CSST Bonding and Lightning: What the Code Requires and What It Leaves Out

CSST bonding means connecting a home’s corrugated stainless steel tubing (CSST) gas piping to the electrical grounding electrode system with a dedicated copper jumper. Under the International Fuel Gas Code and the International Residential Code, yellow-jacketed CSST needs a jumper of at least 6 AWG copper, no longer than 75 feet, attached with a listed clamp to rigid pipe or a fitting downstream of the gas meter (ICC CodeNotes). The point is to cut the voltage difference that lets lightning arc through the tubing’s thin wall. Bonding lowers that risk. It doesn’t remove it, and that’s where a lightning protection system comes in.

This article covers the code rules, the difference between yellow and black CSST, what bonding can and can’t do, and how gas piping fits into a full lightning protection system.

Why lightning damages CSST

CSST is flexible gas tubing with a much thinner wall than black iron pipe. When lightning hits a house or the ground nearby, stray current looks for every path to earth. If the CSST becomes energized and sits close to other metal (water pipe, wiring, ductwork), an arc can jump between them and burn a hole in the tubing. Gas escapes and ignites. The International Association of Fire Chiefs describes exactly this sequence and notes that leaks tend to develop near bends and flexed points (IAFC).

The strike doesn’t have to hit the house. Guy Maxwell of the Lightning Safety Alliance told the Lightning Protection Institute that the CSST fires he had seen involved strikes near the structure (LPI).

How common is it? The IAFC estimates that about 5 million US homes were built with CSST since it came into wide use in the mid-1990s. A 2018 ICC code session presented NFPA figures for 2010 to 2014: about 4,300 lightning fires a year in one- and two-family homes, of which about 210 involved lightning and fuel gas (ICC session slides). That makes it uncommon, but when it happens the fire starts at a gas leak inside a wall or attic.

CSST bonding requirements at a glance

These are the rules in the 2021 IFGC and IRC as summarized by the International Code Council. Your jurisdiction may run an older edition or local amendments, so check with your local building department.

Item	Requirement	Code reference
Which CSST	Yellow (non-arc-resistant) CSST, and any system with even one yellow segment	IFGC 310.2 / IRC G2411.2
Bonding jumper	Not smaller than 6 AWG copper, or the aluminum equivalent	IFGC 310.2
Jumper length	75 feet or less; shorter works better	IFGC 310.2
Where the jumper lands	A grounding electrode, the grounding electrode conductor, or the service enclosure	IFGC 310.2
Clamp	Listed to UL 467, on rigid pipe, a malleable fitting, a manifold or a brass CSST fitting, never on the corrugated tubing	IFGC 310.2
Clamp location	Downstream of the meter (or the LP second-stage regulator), accessible, on clean bare metal	IFGC 310.2
Number of clamps	One for the whole system	IFGC 310.2
Additions	Adding any yellow CSST to an existing steel or copper system means the whole system gets bonded	IFGC 310.2
Separate gas ground rod	Not allowed; everything ties into one grounding electrode system	IFGC 310.2.3

Source for the table: ICC CodeNotes, 2021 IFGC/IRC.

This bonding is extra. It’s separate from the ordinary bonding that the electrical code already requires for gas piping that might become energized by a fault. The National Electrical Code covers that in Section 250.104(B), sized by the circuit feeding the gas appliance, which can be a much smaller wire (EC&M). The 2018 ICC session made the same point: a 12 AWG equipment grounding conductor sized for a branch circuit isn’t designed for lightning current, which is why the CSST rules call for a 6 AWG jumper.

Yellow CSST vs black (arc-resistant) CSST

Since the 2018 editions, the IFGC and IRC treat the two products differently. Black-jacketed CSST listed as arc-resistant under the ANSI LC-1 standard is marked “AR.” Its jacket either absorbs the arc energy or spreads it to ground, so the extra 6 AWG bond isn’t required. It still has to be bonded through an appliance’s equipment grounding conductor (ICC CodeNotes).

Two exceptions catch people out. If no appliance on the system has an equipment grounding conductor, or if any yellow segment is in the system, the black CSST gets bonded the same way as yellow. And jurisdictions still on the 2015 IFGC or earlier may require the extra bond on black CSST too.

