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.