4.2 CSST Installation Standards, Mechanical Protection & Electrical Bonding

CSST Installation Standards, Mechanical Protection & Electrical Bonding

Quick Answer: Corrugated Stainless Steel Tubing (CSST) listed to ANSI LC 1 / CSA 6.26 provides a flexible alternative to rigid Schedule 40 black pipe, but introduces unique life-safety and electrical bonding requirements. Standard yellow-jacketed CSST is highly vulnerable to sidewall perforation from indirect lightning strikes. To prevent catastrophic arcing fires, NFPA 54 Section 7.13.2 and NEC Section 250.104 mandate that yellow CSST be directly bonded to the electrical service grounding electrode system using a minimum 6 AWG bare or insulated copper bonding jumper. The bonding clamp must connect to a brass CSST fitting or rigid steel pipe component—never directly to the corrugated stainless tubing. Black arc-resistant CSST meeting ANSI LC 1 Section 5.16 incorporates energy-dissipating conductive jackets that eliminate the requirement for a separate 6 AWG bonding jumper under model codes.

Over the past three decades, Corrugated Stainless Steel Tubing (CSST) has revolutionized residential and commercial gas fitting by dramatically reducing installation labor, eliminating threaded joints, and enabling continuous flexible runs through structural framing. However, the thin sidewall profile of stainless steel tubing—typically 0.010 to 0.012 inches (0.25 to 0.30 mm) thick—makes it susceptible to puncture from mechanical fasteners (drywall screws, finish nails) and dielectric perforation from high-voltage electrical surges induced by nearby lightning strikes. Michigan mechanical contractors must strictly observe mechanical protection and electrical bonding rules to ensure code compliance and fire safety.

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ANSI LC 1 / CSA 6.26 Standards & Manufacturer Certification

Unlike rigid iron pipe, which is governed by generic ASTM standards, CSST is an engineered proprietary system governed by ANSI LC 1 / CSA 6.26 ("Fuel Gas Piping Systems Using Corrugated Stainless Steel Tubing"). Key regulatory mandates include:

• Manufacturer Certification Card: Michigan mechanical inspectors require installing technicians to produce an active, personalized certification card issued by the specific CSST manufacturer (e.g., Gastite, TracPipe, Wardflex, Pro-Flex). A certification card from one manufacturer does not authorize a technician to install a competing manufacturer's system.
• System Component Exclusivity: Intermixing components between different manufacturers is strictly prohibited. CSST tubing from Manufacturer A cannot be terminated with mechanical fittings, striker plates, or manifolds produced by Manufacturer B. Doing so voids the ANSI LC 1 listing and violates IFGC Section 403.
• Operating Pressure Ratings: Standard CSST systems are listed for operating pressures up to 5.0 psig (34.5 kPa) in residential and commercial applications, with elevated pressure ratings up to 25 psig available for specialized industrial listings.

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Mechanical Protection & Physical Routing Standards

Because CSST is semi-rigid and easily punctured by sheetrock screws, framing nails, and reciprocating saw blades, the Michigan Mechanical Code and ANSI LC 1 mandate strict physical routing and mechanical shielding protocols:

1. The 3-Inch Framing Rule & Striker Plates

Wherever CSST passes through structural framing members—such as wall studs, floor joists, rafters, or sole/top plates—it must be protected against puncture:

• Concealed Clearance Distance: If tubing is installed within 3 inches (76 mm) of the nearest finished surface or face of a framing member where nails or screws may penetrate, physical protection is mandatory.
• Hardened Steel Striker Plates: Puncture protection must be provided by factory-listed, hardened steel striker plates meeting ANSI LC 1 requirements (minimum No. 16 gauge, 0.0598 inch thick, case-hardened steel). Standard electrical nail plates do not possess the hardness required to deflect hardened drywall screws and are not code-compliant.
• Extension Past Framing: Striker plates must extend at least 4 inches (102 mm) beyond the outer edge of structural framing members to shield the tubing as it transitions through the wall cavity.

2. Floppy Flexible Armored Conduit

Where CSST runs horizontally through hollow wall cavities without rigid framing support, or where striker plates cannot be physically anchored, listed floppy steel conduit (flexible steel armored sleeve) must be slipped over the tubing. The floppy sleeve must extend continuously across the vulnerable zone plus 4 inches on either side.

3. Support Spacing Standards

CSST must be supported at regular intervals using listed metallic pipe straps, J-hooks, or conduit clamps that do not pinch, compress, or crush the corrugations:

In addition to interval supports, CSST must be secured within 12 inches (305 mm) of every termination fitting, appliance shutoff valve, or manifold connection to prevent rotational torque from transferring into the flexible corrugations.

4. Prohibited Installations

• Direct Concrete Contact: CSST cannot be embedded directly in poured concrete, masonry mortar, or exterior plaster. When passing through concrete floor slabs or foundation walls, CSST must be sleeved inside an approved nonmetallic water-tight conduit (such as Schedule 40 PVC) that is vented to the exterior.
• Moving Appliance Connection: CSST cannot be used as a flexible appliance connector for appliances subject to movement, vibration, or periodic pull-out (such as domestic clothes dryers or free-standing cooking ranges). CSST must terminate at a rigid drop fitting anchored to the building structure, followed by an appliance shutoff valve and a listed ANSI Z21.24 flexible connector.

