Wiring Device Manufacturing (U.S.) — NAICS 33593

A rollup investor's primer. Figures marked as reported come from federal statistics and company filings; statements about where things are headed are labeled as judgments, not facts.

1. Overview

Behind every wall in every building is a hidden electrical layer, and this industry makes the small, code-governed hardware that lives in it. NAICS (North American Industry Classification System) code 33593 — Wiring Device Manufacturing is a five-digit industry with two very different halves [1]:

• 335931 — Current-carrying wiring devices: the parts that touch live electricity at the point where wiring meets a person or a machine — light switches, outlets (receptacles), ground-fault and arc-fault protective devices, dimmers, lamp holders, bus bars, terminal blocks, and surge arrestors [2].
• 335932 — Noncurrent-carrying wiring devices: the parts that route, protect, support, and enclose the wiring rather than deliver power through it — electrical boxes, conduit (raceway tubing) and fittings, faceplates, cable trays, pole-line hardware, and insulators [3].

One precision the children add: "noncurrent-carrying" describes a product's primary function, not an absolute. Metallic conduit, boxes, and fittings can and often do form part of a grounding or fault-current path — they simply are not there to deliver power [3]. Put simply, one child makes the things you can touch and switch; the other makes the pipes and boxes that hold everything together.

Both are unglamorous, essential "picks-and-shovels" manufacturing tied to how much building, factory work, and grid work is happening in the country. Together they shipped about $18.0 billion of product from U.S. plants in 2022 and employed roughly 38,400 people across about 552 factories [4][5].

Why an investor should care — and why the split matters. Despite sitting under one classification, the two halves are almost opposite businesses: different inputs (copper versus steel and plastic resin), different profit engines (product mix versus commodity spread), different plant scale (the federal small-business ceiling is 600 employees for one half and 1,000 for the other), different ownership (no public pure play in one half; a near-pure-play public company in the other), and different ways in for public versus private money [6][7][9]. The distinctive value of looking at 33593 as a whole is the contrast — which is where this primer starts.

2. What's inside — the two children and how they differ

The level splits almost evenly by revenue but the economics diverge sharply. The single most revealing number is output per worker: noncurrent-carrying (conduit and boxes) generates roughly twice the shipments per employee of current-carrying (switches and outlets), because it is a metal-and-resin throughput business run on high-capacity mills and extrusion lines, while current-carrying is a higher-labor, higher-SKU (stock-keeping-unit) assembly business [6][7][8].

Three takeaways from the table. First, the level looks unconcentrated in aggregate (see Section 3) but its two halves are structured differently — 335932 is materially more top-heavy, with roughly one-third as many firms producing a slightly larger share of output. Second, "wiring device" is a single label over two distinct investment cases: a defensive, code-driven, copper-exposed mix business, and a cyclical, commodity-spread, steel-and-resin business. A thesis on one is not a thesis on the other. Third, the federal small-business definitions encode the difference — Washington treats a 900-employee conduit plant as a small business and a 700-employee device plant as a large one [9].

3. How big it is (the rollup)

Federal statistics for the whole of NAICS 33593 (our ground-truth figures for this level) [4][5]:

That works out to roughly $69,600 in average annual pay per worker, about 69 employees per plant, and about 1.2 plants per firm [5]. Pay is strikingly similar across the two halves — about $69,000 in 335931 and $70,700 in 335932 — so the productivity gap between them is about capital intensity, not wage levels [6][7][8].

Does the rollup reconcile? Mostly. Establishments (397 + 155 = 552) and employees (24,429 + 13,934 = 38,363) match the parent exactly, and shipments ($8.38B + $9.63B) reconcile to ~$18.0B [4][5][6][7][8]. Firm counts are the one place the arithmetic does not close: 359 + 111 = 470 against 464 for the level [4][6][7]. That is expected rather than an error — a company operating plants in both halves is counted once at the parent and twice across the children — but it is a useful reminder that firm counts are not additive up a NAICS tree, while plant and employment counts are.

