You're in a tough spot, balancing code interpretation with practical considerations. Let's break down the code requirements and address the inspector's request.

NEC Requirements and Grounding/Bonding Principles Gas Piping Bonding (NEC 250.104(B))

The NEC requires bonding of metal gas piping systems that are likely to become energized. This means bonding the metal gas pipe to the service equipment grounding electrode system (or other allowed methods). This requirement aims to provide a low-impedance path for fault current back to the source, facilitating the operation of overcurrent protective devices (breakers/fuses) if the gas piping becomes energized due to a fault.

Metal Ductwork Bonding (NEC 250.104(E))

The NEC requires bonding for metal ductwork and other metal piping systems that may become energized.

Equipment Grounding Conductor (EGC) in the Branch Circuit (NEC 250.134)

The EGC in the branch circuit supplying the furnace is essential for grounding the furnace's metal parts. This EGC, run with the circuit conductors, provides a path for fault current to return to the source if there's a fault within the furnace.

Analysis of the Inspector's Request

The inspector's request to bond both the gas line and the ductwork to the GEC is not explicitly prohibited by the NEC. In fact, it could be argued that it enhances safety by providing additional bonding paths.

Potential Concerns and Considerations Creating a Ground Loop

This is the biggest concern. A ground loop occurs when there are multiple paths to ground. These multiple paths can create circulating currents, which can, in some (rare) cases, cause noise or interference in sensitive electronic equipment, or even slight heating of the conductors. However, in a residential setting with a furnace and typical ductwork, the likelihood of a significant ground loop causing problems is very low. It's a theoretical risk, not a highly probable one.



Unnecessary Bonding

If the metal gas piping and ductwork are already effectively bonded to the service grounding system through other means (e.g., contact with grounded metal building components), additional bonding might be redundant. However, determining whether adequate bonding exists without the added bonding is where the ambiguity and potential for disagreement with the inspector lie.

Why the Inspector is Likely Requiring This

Local Interpretation/Amendment

The inspector might be interpreting the code more stringently or there might be a local amendment in place.

"Belt and Suspenders" Approach

Some inspectors take a "belt and suspenders" approach to safety, preferring to err on the side of caution. They might feel that additional bonding ensures a more robust grounding system.

Covering All Bases

The inspector may not be able to definitively assess the existing bonding effectiveness without destructive testing, making additional bonding seem like the safest course of action.

He might also just not be up to date on current codes. It is VERY easy to misinterpret the NEC

Your Proposed Solution and RecommendationsYour plan to bond both the gas line and the ductwork to the GEC is a reasonable way to appease the inspector while minimizing potential negative consequences.Here's a refined approach:1.

Clarify with the Inspector

Before doing anything, politely ask the inspector to cite the specific NEC section (or local amendment) that requires this bonding. This helps you understand his reasoning and potentially identify a misunderstanding.2.

Bonding Connections

Use approved bonding clamps listed for the purpose (e.g., ground clamps rated for grounding and bonding gas piping). Ensure the bonding jumpers are sized appropriately (typically #6 AWG copper for gas piping; #8 or #6 AWG for ductwork, depending on the size of the associated circuit). #6 is generally a good default. Connect the bonding jumpers to the GEC at a point that provides a solid, low-impedance connection. Keep the bonding jumpers as short and direct as possible. The inspector may frown on the idea of bonding the ductwork to the gas line. It would probably be more correct to have individual wires run to each.3.

Documentation

Take photos of the bonding connections before covering them up. This provides evidence that you complied with the inspector's request.

In summary: While the inspector's specific requirement might not be explicitly required by the NEC in every situation, it's not prohibited either. The risk of creating a problematic ground loop in this scenario is low. Your plan to bond both the gas line and ductwork to the GEC is a practical and reasonable approach to satisfying the inspector and avoiding a failed inspection. Just ensure proper bonding techniques and documentation.The best advice: Politely inquire about the specific code reference the inspector is using. This opens a dialogue and may reveal a misunderstanding or a local amendment you were unaware of. Flag for review