Surge Protector (SPD) Install
Type 1, 2, and 3 surge-protective devices (UL 1449), when NEC 230.67 requires one at a dwelling service (2020+), Article 242 installation rules (2020 and 2023; Article 285 in 2017 and earlier), lead length, specs to read, layering, and common mistakes. This is a field guide for qualified persons, not a substitute for the adopted NEC, the listing, or the manufacturer instructions.
1. Types 1, 2, and 3 (UL 1449)
UL 1449 is the listing standard for SPDs on 50/60 Hz circuits not exceeding 1000 V (and PV applications up to 1500 V dc). The type describes where the device is intended to be installed, not a quality ranking.
| Type | Where it installs | Typical form |
|---|---|---|
| Type 1 | Permanently connected. Intended between the service transformer secondary and the line side of the service overcurrent device; a Type 1 is also permitted on the load side (it may be used in a Type 2 location). | Meter-base, service, or exterior/adjacent unit; some are molded-case and need no external OCPD. |
| Type 2 | Permanently connected on the load side of the service disconnect overcurrent device, including branch panelboards. Do not put a Type 2 on the line side of the service disconnect. | Panel-mounted or adjacent Type 2, including many loadcenter kits. |
| Type 3 | Point-of-use, on the load side of branch-circuit overcurrent protection, typically at or near the equipment served. | Surge receptacle, direct plug-in, or cord-connected strip. Not a substitute for the Type 1 or 2 that 230.67 requires at the service. |
UL 1449 also defines Type 4 / Type 5 component assemblies (often built into equipment). Those are not a field-installed service SPD. An informational note in Article 242 points to UL 1449 for type definitions.[1][2]
2. When an SPD is required - 230.67 (2020+)
Under the 2020 NEC, all services supplying dwelling units must be provided with an SPD (230.67(A)). The SPD must be a Type 1 or Type 2 (230.67(C)), and must be an integral part of the service equipment or located immediately adjacent to it (230.67(B)). Exception: it need not be at the service if an SPD is located at each next-level distribution equipment downstream toward the load. Where service equipment is replaced, 230.67 applies to the replacement (230.67(D)). The 2020 text does not specify a minimum In rating.
Under the 2023 NEC, 230.67(A) requires an SPD on services supplying (1) dwelling units, (2) dormitory units, (3) guest rooms and guest suites of hotels and motels, and (4) areas of nursing homes and limited-care facilities used exclusively as patient sleeping rooms. Location, Type 1 or Type 2, and replacement rules are the same idea as 2020 (230.67(B)-(D)). New 230.67(E): the SPD shall have a nominal discharge current rating (In) of not less than 10 kA.[2]
2023 also added 225.42 for feeders that supply those same occupancies: a Type 1 or Type 2 SPD, In not less than 10 kA, installed in or adjacent to the distribution equipment on the load side of the feeder that contains the branch-circuit OCPDs serving that occupancy. Replacement of that distribution equipment must comply.[3]
Other 2023 locations that call out listed SPDs include emergency-system switchgear, switchboards, and panelboards (700.8), fire pumps (695.15, with a diesel-controller exception), fire alarm control units (760.33), critical operations data systems (645.18), and others (for example 409.70, 620.51(E), 708.20(D)). Those are in addition to 230.67; check the article that applies to the equipment.
3. Article 242 (was 285 through 2017, not 2020)
Edition note - common confusion: Article 242 Overvoltage Protection replaced former Article 285 in the 2020 NEC (2017 and earlier used 285). The 2023 NEC kept Article 242 and renumbered some sections. Some manufacturer manuals still say "Article 285." Use the article in the adopted edition.[4]
- Listed. SPDs must be listed. 2020: 242.8. 2023: 242.6 (listing moved; 2023 242.6 is not the old "uses not permitted" number).
- SCCR. The SPD must be marked with a short-circuit current rating and shall not be installed where the available fault current exceeds that rating (marking does not apply to receptacles). 2020: 242.10. 2023: 242.8.[5]
- Indication (2023). 2023 242.9 requires the SPD to indicate that it is functioning properly. Place the device so the indicator is visible without moving conductors.
- Type 1 connection (2023 242.13). A Type 1 may be connected to the supply side of the service disconnect as permitted in 230.82(4), or as specified for Type 2 (242.14). At the service, connect it to one of: the grounded service conductor, the grounding electrode conductor, the grounding electrode, or the equipment grounding terminal in the service equipment.
- Type 2 (2023 242.14). On a service-supplied building, connect on the load side of the service disconnect overcurrent device required in 230.91, unless installed under 230.82(8). Feeder-supplied buildings: load side of the first OCPD at the building. Separately derived systems: load side of the first OCPD.