Concentration. Measured across the combined level, the industry is unconcentrated: the four largest firms make just 27.4% of shipments (CR4, the top-four combined revenue share), the top eight 40.3%, the top 20 61.5%, and the top 50 80.1% [4]. The Herfindahl-Hirschman Index (HHI, a 0–10,000 market-concentration score) is only 294 — far below the 1,500 mark U.S. antitrust regulators treat as "moderately concentrated" [4]. Note that the blended HHI is lower than either child's (313 and 648) [6][7]. That is arithmetic, not evidence of competition: bolting two distinct product markets together dilutes every firm's share of the combined total. The honest reading is that current-carrying is genuinely fragmented while noncurrent-carrying is meaningfully top-heavy, and the parent-level number describes neither.

Undercount caveat — read this before quoting a bigger number. Federal figures here measure domestic factory output, not U.S. consumption, and they understate the real market for two reasons. First, imports are large and growing — commodity residential switches and outlets, plus steel conduit (notably from Mexico) and fittings (from Asia) — and none of that is counted in the $18.0 billion of domestic shipments [15][16]. Second, the Economic Census counts only plants primarily in these codes, so the boxes, conduit, and devices that diversified majors (Eaton, ABB, Legrand, Schneider) make inside plants classified elsewhere are partly invisible here [7]. Private market-research firms quote roughly $11–17 billion for a 2024 "U.S. wiring device market" because they count total consumption including imports, often add distributor markup, and sometimes stretch the product scope to include electronic connectors — which are NAICS 334417 (Amphenol, TE Connectivity, Molex) and a different industry entirely [12][13][14]. Treat $18.0 billion as the honest measure of what is made here, and the larger consumption figures as a different, broader bundle.

A second trap specific to this level. NEMA (the National Electrical Manufacturers Association) warns that some published industry tables consolidate 335931 and 335932 into a single "wiring devices" line [11]. That combined figure is exactly this parent code — which makes it a poor proxy for either child, since the halves have opposite cost structures and different concentration. Use the parent number for the parent question ("how much wiring hardware is made in the U.S.?") and the child numbers for anything about economics, competition, or ownership. (Also note the mixed vintages: shipments and firm counts are 2022; employment and payroll are 2023.)

Nominal versus real. Factory-gate prices have risen sharply enough to distort any revenue-based growth read. The BLS producer price index for 335931 rose from 204.0 in June 2020 to 321.8 in June 2026, a calculated increase of 57.8% [10]. That is selling prices, not units. An investor comparing nominal 2022 shipments with an earlier census year, or extrapolating market-research revenue growth, will materially overstate volume expansion.

4. The investable universe — where value concentrates across the children

There is no listed company that only makes wiring devices in general, and the two halves route investors very differently.

335931 (current-carrying) — public exposure is indirect only. The two largest American specialists are private and family-owned: Leviton (outlets, switches, GFCIs, USB receptacles, EV chargers; the biggest U.S. pure-play, ~$1.8B estimated revenue) and Lutron (dimmers and lighting/shade controls) [17][18]. Public investors reach the category only through diversified electrical companies where devices are a minority of revenue — Hubbell (NYSE: HUBB) is the closest large-cap proxy, with Eaton (NYSE: ETN) (Arrow Hart brand), Legrand (OTC: LGRDY; EPA: LR) (Pass & Seymour, Wattstopper), Schneider Electric (SBGSY), Siemens (SIEGY), and ABB (NYSE: ABB) rounding it out [19][21][22]. The dilution is quantifiable: Hubbell's Electrical Solutions segment did $2.17 billion of net sales at a 19.3% operating margin in 2025, and that segment is only about 36% of the company — the larger half is utility products [19][20]. Legrand, the most device-weighted large name, ran €9.5 billion of group sales at a 20.7% adjusted operating margin in 2025, with North and Central America about 40% of sales [23].

