TOV Effects on Surge-Protective Devices 

Dalibor Kladar 

Eaton Electrical 

François Martzloff 

Surges Happen! 

Doni Nastasi 

EPRI Solutions 

Reprinted from Conference Record, Power Quality Exhibition and Conference, Baltimore, October 25-27 

Significance 

Part 7 – Mitigation techniques 

Among the diverse equipment permanently installed or plug-connected in low-voltage power distribution 

systems, SPDs have a special position because of the expectation that they perform an effective 

protective function against surges. However, because of the common misuse of the word “surge,” some 

expectations linger that an SPD might also protect equipment against temporary overvoltages (TOVs). 

The reality is that because of their intended deliberate response to any overvoltage, SPDs are perhaps 

more likely to be victims rather than protectors in a TOV scenario. This paper reports TOV susceptibility 

tests on SPDs, which can provide motivation for standards-developing groups toward careful assessment 

of SPD TOV sensitivity. 
Page 1 of 10 

TOV EFFECTS ON SURGE-PROTECTIVE DEVICES 

by 

Dalibor Kladar 

Lead Engineer 

Eaton Electrical 

François Martzloff 

Principal 

Surges Happen! 

Doni Nastasi 

Assistant Lab Manager 

EPRI Solutions 

INTRODUCTION 

Motivation 

Among the diverse equipment permanently installed or plug-connected in low-voltage power 

distribution systems, SPDs have a special position because of the expectation that they perform 

an effective protective function against surges. However (and unfortunately), because of the 

common misuse of the word “surge,” in spite of a specific IEEE definition [1] some expectations 

linger that an SPD might also protect equipment against temporary overvoltages (TOVs). The 

reality is that because of their intended deliberate response to any overvoltage, SPDs (if not 

properly designed or correctly used) are perhaps more likely to be victims rather than protectors 

in a TOV scenario. This paper reports TOV susceptibility tests on SPDs, which can provide 

motivation for standards-developing groups toward careful assessment of SPD TOV sensitivity. 

Test program 

Stresses to be applied to the SPD were defined on the basis of published reviews describing 

TOVs likely to be encountered in low-voltage power systems (ANSI C84.1, 1995 [2]; EPRI, 

1996 [3]; Short, 2004 [4]). It must be emphasized that the prime objective of the tests was 

simply to obtain a description of the behavior of SPDs exposed to real-world TOV occurrences, 

not to perform exhaustive tests to assess the acceptability of failure modes, and even less safety 

issues. Table 1 shows the TOV stress levels selected from the review of TOV occurrences. 

The tests and post-mortem examinations, funded by EPRI sponsors, were performed by the 

laboratory staff of EPRI Solutions in Knoxville, TN (Nastasi, 2005 [5]). 

Table 1 – TOV Stress levels selected for the test program

Test Stress Level Imitated Condition Magnitude Duration 

1 Poor voltage regulation 1.15 PU (138 V) 6 hours 

2 During a fault 1.3 PU (156 V) 2 seconds 

3 Loss of a secondary neutral 1.5 PU (180 V) 4 hours 

4 Ferroresonance 2.0 PU (240 V) 1 minute 

5 Commingling (contact to HV circuits) 3.0 PU (360 V) 1 second 

There is growing recognition among standards-developing groups that a clear distinction must be 

made when assessing the results of an SPD stress test: It is permissible to have a device fail, as 

long as the failure mode is “acceptable” according to some agreed-upon criteria. The difficulty 

in the industry at this point is to agree on what can be called acceptable in the face of welldocumented anecdotes of clearly unacceptable failure modes for some UL-listed SPDs that 

passed the present standardized tests (UL 1449, 1996 [6]). While rare, in-field failures of SPDs 

do occur, for a variety of causes. Manufacturers of SPDs become aware of these occurrences 

from returns that most manufacturers include as part of their warranty programs, allowing for 

some cases to be examined for determination of the cause of failure. The following Rogue’s 

Gallery presents a list (not limiting) of possible causes of SPD failures. As indicated in the 

second category of that list, some of these are not related to the occurrence of a TOV and thus 

will not be addressed in this paper. 
Page 2 of 10 

TOV EFFECTS ON SURGE-PROTECTIVE DEVICES

by Dalibor Kladar, François Martzloff, and Doni Nastasi

A ROGUE’S GALLERY OF CAUSES FOR SPD FAILURES

Category 1 – TOV related failures 

Response to system overvoltages 

3⁄4 Insufficient TOV withstand capability of the SPD 

3⁄4 Utility problem (e.g. fuses opened on transformer primary side during a fault of upstream equipment) 

