THOSE NOT EDUCATED IN ELECTRICAL, we can do some things, but for safety and sanity reasons, I may refer you to a local electrician, and help you find one, help you with pricing and even speak directly with anyone you hire if you have issues,


Over thirty years with a major repair and sales company, VP of Operations, and former owner of my own specialty repair shops, MEAR Services local to Kansas City Missouri EMR Repair Inc., located in Kansas City Missouri, 2014 sold both businesses to JCI Industries, Lee's Summit Missouri wbabbitt@jciind.com Evaluation and repair of electrical/mechanical apparatus. Electrical and mechanical repairs, trouble shooting including, vibration and balance issues. About.com provides this service, and the huge costs to provide help on about any subject. They provide the servers, the people to vet the experts, costs that would be the same as operating a good sized business, They should be appreciated for what they do, the huge costs and the great help they provide for free, Electric motor questions, can be answered here but there is a dedicated category that has other experts to help and add to a solution. Other common questions, are noises in the walls, breakers tripping, devices not starting or shutting down for no apparent reason, smoke alarms buzzing, thermostat change outs, or sizing wire or needing information for a new project, but anything can be resolved, anything, with enough effort and patience, DIY, with electrical is possible, but in most cases the use of a simple ohm meter or volt meter is needed, they can be purchased at any hardware store for a few bucks. If you have smoke, or smell smoke, don't be writing me, call 911 the Fire Department has no problem looking for smoke smells, better then spraying water on a blazing fire. DO NOT GET CAUGHT INVESTIGATING AND TRAPPED IN A BASEMENT LOOKING FOR A BLOWER FAILING< As to the tip jar, it is up to you, it is appreciated, every expert spends out of pocket that I know, we spend on IP time, computer wear, printing documents, books, and of course our time, but if we prevent a $400 service call, we did well,

Former IBEW, EASA, IEEE, UL, ..............


10 plus years, various Technical Schools, followed by Industrial College Credit and non Credit Courses, electronics courses, experience in most any electrical apparatus, electric motors and generators, AC OR DC, fractional to above 5000HP, other electrical apparatus, slip rings, sleeve [plain] bearings, lubrication, identification-no data plate, control components, service and sales. I have continued night schools for decades, the list is extensive. I have been in the business of repairing most anything with wires or mechanical parts for decades, I have some helpful hints and directions you won't have to dig up. Or hopefully not have to pay a huge service call invoice to find.

Awards and Honors

Past/Present Clients
Federal Government, National Weather Service, NOAA, Commercial Power Plants, Major Vehicle Manufacturers, Printers, Other industrial and Commercial Businesses

©2016 About.com. All rights reserved.