There is a lot of confusion in the home inspection and real estate industries about gas pipe bonding.
Grounding and bonding are two different things yet, from my experience, many electricians, plumbers and home inspectors don’t know the difference between the two.
Grounding is done to ensure that electrical 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 metal objects (such as pipes, metal framing, metal appliances, etc.) to the electrical system’s grounding system to ensure continuity in case the metal object is ever accidentally energized and/or potentially damaged due to a nearby lightning strike. Many modern homes serviced with natural gas or propane (LP) have some CSST (corrugated stainless steel tubing) installed.
Similar to how PEX (cross-linked polyethylene) and CPVC piping replaced copper plumbing in many modern homes due to easier installation, CSST has replaced black iron in many situations due to the easier install of this gas piping. The gas line adjacent to the gas meter is still often black iron, but it is usually a combination of black iron and CSST inside the home. It was initially designed to be used in earthquake-prone areas, and it was seen that CSST would be less likely to get damaged (and thus lead to explosions, etc.) compared to rigid pipe in these disasters.
Yellow CSST gas pipe manifold. Each run of gas pipe feeds a different gas appliance in the home
CSST started being used in the USA in the early 1990s. Older CSST generally had a yellow insulation jacket. After some time, however, yellow jacketed CSST started accumulating a documented history of potential damage in the form of arcing if there is a nearby lightning strike. This arcing can puncture the CSST which could allow for a gas leak or even an explosion. CSST is thin walled corrugated metal flexible tubing — the interior pipe walls are approximately 0.010 inch thick. The original yellow colored jacket 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 three or six feet long semi-rigid metallic piping that often has a painted-on yellow covering and is sometimes used to connect gas pipes to gas-fired appliances. The installation requirements for gas pipe and gas appliance connectors are very different.
Yellow CSST damage due to a nearby lightning strike
Due to this potential issue, by 2006 all CSST manufacturers listed bonding as an installation requirement for yellow CSST; however, based upon my experience inspecting homes, bonding this gas piping was rarely, if ever, done. I would estimate that maybe only 10 percent of yellow CSST installed in this area is actually bonded.
By placing the metallic portion of yellow CSST at permanent ground potential (bonding), the risk of possible damage and fire related to nearby lightning strikes is greatly diminished. CSST is approved for use both with natural gas and LP (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 may be a mile away or at a tree in the home’s back yard. When sufficient voltage is present, an electrical current is induced in nearby metallic objects like fencing, wiring, gas pipe, plumbing, appliances, etc.
Properly bonding a gas pipe is fairly simple in most situations and can be done by a qualified electrician. It requires a grounding conductor, most commonly braided or solid copper wiring, to be connected to the gas line where it enters the home and then connected to the home’s electrical grounding system (normally to a grounding terminal in the home’s main breaker panel). The main breaker panel’s grounding bar is grounded via either a driven ground rod and/or the home’s metal water service pipe (within five feet of where it enters the home).
A bonding connection where yellow CSST meets black iron pipe
In modern, new construction some areas rely on the plumbers installing CSST to bond the material upon installation; but it appears that 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). I believe this is a common reason why bonding fell through the cracks when it was installed, although the 2005 National Electrical Code (NEC) specifically required 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 how it must be done. Various lawsuits lead to these technical bulletins being issued.
Non-bonded installations of yellow CSST 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 with drywall ceilings 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. The local code enforcement officials are now requiring that the bonding exists.
In the 2000s manufacturers started manufacturing a different type of CSST with a black exterior sheathing (see above) which has different electrical and chemical 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 — such as a furnace, gas fireplace, etc. — that it is connected to is grounded via its electrical power connection. Most newer CSST installations are black although some installers were still using the yellow jacketed CSST as recently as 2010 in some places.
For more information about gas pipe bonding, go to the following resources:
Matthew Steger, ACI, WIN Home Inspection
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