Testing Light Switch Wiring

Testing Method for Light Switch Wiring
Electrical Problem: I am working on my brothers house to try and help him with his electrical wiring. It is all Romex Type-NM Wire, the house was built in the 198o’s etc.

• The problem is when you push the light switch to on in the bedroom the light switch buzzes and immediately trips the breaker.
• If I reset the breaker all other lights and receptacles work on this circuit as long as the switch to the bedroom lamp is not turned on.
• I removed the light and fan in the bedroom and pulled the switch from the wall and checked the wiring to both. I then disconnected the light completely and moved the wires far apart and capped them.
• I pulled the switch out from the plastic new work box and moved all of the wires away from each other. Hit the switch again and it tripped the breaker. This is where I am unsure.
• Does this mean the short is in the wire from the light switch to the fixture? It appears it is wired straight from the switch into the attic to the fixture. Could any other component in the circuit effect this? If not should I replace the 14/2 from the fixture to the switch?

Thanks for your time. I appreciate it.

This electrical question came from: Greg in Tennessee.

Additional Comments: Very nice website. I read through the trouble shooting and enjoyed it.

Dave’s Reply:
Thanks for your Electrical Repairs Question Greg.

Testing a Light Switch and the Wiring

Greg, there may be a few possibilities that are causing the problem, all of which can be identified using an tester or Ohm Meter.

• Basically, what you need to do is identify each wire set and verify the connections to make sure they are correct.
• If there are two wires from 2-wire cable that are attached to the switch and if these two wires are not connected correctly back at the fixture box then you may be switching a hot and a neutral together and blowing the circuit.
• The other possibility is that a nail has been driven into and across a cable which could be creating a short between a switched leg and the ground wire. Using an ohm meter to check the cable between the switch and the fixture box will reveal exactly what is happening.
• These test should be done with the circuit turned off. This test with the ohm meter is basically a continuity test to verify the cable and see if there is a short between any of the wires, The test should be done with the wires removed from the switch and the light fixture and the wires apart from each other testing wire to wire to see if there is a short.
• If that test proves OK then the test of placing a wire connector with both insulated wires together to see if you have continuity through the two.
• Your basically creating a loop and making sure you have continuity which will verify this.
• Once these tests are made you will no doubt understand more about the circuit wiring and if there is in fact a problem with the wiring which may require you to replace the cable if it is damaged.

See More about Residential Electrical Wiring Repairs

Using Electrical Testers

Electrical Safety and Voltage Testers
When working on home electrical wiring, quality voltage testers can play an important part in electrical safety.
Electrical testers enable you to identify electrical circuits and help prevent the possibility of accidental electrical shock.
More about Troubleshooting Electrical Problems

Home Electrical Troubleshooting

Troubleshooting Electrical Wiring
Licensed Electrician Reveals the Secrets of Successful Electrical Troubleshooting Methods used to solve the majority of the home electrical problems and wiring failures encountered.

Home Electric Circuits

Electric Circuit Listing
The size of the home electrical service panel is designed by calculating the square footage of the home and factoring in the code requirements for the electrical circuits that are required.

Electric Circuit Breaker

Electrical Wiring Protection using Circuit Breakers
A guide to home electrical circuit breakers and how they work to protect your electrical wiring. When properly installed, your home electrical wiring is protected by a circuit protection device.

Residential Electrical Wire

Electrical Wire for the Home
Complete listing of electrical wire types and parts used for home projects with electrical code information serves as selection guidelines.

Testing Method for Light Switch Wiring
Electrical Problem: I am working on my brothers house to try and help him with his electrical wiring. It is all Romex Type-NM Wire, the house was built in the 198o’s etc.

