Fix a Wiring Problem that Causes Electrical Trouble
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Should a white neutral wire have voltage when the circuit breaker is off? A multiwire circuit has been improperly installed, which is causing electrical problems within the home. © By: Dave Rongey |
House Wiring Problem
Electrical Question: Should a white neutral wire have voltage when the circuit breaker is off?
My electrical wiring project involves wiring in the Basement of a Old Home.
- I was updating a few outlets in my home and noticed that when I flipped the breaker my section of the home would go off (as expected) although smaller appliances were flickering on and off along. I was able to identify another breaker that shared the same neutral wires going back to the breaker box. I reverse engineered the wiring and traced the issue back to a Door Bell Transformer.
- The Transformer has a black and white wire (no ground wire) feeding into it. I restored power and tested the black wire on the Transformer, It had appropriate power. I checked the neutral wire, it also had power. What I found was that the transformer was taking the hot from another breaker and sending a decent amount of voltage down the neutral wire this back feeding items that were sharing the neutral wire.
- The setup in the house is somewhat strange. Its all conduit and this part of the home has three wires. Red, Black, White. The black wire was for the the outlets I was working on. The Red wire fed the furnace. The white wire is shared between both Black and Red. So if I turn off the Red Breaker and leave the Black wire breaker on, the Red breaker had voltage going back up to the breaker box. If I flipped the switch on my boiler furnace, the Red Breaker would be dead (as expected, since the breaker was off).
- So right away I knew someone crossed some wires or something is back-feeding.Once I removed the transformer and flipped the Black Breaker off and Left the Red Breaker on my wall outlet was safe to replace. Since the transformer has been pulled from the equation I can safely flip Red or Black Breakers and power is dropped as we would expect. Is this typical behavior for a transformer or do I have an issue?
- The photo is an example of the direction my power is going. Red arrows represent the flow of current. The neutral wire is hot, even if its just hanging in the breeze and i use a mutli-meter and ground the meter to the metal electrical box.
This electrical wiring question came from Jeff, a Handyman in Madison, Wisconsin.
Dave’s Reply:
Thanks for your electrical wiring question Jeff.
How a Wiring Problem Causes Electrical Troubles
Application: Electric Multiwire Circuit Wiring Problem.
Skill Level: Intermediate to Advanced – This electrical project is best performed by a Licensed Electrical Contractor, or Certified Electrician.
Electrical Tools Required: Basic Electricians Pouch Hand Tools, Voltage Tester, and appropriate Safety Gear.
Estimated Time: Depends on the personal level experience, ability to work with tools, install electrical circuit wiring, and the available access to the project area.
Electrical Safety: Identify the electrical power source to the , turn it OFF and Tag with a Note before working with the electrical wiring.
Electrical Wiring Parts and Materials: Electrical parts and materials for the should be approved for the specific project and compliant with local and national electrical codes.
Electrical Codes and Inspections: Installing or changing home electrical wiring should be done according to local and national electrical codes as adopted in Madison, Wisconsin. A permit and inspections may also be required.
How to Correct a Multiwire Circuit Problem
This electrical wiring project is about a Problem with the Electric Wiring in an Old Home.
As described in this question, a multiwire circuit has been improperly installed, which is causing electrical problems within the home and with devices connected to the faulty wiring.
Multiwire Circuit
What has been described with this question is a Multiwire Circuit, which is where two circuits from different poles share the same neutral wire. Type-NM Cable commonly used in house wiring would be 14/3, and 12/3, where each cable contains a ground wire, white neutral wire, a black wire, and a red wire.
Electrical Codes for Multiwire Circuits
In order for the Multiwire circuit to work properly it must be installed and configured according to the applicable NEC, National Electrical Codes. The following is an example of NEC Electrical Codes that apply to Multiwire circuits:
NEC Article 100 states that the power conductors must originate from opposite poles.
NEC Article 210.4B states that the circuit breakers where the multiwire circuit power wires are attaches must have a tie bar or single handle.
Repairing a Multiwire Circuit Problem
The appropriate repairs to correct this type of problem would include inspecting the circuit breakers in the panel where the multiwire circuit originates, and make the corrections so that the right type of breakers have been installed in the right configuration. For example: Install a two pole circuit breaker with a tie bar. The important purpose of the tie bar is to prevent an energized neutral wire in the event that only a one pole circuit breaker is off, while the other one pole breaker is on. Because the neutral wire is shared between the multiwire circuits the neutral wire will be energized if one breaker is left on.
If it is found that there are more than one sources of power to any part of a circuit, or any device that is attached to a circuit, such as described with the door bell transformer, then the circuit wiring that provides power to the device will need to be examined to identify the duplicate power source so that the wiring configuration may be configured properly for only one power source.
More about Home Electrical Wiring
Home Electrical Circuit Breakers
Home Electrical 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.
How to Install Basement Electrical Wiring
Basement Electrical Wiring
Fully Explained Photos and Wiring Diagrams for Basement Electrical Wiring with Code Requirements for most new or remodel projects.
Home Electrical Safety
Electrical Safety Articles covering several topics of home electrical safety and Do-It-Yourself Electrical Safety.
Understanding Digital Volt Meters
When working on home electrical wiring using voltage meter can play an important part in electrical safety. Electrical testers and voltage meters enable you to identify electrical circuits and help prevent the possibility of accidental electrical shock.
Types of Electrical Testers
Using Electrical Testers and Voltage Meters
The following may also be helpful for you:
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Be Careful and Be Safe - Never Work on Energized Circuits!
Consult your Local Building Department about Permits and Inspections for all Electric Wiring Projects.
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