IEC Electromagnetic Compatibility Standards for Industrial Process Measurement and Control Equipment Application Note January 1998 Introduction AN9734 TEST SEVERITY LEVEL The purpose of the International Electrotechnical Commission lEC 1000-4 (previously known as lEC-801) standard is to establish a common reference for evaluating the performance of industrial-process measurement and control instrumentation when exposed to electric or electromagnetic interference. The types of interference considered are those arising from sources external to the equipment. The interference susceptibility tests are essentially designed to demonstrate the capability of equipment to function correctly when installed in its working environment. The type of test required should be determined on the basis of the interference to which the equipment may be exposed when installed while taking into consideration the electrical circuit (i.e., the way the circuit and shields are tied to earth ground), the quality of shielding applied, and the environment in which the system is required to work. The lEC 1000-4 standard is divided into six sections: lEC 1000-4-1. Introduction lEC 1000-4-2. Electrostatic Discharge Requirements lEC 1000-4-3. Radiated Electromagnetic Field Requirements lEC 1000-4-4. Electrical Fast Transient (Burst) Requirements lEC 1000-4-5. Surge Voltage Immunity Requirements lEC 1000-4-6. Immunity to Conducted Disturbances Induced by Radio Frequency Fields Above 9kHz Sections lEC 1000-4-2 through lEC 1000-4-5 will be discussed in this application note. LEVEL TEST VOLTAGE: CONTACT DISCHARGE TEST VOLTAGE: AIR DISCHARGE 1 2kV 2kV 2 4kV 4kV 3 6kV 8kV 4 8kV 15kV X Special Special NOTES: 1. “X” is an open level. 2. The test severity levels shall be selected in accordance with the most realistic installation and environmental conditions. Electrostatic Discharge (ESD) Requirements The purpose of this test is to find the reaction of the equipment when subjected to electrostatic discharges which may occur from personnel to objects near vital instrumentation. In order to test the equipment’s susceptibility to ESD, the test setup conditions must be established. Direct and indirect application of discharges to the Equipment Under Test (EUT) are possible, in the following manner: a) Contact discharges to the conductive surfaces and to coupling planes. b) Air discharge at insulating surfaces. Two different types of tests can be conducted: 1. Type (conformance) tests performed in laboratories. 2. Post installation tests performed on equipment in its installed conditions. CHARACTERISTICS OF THE ESD GENERATOR LEVEL INDICATED VOLTAGE FIRST PEAK CURRENT OF DISCHARGE (±10%) RISE TIME WITH DISCHARGE SWITCH CURRENT AT 30ns (±30%) CURRENT AT 60ns (±30%) 1 2kV 7.5A 0.7 to 1ns 4A 2A 2 4kV 15A 0.7 to 1ns 8A 4A 3 6kV 22.5A 0.7 to 1ns 12A 6A 4 8kV 30A 0.7 to 1ns 16A 8A 10-76 1-800-999-9445 or 1-847-824-1188 | Copyright © Littelfuse, Inc. 1998 Application Note 9734 TYPICAL POSITION FOR DIRECT APPLICATION TYPICAL POSITION FOR INDIRECT DISCHARGE TO VCP HORIZONTAL COUPLING PLANS 1.6m x 0.8m TYPICAL POSITION FOR INDIRECT DISCHARGE TO HCP IN SU LA TI O N 5m 0. x P 5m C 0. V 0.1m POWER SUPPLY 470kΩ RESISTOR WOODEN TABLE 0.8m HIGH GROUND REFERENCE PLANE FIGURE 1. EXAMPLE OF TEST SETUP FOR TABLETOP EQUIPMENT, LABORATORY TESTS TYPICAL POSITION FOR DIRECT APPLICATION INDIRECT DISCHARGE BY VCP TYPICAL POSITION FOR DISCHARGE TO VCP PROTECTIVE CONDUCTOR 0.1m 5m 0. x P 5m VC . 0 POWER CABLE 470kΩ POWER SUPPLY POWER SUPPLY INSULATION 10cm PALLET GROUND REFERENCE PLANE SIGNAL CABLES FIGURE 2. EXAMPLE OF TEST SETUP FOR FLOOR STANDING EQUIPMENT, LABORATORY TESTS 10-77 Application Note 9734 0. 