• The problem is when you push the light switch to on in the bedroom the light switch buzzes and immediately trips the breaker.
• If I reset the breaker all other lights and receptacles work on this circuit as long as the switch to the bedroom lamp is not turned on.
• I removed the light and fan in the bedroom and pulled the switch from the wall and checked the wiring to both. I then disconnected the light completely and moved the wires far apart and capped them.
• I pulled the switch out from the plastic new work box and moved all of the wires away from each other. Hit the switch again and it tripped the breaker. This is where I am unsure.
• Does this mean the short is in the wire from the light switch to the fixture? It appears it is wired straight from the switch into the attic to the fixture. Could any other component in the circuit effect this? If not should I replace the 14/2 from the fixture to the switch?

Thanks for your time. I appreciate it.

This electrical question came from: Greg in Tennessee.

Additional Comments: Very nice website. I read through the trouble shooting and enjoyed it.

Dave’s Reply:
Thanks for your Electrical Repairs Question Greg.

Testing a Light Switch and the Wiring

Greg, there may be a few possibilities that are causing the problem, all of which can be identified using an tester or Ohm Meter.

• Basically, what you need to do is identify each wire set and verify the connections to make sure they are correct.
• If there are two wires from 2-wire cable that are attached to the switch and if these two wires are not connected correctly back at the fixture box then you may be switching a hot and a neutral together and blowing the circuit.
• The other possibility is that a nail has been driven into and across a cable which could be creating a short between a switched leg and the ground wire. Using an ohm meter to check the cable between the switch and the fixture box will reveal exactly what is happening.
• These test should be done with the circuit turned off. This test with the ohm meter is basically a continuity test to verify the cable and see if there is a short between any of the wires, The test should be done with the wires removed from the switch and the light fixture and the wires apart from each other testing wire to wire to see if there is a short.
• If that test proves OK then the test of placing a wire connector with both insulated wires together to see if you have continuity through the two.
• Your basically creating a loop and making sure you have continuity which will verify this.
• Once these tests are made you will no doubt understand more about the circuit wiring and if there is in fact a problem with the wiring which may require you to replace the cable if it is damaged.

See More about Residential Electrical Wiring Repairs

Using Electrical Testers

Electrical Safety and Voltage Testers
When working on home electrical wiring, quality voltage testers can play an important part in electrical safety.
Electrical testers enable you to identify electrical circuits and help prevent the possibility of accidental electrical shock.
More about Troubleshooting Electrical Problems

Home Electrical Troubleshooting

Troubleshooting Electrical Wiring
Licensed Electrician Reveals the Secrets of Successful Electrical Troubleshooting Methods used to solve the majority of the home electrical problems and wiring failures encountered.

Home Electric Circuits

Electric Circuit Listing
The size of the home electrical service panel is designed by calculating the square footage of the home and factoring in the code requirements for the electrical circuits that are required.

Electric Circuit Breaker

Electrical Wiring Protection using Circuit Breakers
A guide to home electrical circuit breakers and how they work to protect your electrical wiring. When properly installed, your home electrical wiring is protected by a circuit protection device.

Residential Electrical Wire

Electrical Wire for the Home
Complete listing of electrical wire types and parts used for home projects with electrical code information serves as selection guidelines.

Testing Light Switches
Electrical Question:  Can a Light Switch Leak Voltage?

• I wired a single pole switch to a fluorescent fixture in my garage, and with the switch off, and power restored.
• Now I get a faintly lite bulb in my bulb tester if I place one probe to the top and bottom screws.  Does this mean the switch is leaking?
• Is it normal for new switches to do this? I have wired three different new switches, all do this. Should I be placing a tester probe on the ground and then the upper screw to test for a faulty switch? I have ensured that the black wire (hot) wire from my panel is on the bottom screw.
• The black feed wire to the light is on the top screw of the switch. The two white wires are wire nutted together properly. The bare copper wires go to the switch’s green ground screw. The ground wire is also pigtailed to the metal box I have it all in.

Electrical Wiring at the Light Fixture:

• I have white to white
• Black to black
• Copper ground to the metal fixture’s ground screw.