3⁄4 Commingling of power lines (conductors of higher voltage falling on conductors of lower voltage) 

3⁄4 Voltage oscillations when local load is larger than local power generation capability 

3⁄4 Switching on and off capacitor banks 

3⁄4 Unregulated voltage or poor voltage regulation 

3⁄4 Conductor isolation breakdown

3⁄4 Generator overspeed or overexcitement

Interactions with adjacent electrical equipment 

3⁄4 Electrical arc furnace 

3⁄4 Sudden failure on nearby large loads 

3⁄4 Voltage notches caused by rectifiers 

3⁄4 Voltage oscillation due to switching on and off large loads or sudden loss of load 

3⁄4 Voltage oscillation due to ferro-resonance 

3⁄4 High frequency harmonics from various sources 

3⁄4 Reflection waves caused by variable-frequency drives 

3⁄4 Arcing on circuit breakers during opening and closing 

3⁄4 Unbalanced current flow in multi-phase systems 

3⁄4 Uncoordinated alternate or secondary power source on site 

3⁄4 Non-synchronized coupling of local generator with utility power grid 

Category 2 – Not-TOV related failures

Incorrect installation practices 

3⁄4 Miss-wiring (SPD or other equipment surrounding SPD) during installation 

3⁄4 Misapplication (e.g. SPD designed for 208 Vac system was connected to the 480 Vac) 

3⁄4 Elevated ambient temperature from external sources (not caused by SPD) 

3⁄4 Neutral conductor connected to SPD was lost after installation 

3⁄4 High potential test applied to evaluate dielectric strength of isolation 

Mis-wiring of power grid 

3⁄4 Poor power quality on construction sites with unfinished power grid 

3⁄4 Bad or non-existing neutral connection somewhere else in the grid 

3⁄4 Bad connection between phase conductors connected in series 

3⁄4 Poor grounding connection 

Imposed surge currents 

3⁄4 Lightning surge on secondary system 

3⁄4 Direct flash to the building 

Inherent SPD problems 

3⁄4 SPD (MOVs, SAD, gas-tube) components aging 

3⁄4 SPD auxiliary (monitoring ) components breaking down 
Page 3 of 10 

TOV EFFECTS ON SURGE-PROTECTIVE DEVICES

by Dalibor Kladar, François Martzloff, and Doni Nastasi

TEST PROCEDURES 

Selection of specimens 

The SPD test specimens were obtained on the basis of being readily available from local 

vendors, typical cord-connected types used for point-of-use protection of appliances (three 

varieties), and permanently connected intended for installation at service entrances (two 

varieties). This selection was arbitrary, emulating the choice that an end-user (for a cord 

connected SPD) might make when browsing the shelves in a store, or the choice that an 

electrician might make at the warehouse for a permanently connected SPD. Price was not a 

consideration . To avoid identification of specific brands – not the objective of the project – 

only a generic description of the specimen SPDs is provided in this paper. Tables 2 and 3 show 

the features that are listed on the respective SPD packages. In addition to the SPD under test, a 

60-W incandescent lamp was connected as a “pilot” in parallel with the specimen SPD to give 

the test operator a visible indication of what a dweller would see in a residential environment. 

In cases of moderate TOVs lasting for several hours (quasi-oxymoron notwithstanding), such a 

visible indication could provide to the occupant a warning, if noticed, of an abnormal condition, 

giving a chance to turn off sensitive equipment before damage might occur. 

Cord-connected SPD specimens

Three specimens were included in the program, identified as SPD1, SPD2, and SPD3. The first 

two SPDs were of the power-strip (bar) type, typical of what consumers can find in electronic 

and electrical supply stores. The third type, slightly more sophisticated, was a box-type, still a 

consumer-oriented product. 

Cord-connected SPDs generally have thermal fuses to aid toward an acceptable failure mode (no 

fire hazard). These fuses are not replaceable, so the SPD must be discarded (if that situation is 

made clear to the user, because some designs can leave the output energized after opening of the 

fuse (see Martzloff, 1998 [7*]) 1, a situation that was noted for some of specimens in this project. 

