Square D Electrical Panelboards with Phenolic Arc Chutes (1940s–1978)

Product Description

Square D Company was among the most prominent manufacturers of electrical distribution equipment in the United States throughout the mid-twentieth century. The company produced a broad line of panelboards, load centers, motor control centers, and switchgear components that were installed widely across industrial facilities, commercial buildings, power plants, refineries, shipyards, and manufacturing plants from the 1940s through the late 1970s.

Panelboards manufactured by Square D during this period served as the central distribution points for electrical circuits throughout large facilities. These units housed circuit breakers, bus bars, and arc-interrupting components designed to manage and protect electrical systems from fault conditions and overloads. The panelboards were built to industrial standards and were considered durable, long-lasting equipment — meaning units installed decades ago may still be present in older structures today.

A critical internal component of these panelboards was the arc chute, also referred to as an arc suppressor or arc interrupter. Arc chutes are designed to safely extinguish the electrical arcs generated when circuit breakers interrupt current flow. During the decades covered by this article, Square D incorporated phenolic-based materials into arc chute construction. Phenolic compounds used in this era of industrial electrical manufacturing frequently contained asbestos as a reinforcing and heat-resistant filler, reflecting the standard industry practice of the time.

Asbestos Content

Asbestos was incorporated into phenolic arc chute assemblies primarily because of its exceptional thermal stability and electrical insulating properties. When a circuit breaker trips, the resulting electrical arc generates intense, localized heat. Asbestos-containing phenolic materials were capable of withstanding these conditions repeatedly without degrading, making them a practical engineering choice for manufacturers operating under mid-century material standards.

Litigation records document that Square D panelboards produced during the 1940s through approximately 1978 contained asbestos-reinforced phenolic components within their arc chute assemblies. The transition away from asbestos-containing materials in electrical equipment accelerated following the Environmental Protection Agency’s regulatory actions in the 1970s and increased awareness of asbestos health risks during the same period. However, because panelboards are long-service-life equipment, units manufactured before the phase-out remained in service in many facilities well into subsequent decades.

The arc chutes themselves are internal, enclosed components under normal operating conditions. However, the asbestos-containing phenolic material could be disturbed during installation, maintenance, circuit breaker replacement, panel modification, or demolition and renovation of facilities containing these units.

How Workers Were Exposed

Occupational exposure associated with Square D phenolic arc chute panelboards occurred across multiple trades and work scenarios encountered in industrial and commercial settings.

Electricians and electrical maintenance workers represented the most directly exposed occupational group. Routine maintenance activities — including inspecting or cleaning interior panel components, replacing circuit breakers, troubleshooting faults, or servicing aged equipment — could bring workers into close contact with arc chute assemblies. Removing, handling, or inadvertently breaking phenolic arc chute components could release asbestos fibers into the breathing zone of workers performing these tasks.

Industrial workers generally — including plant maintenance personnel, facility engineers, and utility workers assigned to keep industrial operations running — often worked in close proximity to electrical panelboards. In facilities where panels were located in confined mechanical rooms, equipment enclosures, or poorly ventilated spaces, even incidental disturbance of arc chute materials could result in elevated fiber concentrations in the immediate work area.

Renovation, demolition, and retrofit crews encountered these panelboards when upgrading electrical systems in older industrial and commercial buildings. Workers tasked with removing legacy equipment, cutting away conduit connections, or demolishing enclosures around installed panels may have disturbed asbestos-containing components without awareness of the hazard.

Plaintiffs alleged in litigation that asbestos exposure from arc chute components was a foreseeable consequence of normal use and maintenance of these panelboards, and that manufacturers and distributors of such equipment knew or should have known of the health risks associated with asbestos inhalation during the decades of production.

OSHA standards governing occupational asbestos exposure — including permissible exposure limits established under 29 C.F.R. § 1910.1001 (general industry) and 29 C.F.R. § 1926.1101 (construction) — reflect the regulatory recognition that asbestos-containing materials in building components and equipment pose ongoing exposure risks during maintenance and disturbance activities. Workers exposed to asbestos-containing electrical components in the course of industrial work may have accumulated significant cumulative fiber burdens, particularly if such exposures were repeated over years or decades of employment.

The diseases most commonly associated with occupational asbestos exposure include mesothelioma, asbestos-related lung cancer, asbestosis, and pleural disease. Mesothelioma — a malignancy of the lining of the lungs, abdomen, or heart — is considered a signature asbestos disease and has been the subject of substantial litigation involving industrial electrical equipment manufacturers.

This article is provided for informational reference purposes. It does not constitute legal advice. Individuals with potential asbestos-related claims should seek qualified legal counsel.

Documented Product Identification

The following details are drawn from public asbestos litigation records, manufacturer catalog pages, technical manuals, and corporate history materials. Each item reflects the product as documented in those sources.

Documented asbestos-use period: 1982

Corporate context: Founded December 15, 1902 as McBride Manufacturing Co. in Detroit. Changed name to Square D Company in 1917 after selling fuse business. Merged with Schneider Electric in 1991 and continues as flagship brand of Schneider Electric North American Division.

Brand identification: Embossed letter D within a square border; known as the SQUARE D trademark

Documented asbestos components: insulation, wiring insulation.

Industries served: residential, commercial, industrial, semiconductors, food and beverage, automotive, pharmaceutical, defense.

Documented product lines:

  • Cartridge-type electrical fuses (1902-1917). Original product line of cartridge fuses assembled in Detroit
  • Safety switch (metal-enclosed) (1915-present). Sheet metal enclosed safety switch with embossed D within square border, replacing earlier cast iron version
  • QO circuit breaker (1955-present). Revolutionary circuit breaker for commercial, residential and industrial applications replacing traditional screw type fuse boxes
  • ASB Insulated Wiring (1982). Asbestos insulated wiring product — asbestos components: insulation.

Square D reported to EPA in 1982 that it was still using asbestos. Company had plant in Columbia, MO associated with asbestos. Manufacturing locations included Detroit, Peru IN, Milwaukee, Los Angeles, San Francisco, Houston, Iowa, Kentucky (Lexington), Ohio, Wisconsin, Nebraska, North Carolina, and South Carolina.