Written By: Charles F. Kerchner, Jr., P.E.

Copyright 1985
Charles F. Kerchner, Jr.
All rights reserved
Last revised 13 May 1996

While much has been written about power-line voltage spikes, surges, dips and conducted high frequency noise, very little has appeared in personal and small business computer magazines about another electrical problem--miswired and defective electrical wall outlets.

All modern electrical wiring systems used in standard household and office environments use an electrical system consisting of three wires. They are the hot, the common or neutral, and the ground. There is only one correct way to wire these wires to your wall outlet. The hot black wire goes to the smaller rectangular slot, the neutral white wire goes to the large rectangular slot, and the bare copper or green ground wire goes to the U shaped opening. There are several other incorrect ways to wire wall outlets some of which result in the electrical device not working at all or in blown fuses. We won't discuss these, since these are immediately found and corrected. It is the miswiring and defect cases where the electrical equipment continues to function but internal ground planes and EMI/RFI shields are defeated or where safety is compromised that is the subject of this article. These miswiring and/or defective outlet conditions are:

1. Hot and neutral reversed.
2. Neutral and ground reversed.
3. Open ground connection.

Occurrence of item two above is not very common due to the greater inherent difficulties in mixing up the ground and other wires due to the obvious physical differences in most ground wires. Occurrence of items one and three, however, is much more frequent and is a problem worth discussing. In all of the above cases the computer or other high-tech device will probably continue to work. However, the user may experience intermittent unexplained glitches. The user then gets a surge protector and/or power-line noise filter, however, the problem still doesn't go away. The reason is that the electrical energy is not being correctly applied to the computer, therefore, it's ground planes are not operating properly and also there could be high frequency sneak paths into the logic that the equipment designer never considered since the engineer assumed your outlet would be wired correctly. The protector manufacturer also assumes the outlet is wired correctly so it is of no help. In addition, the third case above, exposes the operator to potential shock if his equipment's insulation or a part malfunctions. Miswired outlets can also damage other energy generating devices such as emergency power systems and UPSs. This is because most UPS systems switch only the hot wire relative to the common neutral and if the hot wire is not hot but is instead the neutral it is possible to have the UPS and the electrical system both energized simultaneously and cross connected such that voltages higher than 120V exist causing damage to the UPS and/or other equipment. As a manufacturer of both power-line surge/noise protectors and standby UPS systems we have seen that the instance of miswired and defective outlets is somewhere between 1/2 to 1%. While this is not a very large percentage, when you consider the number of outlets installed this is indeed a very large number of miswired and defective outlets. And while the percentage is small the potential headaches and damage these unseen (but trusted) bad outlets cause has given many an equipment maker a black eye until the cause is ultimately found.

How does one check the outlets? Well actually it is quite easy. A simple hand-held plug-in device called an outlet wiring integrity checker having three lights on it will simply and quickly test your outlets. Every homeowner or office manager should have one of these. A low-cost model is Radio Shack catalog number 22-101 which retails for about $6.00. In addition to this, many surge/noise protectors such as the Kalglo model QPC+ have built in wiring integrity checkers. Everyone should have an outlet wiring integrity checker and several times a year go around your building and check all the outlets. Also, if you order a surge/noise protector, get one with a built-in wiring integrity checker so that you can be assured you are plugging your computer into a properly wired outlet. So buy a wiring integrity checker and test all your outlets. Do it now. Your equipment will perform better if you find and correct a faulty outlet. Plus you'll have the peace of mind knowing all the safety ground and interference control features designed into your wiring system and equipment are fully enabled.

Copyright ©1985
Charles F. Kerchner, Jr.
All Rights Reserved
Last Revised - 13 May 1996
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