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The Physics of Lightning-Induced Arcing

The fundamental vulnerability of traditional yellow-jacketed CSST stems from the physics of indirect lightning strikes. When cloud-to-ground lightning strikes a building, an adjacent tree, or nearby utility lines, massive electrical transient currents flow through the earth and structural paths to ground.

Because yellow polyethylene jacketing is an electrical insulator (dielectric), an unbonded CSST system acts as a high-capacitance conductor. A nearby lightning strike induces tens of thousands of volts between the CSST and adjacent grounded metal systems (such as copper water lines, metal HVAC ductwork, structural steel, or Romex electrical wiring). When the electrical potential difference exceeds the dielectric breakdown voltage of the yellow jacket:

1. An electrical arc jumps across the air gap between the CSST and the adjacent grounded metallic object.
2. The high-energy electrical arc generates temperatures exceeding 10,000°F (5,500°C) at the localized arc attachment point.
3. This intense thermal concentration instantly melts a pinhole perforation through the thin 0.010-inch stainless steel wall.
4. Pressurized fuel gas immediately escapes through the perforation and is ignited by the arc, creating a pressurized blowtorch flame inside concealed combustible wall or ceiling cavities.

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Direct Electrical Bonding Mandate for Yellow CSST

To prevent the formation of arc-producing voltage differentials, NFPA 54 Section 7.13.2, the Michigan Mechanical Code, and the National Electrical Code (NEC Section 250.104(B)) mandate direct equipotential electrical bonding for all standard yellow-jacketed CSST systems:

Technical Bonding Specifications

• Bonding Conductor Material & Sizing: The bonding jumper must be a minimum 6 AWG copper conductor (solid or stranded, bare or green insulated) or a minimum 4 AWG aluminum conductor.
• Connection Point Location: The bonding jumper must be attached directly to a listed brass CSST termination fitting, a brass manifold, or a rigid black iron pipe component located immediately adjacent to the meter or manifold. The bonding clamp must never be clamped directly to the corrugated stainless steel tubing itself, as mechanical clamping forces will crush the thin corrugations and compromise the pressure boundary.
• Listed Grounding Clamp: The clamp must be listed to UL 467 for grounding and bonding, specifically rated for the pipe diameter and metal type (bronze for copper/brass connections; iron or plated steel for black pipe).
• Termination Point: The opposite end of the 6 AWG bonding conductor must connect directly to the building's electrical service grounding electrode system, which includes:
  1. The electrical service equipment enclosure (ground bus bar inside the main electrical service panel);
  2. The grounded service conductor (neutral bus at the main disconnect);
  3. The grounding electrode conductor (GEC);
  4. One or more verified grounding electrodes (ground rod, ground plate, metal underground water pipe, or concrete-encased Ufer electrode).
• Maximum Recommended Length: To minimize inductive impedance (Z = R + jωL) during high-frequency lightning transients, the bonding jumper should be kept as short as practically possible. Many manufacturers and municipal guidelines enforce a maximum recommended length of 75 feet (22.9 m).

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Black Arc-Resistant Jacketed CSST (ANSI LC 1 Section 5.16)

In response to lightning litigation and bonding complexity, CSST manufacturers engineered advanced arc-resistant CSST, visually identified by a black exterior jacket (marketed under trade names such as TracPipe CounterStrike and Gastite FlashShield+):

Engineering of Arc-Resistant Systems

Black arc-resistant CSST incorporates a multi-layer composite protective sheath complying with the stringent electrical testing protocols of ANSI LC 1 Section 5.16:

1. Outer Protective Layer: UV-resistant, fire-retardant extruded polymer.
2. Conductive Shielding Layer: An energy-dissipating metallic mesh or conductive carbon-loaded polymer matrix that rapidly disperses electrical charge across the entire surface area of the tubing.
3. Inner Dielectric Layer: High-dielectric strength insulating polymer separating the conductive shield from the stainless steel core.

When lightning energy encounters arc-resistant CSST, the conductive layer dissipates electrical current across a wide surface without concentrating energy at a single arc point, preventing sidewall melt-through.

Code Bonding Status of Arc-Resistant CSST

Under the International Fuel Gas Code and NFPA 54, arc-resistant CSST meeting ANSI LC 1 Section 5.16 is exempt from the requirement for an independent 6 AWG direct bonding jumper, provided the system is electrically connected to an appliance that is grounded via the standard Equipment Grounding Conductor (EGC) of its electrical branch circuit.

Exam Trap Alert: Always check local Michigan municipal code amendments. While model NFPA 54 exempts arc-resistant black CSST from the dedicated 6 AWG bonding jumper, certain local enforcing jurisdictions in Michigan retain local ordinances requiring direct 6 AWG bonding on all CSST regardless of jacket color.