3 m PROTECTIVE CONDUCTOR 2m POWER SUPPLY GROUND REFERENCE PLANE FIGURE 3. EXAMPLE OF TEST SETUP FOR EQUIPMENT, POST-INSTALLATION TESTS The only accepted method of demonstrating conformance to the standard is the of type tests performed in laboratories. The EUT, however, shall be arranged as closely as possible to the actual installation conditions. Examples of laboratory ESD test setups can be seen in Figure 1 for tabletop equipment and in Figure 2 for floor standing equipment. Post installation tests are optional and not mandatory for certification. If a manufacturer and customer agree post installation tests are required, a typical test setup can be found in Figure 3. and surfaces of the EUT which are accessible to the human operator during normal usage. • Indirect application of the discharge: Discharges to objects placed or installed near the EUT shall be simulated by applying the discharges to a coupling plane (a horizontal coupling plane under the EUT or a vertical coupling plane). Test Results The results of the ESD tests are reported as follows: 1. Normal performance within the specification limits. 2. Temporary degradation or loss of function or performance which is self-recoverable. Test Procedure • For conformance testing, the EUT shall be continually operated in its most sensitive mode which shall be determined by preliminary testing. • The test voltage shall be increased from the minimum to the selected test severity level. • Number: at least 10 single discharges (in the most sensitive polarity). • Time interval: initial value 1 second, longer intervals may be necessary. • Direct application of discharge to the EUT: The static electricity discharges shall be applied only to those points 10-78 3. Temporary degradation or loss of function or performance which requires operator intervention or system reset. 4. Degradation or loss of function which is not recoverable, due to damage of equipment (component) or software, or loss of date. lEC 1000-4-3 Radiated Electromagnetic Field Requirements This test shows the susceptibility of instrumentation when subjected to electromagnetic fields such as those generated by portable radio transceivers or any other device that will generate continuous wave (CW) radiated electromagnetic energy. Application Note 9734 TEST SEVERITY LEVELS Frequency band: 27MHz to 500MHz Small objects (25cm x 25cm x 25cm) can be tested using a stripline antennae. This is a parallel plate transmission line to generate an electromagnetic field as shown in Figure 6. LEVEL TEST FIELD STRENGTH (V/M) 1 1 Test Procedure 2 3 • The test is performed with the EUT in the most sensitive physical orientation. 3 10 X Special NOTES: • The frequency range is swept from 27 MHz to 500 MHz. The sweep rate is in the order of 1.5 x 10-3 decades/s. Test Results 3. “X” is an open class. 4. The test severity levels shall be selected in accordance with the electromagnetic radiation environment to which the EUT may be exposed when finally installed. Test Setup Examples of the test configuration for radiated electromagnetic fields can be found in Figure 4 and Figure 5. • The procedure requires the generation of electromagnetic fields within which the test sample is placed and its operation observed. The tests shall be carried out in a shielded enclosure or anechoic chamber The test procedure assumes the use of biconical and log-spiral antennae or stripline. • All testing of the equipment shall be performed in conditions as close as possible to the actual