Yellow CSST and the Bonding Question

Why this matters

Yellow corrugated gas tubing is in millions of houses built or re-plumbed since about 1990, and most of it will never cause a problem. The concern is narrow and serious: a nearby lightning strike can energize the building, and the thin tubing wall can be the place the current arcs through, opening a hole in a pressurized gas line inside the house. Whether that tubing is bonded is a question almost every trade can see from where it stands, and almost none of them is qualified to answer. The roofer, the HVAC tech and the electrician who notice it and write it down are doing the most useful thing available to them.

Safety first: what to do if gas is involved right now

If you smell gas, hear a hiss near the tubing, or are on site after a lightning strike and anything smells like gas: everyone leaves the building now. Do not operate light switches, unplug anything, start a vehicle in the garage, or use a phone inside. From outside and upwind, call the gas utility's emergency line or 911, and keep people away until the utility clears the house. If the tubing is visibly scorched, pitted or holed and there is no odor, do not touch, flex or bend it to look closer; leave it as found, photograph it from where you stand, and get a gas-qualified person there before anyone fires an appliance.

Everything below assumes none of that is happening.

What CSST is and how you recognize it

Corrugated stainless steel tubing (CSST) is a flexible, thin-walled stainless steel gas line with a plastic jacket over the corrugations. It is run in long continuous lengths from a manifold or the meter area to each appliance, joined only at the ends with brass fittings made for it. Installers like it because it snakes through framing with few joints.

On sight: a jacketed tube, usually 3/8 to 1 inch, that you can see is corrugated under the plastic, ending at a brass fitting at a manifold, an appliance shutoff valve, or a black-steel stub. The jacket carries a print line: the maker, the size, the listing standard (ANSI LC 1/CSA 6.26 is the North American standard CSST is listed to), and on newer products a statement about the jacket type.

Yellow vs black. The original and still common product has a yellow jacket. Since roughly the late 2000s, several manufacturers have sold tubing with a black jacket that is designed to resist lightning arc damage, often called arc-resistant CSST. Color is a strong cue and not proof: read the print line, because the print, not the color, says what the jacket is listed as. Do not confuse either one with yellow-jacketed polyethylene gas pipe, which is a buried service material, or with a flexible appliance connector, which is a short, single-appliance tube (see related: Old Flexible Gas Connectors at Appliances).

Why lightning is the issue

A direct strike is not the main scenario. The common one is an indirect strike: lightning hits a tree, a utility line, or the ground near the house, and the surge enters the building through the electrical service, the cable or phone line, or the ground itself. For an instant, different metal systems in the house sit at very different voltages. If the CSST runs close to a metal duct, a water pipe, a chimney flashing or electrical wiring, the current can arc across the gap, and the point where it arcs is a tiny area of a thin stainless wall. The arc can melt a pinhole through it. The result is a gas leak, sometimes ignited by the same arc, inside a wall, floor or attic.

Bonding reduces the voltage difference that drives the arc. A bonding conductor connects the gas piping system to the building's grounding electrode system, so that during a surge the gas piping rises in voltage together with everything else instead of sitting far apart from it. Bonding does not make CSST lightning-proof and does not mean the tubing will survive a direct strike; it reduces the likelihood of arcing damage from an indirect one.

What the codes and the instructions call for

Read this as layered, because it is.

Manufacturers' installation instructions for yellow CSST have, since about 2007, required direct bonding: a bonding conductor not smaller than 6 AWG copper, attached to the gas piping at a rigid point (a black-steel pipe segment, the CSST manifold or a brass fitting, never to the corrugated tubing itself) and run to the electrical service grounding electrode system. Instructions generally also limit how long that conductor may be. The installation instructions are part of the product's listing, and most codes require equipment to be installed per its listing, so the instructions bind through the code.

The model fuel gas codes picked this up. The National Fuel Gas Code (NFPA 54) and the International Fuel Gas Code (IFGC), along with the fuel gas chapter of the IRC, added CSST bonding requirements in editions from about 2009 onward, and later editions treat arc-resistant jacketed CSST differently, generally accepting the equipment grounding path required by the electrical code instead of a separate direct bond. None of that is law until your jurisdiction adopts an edition, and states split between NFPA 54 and the IFGC. Which edition is in force where the house sits, and which edition was in force when the gas line was installed, are two different questions, and the second one decides whether an unbonded installation was a code violation when it went in.

What that means for an older yellow-CSST house. A system installed before bonding requirements existed may have no bond and may have been legal at the time. That does not make it safe in a lightning-prone area, and the manufacturers have published guidance encouraging owners of older installations to have them bonded. Adding a bond to an existing system is a gas-and-electrical task: a licensed plumber or gas fitter, an electrician, or both, depending on how your state licenses the work.

What each trade should notice

Roofers. You see the attic and the roof penetrations. CSST that runs along a ridge, near a chimney, close to metal flashing, or near a roof-mounted antenna or satellite mast is in the places most associated with arcing. Note its route. Never fasten anything through or against it, and keep new metal (drip edge, step flashing, vent pipes) from being installed touching it.

