Subject: Surge Suppression Guidelines, FAQ Sheet, and Proper Connection
Date: October 04, 1995

Here is a FAQ Sheet, quick tutorial, and some Guidelines...

Surge Suppressor Specification recommendations:

UL TVSS 1449 Suppression Rating for _all_ 3 modes:
Hot to Neutral      : 330 volts
Hot to Ground       : 330 volts
Neutral to Ground   : 330 volts
UL 1283 EMI Filter
UL 497A  [ Telco/Modem models ]
CSA listing

Energy Dissipation Minimum 480 Joules [ AC ], 240 Joules [ DC ].

EMI/RFI Filtering: >50 dB rejection over 100 kHz to 10 Mhz for both Normal (NM) and Common (CM).

IEEE 587 A Let-through Voltage < 40 Volts  [ 6kV ANSI/IEEE C62.41 (587) Category A Ring Wave test ].

Peak Surge Current @ 8 x 20 us pulse: 26,000 Amps Common Mode.
--------------------------------------------------------------------------

In addition...

1) Heavy Duty MOV arrays used at BOTH the Line side and the Load side for bi-directional, forward and reverse suppression

2) High Frequency Capacitors used at BOTH the Line side and the Load side

3) Series Blocking Inductor Coils used on BOTH the HOT and the NEUTRAL

4) The Series Blocking Inductor Coils must be positioned AFTER the MOV array and the High Frequency Capacitor arrays on the Line side and
BEFORE the MOV array and the High Frequency Capacitor array on the Load side, so that both forward and reverse suppression is provided and so that MOV harmonics are filtered on both the Line side and the Load side

Line -> [HFC] -> [MOV] -> [SBI] <- [MOV] <- [HFC] <- Load

5) The Series Blocking Inductor Coils must be sufficiently sized and properly located so that RFI Emissions and EMI conduction due to saturation at higher loads do not become a problem

6) The suppressor should have a Positive Shutdown Circuit that automatically stops all current flow to the Load in the event of a catastrophic surge hit _or_ in the event of a failed critical suppression component

7) There should be a Diagnostic Circuit that will identify 

a) An Open Ground, Neutral or Hot?
b) A Hot-Ground or Hot Neutral Reverse?
c) Verified components of the surge suppressor are functioning?

8) The suppressor manufacturer's warranty should cover Power Surges resulting from lightning, and should be transferrable

Subject: Computer and Modem Surge Protection and Electrical Connection

Problem: During the last few weeks there have been numerous complaints of Modem problems and damage, ranging from disconnects to slow transmission, to actual damage in use. Many Modem problems are caused by the lack of proper hardware configuration/connection information and the lack of proper Modem/System safeguards. These will be discussed here.

An Internal Modem has two electrical paths...one from the Telco (DC) and one from the System (AC). If proper care is not tken to assure the integrity of these two electrical paths, damage to the Modem, the COM port, and the MOBO can result, depending upon the severity of the electrical abberration.

Proper Electrical Considerations....

Rule #1: It is very important that your computer system be plugged into a *Grounded* AC outlet, and that all peripherals connected to your system *reference the same AC Ground*.

Explanation: This means that the AC Duplex outlet that your system is plugged into must have a good electrical Ground, as verified by a 3-light tester or by a surge suppressor with site wiring diagnostics. 

It also means that any printers, plotters, scanners, external tape drives, CD ROM or Optical Drives must be plugged into the *same* circuit leg as the rest of the system! 

In most cases, this means a surge strip must be used for each of the two outlets available in a Duplex outlet receptacle, and that all connected equipment must be plugged correctly into these surge strips.

Rule #2: Any Internal OR External Modem must reference the SAME AC Ground as the rest of the system.

Explanation: When AC electricity reaches your wall outlet receptacle, it has its own AC Ground reference (called the Ground wire) at that outlet.
 
One purpose of the Ground is to provide a low resistance path for electrical surges and noise, but to remain at a zero voltage potential most of the time. But...at any given instantaneous moment, an AC ground "could" have a non-Zero voltage potential, as when an electrical surge gets diverted to it.

If you do NOT use the same circuit leg for your system, and in fact, sometimes if you do not use the same Duplex outlet, you may be referencing TWO different Grounds which may at a given moment be at TWO different voltage potentials...the result is that current can travel from one ground, to the other, *through* your equipment. This is called a "Ground Loop".