	Yellow CSST	Black arc-resistant CSST
Jacket marking	Yellow	Black, marked “AR”
Dedicated 6 AWG bond (2018+ codes)	Required	Not required unless mixed with yellow or no grounded appliance
Older code editions (2015 and earlier)	Required	Often required, check locally

Does bonding stop lightning damage?

Bonding reduces the risk. The National Association of State Fire Marshals, as reported by EC&M, says direct bonding doesn’t completely eliminate the potential for damage but makes it less likely. Fire officials are less optimistic. The IAFC’s position is that the bonding rules introduced in 2009 have not significantly reduced fires involving CSST. Based on anecdotal reports from state and local fire officials, it says CSST in lightning-prone areas may make a house fire after a lightning event up to 10 times more likely (IAFC).

The IAFC pushes for a tougher lightning test for new CSST (the ICC-ES LC1027 criteria), plus disclosure at sale for homes in areas averaging more than 4 cloud-to-ground flashes per square kilometer a year.

Lightning Protection Institute director Bud VanSickle put the other half of the problem plainly in 2016: bonding and grounding the building’s internal systems is just one element of a complete lightning protection system (LPI). The jumper evens out voltage on the gas piping, but a direct strike still needs a planned path from the roof to the ground.

Where a lightning protection system fits

The pages that rank for CSST bonding come mostly from the plumbing, electrical and home inspection side, and they rarely mention lightning protection systems. The standards connect the two in several places.

NFPA 54, the National Fuel Gas Code, says that where a lightning protection system is installed, gas piping bonding follows NFPA 780 (Fire Engineering). The 2018 IFGC lets the CSST bond land on the electrical grounding electrode system or, where one is provided, the lightning protection grounding electrode system (ICC session slides).

NFPA 780, the lightning protection standard, calls for bonding all metallic systems, gas piping included, so they rise and fall in voltage together during a strike (Torbin, Indiana code supplement).

The 2007 class action settlement with four CSST makers listed installing a lightning protection system, or making bonding and grounding connections, as remedies for homes with pre-2006 CSST (LPI).

Metal flues are a common weak spot. The 2018 ICC session pointed to metal appliance vents that rise above the roofline and aren’t tied to the grounding system. Such a vent behaves like a lightning rod with no down conductor, sitting right on top of a gas appliance. A lightning protection designer puts an air terminal near that vent or bonds it into the system.

If you have yellow CSST and you’re on an exposed lot, the bonding jumper is the minimum. A full system gives the strike its own route from the roof to the ground, away from the gas appliances and their piping. Our article on grounding vs bonding explains how the two jobs differ.

Colorado, Texas and Oklahoma homeowners

The IAFC’s suggested disclosure line of 4 flashes per square kilometer a year matters locally. The National Weather Service office in Pueblo puts Colorado’s statewide average at 4.8 cloud-to-ground flashes per square kilometer (2009 to 2018), which is above that line before you even look at the Front Range foothills (NWS Pueblo). In Oklahoma, EC&M reported that the state adopted a home inspector rule based on the fire marshals’ CSST bonding campaign. Texas and Oklahoma homes built during the CSST boom deserve the same check.

A 10-minute CSST check

You can do most of this without tools. Leave anything electrical or gas-related to a licensed pro.

1. Find where the gas line enters the house and look for flexible tubing with a yellow or black jacket. Check the attic, basement or crawlspace near the furnace and water heater too.
2. If it’s black, look for the “AR” marking.
3. Look for a clamp on rigid pipe or a fitting with a bare or green copper wire running to the electrical panel, the grounding electrode conductor or a ground rod.
4. Make sure the clamp isn’t on the corrugated tubing itself.
5. Note any metal vents or chimneys above the roof and how close the CSST runs to water lines, ducts or wiring.
6. If the bond is missing, call a licensed electrician or the plumber who services your gas system. Who’s allowed to do the work varies by jurisdiction (EC&M).

After a nearby strike, check for a gas smell around the appliances and in the attic or basement. If you smell it, get out and call the gas utility from outside. Our guide to signs your house was struck by lightning lists other things to check.

Talk to Site Safe Lightning Protection

Site Safe Lightning Protection installs lightning protection systems for homes and inspects existing ones. Colorado, Texas and Oklahoma are the areas listed on our site. If your house has CSST and sits on an exposed lot, contact Site Safe Lightning Protection to talk it through, or start with our residential lightning protection services.