335932 (noncurrent-carrying) — one near-pure play plus engineered-systems names. Atkore (NYSE: ATKR), at ~$2.85 billion FY2025 net sales with a $2.0 billion Electrical segment, is the closest thing to a pure conduit/raceway play [24]. The revised child adds a second narrow name the parent previously omitted: Preformed Line Products (NASDAQ: PLPC), ~$669 million of 2025 revenue in formed-wire transmission, distribution, and communications hardware — the tightest listed exposure to utility pole-line products [25]. nVent Electric (NYSE: NVT) (~$3.3 billion, 2024) offers an engineered-systems profile (enclosures, cable management, fastening), and Hubbell again carries rough-in boxes (RACO) inside Electrical Solutions [19][26]. Much of the half is private: Zekelman/Wheatland Tube (the largest independent North American steel pipe-and-tube maker), Southwire, Cantex, Robroy Industries, IPEX/Aliaxis, and specialty fiberglass/flexible-conduit makers, plus Nucor's Republic Conduit position [15][29][30].

Don't double-count the overlap. Hubbell and nVent appear in the investable universe of both children — Hubbell sells switches and rough-in boxes, nVent sells electrical connection products and cable management. Owning one share of either is exposure to both halves at once, not two independent bets, and it is a small share of a much larger electrical franchise in each case [19][26].

Where value concentrates. For a public investor, the cleanest direct exposure to the level sits in the noncurrent-carrying half via Atkore — but that is also the most cyclically volatile business in the level (Section 5). The current-carrying half, which is the more defensive and code-driven business, offers no direct public route at all — its best assets (Leviton, Lutron) are unavailable to public markets. The result is a mismatch worth internalizing: the steadier economics are locked up privately, while the most investable public name is the most commodity-exposed. (Tickers and any valuation work belong here and in Section 10, not in the industry description above.)

5. How the money works

Both halves make money the way volume component manufacturers do — cheap parts, enormous unit counts, high fixed plant cost — but the lever differs, and this is the core of the level.

• 335931 earns on mix. A basic residential outlet or switch retails for roughly $1–$5 and costs the maker cents; the money is in shifting the mix toward spec-grade commercial, hospital-grade, industrial high-amperage, protective (GFCI/AFCI), tamper-resistant, USB, and connected "smart" devices, all of which carry far higher margins [2]. The dominant input is copper, the most volatile cost; when copper spikes, gross margin compresses until price increases catch up, so the ability to pass metal costs through to distributors is a core skill [19].

• 335932 earns on spread. Buy commodities (hot-rolled and galvanized steel, PVC resin, aluminum, HDPE, fiberglass), convert them on high-fixed-cost mills and extrusion lines, and sell the difference. Because so much cost is fixed, capacity utilization swings margins hard — and pricing mean-reverts. The case study is Atkore's Electrical segment: pandemic-era shortages let selling prices run far above replacement cost and pushed adjusted EBITDA (earnings before interest, taxes, depreciation, and amortization) margin above 30%; as supply and imports returned, fiscal 2025 average selling prices fell 15.1% while volume rose only 0.2%, taking the segment margin to 16.5% from 30.9%, with full-year net sales down ~11% to $2.85 billion and adjusted EBITDA more than halved [24]. Atkore does not generally hedge raw materials, which amplifies the swing [24]. The investor lesson is to underwrite the through-cycle margin, not the peak.

• The engineered end behaves differently in both halves. Value migrates away from plain commodity product toward listed, spec-driven systems — enclosures, cable management, specialty conduit, protective and smart devices. Preformed Line Products illustrates the payoff on the noncurrent side with a 31.2% gross margin on engineered utility-line hardware [25]; on the current-carrying side the same principle shows up as spec-grade and protective-device mix.

• Shared mechanics. Materials are roughly half of cost of goods sold at a representative player in both halves, so both are fundamentally cost-pass-through businesses [19]. Both sell almost entirely through electrical distributors (Graybar, Rexel, WESCO, Sonepar) to professionals and through big-box retail to consumers, and the concentration is real — Hubbell's ten largest customers are about 42% of company sales [19]. Distributor destocking and restocking amplifies the construction cycle, and both carry inventory holding gains and losses as metal and resin prices move [24]. Both are seasonally stronger in the warmer construction quarters [24]. Both defend the premium end with brand trust, catalog breadth, and — critically — the safety listings discussed in Section 7, which low-cost imports struggle to obtain. And both enjoy a replacement/MRO (maintenance, repair, and operations) base that cushions downturns, since the vast installed stock of U.S. buildings needs code-driven replacement regardless of new construction.

