— WHITE PAPER Regulatory and industry updates for surge protective devices (SPDs) The National Electrical Code® (NEC), sets minimum standards for safe electrical design, installation and inspection to keep people and property protected from electrical hazards. NEC requires the use of SPDs in applications such as emergency facilities, renewable energy, and in 2020 edition, the NEC expanded its requirements to include dwelling units [1]. What is a surge? A power surge or transient is a subcycle disturbance in the ac waveform that is evidenced by a sharp, brief discontinuity of the waveform[2]. In the United States, standard voltage for residential and commercial structures is 120 and 240 volts [3]. When the voltage deviates from these levels, damage can occur to connected equipment. Electrical surges can cause disruptions in computer signals and microprocessors, degradation of component junctions that cause random, delayed failure, or instant damage to electrical components. While lightning might be thought to be the major cause of electrical surges, it actually is one of the least common. Approximately 80 percent of surges are caused by internal disturbances, such as load switching, variable frequency drives, lighting and HVAC systems. Even though surges from internal disturbances are usually relatively low in intensity, they can add up over time, weakening the sensitive circuitry in today’s electronic devices. External disturbances, like surges from utility line switching or lightning, occur approximately 20 percent of the time, but their strength can be devastating [4]. Surge Protective Devices (SPDs) help prevent damage to electrical equipment, electronic devices, or appliances. They also play a critical role during an emergency or for the proper operation of the electrical grid. Knowing and specifying the correct type of SPD for the applications or using the right methods to test SPDs is critical.
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— W H ITE PA PER
Regulatory and industry updates for surge protective devices (SPDs)
The National Electrical Code® (NEC), sets minimum standards for safe electrical design, installation and inspection to keep people and property protected from electrical hazards. NEC requires the use of SPDs in applications such as emergency facilities, renewable energy, and in 2020 edition, the NEC expanded its requirements to include dwelling units [1].
What is a surge?A power surge or transient is a subcycle disturbance in the ac waveform that is evidenced by a sharp, brief discontinuity of the waveform[2]. In the United States, standard voltage for residential and commercial structures is 120 and 240 volts [3]. When the voltage deviates from these levels, damage can occur to connected equipment.
Electrical surges can cause disruptions in computer signals and microprocessors, degradation of component junctions that cause random, delayed failure, or instant damage to electrical components.
While lightning might be thought to be the major cause of electrical surges, it actually is one of the least common. Approximately 80 percent of surges are caused by internal disturbances, such as load switching, variable frequency drives, lighting and HVAC systems. Even though surges from internal disturbances are usually relatively low in intensity,
they can add up over time, weakening the sensitive circuitry in today’s electronic devices. External disturbances, like surges from utility line switching or lightning, occur approximately 20 percent of the time, but their strength can be devastating [4].
Surge Protective Devices (SPDs) help prevent damage to electrical equipment, electronic devices, or appliances. They also play a critical role during an emergency or for the proper operation of the electrical grid. Knowing and specifying the correct type of SPD for the applications or using the right methods to test SPDs is critical.
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2 R EG U L ATO RY A N D I N D U S TRY U PDATE S FO R S U RG E PROTEC TI V E D E V I CE S (S PDS)
SPDs are designed to relieve pressure-sensitive valves, diverting this extra current to ground.
At the heart of many SPDs are metal oxide varistors (MOVs) that have an internal crystalline structure, containing zinc oxide. When exposed to over-voltage, or a transient surge, the varistors switch from a nearly open state to a clamping state. This is enough to bridge the gaps within the crystalline structure, and the MOV becomes an active part of the circuit, providing an attractive path to ground to protect the equipment downstream.
Turn-on voltage: This is the level at which the MOV begins to activate.
Clamping voltage (also referred to as “let-through voltage”): This specifies the voltage that will be seen by the downstream (connected) equipment. Clamping voltages vary and they also are directly influenced even more so by the quality of the SPD installation . According to the UL 1449 4th Edition VPR (voltage protective rating) surge value of 6 kV/3 kA, a good clamping voltage for a 120 V system would be 700 or 800 volts. A lower clamping voltage indicates better protection.
Critical operations power systems NEC guidelines have been established to increase
the protection and reliability of power infrastruc-ture for critical operations power systems (COPS) located inside critical facilities. COPS areas are identified by government agencies and autorities having jurisdiction (AHJs) and designated by spe-cific codes listed within Section 708.
One can have a designated critical operations area (DCOS) or COPS within a critical facility. Critical facilities include any entity that, if damaged, might disrupt national security, the economy, public health or safety. Obvious critical facilities include:• Law enforcement• Fire departments• Military installations• Hospitals, doctors’ offices• Financial institutions• Water and wastewater treatment• Airports and air traffic control• Traffic light systems• Other government agencies
Both the NEC and National Electrical Manufacturers Association (NEMA) specify that SPDs must be used for each voltage level of the facility’s service entrance and distribution panels:• NEC Article 708.20 (D): Surge protection
devices shall be provided at all facility distribution voltage levels[5].
— Emergency systems surge protection
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Emergency systems• NEC Article 700.8: A listed SPD shall
be installed in or on all emergency switchboards and panel boards [5].