HVAC. CSST often feeds your furnace or boiler. You will see whether there is a bonding clamp and conductor near the appliance or the manifold. A bonding clamp found on the corrugated tubing itself, rather than on a rigid fitting or pipe, is a wrong installation worth writing down. Replacing a furnace does not authorize you to remove a bonding conductor attached to the old gas stub; if the stub changes, the bond has to be re-established by whoever is qualified to do it.

Electricians. You are the one trade that can usually see both ends: the bonding conductor at the gas piping and its landing at the grounding electrode system. A panel or service replacement is exactly the moment an existing bond gets disconnected and not reconnected. Your scope may or may not include the bond under your state's licensing; your note should say what you found either way.

Everyone else (handyman, cleaner, low-voltage, pest). Do not run cable, wire or metal strapping along or against CSST. Do not hang anything from it. If you are drilling or nailing near framing it runs through, stop and locate it first; a screw through the jacket is a gas leak.

The worked example: a reroof on a 2004 house

The situation. A roofing crew is tearing off and reroofing a 2004 two-story house in a region with frequent summer thunderstorms. The owner wants a new ridge vent cut in. Before cutting, the crew lead goes into the attic through the hatch to check the ridge area and sees yellow-jacketed corrugated tubing running along the top of the attic, roughly parallel to the ridge, then dropping down a chase beside the chimney toward a gas fireplace.

What the lead checks, without touching it. Distance to the planned ridge cut: the tubing runs about 10 inches below the ridge board for most of the run. Distance to the chimney flashing: it passes within a hand's width of where the chimney meets the roof deck. The print line on the jacket names the product, a size of 1/2 inch, and the LC 1 listing, with no arc-resistance statement. Outside, at the gas meter, the lead looks at the house piping just downstream of the meter and sees no bonding clamp or green or bare copper conductor attached to it.

What changes the roofing plan. The ridge vent cut is made with a depth-set circular saw. Ten inches is plenty of clearance from a blade set to deck thickness, but the crew adds two rules for this house: the cut is made only where the lead has confirmed the tubing line from inside, and no fasteners or new metal go near the chimney chase area until the tubing route there is marked. The crew lead also cancels a plan to strap a new satellite mast bracket to a rafter beside the chase.

The note on the job record.

LEGACY MATERIAL NOTE - JOB 2214 - ATTIC / GAS
What: yellow-jacketed corrugated gas tubing,
  1/2 in, print shows LC 1 listing, no
  arc-resistant statement on jacket.
Where: runs along attic below ridge, drops
  down chase beside chimney to fireplace.
  Passes within ~4 in of chimney flashing.
Bond: no bonding clamp or conductor visible
  on house piping at meter. Bond elsewhere
  NOT verified (other end not inspected).
Disturbed: no. Ridge cut kept clear of run.
Told owner: yes, 10/14, in person.
Route: plumber/gas fitter + electrician to
  verify or add bond per mfr instructions.

Reading the note back. The note does not say "unbonded." It says no bond was visible at the one place the lead looked, and it names the place not inspected. That distinction matters: some installers bonded at the manifold or at a black-steel segment elsewhere, and a reader who sees "unbonded" on a job record treats it as a finding nobody made.

The conversation. The lead tells the owner the tubing is common, the concern is lightning, the fix if needed is a bonding wire a gas fitter or electrician adds, and that a roofer cannot judge whether it is already bonded somewhere else. The lead does not quote a probability. See related: Telling a Customer About an Old Material Without Scaring or Understating.

What would change this call. If the print line had shown an arc-resistant jacket, the note would still record the route and the bonding observation, but the urgency of the recommendation would drop, because the codes and instructions generally treat that product's grounding differently. If there had been a strike on or near the house recently, the recommendation would rise to "have the gas system leak-checked before the next appliance firing," because a pinhole from a past arc may not be large enough to smell.

How to verify you got this right

The route is drawn, not described. A sketch or a photo set showing where the tubing runs relative to the roof, the chimney and any metal is more useful to the gas fitter than a paragraph.

The bonding observation is scoped. You wrote where you looked and where you did not. "Not visible at meter" and "not verified elsewhere" are both on the record.

You stayed out of the fix. You did not add a clamp, move the tubing, or tell the owner it was fine. Adding a bond is the professional's job; the plumbing trade procedure for it is the reference. See related: CSST Bonding Verification.

Your own work did not create a new path. Nothing you installed touches the tubing or sits within the arc gap of it.

References

• Manufacturers' CSST design and installation guides, for the bonding conductor size, attachment point and length limits required by the listing.
• NFPA 54 (National Fuel Gas Code) and the International Fuel Gas Code, CSST bonding sections, in the edition your jurisdiction has adopted.
• ANSI LC 1/CSA 6.26, the listing standard for CSST.
• See related: CSST Bonding Verification (plumbing trade procedure).
• See related: Recognize, Record, Route: The Rule for Legacy Materials.