Efforts to combat damaging, disruptive spike, surge and interference threat should address data lines, network cables, phone- modem lines and AC power lines individually. We'll address AC Power in this segment.

In many cases, high performance wire in AC power Line Filter/Suppressor can be installed in the electronic equipment junction box or mounted directly within sensitive equipment. A typical wire in unit is shown in Figure 1. Generally wire in units are available with ratings up to 30 Amp load capacity. Models designed for 125/250 Volts, 250 Volts and 3 Phase Voltage ratings  are manufactured. The power line  filter attenuates electrical, RFI and noise interference, while the integral suppressor absorbs high voltage spikes, transients and surges. Models are available with wire leads, push on tabs, screw or solder terminals.

Several companies offer distinct filter grades to combat various interference conditions & problems. Electronic Specialists offer Commercial, Industrial and Laboratory grades suitable for most industrial situations likely to be encountered.

Effective interference filtering requires presence of both differential mode and common mode filters. Spike-surge suppressors should also provide differential and common mode suppression. In addition, quality suppressors should provide high current, high energy suppression, with a very fast response time.

Filter/Suppressors similar to that shown in Figure 1 can also be installed at machines which are known to cause interference or spikes. Be certain  to specify correct operating voltage & current, as well as temperature and mounting criteria.

Stand alone controllers, computers or other apparatus can readily be protected by line cord type protective systems. Figure 2 shows an Industrial grade line cord unit. This model is typical of the over 50 line cord models which are manufactured by Electronic Specialists. Additional models are available for Direct Plug wall socket connection, 250 Volt operation and 3 Phase electrical systems.

Again, quality manufacturers offer choices of several grades and models to permit adapting to industrial situations as encountered. Twist type industrial electrical connector systems can be protected with Twist Protect models similar to the unit illustrated in Figure 3. Standard NEMA Twist Type socket designations for voltage, phase and current can be accommodated.

High performance protection designs have contributed to longer equipment life and improved system performance for thousands of computer, audio, industrial and scientific installations throughout the world

Note that some manufacturers offer direct plug suppressors with   specifications identical to line cord models.  Eliminating the line cord, direct plug units offer a  more compact system installation.

Computer stores, office supply outlets, computer supply catalogs and local hardware stores sell spike-surge suppressors. Some suppressors are quite good, some not so good, and some are little more than (poor quality) extension cords. Unfortunately, it is a bit difficult to determine quality.  Price alone is not always a good indicator - some units with very low suppression capabilities and no interference filtering sometimes sell for about the same price as good units.

Later in this tutorial segment I'll give you some evaluation criteria to aid your purchase decisions.

High performance audio or home theatre systems have also shown considerable power line interaction vulnerability.  Power amplifier demands subtly affect power entering the low level pre-amp and balancing stages, casting  a discernable distortion into the reproduced sound (and sometimes affecting video). Audio and video enthusiasts (a discriminating group) describe the effect of filter-Isolator installation as "lifting a veil that enshrouds the performance".

Significant performance improvement, in those systems suffering from equipment interaction, can be achieved using line cord or wire in filter Isolators. Isolators incorporate filter isolated channels coupled with high performance suppression; a particularly effective combination which isolates protected equipment from power line pollution in addition to providing isolation between  interacting components.   Not needed for every installation, these AC Power Line filter Isolators have rendered many erratic systems blissfully stable.

Offered by several manufacturers, Isolators are available with various grades of performance.

We'll present a segment later, with much more on AC Power Line Equipment Interaction

This tutorial segment has introduced several devices widely used to convert unfriendly industrial or commercial electronic systems into the very model of docility.

A later segment will discuss voltage regulators, isolation transformers, power interrupters and filter-isolators.

Most folks refer to any AC Power protector as a "suppressor".   That's the reason many people question why they should pay $25, or $50  or even $100 for a real suppressor since their dealer "threw in" a perfectly good $7.50 suppressor when they purchased their equipment.

A great majority of suppressors on the market today employ MOV technology - some in a hybrid version with other type suppression devices.  Some units use only one MOV; Others use an array of 10 (or more) suppressing devices.

At the very low end, units are sold with a single 6,500 (or 4,500 !) ( or worse - 2,500 !!) Surge Amp MOV suppressor positioned between the power line "hot" and "neutral" bus.  I've seen many of these where the MOV got hit hard and literally vaporized. All that remained were 2 wire stubs where the MOV used to be - the suppressor case inside was coated with fine dust!

Between the time the MOV vaporized and the time I inspected the device, these owners thought they were protected!

Their equipment was continuously being stressed by lower level spikes and surges which exist on power lines almost daily. Luckily, a major surge didn't wipe them out.

Once you get past the bottom-feeding single MOV suppressors, you encounter 3 MOV devices.  These are usually 6,500 surge amp MOVs, but I've seen 4,500 surge amp units used.  These suppressors may give up to 3X more protection than a single MOV device, but that's still a very slim safety reed to lean on. I've seen vaporized MOV's   in these, with power still being delivered to the sockets.  Connected equipment was still unprotected!

Three MOV units might advertise as 18,500 Surge Amp, or 5,000,000 Surge Watts, or .... some of their specifications may get a little rubbery! They might talk about common and differential mode protectors (which they are) without any protection level indication.  Sometimes there is no protection information - relying on a snappy package and glib salesman to move product.

Quality suppressors generally provide a minimum 39,000 Surge Amp capability, ranging upwards to 60,000 Surge Amps.

