CSST Bonding Verification

Purpose

Corrugated stainless steel tubing carries fuel gas through a wall thin enough that an arc which would only pit schedule 40 black iron burns straight through it. The arc does not come from the gas system: a nearby lightning strike raises the potential of one metallic system in the building against another and jumps the gap, usually in a joist bay where the tubing runs near a duct, a water line or a cable.

This procedure guarantees the bond is one you have measured, on a conductor you have sized, landed where the code says. The failure it prevents is the assumption that the furnace's equipment grounding conductor is doing the job: that path runs through a flex connector and an appliance chassis and was never sized or routed for a surge.

Scope

Covers verification, and the write-up of a defect, on residential and small commercial gas systems containing any CSST, whether you installed the tubing or found it.

It does not cover the design of the grounding electrode system, which is an electrician's work. It does not cover physical protection of the tubing at framing, which the gas piping support and protection inspection SOP owns. It does not cover a gas odor or the aftermath of a suspected strike, which the gas odor call response SOP owns and which step 1 hands off to. All-black-iron systems carry no separate CSST bond requirement.

Roles and the handoff

The handoff that fails is the last one. A tech who finds no bond and says nothing because "we did not put it in" leaves the customer worse off than one who never looked.

Procedure

1. Rule out an active leak before you look at anything electrical. Sweep every accessible connection, the meter riser and each CSST penetration with a combustible gas indicator against a background taken outside. Acceptance: no response above outdoor background anywhere on the route, no reported odor. Wrong: a faint reading dismissed as the smell of the crawl. Stop: any odor or any response above background ends this procedure and starts the gas odor call response SOP - everyone out, no switch or plug operated, call made from outside. Hazard: you are searching for a flammable atmosphere, so the instrument goes in ahead of you, nothing electrical is operated in the space, and on propane you read low first because it is heavier than air and pools.

2. Identify the tubing product family off the jacket print. Read the manufacturer and product name along a visible run and pull that product's design guide. Standard yellow-jacket CSST carries the direct bond requirement in full; some black-jacket arc-resistant products are listed with a different bonding provision in their own guide, and that guide governs the product installed. Acceptance: manufacturer, product name and the guide's bonding clause on the ticket. Stop: unreadable print means you treat it as standard CSST, the more demanding requirement, and note the assumption. Hazard: do not scrape or cut the jacket to find legible print - the jacket is the tubing's abrasion and arc protection, and a nick you make is a defect you introduced.

3. Confirm the gas-side attachment is a legal point on clean rigid metal. The clamp goes on a rigid pipe component or a CSST fitting body downstream of the point of delivery, listed for grounding, coating removed under it. Acceptance: clamp on bare rigid metal, screw tight against a wrench, nothing bearing on the corrugated tube or jacket. Wrong: a clamp squeezed over the yellow jacket, which reads as a bond from six feet away and is an insulator. Stop: no attachment point anywhere means the system is unbonded, a written finding rather than a field improvisation. Hazard: reaching blind into a joist bay puts your hand on tubing and whatever shares it, so light it before you reach, and never use gas piping as a handhold.

4. Verify conductor size against the fuel gas minimum, not the electrical table. NFPA 54, the National Fuel Gas Code, in the edition your authority having jurisdiction has adopted, sets this conductor at no smaller than 6 AWG copper in its electrical bonding section, numbered 7.13 in recent editions; confirm that number in your edition before quoting it to an inspector. The adopted NEC would size a jumper for other metal piping from the circuit that could energize it, far smaller on a furnace circuit. Where they disagree the fuel gas minimum governs. Acceptance: 6 AWG copper or larger read off the marking, within the design guide's length cap, commonly 75 ft. Stop: undersized is written up, not left undocumented because the house has been fine so far. Hazard: none at this step, a marking read, but do not flex a suspect solid conductor to read it - one worked at the clamp breaks inside its insulation.

5. Trace the other end to the service, and confirm who may open it. The bond terminates at the service equipment enclosure, the grounded service conductor, the grounding electrode conductor where sized for it, or a grounding electrode, per the bonding-of-other-piping section of the adopted NEC. Acceptance: the far end traced to one of those and seen landed under a listed connector. Wrong: a conductor that vanishes into insulation and is assumed to reach the panel, or one landed on an interior water pipe because the water pipe is bonded too. Stop: if tracing needs the enclosure opened and nobody on site is a qualified person under 29 CFR 1910.332 and 1910.399, it goes to an electrician. Hazard: the line side of a service enclosure cannot be de-energized by any switch in the building, so the cover comes off only under 29 CFR 1910.333(b)(2) practices, standing to the hinge side, with the meter proved on a known live source before and after per NFPA 70E-2021, 120.5.

