A flexible gas connector passing through a wall or cabinet partition is a concern because:

A flexible gas appliance connector is listed for a specific, narrow job: making the final connection between a rigid gas piping system and a movable appliance, in the open, where it can be seen. It is thin-walled corrugated tubing and it is not rated to pass through a wall, floor or cabinet partition. Two failure modes drive the rule. Abrasion — the tubing chafes against the sheet metal or framing at the penetration every time the appliance is moved or vibrates, and the wall is thin enough that wear becomes a leak. Concealment — a leak inside a partition escapes into a cavity where gas accumulates and where no one can smell it early. Rigid pipe is what passes through building elements; the flexible connector stays outside them.

Flexible appliance connectors are not listed or rated to penetrate walls, floors or cabinet partitions. Running one through a partition exposes it to abrasion at the opening and puts a potential leak inside a concealed cavity, so the installation is reported for correction.

Gas appliance connectors are listed for connecting a single appliance to a rigid supply, in an accessible location, without concealment. Penetrations through building elements are made with approved rigid piping, and connectors are not to be joined together or extended.

Connectors Stay in the Open. Rigid pipe goes through walls; flexible tubing lives where you can see it. If it disappears into something, report it.

Look for the related defects in the same scenario — connectors spliced together, run behind cabinetry, or used in place of rigid pipe are all commonly tested and all reportable.

• •Reading the defect as a flow or sizing problem
• •Concluding flexible connectors are prohibited indoors generally
• •Overlooking that concealment prevents a leak from being detected