Product certification procedures have been developed to help facility engineers select the proper surge suppressors for a transient voltage protection design. These standards include information pertaining to safety, performance, and applications.
ANSI/IEEE C62.41-Guide for Surge Voltages in Low-Voltage AC Power Circuits
This standard describes a transient in terms of current, voltage, and duration as it would appear within a typical facility. Sections are included that characterize the facility and discuss the factors to be considered when selecting a suppressor for a specific facility. The bi-wave is the standard waveshape used for externally generated transients from lightning and utility switching and represents transients at the service entrance. The ring wave is the standard waveshape for internally generated transients from inductive loads and represents transients at subpanel locations or individual outlets.
IEEE TRANSIENT WAVESHAPE DESCRIPTION
The following table is an excerpt from C62.41 and describes the bi-wave for high, medium, and low exposure transients at service entrance categories (Category C1, C2, C3) and high, medium and low exposure transients for categories (B1,B2,B3) at distribution panel locations.
CATEGORY
Service Entrance |
EXPOSURE |
VOLTAGE/AMPERAGE |
IMPULSE WAVEFORM |
| C1 |
LOW |
6,000 - 3,000 |
1.2usX50us Voltage |
| C2 |
MEDIUM |
10,000 - 5,000 |
8usX20us Amperage |
| C3 |
HIGH |
20,000 - 10,000 |
|
| |
|
|
|
| B2 |
MEDIUM |
4,000 - 2,000 |
1.2usX50us Voltage |
| B3 |
HIGH |
6,000 - 3,000 |
8usX20us Amperage |
| |
|
|
|
| |
| B2 |
MEDIUM |
4,000 - 350 |
.5usX100KHZ |
| B3 |
HIGH |
5,000 - 500 |
.5usX100KHZ |
| |
|
|
|
| A2 |
MEDIUM |
4,000 = 130 |
.5usX100KHZ |
| A3 |
HIGH |
6,000 - 200 |
.5usX100KHZ |
As can be seen, the magnitude of the transient diminishes as it travels farther inside the facility, from Category C to Category B. This is largely due to the impedance of the service conductors. The highest magnitude transient depicted in the C62.41 table is 20,000 volts and 10,000 amps; this value does not represent the largest possible transient since lightning can generate substantially higher values. The IEEE has stated the magnitudes presented should not be considered as "worst case." Clearly, a secondary suppressor rated for 10kA can protect adequately in case of a mild strike or of a more severe strike divided among several paths to ground. However, a very high magnitude strike will exceed the capability of an ANSI-rated secondary suppressor. One should think in terms of statistical distribution where the consequences of a failure are not catastrophic, but merely represent an economic loss. It is appropriate to make a tradeoff of the cost of protection against the likelihood of a failure caused by a high, but rare, surge. In the present marketplace, the capacities offered make it possible to protect against all but the rarest of transient voltages. Capacities up to several hundred thousand amps are economically justifiable.
ANSI/IEEE C62.45 - Guide on Surge Testing for Equipment Connected to Low-Voltage AC Power Circuits
This standard provides a guideline for the complete testing of surge suppressors. This includes: detailed procedures, test equipment, and recommendations for different levels of testing, depending on whether you are conducting design, prototype, certification, or production testing. Many of these test procedures have been adopted by Underwriters Laboratories to evaluate the safety and performance of surge suppressors. Various test connections, surge generators, coupling and decoupling circuits are examined in order to facilitate uniform testing of surge suppressor devices.
Underwriters Laboratories 1449 Test Standard
U.L. is recognized by the surge suppressor industry as the agency chartered with evaluating the safety and performance of surge suppressors. The test procedures for these evaluations incorporate recommendations from IEEE C62.45, C62.41 and U.L. designed safety tests. The safety testing focuses on mechanical and electrical failure mode and insures that the suppressor being evaluated fails safely. The U.L. MARK for TVSS 1449 cannot be used if the unit fails the safety test. Additional requirements for the U.L. MARK includes various performance testing. These tests do not include a pass/fail performance grade, but result in a suppression rating assigned to the specific product. The primary test is a peak let through test that measures the amount of transient voltage remaining when a specific magnitude transient is injected at the input of the suppressor.
The test procedures classify surge suppressors into two major categories, permanently connected (hardwired) and plug in devices. The hardwired devices have a Category C1/B3 bi-wave impulse injected at the 90 degree phase angle of the sine wave, either at the lugs where the service conductors are connected to the suppressor, or with six inches of lead length if the suppressor does not have any connecting lugs. The output of the suppressor is then measured for the amount of residual voltage remaining from the impulse. The measurement is taken from the zero reference to the peak of the residual impulse. This value is then assigned to a U.L. Suppression Rating. The achievable ratings are: 330 volts, 400 volts, 500 volts, 600 volts, 800 volts, 1000 volts, 1200 volts, 1500 volts, 2000 volts, and 2500 volts continuing to 6000 volts in 500 volt increments. This information is taken for each phase to ground, each phase to neutral, neutral to ground, and phase to phase if there is no neutral. This information is then recorded in a permanent file that can be requested by an engineer or customer, as well as being recorded on a U.L. label affixed to the product before shipment. A pulse life test is also conducted as part of the 1449 listing; this is a pass/fail test and measures the ability of a suppressor to survive multiple transients in succession. U.L. tests all models.
Additional Standards Referencing Transient Voltage Surge Suppressors
Federal Information Standards Publication 94 This is often referred to as FIPS PUB 94. This document provides guidelines for Federal data processing centers and covers the complete environment for installing computers. Topics covered include air conditioning, grounding, transformers, lightning protection, and surge suppression.
U.L. 1283
This U.L. listing is the safety testing procedure for EMI/RFI filters. This is a safety only standard, not a performance standard. Some surge suppressors include a capacitive filter as part of the suppression circuit.
U.L. 67
This U.L. listing is for panelboard interiors. This is a safety listing describing clearances , heat dissipation, and conductor material and sizes. This standard covers panelboards rated 600 volts and less. This would pertain to suppressors mounted internal to panelboards.
U.L. 50
This U.L. listing is for panelboard enclosures. This is a safety listing describing the size and material used for panelboard enclosures.
U.L. 845
This U.L. listing is for motor control centers. This would pertain to suppressors mounted internal to a motor control center bucket.
U.L. 857
This is the U.L. listing for busplug devices. This would pertain to a suppressor mounted internally to a busplug.
CSA C22.2M-1986
This is the CSA guideline for compliance with Canadian Electrical Code for bonding and grounding and surge suppressors. CSA and U.L. have a reciprocal agreement allowing the sharing of testing information to accommodate CSA certification and U.L. listing of surge suppressors.
IEEE P1100 Emerald Book
Section 5.20.9 provides guidelines for installations utilizing UPS systems. Specifying surge suppression should be placed on the rectifier/charge input circuit and the bypass circuits including the manual bypass. The Emerald book also contains information concerning the installation of suppressors within a facility.
NEC Article 280-1.3.4.12.21.25
This covers general requirements, installation requirements, and connection requirements for surge suppressors installed on premise wiring systems on circuits of less than 1000 volts.
Mil Standard 220A
The military standard for measuring filter attenuation using the 50 ohm insertion loss method. This standard is used for surge suppressors with EMI/RFI filtering circuits.
NEMA LS-1
This pertains to the National Electrical Manufacturers Association proposed standard for surge suppression. This document provides standard definitions and specification format.