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  • Writer's pictureDennis Paulson

CSST Bonding

What is CSST you might ask? CSST stands for Corrugated Stainless Steel Tubing. CSST is a flexible, stainless steel pipe used to supply natural gas and propane to residential, commercial and industrial structures. If you have recently had gas line installed or own a newer home, there is a good possibility CSST was used. This is a relatively new, flexible tubing that is approved for the distribution of natural gas and propane inside homes.

CSST History: CSST was developed in Japan in the 1980s. It was developed as a safety improvement over rigid black iron gas pipes that often failed and started fires during earthquakes. The flexible nature of the CSST system allows it to handle seismic activity without leaking gas. Sales of CSST in the U.S. began in 1990 with approximately 100,000 ft. sold. Use of CSST grew in the U.S. as contractors quickly discovered it could be installed in 1/3 the time of rigid black iron pipe systems. Beyond the time saved on installations, contractors and code officials appreciated the reduction of fitting joints in a flexible gas piping system. Joints are areas for concern in gas piping systems as they represent potential leak paths. Flexible CSST systems have approximately 75% fewer fitting joints than rigid black iron pipe systems. In August,2006 all manufacturers of CSST added a Bonding and grounding procedure to their installation requirements. Reducing the likely hood of an electrical surge that can potentially cause a fire.

CSST needs to be bonded. A common issue observed by home inspectors is CSST not being bonded. When CSST has been installed without being bonded to Current Standards there is an increased risk of the gas line being damaged due to lightning strike, causing the CSST to leak gas and cause a fire or explosion.

What about existing installations? Building codes are ever changing and have something called “grandfathering”, meaning that if something was installed to code, it’s still a code compliant installation today, even if the codes change significantly. The great thing about home inspection is we don’t have to dwell on code requirements. If something is deemed unsafe due to changes in accepted construction standards, our Standards of Practice requires us to report on it. If CSST was installed in 2004 and the manufacturer didn’t have special requirements at the time of installation, that install still meets code today. However, that doesn’t stop a home inspector from recommending this important safety upgrade. Manufacturers of CSST have modified their installation requirements because they learned the old methods left an unacceptable risk of fire from nearby lightning strikes.

How do you know if you have CSST in your home? Look for a flexible tubing with either a yellow or black jacket over the ridges. Most CSST before 2015 has a yellow jacket. The material shouldn’t be confused with appliance connectors, which have a yellow coating that follows the contours of the ridges.

What does proper bonding look like? Proper bonding requires a separate 6AWG bonding wire connected either to the ridged gas piping before the CSST or directly to the CSST nut. This needs to be done anytime CSST is installed regardless of the length of CSST used.

The other end of the wire should attach to the electrical service grounding system. This connection may be made at either the ground rod, on the ground wire running to the rod, or in the electric service panel. Some manufacturers of CSST offer a product with a black outer “arc-resistant” jacket, which is designed to show it is an arc-resistant product. Two of these products are CounterStrike and FlashShield. The manufacturers of these products do not require special bonding, current codes make no exception to the bonding requirements of these products. They still need to be bonded. In April of 2012 the NFPA 54 Technical Committee commissioned the Gas Technologies Institute (GTI) to conduct a study to determine the most effective methods to address the dangers of lightning strikes and CSST. In September of 2013 they issued a report entitled “Validation of Installation Methods for CSST Gas Piping to Mitigate Indirect Lightning Related Damage”. The testing included 4 different brands of CSST and in that report the following conclusion was drawn: “With a sufficiently short bonding conductor, arcing is suppressed entirely, and the possibility of an arc discharge perforation is eliminated”. After that report, the NFGC issued their 2015 code. As it relates to the electrical grounding and bonding code (section 7.13.2 * CSST.) the code states: “CSST gas piping systems and gas piping systems containing one or more segments of CSST, shall be bonded to the electrical service grounding electrode system or where provided, lightning protection grounding electrode system.” The bonding requirements stayed the same as the previous code and no provisions or exceptions for CSST with “arc-resistant” jackets were included in the latest version of this code (NFPA 54), even though the authors are fully aware that “arc resistant” CSST products have been on the market for several years. If there was a safer alternative available, wouldn’t they have included it in their code? Conclusion Although extremely rare, electrical arcing is the single most dangerous threat to safety in a lightning scenario. “Arc-resistant” CSST does not eliminate the chances of an arcing event. In addition, no scientific test results have been put forth that confirms that “arc-resistant” CSST provides more safety than bonded standard CSST. You can be certain that if CSST jacketing was instrumental to safety based on all of the research available to them, NFGC would have addressed it in their code – they did not. The equalization of voltage resistance in the electrical system, which only bonding accomplishes, is what makes the system safe. That is why the gas and electrical industries, code bodies, and even CSST manufacturers are clearly moving toward more strict bonding requirements for all metallic systems including CSST. Lastly, the claims that “arc-resistant” CSST requires the same bonding requirements as steel pipe (bonded to an appliance in lieu of the grounding electrode), are just that – claims. The code does not make that distinction! By educating yourself you needn’t be lost in the fog of conjecture, half-truths, contradictory information, unsubstantiated claims, or even scare tactics.

In Conclusion: If you have CSST in your home, you should make sure it is properly bonded to today’s standards, regardless of whether the installation met code when it was originally installed.

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