• How thin the pass-through margin is. Hubbell attributed roughly six percentage points of 2025 margin expansion to pricing, productivity, and volume — almost entirely offset by about five points of contraction from material and other inflation, tariffs, and unfavorable mix [19]. That is the level in miniature: the operating gains are real but they are consumed year to year by input costs and trade policy.

6. What drives demand

Demand for both halves is derived from the same construction and electrification activity, which is why the level moves together despite the different economics:

• Construction and renovation — new residential and, especially, nonresidential building is the biggest single driver; remodeling, repair, and replacement add a steadier base. Both are interest-rate sensitive [31]. End-market mix can matter as much as the aggregate: Hubbell reported 2025 Electrical Solutions strength in data centers and light industrial offset by softness in nonresidential and heavy industrial [19].
• Data centers and the AI buildout — the standout tailwind for both halves: high-amperage receptacles, busway, and power-distribution devices (335931) and enormous volumes of conduit and cable containment (335932), where industry estimates put roughly a quarter of a large data center's electrical budget into cable containment [32][33]. The underlying load growth is documented: data centers went from 1.9% of U.S. electricity consumption in 2018 to 4.4% in 2023 and could reach 6.7–12% by 2028 [34].
• Electricity demand growth generally — EIA reports U.S. electricity demand grew about 1.7% a year from 2020 through 2025 against 0.1% a year from 2005 through 2019, with forecasts of 1.9% in 2026 and 2.5% in 2027 [36]. More load means more circuits, more raceway, and more devices.
• Grid and utility capital spending — real U.S. electric-distribution capital expenditure reached $50.9 billion in 2023, up $6.5 billion year over year, including $17.4 billion on overhead lines, poles, and towers and $11.8 billion on underground lines; transmission capex added another $27.7 billion [35]. These are not this industry's revenues — they are the pools against which pole-line hardware, conduit, and enclosures are sold.
• Electrical-code content growth — each revision of the National Electrical Code tends to require more protective devices and defined wiring methods per building, a structural tailwind that leans harder on the current-carrying half [38][39]. A concrete example already scheduled: special-purpose GFCI requirements extend to specified refrigerated-transport receptacles effective January 1, 2029 [40].
• Manufacturing reshoring — new chip fabs and battery/EV (electric-vehicle) plants are large, electrically dense buildings that consume both device and raceway product [31].
• Electrification at the endpoint — EV charging, USB-integrated outlets, connected switches and dimmers, solar/wind balance-of-system, and energy-management controls push mix toward higher-value product across both halves [33].

Counterpoint worth holding. "Grid investment" does not convert dollar-for-dollar into new hardware. Dynamic line ratings and other grid-enhancing technologies can raise capacity on existing corridors and defer physical expansion; DOE cites one deployment that increased line capacity by 6–14% while reducing infrastructure-investment needs [37].

7. Regulation

Regulation shapes the whole level the same way — less by licensing the makers, more by mandating what must be installed and how it must be certified — both of which create and expand demand.