- Uses / voltage. Do not install an SPD on a circuit over 1000 V, or on an ungrounded / impedance-grounded / corner-grounded system unless it is listed for that use. The SPD voltage rating must be at least the maximum continuous phase-to-ground voltage at the point of connection.
4. Location and conductors - short, straight leads
NEC conductor routing (quoted sense): the conductors used to connect the SPD to the line or bus and to ground shall not be any longer than necessary and shall avoid unnecessary bends. 2020 sources cite this as 242.12; 2023 sources commonly cite 242.24 (renumbered). See source notes.[6]
Manufacturer install guides (Eaton, Siemens, Leviton, and others) repeat the same workmanship: mount the SPD as close as practicable to the panel or equipment, use the shortest and straightest phase, neutral, and grounding leads, and prefer the nearest breaker positions to the SPD and to the neutral/ground bars. When a longer lead cannot be avoided, guides often say to gently twist or tie the leads together (about one to two twists per foot in the Leviton instructions).[7][8][9]
5. Breaker vs lug connection
Follow the manufacturer instructions and the SPD listing for how it lands in the equipment:
- Dedicated breaker or fused switch (common for Type 2, and for Type 1 used on the load side). Use the manufacturer-specified breaker size and type; there is no single NEC ampere rating for every SPD. Examples from instructions (not a universal rule): Leviton suggests 20 A for its R, P, and B series and 30 A for the M series; Eaton application guides give suggested breaker or fuse sizes by product family. Use a common-trip breaker, located as close as practicable to the SPD.[9][7]
- Lug / feed-through connections, where the instructions allow them (some Type 1 line-side or bus connections). Confirm the lug is listed for the conductor size and count; Eaton warns not to land more than one lead in the same lug port, and not to use a lug that is not rated for the lead size.
- Some Type 1 molded-case SPDs are listed for use without an external OCPD. That is a listing condition, not a field shortcut for a device that requires a breaker.
6. Specs to read on the label
| Spec | What to check |
|---|---|
| System voltage and configuration | Must match the system (120/240 1ph, 208Y/120, 480Y/277, high-leg, delta, and so on). A mismatch can destroy the SPD. Measure with a meter before you land it.[10] |
| MCOV (maximum continuous operating voltage) | Must be suited to the system voltage at the point of connection (and not less than the maximum continuous phase-to-ground voltage). Example from one Eaton SP2 family: 150 V MCOV on 120 V legs, 320 V on 240/208 V-to-line products - use the value on your label, not a memory number. |
| VPR (voltage protection rating) | UL 1449 let-through rating. Lower is tighter protection at the defined test. Compare same-mode ratings (L-N, L-G, L-L). Lead length adds to what the load actually sees. |
| SCCR | Must be at least the available fault current at the install point (110.10 / 242 SCCR rule). Many panel kits are marked 200 kA; do not assume that. Receptacle Type 3 devices are excepted from the marking rule but still belong on a correctly protected branch circuit. |
| In (nominal discharge current) | UL 1449 In (often 3, 5, 10, or 20 kA). 2023 230.67(E) and 225.42(E) require not less than 10 kA for those required service/feeder SPDs. 2020 230.67 has no In floor in the requirement itself - still use a listed Type 1 or 2 that fits the application. |
| kA surge current (Imax / per phase) | Manufacturer surge-current capacity. It is not the same number as In or SCCR. A bigger kA number does not make up for long leads or a missing grounding connection. |
7. Status lights and when to replace
Treat the indicator as a go/no-go for the protection elements, per the instructions. A typical pattern (Eaton SP2 and many others): green = protection elements intact; red or off (with voltage present) = protection lost - replace the SPD. Some units also use an audible alarm or a Form C contact.[10]
MOVs wear with surge events and sometimes fail quietly. If the light is wrong, or the unit has obviously taken a hit, replace it. After a known severe surge or nearby lightning, inspect the SPD even if the light is still green. 2023 242.9 makes a functioning indication a code requirement on the device; keep it visible for the next inspection and for the owner.
8. Whole-home plus point-of-use layering
230.67 requires a Type 1 or Type 2 at the service (or at each next-level distribution equipment under the exception). That is the whole-home / service layer. Sensitive loads still benefit from a Type 3 (or a listed surge receptacle) at the point of use. The service SPD and the point-of-use SPD work as a system; one does not replace the other. 230.67 does not require the Type 3 layer.
9. Grounding and bonding
An SPD diverts surge energy into the grounding and bonding system. A loose, long, or missing grounding connection, a poor bonding jumper, or a separated neutral-ground bond at the wrong place will limit what the SPD can do and can create flash or shock hazards. Before energizing, confirm the system is grounded per Article 250, the service or SDS bond is in the right place, and the SPD grounding/bonding lead is as short and straight as the phase leads. Do not install a normal Type 1/2 SPD on an ungrounded system unless it is specifically listed for that system.
