You've identified a nuance in the NEC wording, and your reasoning is sound. Let's break it down: 424.22(B) establishes the limits

It sets the maximum amperage for heating elements and requires subdivision of loads exceeding 48A. This means a single heating element cannot exceed 48A.

Implicit vs. Explicit Protection

The NEC heavily implies the need for supplementary overcurrent protection for these subdivided loads through sections like 424.22(C), which discusses access and location of these devices. However, you are correct, there's no explicit statement in Article 424 that mandates supplementary OCPD for subdivided loads.

Your Example: 2 x 32A Elements on 40A Circuits

Based solely on Article 424, your scenario appears acceptable. Each 32A element is protected by a 40A branch circuit breaker, which could be argued as fulfilling the overcurrent protection requirement for that branch circuit. The subdivision requirement in 424.22(B) is met.

However, here's why that interpretation is likely incorrect in practice and why supplementary OCPD are virtually always required


Listing and Labeling (Article 110.3(B))

This is the key. The NEC requires equipment to be installed per its listing and labeling. Almost all listed electric space-heating equipment designed with subdivided loads will be tested and listed with specific supplementary overcurrent protection. The installation instructions will mandate their use. If the equipment is not listed with supplementary OCPD, and it is designed to be installed that way, then there is no explicit NEC rule against installing it per the plan you presented. But it's hard to imagine such equipment existing.2.

Manufacturer's Instructions (Article 110.3(B))

Even if the listing is vague, the manufacturer's instructions are legally binding. These instructions will almost certainly call for supplementary overcurrent protection, especially for elements as large as 32A each.3.

Purpose of Subdivision

The main reason for subdividing is to limit the potential fault current through each element. A 40A breaker protecting a 32A element is not providing particularly close overcurrent protection within the equipment. Supplementary OCPD (fuses or circuit breakers) within the equipment offer much better protection against internal faults within the heating element or its associated wiring.4.

UL Standards (Your Mention)

You are correct that the relevant UL standard (likely UL 1995 for Heating and Cooling Equipment) does require supplementary overcurrent protection for subdivided loads within listed equipment. This is a key factor.5.

Practicality

It's also not practical to build such equipment without internal protection. If an element fails in a shorted condition, a 40A breaker might not trip quickly enough to prevent significant damage or fire.

In summary

While Article 424 is, strangely, silent on explicitly requiring supplementary OCPD, the listing and labeling requirements of 110.3(B), combined with UL standards and the practical need for better fault protection, virtually always make their use mandatory. Your interpretation, based solely on the literal wording of Article 424, is technically defensible, but highly unlikely to be a compliant or safe installation in the real world.

Therefore, it is not acceptable to install fixed electric space heating equipment with subdivided loads (like your example) without supplementary OCPD, even if each element is protected by a standard branch circuit breaker of appropriate size.

Always prioritize the equipment's listing, labeling, and manufacturer's instructions. They will almost certainly specify supplementary overcurrent protection. If you have a specific* piece of equipment in mind, reviewing its installation manual will provide the definitive answer. Flag for review