Wind electrical system protectionNEC also specifies that SPDs must be incorporated into wind-powered electrical supply systems to prevent damage from surges.• NEC Article 694.10 (D) states: An SPD shall be
installed between a wind electric system and any loads served by the premises electrical system [5].
Dwelling unitsNEC requires that new and replaced service equipment supplying dwellings are protected by listed Type 1 or Type 2 Surge Protective Devices. These protect electrical devices and appliances that may not be protected by point-of-use SPDs. It is estimated that the average home has over $15,000 worth of equipment that can be damaged by surges[1].
dwelling units shall be provided with a surge protective device (SPD).
• Location - The surge protective device shall be an integral part of the service equipment or shall be located immediately adjacent thereto. Exception: The surge protective device shall not be required to be located in the service equipment if located at each next level distribution equipment downstream toward the load.
• Type - The surge protective device shall be a Type 1 or Type 2 SPD.
• Replacement - Where service equipment is replaced, all of the requirements of this section shall apply[6].
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4 R EG U L ATO RY A N D I N D U S TRY U PDATE S FO R S U RG E PROTEC TI V E D E V I CE S (S PDS)
—01. SPDs for mounting on main distribution —02. SPDs for mounting on sub distribution—03. Component SPDs—04. SPDs for protection of downstream equipment
— Types of surge protection devices
—01
Type 1 SPD — Line side Type 1: Permanently connected, intended for installation between the secondary of the service transformer and the line side of the service disconnect overcurrent device [7](service equipment). Their main purpose is to protect insulation levels of the electrical system against external surges caused by lightning or utility capacitor bank switching (does not require an upstream fuse or breaker).
Type 2 SPD — Load side A Type 2: Permanently connected, intended for installation on the load side of the service disconnect overcurrent device [7] (service equipment), including brand panel locations. Their main purpose is to protect the sensitive electronics and microprocessor based loads against residual lightning energy, motor generated surges and other internally generated surge events.
Type 3 SPD Type 3: Point-of-utilization SPDs installed at a minimum conductor length of 10 meters (30 feet) from the electrical service panel to the point-of-utilization[7]. Examples include cord connected, direct plug-in and receptacle type SPDs.
Type 4 SPDType 4 SPDs are considered component SPDs. Component SPDs typically consist of one or more Type 5 components assembled together[7]. Type 4 SPDs are not intended to be used by themselves, and must be integrated into other systems.• Type 1 component assembly is a Type 4 SPD that,
once installed inside another piece of equipment, would be tested as a Type 1 SPD (would not require external over-current protection).
• Type 2 component assembly is a Type 4 SPD that, once installed inside another piece of equipment, would be tested as a Type 2 SPD (would require external over-current protection).
Type 5 SPD Discrete component surge protection devices,such as MOVs that may be mounted on a printed wiring board, connected by its leads or provided within an enclosure with mounting means and wiring terminations. These Type 5 SPD components are incomplete as an SPD, require further evaluation and are not permitted to be installed in the field as a stand-alone SPD. Type 5 SPDs are generally the components used in the design and construction of complete SPDs or other SPD assemblies[7].
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Surge protection devices are available in a range of ratings to accomodate the level of protection needed. Higher surge current ratings provide a level of protection with greater redundancy that intended to extend the useful life especially for installations where stronger and more frequent surge activity will occur. However, much like any insurance policy, better protection comes at a higher cost.
Surge current ratings used to classify SPDs can be determined in two ways:• Calculated: The surge current rating is the sum of
all the MOVs in a given mode or phase; three 50 kA MOVs A-N are equal to 150 kA per mode. However, there are elements that may reduce the ability of the SPD to successfully address a surge current of this calculated size. Design and assembly factors such as internal wiring, overcurrent protection devices and overall component quality can diminish the SPD's ability to perform as advertised.
• Independently verified: An independent testing laboratory tests the SPD to measure the surge current rating. This ensures the SPD has successfully passed surge current testing that meets or exceeds the SPD's surge current rating.
To help provide confidence that the SPD will perform at its stated strength and redundancy, it is recommended that independent laboratory tests be conducted for any project requiring surge protective devices.
