That's a really interesting question that touches on the philosophy behind the NEC and the nuances of different electrical systems. Here's a breakdown of why corner-grounded delta systems haven't been outlawed, even though they're less common and have some potential safety considerations: NEC Focus on Installation Standards, Not System Elimination

The NEC's primary goal is to provide minimum safety standards for electrical installations. It's less about dictating which types of electrical systems can exist, and more about ensuring that any electrical system installed meets certain safety requirements. If a corner-grounded delta system can be installed and operated safely according to NEC standards, it's generally permitted.

Specific Use Cases & Historical Context

Corner-grounded delta systems have some specific use cases where they're still considered beneficial. Older Industrial Facilities: They're common in older industrial facilities, where they may have been installed decades ago for specific motor control or other applications. Retrofitting these entire systems can be incredibly expensive and disruptive. Simple 3-Phase Motor Loads: They can be a cost-effective solution for powering simple 3-phase motor loads in some industrial settings. Protection from High Voltage: Some industrial processes may require a corner-grounded delta system to protect against the high voltage produced from certain types of equipment.

Safety Can Be Addressed with Proper Installation & Maintenance

While corner-grounded delta systems do have safety considerations (like a higher voltage to ground on two phases), these can be mitigated with proper installation, grounding, overcurrent protection, and regular maintenance. The NEC addresses these specific concerns with specific rules related to corner-grounded delta systems.

Cost & Practicality of Eliminating a System

Eliminating a system type altogether would have huge economic and practical implications. It would force many existing installations to be completely redesigned and rebuilt, which is a massive undertaking. The NEC balances safety with the practicality and cost-effectiveness of its rules.

Acceptable Risk

NEC standards aim to reduce risk to an acceptable level, but they don't necessarily eliminate all risk. The code writers consider the statistical probability of different types of electrical accidents and focus on the most common and dangerous scenarios.

Alternative System Choices

While not outlawed, other more common systems such as wye systems offer better overall safety and efficiency in most modern applications.

In summary: The NEC is concerned with how a system is installed and maintained, not necessarily which* system is used, as long as the installation meets the minimum safety standards. Corner-grounded delta systems are allowed because they can be operated safely when properly installed, and because outlawing them would have significant economic and practical consequences. Flag for review