However, at least one brand is available on the market, but could not be included in this project, 

which has a resettable disconnect circuit. That feature protects the SPD itself AND the load 

from a TOV, by opening the resettable circuit. Such a load interruption might be unnecessary 

for a benign TOV, but is likely to be preferred by users who desire the extra protection and will 

gladly accept to reboot their computer rather than risk having it fried by a TOV. 

Permanently wired SPD specimens 

The two specimens obtained for this project are of the type for which a permanent connection 

requires installation by a qualified electrician. They are of the type classified as “one port” by 

SPD standards, meaning that they are connected in shunt at some point of the installation, and do 

not carry the load current, in contrast to the cord-connected SPDs that have an input port (the 

cord) and an output port (receptacles) with or without some series impedance between the two 

ports. Any disconnect included in these permanently wired SPDs, by design, will not interrupt 

power supply to the installation, but merely separate the failed SPD from the installation. 

 

1

 Bibliography citations for reference numbers with an asterisk [N*] can be accessed on line via a 

hyperlink shown in the bibliography listing. 
Page 4 of 10 

TOV EFFECTS ON SURGE-PROTECTIVE DEVICES

by Dalibor Kladar, François Martzloff, and Doni Nastasi 

Table 2 – Features of cord-connected SPD1, SPD2, and SPD3

Specimen 

ID 

Technology Nominal 

MOV Voltage 

Manufacturer claims 

SPD1 130-V MOVs 195 V 

10 kA 

490 joules 

$25,000 protected equipment guarantee 

Building wiring fault indicator 

Catastrophic event protection 

Fail Safe Mode 

IEEE let-through rating and UL 1449 compliance 

Noise filtering 

Protection working indicator 

Status indicator LEDs 

TVSS ratings 330 V (L-N) (L-G) (N-G) 

SPD2 130-V MOVs 201 V 750 joules 

$25,000 connected equipment warranty 

TVSS 330 V (L-N) (L-G) (N-G) 

SPD3 

multiple 

MOV paths 

+ inductors 

and 

capacitors 

231 V 

218 V 

140 V RMS clamping 

2200 joules/85,000 amps 

$50,000 ultimate lifetime insurance 

UL1449 listed - surge suppression (330V let-through), 

UL1283 listed - EMI protection, 

UL1363 listed – power tap, CUL approved to CSA 

Transient suppression voltage 330 V (L-N) (L-G) (N-G) 

Table 3 – Features of permanently connected SPD4 and SPD5

Specimen 

ID Technology Nominal 

MOV Voltage

Manufacturer claims

SPD4 

Multiple MOV 

+ multiple gas 

discharge + 

sine-wave 

tracking 

176 V 

Multiple MOVs with built-in thermal fuses 

Gas discharge tubes in series with MOVs 

100-kA 8/20-μs protection (50 kA per mode) 

Transient discriminating technology for long service life 

Ideal for sites with poor voltage regulation 

Thermal protection 

Over-current fusing 

UL 1449 Edition 2 listed 

All modes protected 

Dual LED status indication 

EMI/RFI sine-wave tracking filter 

SPD5 

Multiple MOV 

+ multiple gas 

discharge 

206 V 

Multiple parallel MOVs 

Gas discharge tubes in series with MOVs 

Thermal fusing 

Catastrophic surge circuit 

Single-pulse energy dissipation 2700 joules 

Spike capacity 60 kA (each wire) 

Line voltage 120/240 1 phase 50/60 Hz 

Clamping level (TVSS voltage) 400 V 

Initial clamping level 240 V 
Page 5 of 10 

TOV EFFECTS ON SURGE-PROTECTIVE DEVICES

by Dalibor Kladar, François Martzloff, and Doni Nastasi

Note that association of MOVs and fuses simply means that the thermal cutout is physically 

located on the circuit board so that it has intimate contact with the associated MOV(s). The heat 

generated by the overstressed MOV then triggers the heat-responsive cutout to open the circuit 

before a massive failure of the MOV can occur. The method of creating intimate contact 

between the MOVs and the cutout varies from manufacturer to manufacturer. Some rely only on 

proximity of the two components. Others wrap a piece of tape around the MOV and the cutout 

to help ensure that they are held in contact. At least one MOV disc manufacturer is now offering 

MOV discs which include a series-connected thermal cutout maintained in intimate contact with 

the disc by applying the usual coating after the cutout has been added. 

