Original Question No. 1:
One morning, three years ago, my family and I got up early to go on a trip. Suddenly, we saw smoke coming out of our TV, even when it was off. Immediately, my daughter screamed from the bathroom telling us that the light bulb exploded. My son yelled from his bedroom too, and my wife from the kitchen. It was pandemonium in our house. I had no idea what was going on.
After turning off the main panel breaker, I went out to check the transformer at the pole. I did not see any obvious damage in the transformer, but I saw the bare aluminum (neutral) wire cut. I called the power company, and when they came to check the problem, they told us that the squirrels ate the wire until it was cut. We lost all of our electronic equipment, two refrigerators, fire alarms, etc.
I have two questions: Is there anything the power company can do to the neutral wire to protect it from the rodents? What can I do to prevent future damage to our electronic components? Yesterday, I checked the wire and it looks like the squirrels already ate some sections of the neutral wire again. The power company does not take any responsibility for this, and they do not have a solution to the problem. Please advise!
Henry De Leon, firstname.lastname@example.org
Original Question No. 2:
Over this past weekend I was in helping my son move to a new house. We met the next-door neighbor, who told me that she and her husband had inherited their house from his father. Not long before his death, the father had complained to his son about the squirrels eating the insulation off the wires in the attic of his 170-year-old house. The neighbors had inherited the house and moved there in April 2000. In September 2000, the house burned down from an electrical fire.
I think I will have to be more vigilant in getting rid of the flying squirrels in my attic.
Victor M. Ammons, VAmmons@PRISCO-EDWARDS.com
Original Response No. 3:
It is obvious that neither home was updated electrically for a very long time. Otherwise, the ground rods and bonding to the water system would have protected the equipment from the 220 volts that destroyed everything.
Original Response No. 5:
A couple of things come to mind when I read articles like this. One, while the grounding system isn't supposed to take the place of the neutral conductor, it may have prevented the electrical components from going 120V to 240V once the neutral was lost.
Original Response No. 8:
Most homeowners should have a water pipe or driven ground tied into their system. This prevents damage as described in your two letters. It should be in the electric Code. If there is no electrical path back to the transformer (via earth or via the neutral on the service drop) you will expose your equipment to 240 volts. This path through the ground can only return to the transformer if the utility has alternate (common) grounding.
New Response No. 1
Responses numbers 3, 5, and 8 all refer to adequate ground rods and water pipe grounds preventing this kind of problem. I don't see how a ground rod, meeting code requirements and having 25 ohms resistance, would have helped much. We need to really understand what grounding is for and what it can and can't do to protect persons and property.
New Response No. 2
Wouldn't you agree that some of these guys are expecting too much from the earth return path to the utility transformer? Many utilities use non-metallic entrances and the telephone or cable sheaths aren't designed to carry significant current. At the maximum 25 ohms, an amp of current flow develops 25 volts of drop, enough to create havoc with equipment. The neutral current would likely be much more than 1 amp. Your information about using the earth as a ground on light poles would seem to verify this theory. The low impedance path, in all actuality, ends at the neutral bar if the utility neutral is open.
New Response No. 3
Mike, I have the following suggestion for the gentlemen who said that if you have a good connection to your local grounding electrode you don't have to worry about damage if your neutral opens:
When you go home tonight, open your main switch. Disconnect your neutral. Turn off all breakers. Now switch on the main and switch on one 120V load. Try to have the load, like a motor, nearby and be holding a fire extinguisher. As the load starts to smoke, measure the line to ground voltage. Also clamp an ammeter around the grounding electrode conductor and see how much neutral current the earth is conducting back to the transformer. Extinguish fire. Apologize to wife for the smoke. Turn off main. Reconnect neutral. Chase any squirrels away.
DO NOT FOLLOW THIS ADVICE. JUST KIDDING!
Karl Riley, Karl Riley
Mike Holts Comment: Im sorry that I allowed Responses 3, 5, and 8 in the original Newsletter on this topic. Yes, the lower the ground resistance, the lower the elevated voltage on one phase. But to limit the voltage to within the equipment rating (120V + 10%) the ground resistance would have to be less than 2.5 ohms. Download a spreadsheet and work out the examples for yourself, visit http://mikeholt.com/free/neutral3wire.xls. Im sorry; I dont have the time to fully explain the voltage distribution of a multiwire circuit when the neutral impedance is above one ohm.
Copyright © 2002 Mike Holt Enterprises,Inc.