• National Electrical Code (NEC / NFPA 70). Published by the National Fire Protection Association and adopted (often with amendments) by states and municipalities on roughly a three-year cycle, the NEC dictates where GFCI (ground-fault circuit interrupter) protection is required (Article 210.8), where AFCI (arc-fault circuit interrupter) protection is required (210.12), and where tamper-resistant receptacles are required (406.12), plus wiring methods, raceway requirements, and box-fill limits [38][39]. Each adoption cycle directly changes how many and which products go into every building.
• Third-party listing by an NRTL. Products must be tested and "listed" by a Nationally Recognized Testing Laboratory (most commonly UL, formerly Underwriters Laboratories, or Intertek/ETL) before inspectors will accept them. The relevant standards differ by half — UL 498 (receptacles and plugs), UL 20 (snap switches), UL 943 (GFCIs), and UL 1699 (AFCIs) on the current-carrying side; UL 514A (metallic outlet boxes), UL 514B (fittings), UL 514C (nonmetallic boxes), and UL 6 (rigid steel conduit) on the noncurrent side [39][41]. Listing is effectively mandatory, expensive, and slow — a real barrier to entry and to low-cost imports across both halves, and a real cost when a code change forces retesting.
• Workplace and installation rules. OSHA requires conductors entering boxes and fittings to be protected from abrasion, openings to be closed, and covers to be fitted on pull boxes, junction boxes, and fittings — a reminder that this is safety-critical hardware, not decorative trim [42].
• NEMA configurations. The National Electrical Manufacturers Association defines the standardized plug/receptacle and hardware dimensions that make devices interchangeable.
• Trade and domestic content. Because commodity devices, steel conduit, and fittings are heavily imported, trade policy hits the level directly. Section 301 tariffs on Chinese electrical goods, Section 232 steel/aluminum tariffs, a 2025 50% tariff on copper-intensive derivatives, and antidumping/countervailing-duty (AD/CVD) actions on conduit all cut both ways — protecting domestic makers while raising input costs [43][44][15]. This is an active battleground rather than a background condition: after a surge in Mexican steel-conduit imports, Zekelman/Wheatland closed a Chicago plant (about 237 jobs) in 2024 and pursued legal and trade actions, winning a 2025 Pennsylvania ruling restricting Mexican-made conduit in that state's public works [16]. Build America, Buy America (BABA) domestic-content rules on federally funded projects favor U.S.-made product in both halves.

8. Consolidation

The level's structure is a stable pattern of scaled players rolling up niche brands on top of a fragmented commodity tail, and the acquisition histories run through both halves:

• Eaton absorbed Cooper Industries (2012), bringing Arrow Hart devices into its portfolio; Legrand is a serial acquirer of device and controls brands (Pass & Seymour, Wattstopper) [21][22].
• ABB acquired Thomas & Betts (2012), folding a leading conduit/fittings/box franchise into its Electrification arm [28].
• Atkore was assembled from Tyco's Allied Tube & Conduit and Unistrut under private equity (Clayton, Dubilier & Rice) and went public in 2016 [24].
• nVent was spun out of Pentair (2018), bought ECM Industries (~$1.1B, 2023) and utility-enclosure maker Trachte, and in January 2025 sold its Thermal Management business to Brookfield for $1.7 billion to focus on enclosures and electrical connections [26][27].
• Nucor bought Republic Conduit (2017), giving a mega-cap steelmaker a downstream conduit position [15].

Judgment: expect more of the same — M&A concentrated on higher-margin engineered, listed, spec-driven systems (enclosures, cable management, grounding, protective and smart devices), while plain commodity conduit and builder-grade outlets stay price- and import-driven, with scale, freight geography, and low-cost operations deciding winners.

