CSST (Corrugated Stainless-Steel Tubing) bonding is a technique in which a conductor is electrically bonded to CSST metallic gas piping and then connected to a grounding electrode system to provide a low-impedance path to earth. . CSST bonding is used to reduce the probability and severity of arcing between conductive systems when energizing a lightning strike in or around a CSST gas pipe.
The CSST must be permanently connected to the grounding electrode system of the electrical service of the home in which the CSST is installed. This arrangement provides an electrically continuous path for stray voltage/current safely to ground.
CSST Bonding is Necessary:
When CSST is installed without proper bonding, there is an increased risk of fire or damage to gas lines in the event of a nearby lightning or lightning strike.
Note that lightning is a highly disruptive force and can travel along the CSST gas pipe when it approaches. This traveling energy can jump near the metal and dissipate its energy.
Now if the CSST is not being properly bonded, the difference in potential between the gas pipe and the metal can create an arc that can damage the CSST gas pipe. When the CSST is damaged, it may leak gas and cause a fire or explosion.
CSST bonding will help achieve an even condition between the CSST gas line and the bonded metallic conductor. Therefore, CSST bonding is essential to reduce the risk of fire or explosion resulting from damaged gas lines in the event of power surges and lightning strikes. The picture below shows the damage to CSST gas line due to lightning strike.
CSST Bonding Diagram:
For proper bonding of the CSST, a separate bonding wire is attached to the rigid gas piping before the CSST, or directly to one of the CSST nuts. The figure below shows the CSST bonding diagram.
CSST Bonding Code:
CSST bonding, bonding conductors, grounding electrode systems, bonding clamps, and grounding conductors must conform to code. Let’s discuss them one by one.
Direct bonding is provided for CSST gas piping systems for homes and buildings in accordance with the National Fuel Gas Code, International Fuel Gas Code, and Uniform Plumbing Code. Bonding of CSST should be considered as electrification work and should be installed and inspected by a qualified electrical contractor and electrical inspector.
The bonding conductor must be installed, protected, and connected to the grounding electrode system in accordance with the National Electrical Code, NFPA 70, and the Canadian Electrical Code, CSA-C22.1.
The bonding conductor may be a solid or stranded aluminum or copper conductor. The size of the bonding conductor shall not be smaller than 6 AWG (American wire gauge) copper wire or the equivalent size of aluminum if the bonding conductor is made of aluminum. The figure below shows an example of a bonding conductor.
According to the National Fuel Gas Code, the International Fuel Gas Code, and the Uniform Plumbing Code, the bonding conductor must not exceed 75 feet (22860 MM) in length.
Bonding clamps are never attached to corrugated stainless steel tubing. It can be attached anywhere within the gas piping system.
It is important to choose the location of the bonding clamp on the gas piping system so that the shortest length of the bonding wire improves the effectiveness of the direct bond. The image below shows an example of a bonding clamp.
Bonding clamps must be installed per UL467 and make metal-to-metal contact with a rigid pipe component or CSST fitting. Gas pipe surfaces must be clean, free of paint and coatings to allow proper metal-to-metal connection.
Grounding electrodes should be metal conductors and connected to earth. The following materials are commonly used as grounding electrodes.
- Structural Steel.
All electrodes must be connected together in a common grounding electrode system. Grounding electrode and grounding system for gas piping system cannot be installed separately. The figure below shows the grounding electrode connection.
Grounding Electrode System:
A grounding electrode system consisting of a grounding electrode and a grounding electrode conductor. Installation and inspection of grounding electrodes and grounding systems should be performed by a qualified electrical contractor and electrical inspector.