The Myth of the Safer Standard: NEMA and IEC examined against the normative, regulatory and industrial record: design philosophies, certification regime, enclosures and the positions of global manufacturers.

Few beliefs in North American and Latin American electrical practice have proved as durable as the idea that equipment built to NEMA (National Electrical Manufacturers Association) practice is ‘safer’ than equipment built to IEC (International Electrotechnical Commission) standards. This report tests that idea against three bodies of evidence: the standards and regulations now in force; the publications of the bodies that write, certify and enforce them; and the technical literature of manufacturers that build both product lines, Schneider Electric, Siemens and ABB among them.The belief does not survive the exercise. None of the bodies or manufacturers consulted endorses it, and several reject it in terms (Schneider Electric, 2015; Smith, 2001). The North American system has, moreover, taken IEC 60947-4-1 as the basis of its own standard for contactors and motor starters, UL 60947-4-1, which applies in the United States, Canada and Mexico (Siemens Industry, 2018; Underwriters Laboratories, 2012). As far as certified safety is concerned, ‘NEMA versus IEC’ now describes two ways of sizing equipment that are tested under a single regime.The myth persists because it is not baseless. It draws on three things that are true in a narrower sense: the reserve capacity built into NEMA sizes, the 1.15 service factor common on NEMA motors, and the wider environmental testing behind NEMA enclosure Types compared with the IP code. The first two describe tolerance of misapplication. The third concerns the environmental performance of enclosures, and NEMA itself states that its enclosure standard does not address arc flash (National Electrical Manufacturers Association [NEMA], n.d.). In the other direction, IEC practice made IP20 finger-safe construction a standard feature and gave the industry Type 1 and Type 2 coordination, which UL has since adopted.