You're right to question the specific number of 601A as a standard OCPD (Overcurrent Protective Device) size. It does seem like an odd choice at first glance. Here's the likely reasoning behind its inclusion: Gradual Evolution and Incremental Increases

Electrical standards and equipment ratings don't appear out of thin air. They evolve based on real-world needs, technological advancements, and industry consensus.

Load Demand and System Design

The 601 amp standard size breaker likely arose to meet the specific load requirements of some types of industrial equipment that were used in the past. In general, engineers want to select equipment based on the next highest standard size rating available.

Manufacturer Capabilities

Another consideration is the manufacturing capabilities of the major players in the electrical equipment industry at the time. If it was relatively straightforward to produce breakers in the 600-650 amp range, setting the standard close to the low end of that capacity might make sense from a production standpoint.

Standardization Bodies and Collaboration

Standard sizes are typically hammered out by organizations like UL (Underwriters Laboratories), NEMA (National Electrical Manufacturers Association), and IEEE (Institute of Electrical and Electronics Engineers). These groups bring together manufacturers, engineers, and other stakeholders to agree on standardized equipment ratings.

Regarding the Lack of a "401" or "501": Load Density

The standard increment sizes will depend on the potential load density. For example, if loads are often larger, then the increment between standard sizes is going to be larger as well.

Important Considerations



Consult the NEC

Always refer to the most current version of the National Electrical Code (NEC) for the definitive list of standard OCPD sizes and any applicable rules or exceptions.

UL Standards

UL (Underwriters Laboratories) standards for circuit breakers and fuses also play a crucial role in establishing ratings and safety requirements.

Manufacturer's Data: Check the manufacturer's specifications for the specific OCPD you intend to use. They will provide detailed information on its rating, performance characteristics, and compliance with applicable standards.In short, the choice of 601A as a standard size is a result of the electrical industry's response to load demand, manufacturing capabilities, and the need for standardized components. While it may seem arbitrary, there's a logical (albeit historical) reason for its inclusion. Flag for review