Okay, you've hit upon some of the most confusing aspects of grounding and bonding for lightning protection. Let's break it down. It's a complex issue, and the videos you're watching are likely simplifying, which can lead to these contradictions.

Here's the general principle



Goal

Provide a low-impedance path for lightning current to travel to ground without creating dangerous voltage differences within a structure. This prevents flashover (arcing) between different pieces of equipment or from equipment to personnel.

Why the Contradictions?

The "correct" answer depends heavily on the specific system (grounded, ungrounded, size of building, type of equipment, soil conditions, etc.). Here's a breakdown of the common scenarios and principles involved.1. Bonding, Bonding, Bonding

The most crucial thing is to bond everything metal together: Equipment enclosures Metal conduit Metal piping (water, gas) Structural steel Grounding electrode conductor (GEC)This creates an "equipotential plane". The idea is that if everything is connected, everything rises in voltage together during a lightning strike. This minimizes the potential difference between objects, which is what causes arcing.2.

The Single Grounding Electrode System



Concept

The modern approach is to have ONE primary grounding electrode system. Ideally, it should be a ground ring around the perimeter of the building, supplemented by ground rods, buried plates, or connections to the building's foundation steel (if properly designed as a grounding electrode).

Why only one? The problem with multiple, widely separated grounding electrodes is this: During a lightning strike, the current travels outwards through the earth from each electrode. Since soil has resistance, a significant voltage gradient can develop in the ground. If two pieces of equipment are grounded to different, widely separated ground rods, they can be at significantly different potentials relative to "true" earth ground. This voltage difference between the two pieces of equipment is a shock hazard and can cause arcing between them.

Auxiliary Electrodes (Local Rods) - When are they OKAY? Local rods are okay when you BOND them to the main grounding electrode conductor so that they ALL work in the same potential plane.3.

Grounded vs. Ungrounded Systems

The core principles of bonding apply to BOTH grounded and ungrounded electrical systems. You still need to bond equipment enclosures, metal conduit, etc. to the grounding electrode system.4.

Why ground GECs to an Ungrounded System? Even in an ungrounded system, the system is still capacitively coupled to ground. This means that there's some level of voltage present between the ungrounded conductors and earth. A lightning strike induces voltages everywhere. Grounding the GEC provides a path for these induced voltages to dissipate and helps keep the overall voltage of the ungrounded system from rising to dangerous levels. A lightning strike is an overvoltage event. The point of grounding is to provide a low impedance path for this excess voltage to get to ground without creating excessive potential differences within the system.

Addressing Your Faraday Cage PointYou're right to think about Faraday cages. Here's why the transformer enclosure isn't a perfect one:

Openings

Transformer enclosures have openings for ventilation, cables, and bushings. These openings compromise the shielding effect. Even small openings allow electromagnetic fields to penetrate.

Thickness and Material

The effectiveness of a Faraday cage depends on the material's conductivity and thickness. Transformer enclosures are usually steel, which is reasonably conductive, but they are often not thick enough to provide complete attenuation of a lightning strike's intense electromagnetic pulse. Also, some enclosures are not properly bonded at seams, further reducing the effectiveness.

Induced Currents in Windings

Even if the enclosure significantly reduced the external field, lightning can induce currents directly into the power lines connected to the transformer. These currents then flow through the transformer windings.

Important Considerations



IEEE Standards

For detailed guidance, consult IEEE standards on grounding and bonding.

Local Codes

Always comply with local electrical codes, as they often have specific requirements for grounding and bonding.

Qualified Professional

Lightning protection system design and installation should be done by a qualified professional experienced in lightning protection.

In Summary

Think of it like this:1.

Bond everything metal to create an equipotential plane.2.

Establish a main grounding electrode system. A ground ring is ideal for a building.3.

Connect all bonded metal to the main grounding electrode system.4.

Minimize ground loops (paths where current can circulate unnecessarily) and voltage gradients by using a single, well-designed grounding system.5.

Supplemental grounding electrodes are acceptable IF properly bonded to the main grounding system to maintain equipotentiality.It's complex, and your confusion is understandable. This is a topic that takes years of experience to fully grasp. Don't rely on just one video – seek out multiple sources and consult with qualified professionals. Flag for review