installation. The results of the radiated electromagnetic field include: • The effect of the electromagnetic field on the output of the EUT - As a consistent measurable effect. - As a random effect, not repeatable, and possibly further classified as a transient effect occurring during the application of the electromagnetic field and as a permanent or semipermanent field after the application of the electromagnetic field. • Any damage to the EUT resulting from the application of the electromagnetic field. The qualitative evaluation of the resultant data needs to be assessed in terms of the existing local ambient electromagnetic level and the specific operating frequencies. FIGURE 4. TEST SETUP FOR RADIATED ELECTROMAGNETIC FIELD TESTS IN A SHIELDED ROOM WHERE THE ANTENNAE, FIELD STRENGTH MONITORS AND EUT ARE INSIDE AND THE MEASURING INSTRUMENTS AND ASSOCIATED EQUIPMENT ARE OUTSIDE THE SHIELDED ROOM 10-79 EU 4. T Application Note 9734 3. T EU OSCILLATOR POWER SUPPLY 1m POWER AMPLIFIER P 1m FIELD STRENGTH MONITOR 2. EUT 2. T EU TEST MEASUREMENT EQUIPMENT FIGURE 5. TEST SETUP FOR RADIATED ELECTROMAGNETIC FIELD TESTS IN AN ANECHOIC CHAMBER, GENERAL ARRANGEMENT OF THE EUT, FIELD STRENGTH MONITOR AND ANTENNAE TERMINAL STRIP FOAM PLASTIC SECTION VIEW METAL BOX WITH FILTERS WOODEN PLANK SUPPLY, INPUT AND OUTPUT CABLES (3 + 2 + 2 WIRES) TERMINAL STRIP (SEE FIGURE 5) EQUIPMENT UNDER TEST SEE FIGURE 3 SUPPORT OF FOAM PLASTIC ALL CABLES ARE TWISTED RF MEASURING PROBE SEE FIGURE 3 FRAMEWORK OF WOODEN BEAMS (SECTION 50 x 50) WOODEN PLANK (SECTION 50 x 10) TERMINAL STRIP (9 TAGS) BLOCKS OF WOOD (DIMENSIONS 400 x 200 x 125) EARTH NOTE: Dimensions in millimeters. FIGURE 6. TEST SETUP WITH STRIPLINE CIRCUIT 10-80 Application Note 9734 lEC 1000-4-4 Characteristics of the Fast Transient/Burst Generator Electrical Fast Transient (Burst) Requirements This test is intended to demonstrate the immunity of the equipment when subjected to interference originating from switching transients. TEST SEVERITY LEVELS Open circuit output test voltage: • Rise time of one pulse: 5ns ±30% • Impulse duration (50% value): 50ns ±30% • Repetition rate of the impulses and peak values of the output voltage: 5kHz ±20% at 0.125kV 5kHz ±20% at 0.25kV 5kHz ±20% at 0.5kV 5kHz ±20% at 1.0kV 5kHz ±20% at 2.0kV LEVEL ON POWER SUPPLY ON INPUT/OUTPUT SIGNAL DATA AND CONTROL LINES 1 0.5kV 0.25kV • Burst duration: 15ms ±20% 2 1kV 0.5kV • Burst period: 300ms ±20% 3 2kV 1kV 4 4kV 2kV X Special Special Test Setup For laboratory testing, the test setup for type testing can be shown in Figure 7 and Figure 8. NOTES: • Power supply lines (See Figure 7): If the line current is higher than 100A, the “field test” shall be used. 5. “X” is an open level. 6. The test severity levels shall be selected in accordance with the most realistic installation and environmental conditions. • Earth connections of the cabinets: The test point on the cabinet shall be the terminal for the protective earth conductor (See Figure 7). • Input/Output circuits and communication lines (See Figure 8). PE = PROTECTIVE EARTH N = NEUTRAL L1, L2, L3 = PHASE LINES DC TERMINALS SHALL BE TREATED IN A SIMILAR WAY CUT EFT/B GENERATOR <1m I ≤ 1m (CABLE) POWER SUPPLY CC L1, L2, L3 Z1 L N N PE PE COUPLING/ DECOUPLING NETWORK 0.1m INSULATING SUPPORT GROUNDING CONNECTION ACCORDING TO MANUFACTURER’S SPECIFICATION. LENGTH TO BE SPECIFIED IN THE TEST PLAN FILTERING REFERENCE GROUND PLANE CC = COUPLING CAPACITORS = 33nF Z1 = DECOUPLING INDUCTOR > 100µH FIGURE 7. EXAMPLE OF TEST SETUP FOR DIRECT COUPLING OF THE TEST VOLTAGE TO AC/DC POWER SUPPLY