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di@si@ AN IMPORTANT LINK IN WHOLE-HOUSE PROTECTION: i,od' pith 

f~aQ EflG SURGE REFERENCE EQUALIZERS 

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Fraqois D. Martzloff 

National Institute of Standards and Technology 

Gaithersburg MD 20899 USA 

Abstract - The increasing use of electronics in residential applications has been paralleled by a realization 

that surge protection may be necessary for this type of 

equipment. Installing a surge-protective device on the 

power-line port as well as on the communications-line 

port of an equipment might appear sufficient to ensure 

this protection. However, the normal operation of one 

of the protective devices during a surge event can create 

differences in the voltages of the references of the two 

ports. This difference in voltages, applied across the 

equipment or across a communication link between two 

pieces of equipment, can result in permanent damage as 

well as upset. Equalizing these voltages can be achieved 

by proper routing of the two lines through a single 

device, called Surge Reference Equalizer, and thus avoid 

the risk of damage. 

THE PROBLEM 

A new generation of smart electronics has 

emerged that involve processing information obtained 

from communication networks: fax and telephone 

answering machines connected to the telephone system, 

television sets connected to a cable system, desk-top 

publishing systems connecting several computers and 

printers, industrial process controls with remote sensors 

and terminals, etc. This type of equipment generally 

requires a metallic connection to the communications 

system, while being powered through a connection to the 

local power system. This dual connection introduces a 

risk of interference or damage to the equipment because, 

during surge events, the two systems can have 

differences in the voltage of the two systems reference 

points. 

In the consumer world, damage is the greatest 

concern, upset may be tolerable; in the commercial and 

industrial world, upset and its consequences are already 

unacceptable. Understanding the topology of the 

equipment and of its connections to the power and 

communications networks, as well as the mode of 

propagation of surges in the two systems, will help in 

defining appropriate solutions and avoiding counterproductive situations. 

Marek Samotyj 

Electric Power Research Institute 

Palo Alto, CA 94303 USA 

A useful concept is to envision the relationship 

of any electrical equipment to its electromagnetic 

environment by means of several 'ports'. According to 

this concept, 'port' means a point of access where 

energy may be supplied or withdrawn. In the most 

general case, six types of ports can be identified, as 

shown in Figure 1. The desirable signals (including 

power) as well as undesirable signals can enter or leave 

the equipment through these ports. Five of them 

involve metallic connections, that is, cables (with the 

exception of fiber optics links). 'The sixth is electromagnetic coupling through the equipment enclosure, 

directly into or out of the equipment inner circuits. 

Enclosure port 

Figure 1 - Six ports for coupling of disturbances 

from electromagnetic environment to equipment 

The general case of Figure 1 shows a separate 

'earth port'. In typical situations, this port can be a 

distinct, direct connection to the local grounding system, 

or it can be included in the connection of the other 

ports, such as the equipment grounding conductor of the 

power line or the shield of the cable TV connection In 

computer-based systems, signal cables usually include a 

'signal reference' conductor which is connected to the 

equipment chassis and, therefore, ultimately to the 

equipment grounding conductor of the power cord. 

Typical smart electronics equipment have at least two 

ports, the ac power port and a communications port. 

In one scenario, a reasonably well-informed 

end-user might have provided surge protection on both 

the power port and the communications port, yet the 

equipment could be damaged by a difference in the 

reference voltages developed during a surge event. 
Figure 2 shows such an arrangement, where the 

telephone port of the Fax machine is assumed by the 

end-user to be protected, thanks to the Network Interface 

Device (NID) installed by the telephone company, and 

the power port is also expected to be protected by the 

plug-in surge-protective device installed by the surgeconscious end-user. Such a plug-in device is often 

called Transient Voltage Surge Suppressor, TVSS for 

short in the U.S., but is now recognized by the acronym 

SPD by the International Electrotechnical Commission. 

rod Metal Water Pipe 

Figure 2 - Incomplete protection of two-port 

equipment, in spite of having two protectors 

If a surge impinges upon the building at the 

power or the telephone port, the expected operation of 

the protective devices will divert the surge current to 

ground ('protective earth' in European terminology). 

The voltage drop caused by the fast-changing surge 

current flowing in the inductive ground connection of 

the protective device leaves the line connection of the 

surge-carrying system at a voltage higher than that of the 

system unaffected by the surge. A difference of voltage 

appears across the two equipment ports during the surge 

event, in particular during the rise time. This difference 

of voltage can cause an upset or hard failure if the 

equipment has not been specifically designed for that 

stress. Thus, separate, uncoordinated protection of each 

of the two ports can still leave the equipment at risk. 

Another scenario involves the voltage difference 

between the two chassis (and thus the signal reference) 

of subunits powered from different branch circuits, as 

shown in Figure 3. In this scenario, a built-in SPD or 

EM1 filter has been provided in each sub-unit by a 

prudent manufacturer. The normal operation of the SPD 

or EM1 filter during a surge event causes a voltage drop 

in the conductor that returns the surge towards the 

service entrance. Meanwhile, the chassis of the other 

sub-unit, unaffected by the surge, remains at the voltage 

of the service entrance reference. The result is that the 

two chassis assume different transient voltages, and the 

data link reference conductor connected to these two 

chassis will attempt to equalize the voltages, with 

possible upsetting or damaging consequences to 

components in the line driver or receiver circuits of the 

two sub-units. 

