There is a lot of confusion in the home inspection and real estate industries about gas pipe bonding.
Grounding and bonding are two very different things yet, from my experience, many electricians, plumbers, and home inspectors don’t know the difference between the two yet they are indeed very different.
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 were to ever become accidentally energized and/or potentially damaged due to a nearby lighting strike. Many modern homes served with natural gas or propane (LP) have some CSST (corrugated stainless steel tubing) installed. It can be understood that the electrical system is grounded whereas everything else is bonded to the electrical system.
Like 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 often either a combination of black iron and CSST inside the home. It was initially designed to be used in earthquake-prone areas, 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 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). 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 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. 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'd estimate, based upon experience, that maybe only 10% of yellow CSST installed in this area is actually bonded.
By placing the metallic portion of yellow CSST at permanent ground potential (bonding), the risks of possible damage and/or 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 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 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, metal plumbing, appliances, etc.).
Properly bonding a gas pipe is fairly simple in most situations and should be done by a qualified electrician. It requires a bonding conductor (most commonly braided or solid copper wiring such as #6 AWG copper or #4 aluminum) to be connected to the gas line and then connected to the home’s electrical grounding system (normally to a grounding terminal in the home’s main breaker panel). Current standards allow for the bonding clamp to be located at any point of CSST gas pipe (just not on the yellow jacket or on the corrugated steel itself); best practice is as close to the electrical panel as possible. Past requirements called for the bonding connection to be made at the upstream-most point of CSST but this is no longer the case. 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 5’ of where it enters the home). The bonding connection must be made on the house side of the gas meter, however.
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). This is a common reason, I believe, why bonding fell through the cracks when it was installed, although the 2005 NEC (National Electrical Code) 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 showing 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 most often 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 visually 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.
Keep in mind that gas appliance connectors are not CSST and do not require bonding. CSST should not be installed at movable (non-fixed) appliances. CSST can be run through walls and floors (but should have protection plates installed), underground (must be protected in conduit), in attics, and outside (but most be physically secured and protected if installed within 6' of grade).
In the 2000s, manufacturers started manufacturing a different type of CSST with a black exterior sheathing (see image below) which has different electrical and chemical properties. This newer black sheathing does not hold an electrical charge unlike the older yellow sheathed CSST. 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 range, etc.) that it is connected to is grounded via its electrical power connection. Most newer CSST installations use the black CSST although some installers were still using the older yellow jacketed CSST as recently as 2010 in some places.
The photo above shows newer black sheathed CSST gas pipe. It is manufactured under various brand names, including CounterStrike® and Flashstrike®.
For more information about gas pipe bonding:
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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© 2019 Matthew Steger
Matthew Steger, owner/inspector of WIN Home Inspection, is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), and an electrical engineer. He can be reached at: 717-361-9467 or firstname.lastname@example.org.
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.