Ask Electrical Question
E Books
Store
Blog
Subscribe

Stray and Induced Voltage

Much research has gone into the problem of stray and/or induced voltage.  In most scenarios, this phenomena is more of a nuisance and a topic for theoretical discussion, than it is an actual safety concern.  However there are situations where stray and induced voltage can cause serious issues, resulting in injury and even death.  Compromised or faulty electrical systems around high voltage distribution, street lighting, and marinas are just a few examples of where serious safety issues are a definite concern.  Livestock are also very sensitive to induced voltage and issues arise around watering systems, especially those that use electricity for heating elements to keep the water thawed.

However, inductance, capacitance, resistance, voltage, and current flow are the basic components of electrical theory, and inductance is how transformers work.  When you take a utility distribution system of 14,400 volts, and step it down to a useable system of 120/240 volts, there is no physical connection between the utility supply, and the wires that provide the power to your home.  It is all through inductance.

So enough of the theory lesson, this now brings me to a question I had from a site visitor regarding induced voltage.

Question:

I have a line that feeds 4 outlets. Disconnected from all outlets the primary feed line neutral (white) has 28 vac with the circuit breaker energized. The main line is about 20′ long and has no other wire near it. Where am I getting the stray voltage from? I’ve found no damaged insulation or wires.

Without testing this myself, or seeing exactly what the situation here is, my response would be is that what you are seeing is that the voltage on the neutral wire is being induced from the live hot wire in the cable.  I’m guessing that you are using a high impedance digital voltmeter to see this 28 volts, and you are measuring an open circuit from the neutral line in reference to ground or earth.  This is likely nothing to worry about and you can find induced voltage in numerous everyday situations.

I myself had an experience that really drove home the reality of induced voltage, and the potential affects it can have when encountered.  We were staying at an R.V. park in Victoria British Columbia in the spring of 2010.  The park has an outdoor storage area where guests can park extra vehicles, R.V.’s, or boats, and many of the stalls are located under a high voltage transmission line.

Trailer in RV Park

Given the topography of this Island R.V. Park, as the lines run down through a valley, they come fairly close to the ground inside this storage compound.  The parking stalls are perpendicular to the lines.

Power Lines Above Trailer

There was a light rain one day when I went to retrieve something from my trailer, and the grass around the parking stall was long and wet.  I was wearing open toed sandals, and when I opened the metal side door to the trailer I could feel a prickling in my toes, much like when you step on a thistle.

Feet on the Grass

I moved my feet to no avail.  I also noticed that when I let go of the metal trailer door, the thistles were gone!  Upon closer inspection of the grass, it was just plain old soft lawn grass and nothing prickly whatsoever.  Then I looked up to see the lines humming away above me and I realized that was I was feeling was induced voltage coming from the high voltage lines, to the metal trailer, running through my body, out of my toes, through the wet grass, and into the earth!  Knowing what kind of voltage is used in utility distribution systems, the realization of what was happening gave me a bit of a scare, so I decided to do some testing.  Just how much voltage was there?

I got out my Fluke multi-meter and stuck the black test lead into the wet ground.

Black Lead Stuck in Earth

Then set my dial to volts AC, and touched the metal frame of the trailer.

Red Lead on Trailer Door

550 Vac!  Wow!  This made me wonder if this was enough to make a florescent lamp flicker or glow so I set up that experiment, but the results were inconclusive.  It was daylight so it would have been very hard to notice any activity inside the lamp with the relatively high level of ambient light.

With the rain falling that first day, I decided to delay creating a post for the website about this issue, so I waited for a better day.  The nicer weather made for better pictures, but without the excess of moisture and humidity, the test results weren’t quite as dramatic, but still astonishing.  Here is a picture of the actual readings on the meter on the day I took the pictures.

Meter Reading 200+ Volts

All it took to effectively drain off this induced voltage was to drop my safety chains to the ground and stomp them into the wet soil a bit.