LINES/TERMINALS FOR LABORATORY TEST PURPOSES 10-81 AC/DC MAINS SUPPLY Application Note 9734 lEC 1000-4-4 the power supply terminals, AC or DC, and on the terminals for the protective or function earth on the cabinet of the EUT. (See Figure 9). - Non-stationary mounted EUT, connected to the mains supply by flexible cord and plugs: The test voltage shall be applied between each of the power supply conductors and the protective earth at the power supply outlet to which the EUT is to be connected. (See Figure 10). Electrical Fast Transient (Burst) Requirements For field testing, the equipment or system shall be tested in the final installed conditions without coupling/decoupling networks. • Power supply lines and protective earth terminals - Stationary, floor-mounted EUT: The test voltage shall be applied between a reference ground plane and each of - WHEN BOTH EUT ARE TESTED SIMULTANEOUSLY: I1 = I2 ≤ 1m BETWEEN CLAMP AND EUT TO BE TESTED EUT - WHEN ONE EUT ONLY IS TESTED: I1 MIN ≥ 5m OR I2 > 5 x I1 FOR DECOUPLING PURPOSES EUT AC MAINS SUPPLY AC MAINS SUPPLY CAPACITIVE COUPLING CLAMP 0.1m 0.1m 0.1m INSULATING SUPPORT GROUNDING CONNECTION ACCORDING TO MANUFACTURER’S SPECIFICATION. LENGTH TO BE SPECIFIED IN THE TEST PLAN REFERENCE GROUND PLANE TO EFT/B GENERATOR INSULATING SUPPORT GROUNDING CONNECTION ACCORDING TO MANUFACTURER’S SPECIFICATION. LENGTH TO BE SPECIFIED IN THE TEST PLAN FIGURE 8. EXAMPLE OF TEST SETUP FOR APPLICATION OF THE TEST VOLTAGE BY THE CAPACITIVE COUPLING CLAMP FOR LABORATORY TEST PURPOSES PE = PROTECTIVE EARTH N = NEUTRAL L1, L2, L3 = PHASE LINES PE AC MAINS SUPPLY (BLOCKING CAPACITORS IF NECESSARY) 2, L 3 N TEST POINT PE TERMINAL ON THE CABINET L 1, L EUT 33nF † TO PERIPHERALS EFT/B TEST GENERATOR AC MAINS SUPPLY I = 1m FLOOR GROUNDING CONNECTION ACCORDING TO MANUFACTURER’S SPECIFICATION. LENGTH TO BE SPECIFIED IN THE TEST PLAN GROUND PLANE PROTECTIVE EARTH FLOOR †DC terminals shall be treated in a similar way. FIGURE 9. EXAMPLE OF FIELD TEST ON AC/DC POWER SUPPLY LINES AND PROTECTIVE EARTH TERMINALS FOR STATIONARY, FLOOR MOUNTED EUT 10-82 Application Note 9734 • Input/Output circuits and communication lines: - A capacitive clamp shall be used for coupling the test voltage into the lines. However, if the clamp cannot be used due to mechanical problems in the cabling, it may be replaced by a tape or a conductive foil enveloping the lines under test. (See Figure 11). Test Procedure • Polarity of the test voltage: both polarities are mandatory • Duration of the test: at least 1 minute NORMAL PLUG PROVIDED FOR CONNECTION OF THE EUT TO THE POWER SUPPLY FROM EFT/B TEST GENERATOR TO AC MAINS SUPPLY TO PERIPHERALS FILTERING EUT Z1 CC AC MAINS INTERCONNECTION CC L Z1 CC Z1 N I ≤ 1m PROTECTIVE EARTH PE TABLE (WOODEN) PROTECTIVE EARTH ACCORDING TO SYSTEM INSTALLATION COUPLING/DECOUPLING DEVICE CC = COUPLING CAPACITORS = 33nF Z1 = DECOUPLING INDUCTOR > 100µH FIGURE 10. EXAMPLE OF FIELD TEST ON AC MAINS SUPPLY AND PROTECTIVE EARTH TERMINALS FOR NON-STATIONARY MOUNTED EUT EUT CABLETRAY COMMUNICATION LINES I/O CIRCUITS THIS CONNECTION SHALL BE AS SHORT AS POSSIBLE AC MAINS SUPPLY PROTECTIVE EARTH FLOOR FLOOR THE COUPLING DEVICE SHALL BE A CONDUCTIVE TAPE OR A METALLIC FOIL IN PARALLEL OR WRAPPED AROUND AS CLOSELY AS POSSIBLE TO THE CABLES OR LINES TO BE TESTED. THE COUPLING CAPACITANCE OF THIS ARRANGEMENT SHALL BE EQUIVALENT TO THAT OF THE COUPLING CLAMP. EFT/B GENERATOR FIGURE 11. EXAMPLE OF FIELD TEST ON COMMUNICATIONS AND I/O CIRCUITS WITHOUT THE CAPACITIVE COUPLING CLAMP 10-83 Application Note 9734 Test Results lEC 1000-4-5 The results are reported as: Surge Voltage Immunity Requirements 1. Normal performance within the specification limits. The goal of the laboratory test is to determine the equipment’s susceptibility to damage caused by overvoltage surges caused by circuit switching and lightning strikes. 