Additional resourcesThe following links are additional resources on the NEC guidelines for surge protection in emergency facilities and renewable energy applications:
Electrical Safety Foundation International.https://www.esfi.org/program/surge-protective-devices-626
The NEMA Surge Protection Institute (NSPI) is an educational outreach effort initiated by the low voltage surge protective devices section of the National Electrical Manufacturers Association (NEMA).http://www.nemasurge.org/
A listing of each state and the status of NEC adoption. https://www.nfpa.org/NEC/NEC-adoption-and-use/NEC-adoption-maps
— Ensuring proper function
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— AC voltage SPD applications and location guide
IEEE C62.41.2 Category C• IEEE: Category C — Service entrance exposure• NEC 242 and NRTL: SPD Type 1, 2 or equivalent
Type 4• N and G are bonded (i.e., L-N and L-G are same)• Higher available fault currents require
appropriate SCCR ratings• Historical kA ratings:
- Per phase: 400 kA to 200 kA per phase - Per mode: 200 kA to 100 kA per mode
(Per phase generally considered sum of L-N plus L-G)
IEEE C62.41.2 Category B• IEEE: Category B — External remnant
or internally induced• NEC 242 and NRTL: SPD Type 1, 2, or equivalent
Type 4• L-N and L-G are different — need L-N, L-G and N-G• Require appropriate SCCR ratings• Historical kA ratings:
- Per phase: 300 kA to 100 kA per phase - Per mode: 150 kA to 50 kA per mode
(Per phase generally considered Sum of L-N plus L-G)
IEEE C62.41.2 Category A• IEEE: Category A, maybe B, maybe C if outdoor
loads are connected• NEC 242 and NRTL: SPD Type 1, 2 or equivalent
Type 4; could be Type 3• L-N and L-G are different — need L-N, L-G and N-G• Require appropriate SCCR ratings• Historical kA ratings;
- Per phase: 160 kA to 100 kA per phase - Per mode: 80 kA to 50 kA per mode
(Per phase generally considered Sum of L-N plus L-G)
Line side
Load side
Line side requires Type 1 SPD per NEC 242 and UL 1449.
UL 96A lightning protection system SPDs at service entrances require 20 kA L-N and UL mark.
Surge current kA ratings for all categories are subjective. Consult SPD manufacturer for specific recommendations.
Distribution
Indoor
Outdoor
Service entrance
Equipment installed outside of the building could increase exposure level to Category C. Consider effects of ground potential rises from direct lightning strikes to earth.
Images depicted herein are for demonstration purposes. Each facility is different and userneeds may vary. Adjust accordingly, based on equipment value and/or downtime expenses.
Wind or PV generation
Indoor lighting
Outdoor lighting
Computers or servers
Indoor HVAC (VFD)
UPS (or PDU, PDM)
Type 1 SPD
Type 1 or 2 SPD
“Pre” SPD (Type 1)
Type 1 or 2 SPD
Type 1 or 2 SPD
Type 1 or 2 SPD
“Post” SPD
Type 1 or 2 SPD
Type 1 or 2 SPD
Branch Branch
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Relevant SPD standards (1000 V and less):• ANSI/UL 1449 — Surge protective devices• UL 1283 — EMI/RFI filtering• ANSI/IEEE C62.41.1 — Guide on surge environment• ANSI/IEEE C62.41.2 — Characterization of surges• ANSI/IEEE C62.45 — Testing• IEEE C62.62 — Testing• IEEE C62.72 — Application guide
Load side of the switch protects service and gen set.
Indoor
Outdoor
Separately derived system
Equipment installed outside of the building could increase exposure level to Category C.Consider effects of ground potential rises from direct lightning strikes to earth.
Series or two-port SPDs may disconnect downstream loads at end of life.
Protect both ends of the busway against reflections.
Establishes a new reference to ground, like a service entrance. L-N only may be sufficient.
Outdoor lighting
Busway
Outdoor HVAC (VFD)
Gen set
Small or office equipment
MCCType 1 or 2 SPD
Type 1 or 2 SPD
Type 1 or 2 SPD
Type 1 or 2 SPD
Type 1 or 2 SPD
Type 3 SPD
Type 1 or 2 SPD
Type 1 or 2 SPD
Type 1 or 2 SPD
Series SPD
Type 1 or 2 SPD
Type 1 or 2 SPD
Type 1 or 2 SPD
Distribution
Branch
Branch
Outdoor equipment
Outdoor equipment
Outdoor equipment
ATS/STS
1TQ
C12
39E
00
04
WP
RE
V.B
AU
GU
ST
20
20
[5] National electrical code handbook, 2014. (2014). Quincy, MA: National Fire Protection.
[6] National electrical code handbook, 2020. (2020). Quincy, MA: National Fire Protection Association.
[7] Surge Protective Device Type Application Considerations. NEMA. https://www.nemasurge.org/wp-content/uploads/2011/09/SPD-Type-Application-Considerations-Rev-Date-01-31-2013.pdf. (accessed August 4, 2020).
[1] ESFI: 2020 National Electrical Code Major Changes." ESFI. https://www.esfi.org/resource/2020-national-electrical-code-731. (accessed August 4, 2020).
[2] IEEE 1100™ - 2005, - IEEE Recommended Practice for Powering and Ground Electronic Equipment (the Emerald Book).
[3] Electrical Voltages. Electrical101. http://www.electrical101.com/electrical-voltages.html (Accessed August 05, 2020).
[4] The Need for Surge Protection Devices . NEMA Surge Protection Institute. https://www.nemasurge.org/wp-content/uploads/2018/03/Surges-What-Where-Why.pdf (accessed August 4, 2020).
References
—ABB Inc. Electrification Products 860 Ridge Lake Blvd.Memphis, TN 38120
electrification.us.abb.com
—We reserve the right to make technical changes or modify the contents of this document without prior notice. With regard to purchase orders and/or contracts, the agreed particulars shall prevail. ABB Inc. does not accept any responsibility whatsoever for potential errors or possible lack of information in this document.
