Bonding Corrugated Stainless Steel Tubing (CSST) Gas Pipe

Corrugated stainless steel tubing (CSST), is used to convey flammable gas inside or outside of a building. It is not mentioned in the 2011 NEC by name, but Informational Note No. 2 to 250.104(B) cites NFPA 54, the National Fuel Gas Code, as a source for additional information for gas piping systems. This document requires that CSST gas pipe to be bonded to the premises electrical grounding system. Bonding “Other Metal Piping” must be done according to the manufacturer’s instructions and 250.104(B).

Direct Electrical Bonding CSST Gas Pipe

Direct Electrical Bonding CSST Gas Pipe

CSST is typically yellow-clad and sold in 75 ft. coils with an inside diameter of ¾ inch. The tubing is a user-friendly alternative to the black steel pipe that often had to be cut and threaded in the field. While it is rugged, corrosion-resistant and generally trouble free, there have been instances of puncture due to lightning strikes. Lightning may damage the pipe by means of a direct strike or induced current.

Damaged CSST Gas Pipe

Damage to CSST Gas Pipe

Lightning Struck CSST Pipe

Lightning Struck CSST Pipe

Either way, bonding the CSST pipe to the premises grounding system, if it is done correctly, is a highly effective way to prevent damage to the gas tubing. As always, the NEC provides guidance. Here are some basic principles for bonding CSST:

• All grounding electrode systems are to be bonded together in accordance with Section 250.50.

• The bonding conductor is to be as short as possible to limit its impedance and exposure to physical damage.

• The bonding conductor is to have as few bends as possible. The bend resembles a part turn in a coil, increasing inductive reactance and raising the overall reactance of the bonding
conductor. An Informational Note in Section 250.4(A)(1) states: an important consideration for limiting the imposed voltage is the routing of bonding and grounding electrode
conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops
are avoided.

• The bonding conductor is to be a minimum of 6 AWG copper or 4 AWG aluminum or copper-clad aluminum. Where used outside, aluminum grounding electrode conductors are not to be
terminated within 18 inches of the earth. Section 250.64(A) and this basic principle should be applied to the installation of bonding conductors as well.

• Listed bonding clamps are to be used on the CSST. Section 250.8 has a list of permitted methods for the connection of grounding and bonding equipment. Some of these will not
accommodate the 6 AWG bonding conductor, so the best choice is to use listed pressure connectors. Avoid the connection of dissimilar metals which can lead to corrosion.

Post written by David Herres.

A special thanks to Mark Harris with CSST Saftey for the photo.

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Posted in Grounding and Bonding
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