Electrician Working With Voltage Problems at Main Service

How to Identify Problems with Main Electrical Service Voltage: Main electrical service with incorrect Line Power and Neutral Voltage readings.

Incorrect Electric Voltage Readings
Electrical Question: Main electrical service with incorrect line power and neutral voltage readings.

Hi Dave, I’d like your help with a emergency service trouble call I am working on.

• This is a residential electrical service panel in a mobile home park, 120/240 volt, grounded.
  • This is a residential service in a mobile home park, 120/240 volt, grounded.
  • Line 1 to Neutral & Ground = 113 volts.
  • Line 2 to Neutral  & Ground = 137 volts.
  • Line 1 to Line 2 = 009 volts, not a typo.
  • Neutral to Ground = 337 volts, not a typo.

• What do I have happening here with the unusual voltage?
• I have been a licensed electrician for 40 years and never run into this.

Thanks,
Roy

This electrical wiring question came from: Roy, a Contractor from Payson, Arizona.

Dave’s Reply:
Thanks for your electric wiring question Roy.

How to Identify Problems with the Main Electrical Service

Application: Testing Incorrect Power Problem and Circuit Wiring of the Main Service.
Skill Level: Advanced. This electrical project should be performed only by a Licensed Electrical Contractor and may require the local utility company or electric service provider if the problem is on the utility side of the electrical service.
Tools Required: Basic Electricians Pouch Hand Tools, Voltage Tester, Multimeter, clamp on current amperage meter.
Estimated Time: Depends on personal level experience, ability to work with tools to troubleshoot and inspect electrical circuits and electrical system components.
Precaution: Depending on the symptoms, identify the main panel or panel circuits in question, turn it OFF and Tag it with a Note before working with the wiring. All precautions and protection gear and clothing must be worn to protect against potential arc flash and electric shock.
Notice: Burnt or damaged electrical wiring and circuit components should be replaced with new electrical materials of the same voltage and amperage rating. Electrical inspections may be required before restoring power to the electrical service.

How to Inspect and Identify Problems with a Main Electrical Service

IMPORTANT NOTE: The following procedures are NOT recommended for Homeowners, however this will help educate Electricians and Electrical Students about the cause and corrections for incorrect voltage problems.
Homeowners: If a homeowner is experiencing a problem like this then please consult a Professional Licensed or Certified Electrician.

• Roy, typically there are two possibilities that are causing these incorrect volt readings:
• One of the main incoming lines has a loose or burnt connection (my guess is L2 because L1 to N reading is correct)
  • Or you have an Open Neutral, which could be a loose or burnt connection as well.
• Roy, you’re getting a voltage feed-back due to one line that has been lost.
  • Also – keep in mind that in Mobile Home Parks they have a 4-wire system, where the ground and the neutral are Isolated and this will explain why the high reading on the neutral to the ground, which is again due to the loss of one of the incoming main lines.
• Inspect the main panel, especially the incoming service wires.
  • Check the cables at the main lugs and at any main breakers.
  • Do not rule out the possibility that a connection of a breaker to the panel buss may be bad due to corrosion or arcing.
• If the problem is not found at the the home panel location then go upstream to where the power source is located.
• Many mobile home parks are fed from a large main distribution panel at a remote location of the facility.

More about Electrical Panels and Troubleshooting Electric Wiring

• Home Electrical Panel

• House Wiring Circuits and Circuit Breakers
• This article looks at common 120 volt and 240 volt house wiring circuits and the circuit breakers that are installed identifying the types and amperage sizes used in most homes.

Electrical 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.

• You identified your project to be about Troubleshooting, so you might find this information useful:

• 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.

• This link is helpful as a Contractor
  • Electrical Code Articles

» You Can Avoid Costly Mistakes! « Here's How to Do It: Wire It Right with the help of my Illustrated Wiring Book Great for any Home Wiring Project. Complete Guide to Home Electrical Wiring Perfect for Homeowners, Students, Handyman, Handy Women, and Electricians Includes: Wiring GFCI Outlets Wiring Home Electric Circuits 120 Volt and 240 Volt Outlet Circuits Wiring Light Switches Wiring 3-Wire and 4-Wire Electric Range Wiring 3-Wire and 4-Wire Dryer Cord and Dryer Outlet How to Troubleshoot and Repair Electrical Wiring Wiring Methods for Upgrading Electrical Wiring NEC Codes for Home Electrical Wiring ....and much more.

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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