You're right to question the common practice and look closely at Article 550. The NEC requirements for mobile homes regarding grounding are nuanced and often misunderstood.Here's a breakdown and why you typically don't run a separate grounding electrode conductor (GEC) to the distribution panel inside the mobile home: 550.32(A) Service Equipment. This section (or its equivalent in older editions) typically requires the service equipment (main disconnect) to be located adjacent to or on the mobile home. This is a crucial point. The intention is that the grounding electrode connection happens at the service equipment. Single Point Grounding

The NEC generally strives for a single point of grounding to avoid circulating currents and ground loops. If you ran a GEC to both the service equipment and the distribution panel inside the mobile home, you'd be creating multiple ground paths, which can be problematic.

Mobile Home as a Single Unit

The mobile home, once connected to the service equipment, is treated more like a single building or a single dwelling unit served from a service.

Here's the typical scenario and why it works


Service Equipment

A service disconnect (breaker or fused disconnect) is located near the mobile home.2.

Grounding Electrode Conductor (GEC)

The GEC connects from the service equipment to the grounding electrode(s) (ground rod(s), ground ring, etc.).3.

Feeder to Distribution Panel

A feeder (typically a 4-wire system: two hots, a neutral, and a grounding conductor) runs from the service equipment to the distribution panel inside the mobile home.4.

Equipment Grounding Conductor (EGC)

The equipment grounding conductor (the green or bare wire) in the feeder is bonded to the enclosure of the distribution panel inside the mobile home. This EGC provides a low-impedance path for fault current to return to the source, tripping the breaker in the service equipment. The neutral is isolated from the enclosure in the distribution panel inside the mobile home.

Why this is different than a separate building



Separate Buildings

In a separate building (e.g., a detached garage or shed), you're dealing with a separate structure. The NEC typically requires a grounding electrode system at that separate structure if it meets certain conditions (usually involving multiple circuits or serving equipment). This is to ensure that the structure has its own grounding reference.

Mobile Homes as a Unit

The mobile home is not treated as a completely separate structure once connected to the service equipment. The connection to the service equipment creates a single electrical system.

Important Considerations and Possible Exceptions



Local Amendments

Always check with your local electrical inspector. Local jurisdictions can have amendments to the NEC that might affect grounding requirements.

Manufacturer's Instructions

Always follow the mobile home manufacturer's instructions, as they might have specific requirements or recommendations for grounding.

Older Mobile Homes

Older mobile homes might have different wiring configurations, and the grounding practices might need to be adapted to meet current code requirements while maintaining safety. This is where consulting with a qualified electrician familiar with older mobile home wiring is crucial.

If the Service is NOT adjacent

If the service disconnect is NOT adjacent to the Mobile home then you would treat it like a separate structure.

Bonding

Pay close attention to bonding requirements within the mobile home, especially bonding of metal frames, water pipes, and other metal components.

In summary: The typical approach for mobile home grounding is to have the grounding electrode system connected only at the service equipment. The equipment grounding conductor in the feeder running to the distribution panel inside the mobile home then provides the necessary ground fault path. You usually do not run a separate GEC to the distribution panel inside the mobile home. However, always verify with your local inspector and follow the manufacturer's instructions. Flag for review