6. Measure the bond path with lead resistance taken out first. Short the probes on the lowest resistance range and record that value, then measure clamp to service-side termination and subtract. No code assigns an ohm value here, so acceptance is the character of the reading, not a published limit. Acceptance: the corrected reading is a fraction of an ohm, indistinguishable from a bolted metallic path, and does not move when you flex the conductor at each end. Wrong: tens of ohms, or a reading that jumps as you wiggle the clamp, both meaning paint, corrosion or a loose screw is carrying the connection. Stop: an unstable reading is treated as no bond until the terminations are remade by whoever is licensed to remake them. Hazard: this puts a probe on the service grounding conductor, so the meter is on resistance, never on a live conductor, and by a qualified person under the step 5 practices.

7. Walk the route for the damage that makes bonding matter more, not less. Look for fasteners driven through or bearing on the jacket, hard contact with ducts, water lines or a metal chimney liner, and unprotected framing penetrations. Acceptance: no fastener bearing on tubing, every penetration protected per the product's guide. Wrong: a bonded system with a drywall screw resting on the jacket in a wall cavity, the exact geometry the bond exists to survive. Stop: a fastener through the jacket means gas off to that section and the section replaced per the manufacturer's instructions, never taped. Hazard: pulling insulation to see the route liberates fibrous dust, so a fitted respirator worn under a written program per 29 CFR 1910.134 goes on before the insulation moves, with eye protection.

8. Restore what you opened and re-verify with the assembly closed. Reinstall covers, re-torque any clamp you touched, reinstate insulation, then repeat step 6. Acceptance: the post-restoration reading matches step 6 within the meter's resolution, and any gas joint you disturbed shows no bubble growth over a full minute and no indicator response above outdoor background. Wrong: a bond that read clean with the clamp held by hand and reads open once the screw is set against a painted surface. Hazard: this step puts hands on a gas line and a grounded metal path at once, so gas joints get their leak check before anyone leaves and the electrical cover goes back on by the qualified person who removed it.

The record this produces

One bonding record per property, filed against the address, because the next tech and the next inspector both start from it:

• Manufacturer, product name and jacket colour, and the design guide clause relied on
• Attachment point on the gas piping, by location and by what it clamps to
• Conductor size read off the marking, and measured length against the guide's cap
• Termination point at the electrical service, and who landed it
• Lead resistance, raw reading, corrected reading, and whether it moved under flexing
• Route defects with locations: fasteners, contact points, unprotected penetrations
• What was corrected today, by whom, under whose license, and what was left open

Worked pass: a 2004 house with yellow CSST and a furnace changeout on the ticket

• Step 1: no odor reported. Outdoor background 0 percent LEL. Meter riser, furnace connection, water heater connection and two attic penetrations all read 0. Passed.
• Step 2: print legible at the attic manifold, standard yellow-jacket product. Guide requires the direct bond and caps the conductor at 75 ft. Passed.
• Step 3: clamp on the rigid black iron nipple at the manifold outlet, bare metal under it, tight against a wrench, nothing on tubing or jacket. Passed.
• Step 4: FAILED. Conductor marking read 10 AWG solid copper against the adopted edition's 6 AWG minimum, two trade sizes light. Measured run 41 ft, inside the 75 ft cap, so length is not the defect; size is.
• Step 5: far end traced along the attic to the service enclosure, landed under a listed lug on the grounding electrode conductor. No cover came off - nobody on the truck is a qualified person.
• Step 6: leads shorted read 0.3 ohm. Clamp to grounding electrode conductor read 0.5 ohm, so 0.5 minus 0.3 leaves 0.2 ohm corrected, steady under flexing at both ends. Passed.
• Step 7: one drywall screw bearing on the jacket above the furnace closet, jacket dented but not penetrated. Screw backed out, tubing eased clear rather than cut.
• Step 8: nothing opened electrically, so the re-measure held at 0.2 ohm corrected. The furnace connection disturbed by the changeout held with no bubble growth over a full minute and no indicator response.

The step 4 stop rule ran as written: bond work stopped, and the finding went to the customer in writing naming the mechanism, the size found, the size required and the code section. Gas was not interrupted, because an undersized bond is a lightning-event exposure rather than a leak and step 1 had already established there was no leak. The correction, 6 AWG copper between the same two points, was quoted with both endpoints specified, so the electrician priced a run rather than a survey.

The instructive part is step 6 passing while step 4 failed. Continuity on the wrong conductor reads beautifully, because 10 AWG copper is a fine path for a milliamp of meter current and an inadequate one for a surge. A shop that measures and never reads the marking certifies an undersized bond every time.

References

• NFPA 54, the National Fuel Gas Code, electrical bonding section, in the edition your authority having jurisdiction has adopted, which sets the 6 AWG copper minimum and binds the work through the gas permit
• NFPA 70, the National Electrical Code, as adopted by your jurisdiction in that edition, for the permitted termination points for bonding other metal piping
• The CSST manufacturer's design guide for the product installed, which governs where its listing differs and sets the conductor length cap
• 29 CFR 1910.333(b)(2), with qualified person at 1910.332 and 1910.399, and NFPA 70E-2021, 120.5 for the before-and-after instrument check
• 29 CFR 1910.134 for the written respiratory program governing any respirator worn in step 7
• See related: the gas odor call response SOP, the gas piping support and protection inspection SOP