Chains on the Ground

The best results came from plugging my trailer into the electrical outlet, thus connecting my trailer ground to the system ground through the supply cable ground wire.

Trailer Connected to Grounded Receptacle

This experience made me reconsider my position regarding the NIMBY (not in my back yard) position that most land owners take when utility companies attempt to gain approval for a new transmission line corridor.  I used to be quite indifferent to their cause and the claims of the potential adverse effect that these electrical magnetic fields can have on their surroundings.  While I’m no physician, after personally feeling the effect on my own body, I can’t help but wonder if there are long-term health issues that may arise from prolonged exposure to these induced voltages.  Care should be taken to ensure these transmission lines have the least impact possible when planning the route they take.

If you ever encounter a similar situation as I did, back away from the problem area taking very small steps, or by shuffling your feet.  Do not hesitate to contact the power company to investigate the source of the stray voltage as the problem may be a serious one involving a poor or compromised ground grid, or other problems that can occur while distributing power we use for our everyday conveniences that we take so much for granted.

This entry was posted in Q & A, Safety and tagged , , , , , , , , , , , , , , , , , . Bookmark the permalink.
  • John

    Not directly related, but another HOT condition: Someone mentioned the hazard of jumper-ing a neutral wire to the ground screw of a house wiring receptacle in order to compensate for an open neutral downstream of this receptacle They said this can result in a HOT appliance. Is this caused by voltage reaching the appliance cabinet via the ground screw ( on receptacle) then thru the appliance cord’s ground prong, then on to the appliance cabinet? Asking only so that I could know what one of the causes of a “hot appliance” might be, if I encounter one. Thx much for any help.

    • Internetelectrician

      Neutral and ground are at the same potential electrically, that being “earth”, or ground because they are bonded together in our main service panel. The neutral conductors are the intended path for electron flow in a circuit, and the ground path is intended for fault current only in the event of a short circuit condition. To jump a neutral to the ground screw to correct is an unacceptable solution. Find the broken neutral! However unless something else is not wired correctly in the system, this shouldn’t cause a “hot appliance”.

  • John

    Would the utility company be liable for any injury to someone under similar circumstances? Also: “f you ever encounter a similar situation as I did, back away from the problem area taking very small steps, or by shuffling your feet. ” Please explain why small steps or shufflling. Thx much.

    • Internetelectrician

      I can’t comment on the liability issue as I just don’t know. Small steps, or shuffling your feet as you move away is to attempt to mitigate what’s called “step voltage”. If there is current flowing in the ground then if you take a large step you can create a potential difference from one foot to the other creating a parallel circuit for harmful (or fatal) current flow through your body.

  • Gary Cooper

    This fits my problem that I encountered pretty well. Although I never had a fantom voltage be so high, when I used my low tech analog volt meter it was only 40 volts,definitely fantom.
    Thanks.

  • gavin

    I have 50volts ac coming in from the utility supply on the neutral line.
    220v single phase supply.
    This is putting 50vac through the neutral line of my whole house electrical system.
    If you test at a power socket you get 220vac on the live wire and 50vac on the neutral wire.
    Disconnect the wires from the meter to my house and you get the same readings on the wires from the utility supply so it is defiantly not a problem with my house wiring.
    The utility company say that it is only 50v and not a problem.
    I have had shocks from it so it is a problem.
    What is causing this?
    Is there something I can add to the neutral wire that will stop this voltage coming in to the house?
    thanks.

 

The Basics of Household Wiring DVD

"If you're looking for a good reference to help you understand simple home wiring, I personally recommend 'The Basics of Household Wiring' DVD".

Terry Peterman, the Internet Electrician
 
Electrical Wiring
Electrical Diagrams
Projects
How To
Electrical Tools
Electrical Videos
Copyright © www.electrical-online.com |  LEGAL DISCLAIMER |  PRIVACY POLICY