TEST RESULTS 

The “Crispy Factor” 

Post mortem examination of the test specimens included measurements of the characteristics of 

the SPD components as well as a visual inspection for which a short-hand description was 

created here. While it is doubtful that these terms will become official IEEE or IEC definitions, 

they will suffice for the purpose of tersely describing the condition of the MOV in the tabulations 

of this paper, Figures 1 through 4 show the extent of MOV damage from extreme to benign.

 

 Figure 1 

Crispy Factor CF3, indicating obliteration 

 Figure 2 

Crispy Factor CF2, indicating a flaky surface 

and some loss of physical structure

 

 Figure 3 

 Crispy Factor CF1, indicating 

 a single split or hole 

 Figure 4 

Crispy Factor CF0, indicating an 

intact MOV covered with 

soot from other MOVs 
Page 6 of 10 

TOV EFFECTS ON SURGE-PROTECTIVE DEVICES

by Dalibor Kladar, François Martzloff, and Doni Nastasi

Results for cord-connected SPDs 

Details of the postmortem analysis of the cord connected SPDs are given in Table 4. The test 

stress levels 1 (138 V – 8 hours) and 2 (156 V – 2 seconds) did not produce any failure so the 

table does not include these tests. Crispy factor (CF) levels for each of the MOV modes (L-N. 

L-G, N-G), and fuse (F1, F2) status are shown. Also note whether the load will be left energized 

or not after failure of the SPD components. 

Table 4 – Results and Postmortems on Cord-Connected SPD1, SPD2, and SPD3 

Test Stress 3 Test Stress 4 Test Stress 5 Type and 

Technology 180 V – 4 Hours 240 V – 1 Minute 360 V – 1 Second 

SPD 1 

Cordconnected 

strip 

130-V 

MOV 

Fail 

Load off 

L-N MOV- CF1, open 

L-G MOV- CF3, open 

N-G MOV – CF2, short 

F1 = open 

F2 = open 

Fail 

Load still on* 

L-N MOV CF0, intact 

L-G MOV CF1, short 

N-G MOV CF0, intact 

F1 = intact 

F2 = open 

Fail 

Load still on* 

L-N MOV – CF0, intact 

L-G MOV – CF1, open 

N-G MOV – CF0, intact 

F1= intact 

 F2 = open 

SPD 2 

Cordconnected 

strip 

130-V 

MOV 

Fail 

Load still on* 

L-N MOV – CF0, OK 

L-G MOV – CF3, open 

N-G MOV- CF3, open 

F1 = intact 

F2 = open 

Fail 

Load still on* 

L-N MOV- CF0, OK 

L-G MOV- CF2, short 

N-G MOV- CF2, short 

F1 = intact 

F2 = open 

Fail 

Load still on* 

L-N MOV- CF1, short 

L-G MOV- CF3, open 

N-G MOV- CF2, open 

F1 = intact 

F2 = open 

SPD3 

Cordconnected 

box 

multiple 

MOVs 

+ 

filtering 

Fail 

Load off 

L-N MOV7 CF2, short 

All other MOV- CF0, OK 

F1 = open 

F2 = intact 

Fail 

Load off 

L-N MOV7 CF3, open 

All other MOV- CF0, OK 

F1 = open 

F2 = intact 

Fail 

Load off 

L-N MOV7 CF3, open 

L-G MOV5, CF1, short 

All other MOV- CF0, OK 

F1 = open 

F2 = open 

Results for permanently-connected SPDs 

Details of the postmortem analysis of the permanently-connected SPDs are given in Table 5. 

Both SPD 4 and SPD 5 survived the “expected possible” occurrences of TOVs as defined by 

tests 1 through 4. The highly abnormal and rare Test stress 5 scenario of commingling, defined 

as 3.0 PU, that is, 360 V for a 120-V-rated device, did cause an acceptable internal failure of one 

of the multiple parallel paths of these SPDs. The significance of that performance is that the 

SPDs emerged with neither loss of their primary surge-protective function (albeit with a 

somewhat reduced capability) nor cut-off of the power to the connected loads. Maintaining 

power to the loads is an implicit requirement for a shunt-connected (“one port”) SPD. 
Page 7 of 10 

