Surge suppressors, also called spike arresters and MOVs (Metal Oxide Varistors), are voltage clamps. That is, they prevent the voltage from going beyond certain preset limits, i.e. they clamp the voltage. They were originally designed to protect devices (such as your TV) from harm during a lightning storm. Although low cost, they provide limited protection and, as explained later, can actually be harmful to your system.
The voltage that enters your home or business is 120 volt AC. The 120v is the average of a voltage sine wave that peaks at 170 volts positive and negative. Clamping devices such as surge suppressors don't want to clip the tops off of the sine wave so they are set to clamp at approximately 204v. A spike that occurs at the top of the sine wave will be limited to 204v-170v or a maximum of 34v. Unfortunately, a spike can occur at any point during the sine wave cycle. If a positive spike occurs at the very bottom of the sine wave, at the negative 170v point, the size of that spike will be 170v+204v or 374v! Your equipment was never meant to withstand that much noise!
The voltage entering your home or business enters on a 3 wire system - hot, neutral, and ground. The spikes just discussed are measured between the hot and neutral wires (called normal-mode noise). There is also an impact upon the ground wire. The excess energy created when the surge suppressor clamps the spike has to go somewhere. It goes onto the ground wire and is called common-mode noise. The logic in your computer-based equipment, around 5v±2v, is referenced to that ground wire and the ground wire is generally not filtered at all when it enters the computer. Noise in excess of ½v will cause your computer to mis-read that bit of logic and perhaps mis-apply the computer instruction involved! Since this noise is from the excess energy from the clamping function, there is no way to tell how large it is. According to the American National Standards Institute (spec. ANSI/IEEE C62.41) the maximum voltage spike that can travel through the wires in your house is 6000 volts because voltage in excess of the 6000v will arc over in your wall receptacle before it gets to your equipment. Therefore, as a worst case, the energy from the voltage spike between 204v and possibly 6000v can be dumped onto the ground wire.
Power conditioners were designed to protect computer and telephone systems. They do not clamp the voltage. Rather they follow the sine wave up and down with a protective shield that limits the maximum voltage to 10v normal-mode and ½v common-mode no matter the size of the incoming noise event. All Oneac power conditioners are measured with a simulated 6000v pulse to assure their protective shield is working before they leave the factory.
In 1986 a semiconductor symposium in San Jose, CA, published a paper discussing the maximum levels of electrical noise a semiconductor system could withstand without damage. They determined that 10v normal-mode and ½v common-mode was the maximum. Since then, the silicon which forms the basis for the semiconductors has not changed. Unfortunately, the computer circuits on those silicon chips has gotten much more dense. Therefore, the insulation between adjacent circuits has gotten much smaller. If anything, adhering to the 10v/ ½v maximums has gotten even more critical.
Surge suppressors were designed to protect 2 wire devices such as a TV. They were not designed to protect 3 wire devices such as a computer. Because of the excess levels of noise on the ground wire they can actually do harm to your computer. Power conditioners were designed specifically to protect computer-based equipment in accordance with the recommendations of the San Jose semiconductor meeting.
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