2. Temporary degradation or loss of function or performance which is self-recoverable. 3. Temporary degradation or loss of function or performance which requires operator intervention or system reset. 4. Degradation or loss of function which is not recoverable, due to damage of equipment (component) or software, or loss of data. TEST SEVERITY LEVELS UNSYM LINES LONG DATA BUS POWER SUPPLY CLASS LINE TO LINE Z=2 LINE TO GROUND Z = 12 LINE TO LINE Z = 42 0 SYMMETRICAL LINES DATA BUS SHORT (DIST) LINE TO GROUND LINE TO GROUND Z = 42 Z = 42 LINE TO GROUND No Test is Advised 1 - 0.5kV - 0.5kV 1.0kV - 2 0.5kV 1.0kV 0.5kV 1.0kV 1.0kV 0.5kV 3 1.0kV 2.0kV 1.0kV 2.0kV 2.0kV - 4 2.0kV 4.0kV 2.0kV 4.0kV - - 5 (Note 8) (Note 8) 2.0kV 4.0kV 4.0kV - X Special NOTES: 7. Z is the source impedance. 8. Depends on the class of the local power supply system. “X” is an open level that has to be specified in the product specification. The class depends on the installation conditions. Characteristics of the Test Instrumentation • Combination wave test generator - Open circuit output voltage . . . . . . . . . . . 0.5kV to 4.0kV - Short circuit output current . . . . . . . . . . 0.25kA to 2.0kA IN ACCORDANCE WITH IEC60-2 • Test generator 10/700 µs (according to CCITT): - Open circuit output voltage . . . . . . . . . . . 0.5kV to 4.0kV - Short circuit output current . . . . . . . . . . . 12.5A to 100A IN ACCORDANCE WITH IEC469-1 FRONT TIME TIME TO HALF VALUE RISE TIME (10%-90%) DURATION (50%-50%) Open Circuit Voltage 1.2µs 50µs 1 µs 50µs Short Circuit Current 8µs 20µs 6.4µs 16µs IN ACCORDANCE WITH IEC60-2 IN ACCORDANCE WITH IEC469-1 FRONT TIME TIME TO HALF VALUE RISE TIME (10%-90%) DURATION (50%-50%) Open Circuit Voltage 10µs 700µs 6.5µs 700µs Short Circuit Current - - 4 µs 300µs NOTE: The surges (and test generators) related to the different classes are: Class 1 to 4: 1.2/50µs (8/20µs) Class 5: 1.2/50µs (8/20ms) and 10/700µs 10-84 Application Note 9734 Test Setup A decoupling network is used to prevent surge energy from being propagated to the other equipment operating from the same source during testing of the EUT. The test setup for evaluating the EUT power supply is shown in Figures 12 15. A capacitive coupling network (preferred) or an inductive coupling network is used for this test. The test setup for evaluating the unshielded interconnection lines of the EUT is illustrated in Figures 16-20. Usually, capacitive coupling is used, but inductive coupling or coupling via gas discharge tube (GDT) surge arrestors is also possible. COMBINATION WAVE GENERATOR COMBINATION WAVE GENERATOR R R = 10Ω C C = 9µF DECOUPLING NETWORK DECOUPLING NETWORK L L = 20mH C = 18µF AC (DC) L POWER SUPPLY N NETWORK PE L = 20mH EUT AC (DC) POWER N SUPPLY NETWORK EUT PE GROUND REFERENCE GROUND REFERENCE FIGURE 12. TEST SETUP FOR CAPACITIVE COUPLING ON AC/DC LINES; LINE TO LINE COUPLING ACCORDING TO 7.2 FIGURE 13. TEST SETUP FOR CAPACITIVE COUPLING ON AC/DC LINES; LINE TO GROUND COUPLING ACCORDING TO 7.2 (GENERATOR OUTPUT FLOATING OR EARTHED) COMBINATION WAVE GENERATOR DECOUPLING NETWORK C = 18µF L = 20mH L1 AC (DC) POWER SUPPLY NETWORK L2 L3 EUT N PE GROUND REFERENCE FIGURE 14. TEST SETUP FOR CAPACITIVE COUPLING ON AC LINES (3 PHASES); LINE TO LINE COUPLING ACCORDING TO 7.2 10-85 Application Note 9734 COMBINATION WAVE