TOV EFFECTS ON SURGE-PROTECTIVE DEVICES

by Dalibor Kladar, François Martzloff, and Doni Nastasi

Table 5 – Results and Postmortems of Permanently Connected SPD4 and SPD5 

Type Technology Test Stress 5 

 360 V – 1 Second 

SPD4 

permanently 

connected 

multiple MOV 

+ multiple gas 

discharge 

+ sine-wave 

tracking 

Internal partial failure 

Acceptable 

One path with three MOVs + associated spark gap open 

Load still on (no provision to open the load, an intended design) 

Parallel MOV paths OK 

SPD5 

permanently 

connected 

multiple MOV 

+ multiple gas 

discharge 

Internal partial failure 

Acceptable 

One MOV shorted, its fuse open 

Load still on (no provision to open the load, an intended design) 

Parallel MOV paths OK 

DISCUSSION 

Susceptibility to TOV 

There are two aspects to consider while defining SPD specifications related to TOV 

susceptibility. One is the Maximum Continuous Operating Voltage (MCOV) of the SPD, 

the second one is the SPD disconnector response time under fault conditions. 

MCOV issues 

The MCOV is a parameter that is declared by the SPD manufacturer on the basis of in-house 

information on what the SPD can accept with long-term stability and without degradation. 

For the last 30 years, industry has focused on offering low clamping voltages, motivated by 

commendable goals of providing surge protection for loads that were assumed to be vulnerable 

to surges occurring on their power supply input. This perception led to selecting MOV disc 

thicknesses that produced relatively low measured limiting voltages for packaged SPDs, perhaps 

without realizing that such a selection made them unduly susceptible to TOVs (Martzloff & 

Leedy, 1989 [8]). Actually, tests performed by independent researchers (Anderson & Bowes, 

1990 [9]; Smith & Standler, 1992 [10]) have shown that typical appliances are robust enough to 

withstand moderate surges and the clamping voltages of well-matched SPDs, thus do not require 

the low clamping level of 330 V for 120 V applications unwittingly encouraged by the first 1985 

edition of UL Std 1449. Of course, more severe surges require protection afforded by SPDs. 

Reports and papers have been published with the conclusion that the actual suppressed voltage at 

the load terminals can be higher than the clamping voltage of the SPD if the distance between the 

SPD and the load equipment is significant IEC 62066 2002 [11]; Jinliang et al., 2005 [12]). This 

means that when a required clamping voltage protection level is specified for load equipment, 

there should always be a margin between the clamping voltage of SPD and the specified 

protection level at the load terminals. 

Although, this misperception of “lower is better” is now being debated, there is unfortunately no 

consensus among SPD experts on what level of MCOV of SPD would be considered a “safe 

level”. 
Page 8 of 10 

TOV EFFECTS ON SURGE-PROTECTIVE DEVICES

by Dalibor Kladar, François Martzloff, and Doni Nastasi 

As a practical matter, commercial MOV discs are produced with a tolerance window on their 

measured limiting voltage, which is directly related to their physical characteristics (thickness 

and ceramic structure). Packaged SPD manufacturers then assemble their SPD packages by 

using discs that can be sorted for a match – a parallel operation goal – as well as for the MCOV 

which their design goals have defined. To repeat the description given above for the MCOV 

rating of an SPD, it is a manufacturer’s rating, which cannot be “verified” by test, it is a declared 

value that reflects the manufacturer in-house and in-field experience. 

In the last few years during meeting of SPD experts, consensus among SPD manufacturers, SPD 

users, and general interest contributors has been somewhat elusive. There were different 

proposals for what the MCOV of the SPDs should be: 1.15 PU; 1.20 PU; 1.25 PU; 1.375 PU; 

1.73 PU, all attempting to provide the desirable goal of low clamping voltage without falling into 

the trap of undesirable risk of TOV-induced failures. Indeed, a quick Internet survey of the 

MCOV offered by SPD manufacturers yields a range of 1.1 PU to 1.25 PU, with some of them 

indicating a higher value, in particular for hybrid designs. In this situation, it might be 

reasonable to accept at least a “middle way” value 1.25 PU as Solomon’s solution although an 

incremental raising of the MCOV would decrease TOV sensitivity. 