9. Risks

• Construction and rate cyclicality. Both halves swing with interest rates and building cycles; a downturn hits volumes and plant utilization across the level, and nonresidential construction was softening into 2025–26 [31].
• Commodity and pricing volatility. Copper (335931) and steel/PVC resin/aluminum/HDPE (335932) are volatile and dominate cost. The commercial risk is the lag between cost movement and repricing — margin is lost during inflation if price increases trail, and again during deflation if high-cost inventory must be sold into falling prices. The noncurrent half additionally carries margin normalization risk as peak-cycle prices mean-revert; Atkore's 30.9% → 16.5% segment swing in one year is the case study [19][24].
• Import and trade whipsaw. Heavy import exposure means tariffs and AD/CVD actions can protect or squeeze; sudden policy shifts disrupt sourcing and input costs on both sides [15][16][43][44].
• Channel concentration. Reliance on a few large distributors and big-box retailers gives buyers pricing leverage — about 42% of Hubbell's sales come from its ten largest customers [19].
• Data-center concentration. A pause in hyperscale capex would remove a major shared growth engine, and grid-enhancing technologies can defer some of the physical buildout investors are underwriting [37].
• Technology and material substitution. Smart-home and low-voltage architectures could erode the traditional device franchise (335931); shifts among steel, PVC, aluminum, fiberglass, flexible conduit, armored cable, and open cable tray reshuffle conduit winners (335932), so a producer concentrated in one material can lose share even as total electrical construction rises.
• Product safety and recall. A small manufacturing defect creates shock, overheating, or fire exposure. In 2020 the CPSC announced a recall of about 98,000 Leviton connectors, plugs, receptacles, and inlets over mislabeled terminals, and Pass & Seymour recalled about 685,000 commercial-grade receptacles over an overheating defect [45][46].
• Labor and workplace exposure. The halves differ measurably: BLS reported a 2024 total-recordable injury and illness rate of 2.5 cases per 100 full-time workers (DART 1.3) for 335931 against 1.7 (DART 1.0) for 335932 — the assembly-heavy half carries the higher rate [47].
• Regulatory double edge. Code and listing changes drive demand but can also obsolete tooling, force redesign and re-certification, or favor a substitute material.

10. How to invest, and the outlook

Public routes. The level offers no clean single-name play, and the two halves pull in different directions. For direct exposure, Atkore (ATKR) is the closest pure play but the most cyclically volatile, moving with commodity spreads; Preformed Line Products (PLPC) is the narrowest listed exposure to utility transmission and distribution hardware; nVent (NVT) is a cleaner engineered-systems growth profile [24][25][26]. For defensive, code-driven exposure, the choices are diversified electricals where devices are a minority slice — Hubbell (HUBB) as the closest large-cap proxy, plus Eaton (ETN), Legrand (LGRDY), ABB, Schneider (SBGSY), Siemens (SIEGY), and steelmaker Nucor (NUE) via Republic Conduit [19][21][23]. In every diversified case you are buying the whole electrical franchise, not the wiring-device business — Hubbell's device-bearing segment is roughly a third of the company — so model the actual portfolio and end markets rather than applying an assumed 33593 market share to consolidated sales [19][20].

Private routes. Much of the level's best assets are unavailable to public markets: the current-carrying specialists Leviton and Lutron are family-held, and the noncurrent-carrying half is dense with private owners — Zekelman/Wheatland, Southwire, Cantex, Robroy, IPEX/Aliaxis, and specialty fiberglass/flexible-conduit makers, plus a churn of private-equity-owned fabricators [15][17][18][29][30]. Private and search-fund investors target these specialty makers, the electrical-distribution layer, and building-products roll-up platforms. Diligence questions are common across both halves: who owns the listings and certifications and what they cost to replace; the split of commodity versus specification-grade revenue; distributor concentration and rebates; SKU-level price-cost history; exposure to copper, steel, resin, and tariffs; inventory accounting through raw-material cycles; warranty and recall history; plant utilization; and — because corporate NAICS codes are unreliable at this granularity — how much revenue genuinely belongs in 335931 versus 335932 at all. Commodity conduit businesses are typically valued on through-cycle EBITDA given the swings.

Outlook (judgment, not fact). The secular volume story is favorable for the whole level: data centers, reshored manufacturing, electrification, grid investment, and expanding code content raise the amount of device and raceway product per project, and domestic-content rules plus trade actions tilt work toward U.S. capacity [13][14][33][35][36]. But the two halves offer different bargains from here. The current-carrying half is the steadier, more defensive story — code-mandated, replacement-cushioned, mid-single-digit demand growth — but its best assets are locked up privately, so public investors buy it diluted inside diversified franchises. The noncurrent-carrying half is more directly investable through Atkore and, more narrowly, PLPC, but the easy margin tailwind is gone: returns now depend on volume and cost discipline rather than windfall pricing. Across the level, near-term results in any given year will be set as much by copper, steel, resin, construction, and tariffs as by the underlying secular trends. These are judgments about direction, not guarantees.

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Sources

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