Note that spike-surge feed through voltage decreases as a unit's Surge Amp capability increases.  Feed through spike / surge voltage for large energy hits may cause equipment stress.  Higher Surge Amp units provide more protection

Many will give a "Surge Watt" and "joule" rating.   Surge Watts sound quite impressive - from 10 to 50 million Surge Watts !! for a 2 micro-second surge pulse, while energy dissipation ranges between 400 and 2,500 joules.   These numbers can be calculated making various assumptions (all more or less valid), while Surge amps is more often based upon device manufacturers ratings.

Some models incorporate thermal shutdown or surge fuses to disconnect equipment in the event of a catastrophic surge.  Surge fusing operates independently of other fuse or circuit breaker protection and is not intended as a primary fuse.

Hybrid suppressor technology refers to the practice of employing 2 or more device types in an arrangement designed to augment equipment protection.

High Speed suppressor diodes and gas tube suppressors are devices most often used with MOVs for hybrid designs.

Gas tubes respond to surges and spikes in 1 or 2 microseconds, about the same as MOV devices. Additionally they will pass more surge current than MOVs, leading to impressive (but suspect) Surge Current and Surge Watt numbers.

On the negative side, they are less reliable than MOVs. Further, once a surge or spike activates the gas tube, it will continue to pass large current until the AC cycle reverses.  If a spike occurs early in the AC cycle, massive power line current could be drawn throughout half the AC cycle.

Suppressor diodes respond to surges and spikes within 1 - 10 pico-seconds; over 1,000 x faster than either gas tubes or MOVs. They are ideal for suppressing sub-nanosecond spikes generated by thyrister controlled devices which now exist in every facet of our life. Sub-nanosecond spikes show up, do their damage, and are gone before the MOV even begins suppressing activity.  Very high short term current and extremely fast response make suppressor diodes a natural for  eliminating damage and disruptive threats from sub-nanosecond spikes

On the negative side - suppressor diodes do their work so fast they add virtually nothing to Surge Amps, Surge Watts or joule specification numbers.

Surge Amp ratings are the critical rating to check. Look for a minimum 39,000 Surge Amp rating.  Units with less capability generally provide no surge amp information.

Remembering that Surge Watt and joule rating values are calculated, varying widely and are not always provided, units claiming 10 million surge watts and / or 400 joules will provide adequate protection. 

Note that Electronic Specialists line cord and direct plug units provide a minimum 58,500 Surge Amp suppression.  Surge Watts conservatively specified at 30 million watts, while an alternative calculation yields 60 million. Energy dissipation is specified at 620 joules, with an alternative computation yielding 2,500 joules.

Electronic Specialists wire-in filter-suppressors are available with ratings from 39,000 Surge Amps to 200,000 Surge Amps. Wire-in filter-suppressors offer options of Commercial, Industrial or Laboratory Grade RFI and noise interference filters

And, of course, we are always available to design protection for your special applications.

Interference can get onto your power lines either via conduction or radiation. 

Power station generated noise interference, as interference caused by connected electrical equipment is carried to your system via conduction down the power lines. 

Interference generated by lightning or other spheric conditions, from various radio / TV stations, RFI from automobile ignition systems or noise from arcing motors gets onto power lines by radiation.  Once on the line, interference is conducted to your system. 

Needless to say, this interference can extend up to 200 MHz with wide amplitude variations.

Depending on interference amplitude and frequency, your equipment may suffer very little, some or extreme reaction.  In extreme cases programs behave erratically, sometimes even causing system crashes.

Some low cost, single MOV suppressors claim to have "filtering".   Usually this is a cheap capacitor. A few low end units claim the inherent MOV capacity provides filtering!

Better units offer various filter grades - - the most common filtering specifications are about 45 db attenuation over a range of 100 KHz to about 10 MHz.   This performance level is usually sufficient to clear up average interference problems. 

Since interference is occasionally present on all power lines, many manufacturers design some filtering into all but their lowest cost units.  These are routinely  installed as a low cost insurance policy by many system owners.

A few companies offer filter-suppressor filtering choices, permitting system operators to purchase capability consistent with their environment requirements.

Filtering ranges extend to about 65 db attenuation between interference frequencies of 10 KHz to 250 MHz.

When coupled with high performance suppressors a wide band, high attenuation filter can tame the wildest system.

Avoid "cheapies" like the plague! Mostly, these offer a false sense of security. If the sales person offers you one "free" when buying a new system - ask for the money.

To get an idea of prevailing costs, browse computer stores, catalogs and computer magazines.  You'll see lots of low end units, a fair number of passable units and maybe a few high performance units. This will give you a price - performance claim range.  There most likely will not be advertisements for very high performance protection.

Why the predominance of "cheapies"? Almost no one understands the interference and spike-surge threat presented to systems, therefore they feel they get adequate protection - maybe a "Suppressor" label will protect them!

High performance units usually cost little more than medium priced filter-suppressors. When weighed against the down time and equipment replacement cost, shortened system life due to undetected spike-surge over voltage stress and general aggravation, the added security and peace of mind is well worth the added cost.

It will be at your in-box in a few weeks.

In the meantime, we invite you to review Electronic Specialists products discussed above
Wire-In Filter-Suppressors
AC Line Cord Filter-Suppressors for 120 Volt (US Standard) applications
AC Line Cord Filter-Suppressors for 240 Volt US applications
Heavy Duty Twist Protect industrial units
Power Line Interaction filter-Isolators