Which primary system is considered safer?

• A. Wye
• B. Delta
• C. Open Delta
• D. Zigzag

Answer: (A)

Having a grounded neutral path on the primary system provides a clear route for fault currents and keeps line-to-ground voltages predictable. The Wye configuration, especially with a grounded neutral, lets single-ground faults flow back through the neutral to ground, which makes fault currents detectable by protective devices and allows a quick, safe interruption. This reduces touch voltages and improves overall protection coordination for people and equipment.

In contrast, a Delta primary has no neutral, so a ground fault doesn’t create a strong fault current path and can be harder to detect, increasing safety risks. Open Delta reduces redundancy and balance, leading to weaker fault paths and voltage imbalances that complicate protection and safety. Zigzag is a specialized transformer arrangement used to provide a grounding path or neutral in certain cases, but it isn’t the standard primary system chosen for general safety because it doesn’t offer the straightforward, robust neutral grounding that Wye with a grounded neutral provides.

So, the configuration with a grounded neutral, offering the safest and most reliable fault path, is the Wye.