The decision about MCOV becomes more complicated in real life, when multiple clamping 

components inside SPD have to be considered. In order to increase surge current capability the 

SPD manufacturers design multiple clamping components that are connected in parallel. See the 

companion paper “Clearing the L-N-G and IEC TN-C-S alphabet soup for SPD protection 

modes” in the proceedings of this Conference for a discussion of using parallel multiple 

clamping components. 

SPD disconnector response time 

Once the weakest clamping component inside SPD fails, the high fault current will flow through 

the SPD, causing the fault energy to be deposited inside SPD in a short period of time. Now, the 

SPD disconnector has to play to role of controlling how much fault current energy will be 

deposited into the shorted SPD. If the SPD disconnector is correctly sized, the fault will be 

contained. The SPD can then be replaced and no additional damage will be observed. 

Unfortunately, an SPD disconnector is not a mandatory part of the SPD design according to the 

present UL Std 1449 [6].

Hindsight on MCOV ratings 

TOV-induced failures of low-voltage SPDs are in part the result of SPD TOV withstand levels 

that do not match the actual TOV environment of low-voltage power distribution systems. In 

contrast, for the high-voltage environment, the well-accepted utility-oriented philosophy of Basic 

Insulation Level (see Fisher & Martzloff, 1976 [13*]) produced caution in the design of arresters 

(Sakshaug et al., 1977 [14*]) with adequate TOV withstand levels. With hindsight, the initial 

enthusiasm for an answer to the quest for an effective and economical transient suppressor in 

consumer products (Harnden et al., 1972 [15*]), is probably at the source of the unfortunate 

selection of low measured limiting voltage levels – and consequently the related MCOV rating – 

of MOV discs with a now questionable perception of “lower is better” for surge protection 

(Martzloff & Leedy, 1989 [8]) when TOV sensitivity issues arise.
Page 9 of 10 

TOV EFFECTS ON SURGE-PROTECTIVE DEVICES

by Dalibor Kladar, François Martzloff, and Doni Nastasi

SUMMARY AND CONCLUSIONS 

Typical commercial surge-protective devices are indeed susceptible to temporary overvoltages 

that are likely to occur on low-voltage power systems. Their responses vary from no damage to 

complete destruction. For the five stress levels selected in the project and the inherent clamping 

levels built-in by the diverse manufacturers of the test specimens, their diverse responses were 

observed as shown in Table 6. The “pilot” 60-W incandescent lamp survived the first three 

stress levels, in particular four hours at Test Stress Level 3 (4 hours at 1.5 PU – visibly brighter), 

a condition that might then be signaled to the occupant, if noticed, in time to take corrective 

action such as turning off appliances and contacting the energy service provider. 

The three specimens of cord-connected SPDs survived the two lower stress levels but could not 

survive the scenario of a lost secondary neutral, which although infrequent, has been documented 

in many instances. Some of these specimens maintained the load outlet energized but with no 

protection against surges, a condition that most end-users would probably not welcome if they 

were informed of that situation by adequate status indicators (assuming that the end-user would 

regularly monitor these indicators (Martzloff, 1998 [7*]). If only the clamping level of the 

MOVs in these packages were slightly higher, they would be able to survive the loss of neutral 

scenario, and still provide adequate surge protection for reasonably robust loads. 

Table 6 – Summary results

Effect on SPD Stress 

Level Imitated Condition Magnitude Duration Permanently 

connected 

Cord 

connected 

1 Poor voltage regulation 1.15 PU (138 V) 6 hours No damage No damage 

2 During a fault 1.3 PU (156 V) 2 seconds No damage No damage 

3 Loss of secondary neutral 1.5 PU (180 V) 4 hours No damage 

4 Ferroresonance 2.0 PU (240 V) 1 minute No damage 

5 Commingling – High 

voltage onto secondary 

system 

3.0 PU (360 V) 1 second Partial failure but 

still functional 

with acceptable 

loss of capacity 

All fail 

Some with load 

left on 

Some with load 

disconnected 

The two specimens of permanently connected SPDs were robust enough to survive four of the 

emulated TOV scenarios, and even for the rare case of commingling (assuming that it would not 

last more than one second because the breaker of the invading high voltage system can be 

expected to clear the fault) these two specimens were not destroyed. A more severe scenario of 

commingling – an unpredictable event from the point of view of SPD users – might still fail 

these SPDs. 