Dave’s Reply:
Thanks for your electrical wiring question Kevin.
Background: Kevin, a Homeowner from Chapel Hill, North Carolina.

Light Switch Voltage Readings

Application: Testing Light Switches.
Skill Level: Intermediate to Advanced – Best performed by a Licensed Electrical Contractor.
Tools Required: Basic Electricians Pouch Hand Tools and Voltage Tester.
Estimated Time: Depends on personal level experience, ability to work with hand tools and electrical troubleshooting skills.
Precaution: Identify the lighting circuit, turn it OFF and then Tag it with a Note before performing any wiring or switch testing.

The Light Switch Circuit

Voltage Tester Readings and Explanations

• What you are experiencing is quite normal if you are using an analog or no-digital tester.
• If your tester leads are on each screw of the light switch then the tester is actually acting as a switch and voltage is passing through your tester wiring to produce the dim light.
• In reality, your tester is completing the circuit but the amount of current is limited by the internal wiring of your voltage tester.
• If you were to disconnect the line to the fixture ballast you would not get the reading on your tester that you had before because the circuit is not complete.
• This is why it is always good to make your voltage tests to a ground for the best reading.

More about Home Electrical Wiring

How to Wire a Switch

Wiring a Light Switch – Diagram 1

Wiring Diagrams
Fully Explained Light Switch Wiring Diagrams. Detailed Electrical Wiring Diagrams and Pictures assist your Home Electrical Projects.

Using Electrical Testers

Understanding Electrical Testers

• When working on home electrical wiring using voltage testers can play an important part in electrical safety.
• Electrical testers enable you to identify electrical circuits and help prevent the possibility of accidental electrical shock.

Using Electrical Testers

Testing Light Switches
Electrical Question:  Can a Light Switch Leak Voltage?

• I wired a single pole switch to a fluorescent fixture in my garage, and with the switch off, and power restored.
• Now I get a faintly lite bulb in my bulb tester if I place one probe to the top and bottom screws.  Does this mean the switch is leaking?
• Is it normal for new switches to do this? I have wired three different new switches, all do this. Should I be placing a tester probe on the ground and then the upper screw to test for a faulty switch? I have ensured that the black wire (hot) wire from my panel is on the bottom screw.
• The black feed wire to the light is on the top screw of the switch. The two white wires are wire nutted together properly. The bare copper wires go to the switch’s green ground screw. The ground wire is also pigtailed to the metal box I have it all in.

Electrical Wiring at the Light Fixture:

• I have white to white
• Black to black
• Copper ground to the metal fixture’s ground screw.

Dave’s Reply:
Thanks for your electrical wiring question Kevin.
Background: Kevin, a Homeowner from Chapel Hill, North Carolina.

Light Switch Voltage Readings

Application: Testing Light Switches.
Skill Level: Intermediate to Advanced – Best performed by a Licensed Electrical Contractor.
Tools Required: Basic Electricians Pouch Hand Tools and Voltage Tester.
Estimated Time: Depends on personal level experience, ability to work with hand tools and electrical troubleshooting skills.
Precaution: Identify the lighting circuit, turn it OFF and then Tag it with a Note before performing any wiring or switch testing.

The Light Switch Circuit

Voltage Tester Readings and Explanations

• What you are experiencing is quite normal if you are using an analog or no-digital tester.
• If your tester leads are on each screw of the light switch then the tester is actually acting as a switch and voltage is passing through your tester wiring to produce the dim light.
• In reality, your tester is completing the circuit but the amount of current is limited by the internal wiring of your voltage tester.
• If you were to disconnect the line to the fixture ballast you would not get the reading on your tester that you had before because the circuit is not complete.
• This is why it is always good to make your voltage tests to a ground for the best reading.

More about Home Electrical Wiring

How to Wire a Switch

Wiring a Light Switch – Diagram 1

Wiring Diagrams
Fully Explained Light Switch Wiring Diagrams. Detailed Electrical Wiring Diagrams and Pictures assist your Home Electrical Projects.