TWO SOLUTIONS 

The radical, well-known solution for this type 

of problem is to provide a fiber optic communications 

link rather than a metallic connection. This solution is 

frequently applied to solve problems in utilities, 

industrial or commercial installations, but its relative 

complication and present cost have kept it impractical 

for residential, consumer-type applications. In such 

cases, another solution is a Surge Reference Equalizer. 

The generic name of this device has been introduced by 

a new IEEE standard [IEEE 11001, giving recognition to 

a concept that has emerged over the last several years. 

The surge reference equalizer combines the 

protective function for both system ports in the same 

enclosure. The device is plugged in the power 

receptacle near the equipment to be protected, with the 

communications system wires (telephone or data link) or 

the coaxial cable (TV) routed through the enclosure. A 

common, single grounding connection equalizes the 

voltages of the two paths that return the surge through 

the grounding connection of the 3-prong power line 

plug, as shown in Figure 4. 

Figure 4 - Complete protection of a PC by insertion 

of a Surge Reference Equalizer 

Such a solution is particularly attractive as an 

element of 'whole-house protection', a concept that has 

been recently introduced by some electric utilities. In the 

whole-house protection scheme, some utilities now offer 
an engineered, coordinated installation of SPDs to their 

customers [Maher, 19911, instead of the do-it-yourself 

approach that can lead to the situation illustrated by 

Figure 2. Several locations can be considered for 

connecting these SPDs, as shown by the numbered SPD 

locations in Figure 5. In the whole-house protection 

scheme, a two-step approach is used: an SPD is installed 

by the utility at the service entrance (location 2), and 

plug-in SPDs are supplied by the utility to the consumer 

for insertion on the input ports to sensitive equipment 

within the residence (location 6). 

Figure 5 - Possible locations for SPDs in a residence 

The objective of the two-step protection scheme 

is to divert most of the impinging surge energy at the 

service entrance, and to complete the protection at the 

point of use by a plug-in SPD. This second device can 

then serve as surge reference equalizer, rather than serve 

only as a TVSS on the power port. 

receiver or recorder is not specified by industry 

standards, leaving the designers of surge reference 

equalizers in the dark as to what level of surge 

suppression they should provide in their devices. 

Fueled by the desire of electric utilities to 

provide enhanced power quality to their customers by 

supplying appropriate SPDs, the response of EPRI has 

been to sponsor the development of test protocols for 

assessing the system compatibility of these devices. The 

approach consists in performing tests on devices 

proposed for installation in the residential environment 

in accordance with a set of consistent and objective 

criteria taking into consideration the surge environment, 

the needs for protection of consumer electronics, and the 

need of the electric utility for compatibility with its 

power delivery system 

In fact, the concept of providing test protocols 

for assessing compatibility of equipment extends far 

beyond the specialized domain of the surge reference 

equalizers discussed in the present paper. -The Power 

Electronic Applications Center (PEAC), sponsored by 

EPRI, is currently developing a family of test protocols 

for equipment such as fluorescent ballasts, adjustable 

speed drives, enhanced computer power supplies, etc. 

TESTING FOR SYSTEM COMPATIBILITY 

Tests for system compatibility of several surge 

reference equalizers were performed at PEAC on 

Surge reference equalizers are now found in devices proposed for a "Whole-House" protection plan 

electronics and computer stores, although neither the by an electric utility. The following brief review of the 

test results illustrates the benefit of the program in name nor the design have been standardized' The identifying adequate performance as well as needs for inrended function can be immediately recognized by the improvements in the 

presence on the enclosure of a power route - a male plug 

and one or more female receptacles - and a communi- The tests were performed in accordance with cations route - cable TV coax fittings, telephone jacks, the test protocol [SC-~U)]. These tests include a 

or RS232 connectors. Until the voluntary standards determination of the clamping voltage on both power process has fostered uniform characteristics, the and communications ports, an assessment of durability, 

performance of these devices can vary from one brand and checking for side effects. A unique aspect of the 

to another, although one could expect each manufacturer SC test protocols is that while expected results are 

to have made reasonable assumptions and mdeoffs in stated, the tests results are not presented as pasdfail, but 

the design of the product. An alert consumer who is rather as a comparison between expectations and results, 

considering on his own the purchase of such a surge leaving room for the sponsor to make a decision based 

reference equalizer has no information on the on the overall performance. 

performance or side-effects of what the store-bought 

device offers. An engineered scheme offered by the Two sets of candidate surge reference equalizers 

utilities can provide the leverage to obtain devices with were tested at PEAC. One set featured power port and 

demonstrated performance. telephone port protection, the other power port and cable 

TV protection. For telephone-port devices, the various 

designs were based on a multi-stage circuit connected 

SYSTEM-COMPATIBILITY CRITERIA between each of the two conductors of the telephone 

cable and ground. For TV-port devices, different design 

The rapid development and marketing of these principles were apparent among the manufacturers. 

surge reference equalizers has left the process of Some had a solid connection between the shield of the 

voluntary standards development behind. At this point, TV signal cable, others had this connection made 

there is no available standard to assess the performance through a surge-suppressing component; all had a gas 

and compatibility of these devices. For instance, the tube for protection between the center conductor and the 

immunity level of the input UHF circuitry of a TV shield of the coaxial cable. 

