C S S T and bonding. Episode eleven of the Gas Service Animated series.

Corrugated stainless steel tubing, or C S S T, is a flexible gas line with a thin stainless wall under a protective jacket. Instead of threading rigid pipe together elbow by elbow, installers route it more like a cable, bending gently around the framing. It is a listed system — the tubing, the fittings, the striker plates, and the manifolds are designed to work together, and the manufacturer's listed instructions govern the installation. And one thing it is not: C S S T is not an appliance connector. That is a different product with different rules.

Remember pipe sizing from the earlier episodes. C S S T does not use the Schedule forty steel tables at all. Its capacity is listed by E H D, the equivalent hydraulic diameter, and every manufacturer publishes sizing tables for its own tubing. So when you size C S S T, the manufacturer's table governs — reading a steel pipe table for flexible tubing gives you the wrong answer.

That thin wall is the tradeoff, so the installation protects it. Where the tubing passes close to stud edges and through plates, listed steel striker plates shield it from nails and screws, extending well beyond the penetration itself. Supports go in at the spacing the listing calls for, and bends stay gentle — never tighter than the listed radius. Now watch the nail. The striker plate is the only thing standing between a drywall screw and a gas leak.

Now the serious part. A lightning strike, even a nearby one, can raise the electrical energy of one system in a building relative to another. If the gas tubing sits at a different potential than a grounded duct or pipe a few inches away, that energy can jump the gap as an arc. Rigid steel pipe has thick walls — C S S T does not. An arc can burn a small hole through the thin stainless wall, releasing gas exactly where the heat is. That is the failure bonding exists to prevent.

So the code requires C S S T systems to be directly bonded. A listed bonding clamp attaches to a rigid pipe segment or a listed fitting, and a copper conductor no smaller than six A W G runs from that clamp to the electrical service grounding electrode system. Keep that jumper as short as practical — the code caps it at seventy five feet. The clamp must be listed for the purpose and stay accessible, and the connection details follow the electrical code. Bonding holds every system at the same potential, so the energy has nowhere to jump.

Not all C S S T wears the same jacket. Arc resistant jacketed products carry a listing that lets the jacket absorb that energy, and their bonding provisions are different — many are treated as bonded through the appliance's equipment grounding conductor. Identify the product by its jacket and the markings printed on it, and follow that specific listing. And if any tubing in the system lacks the arc resistant jacket, the direct bonding rule still applies.

On a service call, here is what you verify. The jacket is intact, with no gouges or exposed corrugation. Striker plates sit where the listing requires them, supports are at the listed spacing, and no bend is tighter than the listed radius. The bonding clamp is present, tight, and on a rigid segment or listed fitting, with the conductor continuous all the way to the grounding electrode system. And nowhere in the house is C S S T doing an appliance connector's job.

C S S T in one breath: a listed flexible system, sized by E H D, shielded by striker plates, and directly bonded with heavy copper to the grounding electrode system. Lightning is the enemy. Bonding is the defense. Next episode: water heaters — the gas side.