I’ve been asked a lot of questions about bonding CSST. CSST is Correlated Stainless Steel Tubing, it is used for natural gas delivery through out residential houses. A normal natural gas system built out of rigid steel pipe does not require special bonding to ground. Bonding is usually achieved via the Equipment Grounding Conductor used to feed the furnace with power.
When installing CSST, most jurisdictions require you to bond the gas system. People generally call this “bonding the CSST”, but you are not actually bonding the CSST itself, you are bonding the gas system, and there is a very important difference.
People will often tell you to put your grounding clamp on the nipple right before the CSST. Now in new construction that makes sense, usually you would have a small nipple coming out of the gas meter and the CSST would connect to that nipple and continue throughout the house. So you would bond at that nipple because it is where the gas line enters the house. The problem is that CSST is often added later.
For example, as an Electrical Contractor I recently had to bond the gas system at a customer’s house because he had a piece of CSST added to his steel gas pipe system about 40 foot away from where the gas enters the house. He had a gas fireplace added to the living room of his house and the plumber tapped into the steel gas pipe near his water heater which was on the back side of his house, far away from where the gas pipe entered the house. The inspector required the gas system to be bonded since CSST was added, so I did it the proper way by installing a ground clamp on the gas system right where it entered the house, within 5 feet.
The plumber didn’t think that was the right way to do it, he felt I should have ran a grounding wire all the way through the house to the back where the CSST started. He felt the ground clamp should have been installed on the nipple right before the CSST, this is the way he has seen it done before. But that doesn’t accomplish the intended purpose of bonding the gas system. Bonding the gas system is required in this instance in case of high voltage surges, such as lightning. Let’s say that a lightning surge comes in through the gas system, and there is some type of metal near the gas pipe, for example, a BX electrical cable. That surge could arc from the gas pipe to that piece of metal cable. With a steel gas pipe, that arc isn’t going to do much damage. However, with CSST, that arc could easily melt a hole through the thin tubing, which can allow gas to escape and ignite.
The purpose of bonding a gas system when CSST is added is to essentially drain out electrical surges before they get deep into the house and into the CSST. And the best place to put that bond is where it first enters the house, limiting the exposure inside of the house. So even though the CSST may be 40 foot into the house, it’s still best (and required) to put the bond near the gas entrance.