- 397 - 
For the telephone ports, industry standards 

[ANSIIEWTIA 5711, used as the basis for the SC-120 

ptotocol, specify a surge-handling capability of 100 and 

200 A with a 10/1000 ps waveform. All devices could 

discharge the 100 A surge, but only one could discharge 

the 200 A without damage. The let-through voltages 

ranged from 230 V to 560 V, levels that are compatible 

with immunity levels of typical telephone equipment. 

A regulatory requirement for telephone 

protectors is that in the event of a power-cross (injection 

of power-frequency voltage on the telephone wiring), the 

resulting power-frequency current must be limited or 

interrupted before the telephone wiring in the residence 

overheats dangerously. Surprisingly, this requirement 

was not satisfied. At this point, the concept of systemcompatibility testing provides an avenue for remedy 

rather than rejection: the tests are conducted with the 

knowledge of the manufacturers and deficiencies in 

performance can be corrected by the manufacturer before 

they become an issue leading to outright rejection of an 

otherwise attractive product. 

The immunity levels of cable TV ports are not 

characterized by published industry standards, and thus 

it is difficult to define performance expectations for the 

devices intended to protect these ports. The PEAC tests 

were performed to determine the clamping level with an 

impinging surge of 1 kV peak, ringing at 100 IcHz, and 

33 A peak available short circuit. The let-trough 

voltages ranged from 50 V to 1000 V, leaving open the 

question of adequate protection. Efforts will be 

continued in obtaining the cooperation of the electronics 

industry in defining the immunity levels of the TV port. 

Functional and regulatory requirements for a 

TV-port &vice include freedom from signal leakage and 

degradation through insertion loss or interference. All 

devices were found satisfactory in this regard. 

ADDITIONAL REMEDIES 

The problem of threatening voltage differences 

created along the return path of a surge diverted at the 

end of a branch circuit can also be reduced by other 

means. Highcunent surges on the power system 

originating outside of the user's premises, associated 

with lightning or major power-system events, are best 

diverted at the service entrance of the premises. While 

such a protection is not mandated at present, trends 

indicate growing interest in this type of surge protection. 

Either the utility or the end-user may provide a highenergy surge arrester at the service entrance. 

In such a scheme, external surges are diverted at 

thc service entrance and no longer flow in the building 

in search of a small protective device installed at the end 

of a branch circuit. There are still surges generated 

within the premises, but these have lower current levels 

and can be diverted by protective devices located close 

to the internal surge source or close to the sensitive 

equipment, for instance by the surge reference 

equalizers. This possibility of dual protection raises the 

issue of coordination of cascaded devices, an emerging 

concern in the application of SPDs in the power system 

of end-user facilities [Lai & Martzloff, 19911. The 

clamping voltages of the service entrance arrester and of 

the surge reference equalizer must be coordinated so that 

the low-energy surge reference equalizer will not 

attempt to divert large surges that the highenergy surge 

arrester is expected to intercept. 

CONCLUSIONS 

The rapid expansion of smart electronics 

involving power and communications connections 

creates the potential for disappointing performance under 

surge conditions if adequate, coordinated protection is 

not provided Separate, uncoordinated surge protection 

of each of the two ports still leaves the possibility of 

damage or upset. 

A new type of device, the 'Surge Reference 

Equalizer', offers a solution to the problem, provided 

that the performance characteristics of the device will be 

coordinated with the environmental stress and with other 

surge-protective devices that may be installed on the 

systems. 

System-compatibility tests performed on several 

proposed surge reference equalizers show that their 

performance characteristics vary from adequate to 

questionable (even unacceptable when regulatory safety 

requirements were not satisfied). However, as a result 

of the basic concept of the test program, these 

deficiencies in performance can be recognized in time 

and corrective action taken before the &vices are 

broadly applied. In this manner, both the consumer and 

the electric utility can be confident in their expectation 

of effective protection of the residential electronics. 

REFERENCES 

ANSI/ELA/TIA 571-1991, Environmental Considerations for Telephone Terminals, 1991. 

IEEE Std 1100-1992, Recommended Practice for 

Powering and Grounding Sensitive Equipment, 1992. 

Lai, J.S. & Martzloff, F.D., Coordinating Cascaded 

Surge-Protective Devices, Proceedings. ZEEEIZAS 

Annual Meeting, 1991. 

Maher, M., Residential Transient Voltage Surge 

Suppression Program, Proceedings, PQA 91, First 

International Conference on Power Quality, 199 1. 

SC-120, Test Protocol for System Compatibility of Surge 

Reference Equalizers Used in Premises PowerCommunic~ion Systems, Power Electronics Applications 

Center, Knoxville TN. Draft, 1992.