Using Electrical Testers

Understanding Electrical Testers

• When working on home electrical wiring using voltage testers can play an important part in electrical safety.
• Electrical testers enable you to identify electrical circuits and help prevent the possibility of accidental electrical shock.

Using Electrical Testers

Testing a Light Switch
Electrical Question: How can I use a voltage tester to check a light switch?

• I have an older home. The bathroom light switch to turn the light on is a little different.
• The two wires there when I measure across them gives me 120 volts.
• On the light I checked before beginning to work on it with my tick tracer and shows there is power in one of the legs.
• So I check across the two wires and nothing happens no power but when connecting the two switch wires and then measuring there are my 120 volts, this was the way this switch has worked for many years.
• I was just curious how this could be?

Any theory will help.
Thank you.

This electrical wiring question came from: Angel, a Handyman from Joliet, Illinois.

Dave’s Reply:
Thanks for your electrical wiring question Angel.

How to Test a Light Switch using Electrical Testers

Application: Testing a Light Switch.
Skill Level: Intermediate to Advanced – Best performed by a qualified electrician.
Tools Required: Basic Electricians Pouch Hand Tools and Voltage Tester or Continuity Tester.
Estimated Time: Depends on personal level experience and ability to work with tools.
Precaution: Identify the light circuit, turn it OFF and  Tag it with a Note before working with the wiring.
Notice: Testing with the circuit power on can be dangerous and should only be done by qualified or experienced electricians.

The Most Common Methods for Testing a Light Switch

• Testing a Switch with a Continuity Tester
  A continuity tester can be used to test the light switch while the circuit is OFF or the switch has been removed. This type of tester has two lead wires that uses the battery voltage of the tester to test a circuit, which in this example is the circuit components of a switch. Toggle the switch into the on and off position with the test leads attached to the terminals of the switch. If the switch is good then there will be a reading or indication, otherwise no reading or indication means that the switch is bad.
• Testing a Switch with a Voltage Tester
  A voltage tester has two lead wires, one for positive and one for negative, however since a switch only has a positive power source connected to it the one test lead will need to be attached to either a ground wire or a neutral wire, while the other test lead is attached to the screw terminals of the switch, one at a time while turning the switch on and off. The tester will produce a voltage reading if the switch is good, however sometimes you can get false voltage reading, which I will explain below.

Why a Tester May Read Voltage while the Light Switch is Off

• Testing a Light Switch
  This is a question that comes up often, and here is the answer. A standard incandescent light bulb has a filament wire that makes the connection between the two wires of the circuit. Therefore when the light switch is in the off position, the connection between the neutral wire is made through the filament and enables the tester to connect back to the neutral wire of the light fixture.
• The Tester as a Light Bulb
  So in essence, your tester is becoming a light when the two tester leads are placed onto the two switch terminals.
• How to Get an Accurate Test Reading
  To prove this, simply remove any light bulbs from the light fixture and the 12o volt reading will stop because the connection to the neutral wire has been disconnected.
• Light Circuit Wiring
  Similar situations occur when one wire has become disconnected within a circuit, and a load is present, which can create a back-feed of electricity which causes lights to glow dim, because the available power is feeding back through other devices in the circuit wiring, and these devices are creating resistance on the circuit.

More about Light Switches

• Electrical Testers for Light Switches
• Using Electrical Testers
  

• Guide to Electrical Testers

• When working on home electrical wiring using voltage testers can play an important part in electrical safety. Electrical testers enable you to identify electrical circuits and help prevent the possibility of accidental electrical shock.
• Troubleshooting Electrical Wiring
• For more information about Light Switch Wiring
  Light Switch Wiring
  
  Wiring a Light Switch – Diagram 1
  Fully explained pictures and wiring diagrams about wiring light switches describing the most common switches starting with photo diagram 1.
• Home Electrical wire
  
  Electrical Wire for the Home
  Complete listing of electrical wire types and parts used for home projects with electrical code information serves as selection guidelines.

