The manufacturers of yellow corrugated stainless steel tubing (also known as "CSST") require that the product be bonded as part of their installation instructions. Bonding is different than grounding and this topic is often confused by home owners, electricians, plumbing, and even some home inspectors.
Yellow CSST gas manifold
Grounding is done to ensure that fault current can return to the utility's transformer and hopefully prevent damage to people or property. Grounding provides safety in case of a fault in a structure's branch circuit wiring that feeds lighting, receptacles, and appliances. A fault is when electricity is flowing on a conductor that it should not be, such as a short circuit.
Bonding, on the other hand, is a permanent connection of metallic objects to the structure's electrical grounding system. Bonding helps prevent a potential shock to someone touching the metallic object or damage to things in contact with the metallic object. These metallic objects include water pipes, gas pipes, appliances, metal framing, etc.
As part of a home inspection, the home inspector should try to verify if the gas pipe is bonded. In many cases, much of a home's gas piping will be located behind insulation or behind or above wall or ceiling coverings. If the inspector can't visually confirm gas pipe bonding, this should be noted in the inspection report as well as a recommendation to have the gas pipe evaluated (to determine if bonding exists but is out of view of the inspector) and/or properly bonded by a licensed plumber or an electrician. If bonding is visible, this should also be noted in the report.
Yellow sheathed CSST has a documented history of potential damage if there is a nearby lightning strike in the form of arcing. This arcing can puncture the CSST and therefore allow for a gas leak or even an explosion. CSST is thin walled corrugated metal flexible tubing (the interior pipe walls are approx. 0.010" thick) with a most-often yellow sheathing around it. The original yellow colored sheathing tends to hold an electrical charge (like a capacitor) and therefore makes it possible for a rupture of the gas pipe due to the induced electrical energy caused by a nearby lightning strike. Yellow CSST is manufactured under various brand names including GasTite®, TrakPipe®, and Diamondback®. Yellow CSST piping should not be confused with gas appliance connectors. Gas appliance connectors are generally 3' or 6' long semi-rigid metallic piping (often with a painted-on yellow covering) sometimes used to connect gas pipes to gas fired appliances.
Arcing holes in yellow CSST caused by a lightning strike.
By placing the metallic portion of yellow CSST at permanent ground potential (bonding), the risks of possible damage and fire related to nearby lightning strikes is greatly diminished. CSST is approved for use both with natural gas and LP (liquified propane). Modern electrical and building standards do not require gas piping to be able to withstand the energy of a lightning strike, whether the strike is direct or indirect. An indirect lightning strike can be to a home a mile away or to a tree in the home's back yard. When sufficient voltage is present, an electrical current is induced in nearby metallic objects (fencing, wiring, gas pipe, plumbing, appliances, etc.).
To accomplish a proper bonding connection, a properly-sized bonding conductor (most commonly braided or solid copper wiring) is connected at the point where the gas line enters the home or where the rigid gas pipe (generally black iron) first connects to CSST. The other end of the bonding conductor terminates onto the electrical service's grounding terminal bar inside the main breaker panel. The main breaker panel's grounding bar is grounded via either a driven ground rod or another electrical grounding method.
Bonding connection where black iron meets yellow CSST
CSST became popular in the 1990s as it allowed for gas piping to be installed in approximately 1/3 of the time it took to install black iron pipe. CSST is flexible making it easier to work with and faster to install, similar to plastic water piping versus copper piping. After a period of time, however, it was observed that close lightning strikes can cause damage to the CSST.
In the 2000s, manufacturers started manufacturing a different type of CSST with a black exterior sheathing which has different electrical properties. This newer black sheathing does not hold an electrical charge, like the older yellow sheathed CSST can. Due to this change, the black sheathed CSST generally does not require special bonding as part of its installation requirements as long as the appliance that it is connected to is grounded via its electrical power connection.
The photo above shows newer black sheathed CSST gas pipe. It is manufactured under various brand names, including CounterStrike® and Flashstrike®.
From my experience inspecting homes since 2002, most installations of CSST inside homes are not bonded as required by the products' manufacturers. In modern new construction, some areas rely on the plumbers installing CSST to bond the material upon installation but most plumbers don't understand bonding and the electrical codes. Other areas rely on electricians who aren't even looking at the home's plumbing (water and gas). This is a common reason why bonding falls through the cracks when it is installed, although the 2005 NEC (National Electrical Code) specifically requires that metal gas piping be bonded. In more recent years, however, all manufacturers of CSST have made it a point to release technical bulletins to CSST installers ensuring they are aware that yellow CSST must be bonded and showing how it must be done. Some of this is due to various lawsuits due to home fires directly attributed to improperly installed CSST.
The lack of bonding increases the potential risk of arcing resulting in a gas leak and/or fire if there is a nearby lightning strike. Product manufacturers' requirements supercede building codes. A non-bonded installation of yellow CSST gas pipe does not meet the CSST manufacturer's installation requirements (nor the National Electrical Code) and should be promptly repaired by a qualified electrician familiar with CSST bonding. Keep in mind, however, that home inspectors are not code inspectors. The cost to have a qualified electrician properly bond CSST per the manufacturer's specifications is inexpensive, however it can be more difficult if the home has a finished basement since the bonding normally takes place at accessible gas plumbing from the basement.
As part of a home inspection, the inspector should try to determine if the home's gas piping is bonded. Depending upon the home, accomplishing this task can range between being very easy to nearly impossible. This often boils down to how visually accessible the home's gas piping is in the basement. In most newer homes that I inspect, I find that builders are finally getting around to bonding gas pipes and the local code enforcement officials are now requiring that the bonding exists.
Additional information about the requirements for yellow CSST bonding can be found in this bulletin: www.csstsafety.com/Images/CSST-Direct-Bonding-Tech-Bulletin.pdf
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© 2017 Matthew Steger
Matthew Steger, owner/inspector of WIN Home Inspection, is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), an electrical engineer, and a US Dept. of Energy Home Energy Score Assessor. He can be reached at: 717-361-9467 or email@example.com.
WIN Home Inspection has provided a wide array of home inspection services in the Lancaster, PA area since 2002. This article was authored by Matthew Steger, ACI - owner of WIN Home Inspection in Lancaster, PA. No article, or portion thereof, may be reproduced or copied without prior written consent of Matthew Steger.