The ground strap on a common single-phase pad mount distribution transformer is connected to which part?

• A. The primary coil end
• B. The secondary winding
• C. The transformer enclosure
• D. The neutral

Answer: (A)

Grounding and bonding are about creating a safe, defined path for fault currents and for any exposed metal parts to be at a known earth potential. On a common single-phase pad-mount distribution transformer, the ground strap serves to bond the high-voltage part of the transformer to the enclosure. Specifically, it connects the end of the primary winding—the high-voltage terminal—to the transformer enclosure, which is tied to the earth through the grounding system. This keeps that winding end at ground potential and ensures that if insulation fails and a fault tries to energize the enclosure, the fault current will have a low-impedance path to ground, tripping the protective devices quickly.

The secondary winding and the neutral are part of the low-voltage circuit, and while the neutral may be bonded to the enclosure in some configurations, the strap described is configured to connect the primary winding end to the enclosure. This bond is what maintains a safe, defined ground reference for the high-voltage side.