The same reasoning applies to the Modem...its ground, if unaltered at your computer location, is the Ground of the Telco Entrance, which may be *substantially* different from the AC ground at the Duplex outlet. In such cases, a Ground Loop is possible, from your Modem RJ11 connection, *through* your Modem, the COM port, and the MOBO of your system, to the power supply of your computer, which is referenced by the AC Ground of the Duplex outlet! There are situations where such Ground Loops can cause serious damage.

Rule #3: All computer equipment at one node must reference the SAME AC ground, and must be *surge* and *noise* protected from the electrical system and from *each other*.

Explanation: The easiest way to explain this is to present a diagram...

Surge and Noise Protection....

The short and simple of it all is that in order to get any kind of real protection for the computers you need a *quality* surge suppressor that has meaningful levels of Surge Suppression capability and Noise Filtration ability.

How 'good' a surge suppressor you need depends on your "surge exposure", the type of equipment to be protected and the system configurations, and, finally, the quality of the electrical wiring and service.

Surge Exposure: Likelyhood of damage due to electrical surges owing to your geographic area...high in Florida, low in NYC...if there is fairly frequent lightening activity, and your home is serviced by overhead utility poles, you need very good protection.

Type of Equipment: If your computer is equipped with a Modem, it needs to be surge protected...protecting the AC line without protecting a Modem is less than halfway protection. If there will be a laser printer, you also need "noise filtration" so that the printer will not interfere with the rest of the system.

Quality of Electrical Wiring & Service: Is your home wiring new and up to the current NEC standards? Are the computers on a dedicated circuit, with verified good AC grounds? Does the electricity seem fairly stable, or is it subject to frequent 'brownouts' or outages as in many rural areas? If the latter, a Line Conditioner or UPS should be used for the computer system (not the laser printer) instead of a surge suppressor.

The following schematic would cover most scenerios calling for a quality Surge Suppression protection scheme:

Figure 1

Duplex Wall Receptacle--has outlets "A" and "B"

              ----------Modem RJ11/RJ45 jacks into Modem surge ports
              |
              |
A--------Surge suppressor with Modem Surge------computer system
         (with noise filtering)
B--------Surge suppressor-----------------------Laser printer
         (with noise filtering)

In the above Figure, there is one Duplex outlet consisting of two outlets, outlet "A" and outlet "B", on the same circuit leg. 

Into one of them ("A") a surge/filtering strip with Modem surge protection built-in, gets plugged, and the computer & Modem RJ11 jacks go into that surge/filtering strip. Into the OTHER outlet ("B") the Laser printer gets plugged into its OWN separate surge/filtering strip. 
The laser printer requires its *own* quality surge/filtering strip because it *produces* and *throws back* large amounts of 'Common Mode' and 'transverse' electrical noise when operating, and would therefore contaminate the electrical system it is plugged into, and all else not isolated from that connection. The separate surge/noise filtering strip for the Laser printer prevents this from happening. A Photo Copier or other 'noisy' piece of equipment also requires its *own* surge/noise filtering strip.

The surge suppressor in the above Figure for the computer system and Modem would be a UL 1449 Listed surge suppression device with built-in UL 497 modem surge protection, and UL 1283 RFI/EMI Noise filtering; the Joule ratings would be a *minimum* of 480 Joules for the AC surge circuit *plus* and *additional* 240 Joules for the Modem. The Modem surge circuit must be properly designed, with *low capacitance*, or it will actually SLOW DOWN a Modem transmission...capacitance should be LESS THAN 50 picofarads, and should be specified as such.

Note that the Surge Suppressor with Modem Surge protection capability is plugged into the same AC Duplex outlet as the rest of the system...the Modem's RJ11 jacks are plugged INTO the protection ports of that DUAL surge suppressor, and when so done, the Modem NOW REFERENCES THE SAME AC GROUND as the rest of the system!

This electrical connection scheme will prevent Ground Loops, and it will also prevent AC Surge Damage *and* Telco/Modem (DC) Surge damage. Instead os a Telephone surge coming in on the Telco line, going *through* your Modem, COM port, and MOBO, as it seeks the AC ground, it will now be 'caught' and suppressed by the Modem surge circuit in the DUAL surge suppressor, and diverted *directly* to the AC Ground.
  
Good quality surge suppressors and DUAL surge suppressors are made by Sutton Designs and others. A good quality unit will run $50+ each.

Hope this helps.

Best Regards,

Fred Noble
Sutton Designs Technical Support
LAN B Vendor Forum (CIS:LANBVE)