GENERATOR R R R R C C C C R = 10Ω C = 9µF DECOUPLING NETWORK L = 20mH L1 AC (DC) POWER SUPPLY NETWORK L2 L3 EUT N PE GROUND REFERENCE FIGURE 15. TEST SETUP FOR CAPACITIVE COUPLING ON AC LINES (3 PHASES); LINE TO GROUND COUPLING ACCORDING TO 7.2 COMBINATION WAVE GENERATOR R = 40Ω C = 0.5µF DECOUPLING NETWORK AUX. EQU. C = 0.5µF PROT. EQU. EUT L = 20mH RL GROUND REFERENCE FIGURE 16. TEST SETUP FOR UNSHIELDED INTERCONNECTION LINES; LINE TO LINE COUPLING ACCORDING TO 7.3; COUPLING VIA CAPACITORS COMBINATION WAVE GENERATOR R R R R C C C C DECOUPLING NETWORK AUX. EQU. PROT. EQU. R = 40Ω C = 0.5µF EUT L = 20mH RL GROUND REFERENCE FIGURE 17. TEST SETUP FOR UNSHIELDED INTERCONNECTION LINES; LINE TO GROUND COUPLING TO 7.3; COUPLING VIA CAPACITORS 10-86 Application Note 9734 COMBINATION WAVE GENERATOR COMBINATION WAVE GENERATOR R = 40Ω R = 40Ω INTERCONNECTION LINE AUX. EQU. PROT. EQU. INTERCONNECTION LINE AUX. EQU. EUT PROT. EQU. EUT GROUND REFERENCE GROUND REFERENCE FIGURE 18. TEST SETUP FOR UNSHEILDED INTERCONNECTION LINES; LINE TO LINE COUPLING ACCORDING TO 7.3; INDUCTIVE COUPLING FOR HIGH IMPEDANCE CIRCUITS FIGURE 19. SIMPLIFIED TEST SETUP FOR UNSHIELDED INTERCONNECTION LINES; LINE TO GROUND COUPLING ACCORDING TO 7.3; INDUCTIVE COUPLING FOR LOW IMPEDANCE CIRCUITS COMBINATION WAVE GENERATOR R = 40Ω 0 1 SWITCH S • LINE TO GROUND: POSITION 0 • LINE TO LINE: POSITIONS 1 TO 4 S DECOUPLING NETWORK AUX. EQU. 2 3 4 C = 0.1µF for frequencies of the transmission signal below 5kHz; at higher frequencies no capacitors are used. C PROT. EQU. EUT L = 20mH RL GROUND REFERENCE FIGURE 20. TEST SETUP FOR UNSHIELDED UNSYMMETRICALLY OPERATED LINES; LINE TO GROUND COUPLING ACCORDING TO 7.3; COUPLING VIA GAS ARRESTORS 10-87 Application Note 9734 TEST GENERATOR The internal matching resistor Rm2 (25Ω) is replaced by external Rm2 = n x 25Ω per conductor (for n conductors, n greater than 2). Rm2 Example for n = 4: Rm2 = 4 x 25 = 100Ω Rm2 shall not exceed 250Ω 0 1 SWITCH S • LINE TO GROUND: POSITION 0 • LINE TO LINE: POSITIONS 1 TO 4 S 2 3 4 DECOUPLING NETWORK AUX. EQU. C = 0.1µF for frequencies of the transmission signal below 5kHz; at higher frequencies no capacitors are used. C PROT. EQU. EUT L = 20mH RL GROUND REFERENCE FIGURE 21. TEST SETUP FOR UNSHIELDED SYMMETRY OPERATED LINES (TELECOMMUNICATION LINES); LINE TO GROUND COUPLING ACCORDING TO 7.4; COUPLING VIA GAS ARRESTORS DECOUPLING NETWORK L N POWER SUPPLY NETWORK PE EUT 2 XXXXXXX EUT 1 XXXXXXX COMBINATION WAVE GENERATOR GROUND REFERENCE FIGURE 22. TEST SETUP FOR TESTS APPLIED TO SHIELDED LINES AND TO APPLY POTENTIAL DIFFERENCES ACCORDING TO 7.5 AND 7.6; GALVANIC COUPLING Test Procedure Test Results • Number of tests: at least 5 positive and 5 negative at the selected points. The results of the test are reported as follows: • Pulse repetition: Max. 1/min. • The maximum repetition rate depends on the built-in protection devices of the EUT. • The surge will be applied between lines and between lines and ground. • All lower levels including the selected test level must be satisfied. For testing the secondary protection, the output voltage of the generator must be increased up to the worst case voltage break down of the primary protection. 10-88 1. Normal performance within the specification limits. 2. Temporary degradation or loss of function or performance which is self-recoverable. 3. Temporary degradation or loss of function or performance which requires operator intervention or system reset. 4. Degradation or loss of function which is not recoverable, due to damage of equipment (component) or software, or loss of data.