10. Testing and inspection steps
- Confirm the adopted NEC edition and whether 230.67 (and 225.42 in 2023) applies to this occupancy and to a service or feeder replacement.
- De-energize and lock out. Verify the equipment is dead.
- Verify system voltage and configuration with a meter; match the SPD nameplate (MCOV, wiring diagram).
- Confirm SCCR vs available fault current, Type 1 vs Type 2 vs the line/load location, and (2023 required locations) In of at least 10 kA.
- Mount so leads are as short and straight as practicable and the status indicator will be visible with the cover on.
- Land phase, neutral, and grounding/bonding leads per the diagram; torque to the listed values. Use the specified breaker or lugs.
- Restore power and confirm the indicator shows a healthy device (and that the dedicated breaker is closed).
- Do not hi-pot or apply other overvoltage insulation tests with the SPD connected - disconnect it (and the neutral on 4-wire units) first, or you can damage the SPD and void the listing.[9]
- For the inspection: Type 1 or 2 at the required location, directory/label (110.22), visible status, short leads, matching voltage, and 2023 In marking where 230.67(E) or 225.42(E) applies.
11. Common install mistakes
- Using only a Type 3 power strip or surge receptacle to "meet 230.67."
- Installing a Type 2 on the line side of the service disconnect.
- Long, coiled, or sharply bent leads (often because the SPD was mounted on a far knockout or a far breaker space).
- Wrong voltage or winding configuration (for example a 208Y unit on 120/240, or a 3-phase unit on a high-leg without the correct kit).
- SCCR below the available fault current.
- 2023: In below 10 kA on a required 230.67 / 225.42 device, or missing the expanded occupancy list.
- Leaving the status light behind a cover or dead-front so nobody can see a failed unit.
- Open or long grounding/bonding lead; or energizing on a system that is not yet bonded.
- Landing two leads in one lug, or using a breaker size that is not the one the manufacturer specified.
- Hi-pot testing the gear with the SPD still connected.
- Assuming a larger kA marketing number offsets a poor location.
Sources
- UL 1449, Standard for Surge Protective Devices (type definitions; Type 3 10 m / 30 ft language in the standard scope).
- Leviton, "NEC Code Requirements For Surge" (230.67 2020 and 2023 text summary, 242.13-242.16, other 2023 SPD locations).
- Eaton Bussmann, 2023 NEC code updates no. 11318 (225.42 feeder SPD; lead-length informational note).
- Electrical Contractor Magazine, "SPD Concerns" (230.67; Article 242 new in 2020, formerly 285 in 2017 and earlier; type locations).
- Electrical License Renewal, SCCR section history (2017 285.7, 2020 242.10, 2023 242.8).
- Schneider Electric, "SPD Wire Length vs. Let-Through Voltage" (quotes 2020 242.12 routing; 100-170 V/ft rule of thumb).
- Eaton Bussmann series application guide no. 3193 (Type 1/2 install, short leads, breaker vs lug, LED check).
- Siemens TPS4 surge protective device installation manual (mount close, keep leads short, confirm grounding).
- Leviton R, P, B, and M Series instruction / installation manual (short straight leads, suggested breaker sizes, no hi-pot, still cites Article 285 in one pre-plan bullet).
- Eaton SP2 installation and operation manual IB158003EN (MCOV examples, 10 kA In, 200 kA SCCR on that family, green-to-red indicator).
Source notes and conflicts
- Article number year: 242 replaced 285 in 2020, not in 2023. The 2023 edition kept 242 and changed some section numbers and 230.67 scope. Leviton's R/P/B/M install manual still says to meet "NEC Article 285" in a pre-plan list - treat that as a leftover 2017 reference.
- Routing section number: Schneider quotes 2020 242.12 "Routing of Connections." 2023 commentary commonly cites 242.24 for the same short-lead / no-unnecessary-bends rule. Confirm in the official edition you are under.
- Listed / SCCR numbers: 2020 listed 242.8 and SCCR 242.10; 2023 listed 242.6 and SCCR 242.8. Do not mix edition numbers.
- Type 3 30 ft rule: UL 1449's Type 3 definition includes a 10 m (30 ft) minimum from the service. NEC 242.16 applies that minimum when it is in the manufacturer instructions. Follow both the listing and 242.16; if they seem to disagree on a specific product, use the instructions and the AHJ.
- V per foot of lead: Published rules of thumb vary (commonly 100-170 V/ft). Not an NEC value.
- Breaker size: Always the manufacturer's specified size for that SPD family, not a single "code size."
UL is a trademark of UL LLC. Eaton, Bussmann, Square D, Schneider Electric, Siemens, and Leviton are trademarks of their respective owners. Morningstar Electric LLC is not affiliated with or endorsed by those manufacturers or by UL or NFPA. Always follow the device instructions and the adopted NEC.