As stated in the introduction, safety considerations were specifically excluded from the scope of 

this project. Nevertheless, in an actual installation, they must be considered. A lower MCOV 

can cause a higher TOV-induced SPD failure rate in the field, and a longer response time of the 

disconnector causes more severe failure of the SPD. This means that from a safety perspective, 

the SPD should be specified with higher MCOV and faster SPD disconnector. 
Page 10 of 10 

TOV EFFECTS ON SURGE-PROTECTIVE DEVICES

by Dalibor Kladar, François Martzloff, and Doni Nastasi

Thus, an “acceptable” response of the SPD depends on selecting an appropriate MCOV level as 

well as an effective disconnector design. The authors are hoping that new TOV testing might be 

conducted in the near future by some independent laboratories. Other important parameters, not 

addressed in this paper, should be tested and documented, such as short-circuit current rating 

with specific power system parameters, effect of available fault current levels on specific energy, 

total energy deposited. Based on those parameters, valuable lessons could be learned about 

relevant SPD characteristics. Hopefully, current discussions in standards-developing groups will 

address these parameters, and this paper might help focusing attention on the need. 

BIBLIOGRAPHY 2

[1] IEEE 100, The Authoritative Dictionary of IEEE Standards Terms, Seventh edition. 

[2[ ANSI C84.1-1989 American National Standard for Electric Power Systems and Equipment Voltage 

Ratings (60 Hz). (Reaffirmed 1995). 

[3] An Assessment of Distribution System Power Quality, Volumes 1–3, EPRI, Palo Alto, CA: 1996. 

TR-106294-V1, TR-106294-V2, TR106294-V3.

[4] Short, T.A., Electric Power Distribution Handbook, CRC Press, Boca Raton, FL, 2004. 

[5] Nastasi, D., Effects of Temporary Overvoltages on Residential Products: System Compatibility 

Research Project, EPRI, Palo Alto, CA: 2005. 1008540 

[6] UL Std 1449 – Transient Voltage Surge Suppressors, Second Edition, 1996. 

[7] Martzloff, F.D., “What Are the Lights on Your Surge Protector Telling You?,” Power Quality 

Assurance Magazine, July/August 1998. (Accessible on line at Lights don't tell)

[8] Martzloff, F.D. and Leedy, T.F., “Selecting Varistor Clamping Voltage: Lower is not Better!,” 

Proceedings, 1989 Zurich Symposium. (Accessible on line at Lower not better) 

[9] Anderson, L.M. and Bowes, K.B., “The effects of power line disturbances on consumer electronic 

equipment,” IEEE Transactions PWRD-5, No.2, April 1990. 

[10] Smith, S.B. and Standler, R.B., “The effect of surges on electronic appliances,” IEEE Transactions 

PWRD-7, No.3, July 1992. 

[11] IEC 62066-2002: Surge overvoltages and surge protection in low-voltage a.c. power systems – 

General basic information – Clause 12.14.2 

[12] Jinliang He, Zhiyong Yuan, Jing Xu, Shuiming Chen and Jun Zou, “Evaluation of the Effective 

Protection Distance of Low-Voltage SPD to Equipment,” IEEE Transactions PWRD-20, No.1, 

January 2005. 

[13] Fisher, F.A. and Martzloff, F.D., “Transient Control Levels: A Proposal for Insulation Coordination 

in Low-Voltage Systems,” IEEE Transactions PAS-95, No.1, Jan/Feb 1976. (Accessible on line at 

TCL proposal) 

[14] Sakshaug, E.C., Kresge, J.S., Miske, S.A., “A New Concept in Arrester Design,” IEEE Transactions 

PAS-96, no.2, March/April 1977. (Accessible on line at Sakshaug) 

[15] Harnden, J.D., Martzloff, F.D., and Morris, W.G., “GE-MOV® Varistor – The Super Alpha 

Varistor,” General Electric TIS Report 72CRD260, December 1972. (Accessible on line at Super 

alpha) 

 

2

 A useful resource of further bibliography references is the public-domain SPD Anthology, from which the hyperlinks 

shown in the citations have been extracted. This Anthology includes an Annotated Bibliography of over 200 papers 

by many researchers (those published before 2001) and Martzloff papers (published 1963-2004) relevant to surge 

protection in low-voltage AC power circuits; it can be accessed at: http://www.eeel.nist.gov/817/817g/spd-anthology/