Testing a Light Switch
Electrical Question: How can I use a voltage tester to check a light switch?

• I have an older home. The bathroom light switch to turn the light on is a little different.
• The two wires there when I measure across them gives me 120 volts.
• On the light I checked before beginning to work on it with my tick tracer and shows there is power in one of the legs.
• So I check across the two wires and nothing happens no power but when connecting the two switch wires and then measuring there are my 120 volts, this was the way this switch has worked for many years.
• I was just curious how this could be?

Any theory will help.
Thank you.

This electrical wiring question came from: Angel, a Handyman from Joliet, Illinois.

Dave’s Reply:
Thanks for your electrical wiring question Angel.

How to Test a Light Switch using Electrical Testers

Application: Testing a Light Switch.
Skill Level: Intermediate to Advanced – Best performed by a qualified electrician.
Tools Required: Basic Electricians Pouch Hand Tools and Voltage Tester or Continuity Tester.
Estimated Time: Depends on personal level experience and ability to work with tools.
Precaution: Identify the light circuit, turn it OFF and  Tag it with a Note before working with the wiring.
Notice: Testing with the circuit power on can be dangerous and should only be done by qualified or experienced electricians.

The Most Common Methods for Testing a Light Switch

• Testing a Switch with a Continuity Tester
  A continuity tester can be used to test the light switch while the circuit is OFF or the switch has been removed. This type of tester has two lead wires that uses the battery voltage of the tester to test a circuit, which in this example is the circuit components of a switch. Toggle the switch into the on and off position with the test leads attached to the terminals of the switch. If the switch is good then there will be a reading or indication, otherwise no reading or indication means that the switch is bad.
• Testing a Switch with a Voltage Tester
  A voltage tester has two lead wires, one for positive and one for negative, however since a switch only has a positive power source connected to it the one test lead will need to be attached to either a ground wire or a neutral wire, while the other test lead is attached to the screw terminals of the switch, one at a time while turning the switch on and off. The tester will produce a voltage reading if the switch is good, however sometimes you can get false voltage reading, which I will explain below.

Why a Tester May Read Voltage while the Light Switch is Off

• Testing a Light Switch
  This is a question that comes up often, and here is the answer. A standard incandescent light bulb has a filament wire that makes the connection between the two wires of the circuit. Therefore when the light switch is in the off position, the connection between the neutral wire is made through the filament and enables the tester to connect back to the neutral wire of the light fixture.
• The Tester as a Light Bulb
  So in essence, your tester is becoming a light when the two tester leads are placed onto the two switch terminals.
• How to Get an Accurate Test Reading
  To prove this, simply remove any light bulbs from the light fixture and the 12o volt reading will stop because the connection to the neutral wire has been disconnected.
• Light Circuit Wiring
  Similar situations occur when one wire has become disconnected within a circuit, and a load is present, which can create a back-feed of electricity which causes lights to glow dim, because the available power is feeding back through other devices in the circuit wiring, and these devices are creating resistance on the circuit.

More about Light Switches

• Electrical Testers for Light Switches
• Using Electrical Testers
  

• Guide to Electrical Testers

• When working on home electrical wiring using voltage testers can play an important part in electrical safety. Electrical testers enable you to identify electrical circuits and help prevent the possibility of accidental electrical shock.
• Troubleshooting Electrical Wiring
• For more information about Light Switch Wiring
  Light Switch Wiring
  
  Wiring a Light Switch – Diagram 1
  Fully explained pictures and wiring diagrams about wiring light switches describing the most common switches starting with photo diagram 1.
• Home Electrical wire
  
  Electrical Wire for the Home
  Complete listing of electrical wire types and parts used for home projects with electrical code information serves as selection guidelines.

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