Flexible coated gas piping (CSST)? is being used in homes. It is spiral steel tubing with a Nonmetallic jacket. Usually yellow. 250.104 NEC requires piping that may become energized to be bonded. A gas appliance with a 20 amp circuit gets bonded with the ground wire in the circuit (250.66).
The flexible gas piping is failing in some areas due to lightning. The pipe manufacturer requires it to be bonded with the same size GEC as used for the service (250.122 NEC) The bond must also be on the Black iron pipe part of the system or at one of the connectors for the tubing. Never on the tubing.
It seems like the installers & makers of the flexible gas pipe are shifting the responsibility for their product onto the electrician to protect it against lightning, something the electrical code isn't designed to do.
What do you think about this ?
Alan--

I can see it now- a 3/0 bonding conductor fastened to a 1/2 inch gas line :-)

What do you think about this ?
Alan--

Alan, it seems to me that this type gas piping needs to be outlawed. I never did like it. Just because you increase the EGC size at the iron pipe joint doesn't eliminate ground current on the flex pipe. Next thing you know we'll have to run a green bonding jumper along the length of flex-pipe.

We have had this question in CT, as well. It has been fueled by a very confusing letter from the manufacturer to every town's building department.

Our official response has been to ignore it. All gas appliances are bonded by the EGC, and thereby the flexible gas pipe as well. Isolated portions of this gas piping are not likely to be energized, and therefore do not require bonding [250.104(B)].
The NEC does not allow the gas piping to be used as a grounding electrode, so where it comes out of the earth is never bonded anyway [250.52(B)(1)], and the gas code requires an insulating fitting where it comes out of the ground.

What I do not understand is how this pipe is "failing due to lighting". A lightning strike is seeking an earth ground. If the service conductors are bonded properly at the service, then there is no way the lightning could make it into the house along the branch circuit conductors, through the appliance, ignore the equipment grounding connection, and follow the gas pipe back through an insulating fitting at the gas meter. Electricity takes every path presented to it, but in this case there is not a path presented through the gas pipe.

My guess is this piping is so thin it is actually failing due to contaminants in the gas delivered, not lightning strikes.

Folks, this piping is indeed failing due to lightning sideflash within structures. The flash may be between piping or wiring to this tubing and arcs a small hole through it resulting in a gas leak. The 'good' leaks (if you will) are ignited by the arc and call attention to themselves. A 'BAD' leak does not ignite and I have heard reports of subsequent explosions. It is a real problem. I am not sure that the recommended bonding will solve the problem however as I have seen cases where it was solidly bonded and still failed as described above. Earlydean, I was at two of these in CT last summer.

Please tell me how this is consistent with electrical theory.

Where is the complete path the lightning would take?

If bonding is done per code, it is beyond my understanding how it could be caused by lightning.

(And how is it these did not make the newspapers here in CT? or did I just not notice? Do you recall the dates and the towns?)

Please enlighten me.

Here's an articl from the Charleston Regional Business Journal. http://www.charlestonbusiness.com/pub/13_1/news/8415-1.html
Interesting reading.

Also found a class action suit.http://www.pddocs.com/csst/faq.aspx#Q23

While Googling around I read that the lawsuit has been settled and the gas pipe manufacturers are allowing X amount of $$ to bond your gas service and install lightning protection. If you live in a place of high incidence of lightning you get more $ to do your electrical work.

Has anyone done any of this work yet? What size bond are we talking about? I read on one plumbers site that a #6 copper was needed. It also said that an electrical permit was needed when this type piping was to be installed as new work or remodel. I'm just a little concerned that ground fault current or accidental neutral current might flow on the gas service pipe and cause fire or even explosion.
[This message has been edited by yanici (edited 02-04-2007).]

[This message has been edited by yanici (edited 02-05-2007).]

[This message has been edited by yanici (edited 02-05-2007).]

I don't understand.

If you bond the CSST, does it not become a better ground path for the lightning, thereby increasing the likelihood of this sort of lightning-induced punctures?

Here is a little history from Canada re bonding of Gas pipes. It was considered acceptable to allow the branch circuit bonding (EG) conductor to do the job. For example the gas furnace fan motor is a #14 with a #14 bond. Now enter a lightning strike and the bond conductor burns off and the voltage is high enough to damage the motor insulation causing leakage to ground. Since the bonding conductor is now burned off the O/C device does not trip and someone steps on a heat register and a grounded surface and gets shocked or worse. This did not just happen once, but enough to cause a change which requires a minimum #6 bonding conductor to the gas pipe.
So a little about lightning. Lightning follows the path of least impedance not lowest resistance. This is not necessarily along the copper ground wire but can jump from a lightning rod to a heat duct to a water line and into the building steel. the energy from a lightning strike has to dissipate and can travel horizontaly over a wide area around the ground strike. It can just as easily follow a gas pipe into the house and cause havok to the interior wiring. In my jurisdiction the gas piping is plastic in the ground and the meter has an isolated section too.

I got a telephone call from the electrical inspector involved with both of those CT lightning strikes. They did not make the papers, but they were very real, he says. The bonding was done per code, and the damage was definately due to lightning. He described the arc burns on the building. Wow!!
I believe him, as he is a respectable inspector and was a local electrical contractor for years. He delivers seminars in CT on electrical code. Very knowledgable.

I wonder how bonding the connections to the black iron is going to solve this problem???

Here is something else to read. The manufacture now requires a # 6 bond on all new installations.
http://www.gastite.com/include/languages/english/downloads/pdfs/TB2007_01.pdf

Any inspectors (electrical or plumbing) out there. Is this going to be enforced? Who has jurisdiction?

[This message has been edited by yanici (edited 02-07-2007).]

I wouldn't expect bonding done to NEC standards to prevent the high voltage arcing situation on the flex pipe. I'm not seeing exactly how the lightning is coupled to the stove (the vent hood, proximity of stove to lightning bolt, CCC's running over the roof???), but dissipating a high frequency transient with a length of 12 or 14 AWG is hopeless. Even 10 AWG is no good.

Here is a concrete example based on a quick lab test I just did (can't spend too much time on the extracurriculars, but I wanted to post with some hard data). I set up a transient generator for transient with a 2 uS rise and a 10 uS fall to half-crest with an open circuit voltage of 2.5KV and a short circuit current of 500 amps. This may sound like a hefty surge, but it is actually a surge that can be carried, without opening, by a typical 1.25A slo-blo fuse. I discharged this transient into a 12 foot length of 10 AWG wire. I have set up a transient waveform monitor (essentially a high voltage scope probe) to measure the voltage at a point half way along this wire to ground. What I find is about a 800 V bump lasting appr 3 uS at the point 6 ft away from ground (earth and generator return). When I increase the generator current to 2000 amps of potential short circuit current, this bump grows to about 1200 volts and stretches to about 12 uS total. (scope JPGs avail upon request)

This 2000 amp surge is what is coupled to ground from a single 4-wire telecom circuit (clamped to earth) that is expected to survive during GR-1089/NEBS testing. This explains why telecomm equipment manufacturers say to ground equipment using a 6 AWG. Ignore this at your customer's peril (had to throw that in since I know there are some who think the instructions to ground telco stuff with #6 is a bunch of hogwash. It isn't.)

But to the point of the flex pipe... Given the relatively low magnitude of my test, it is easy to see how a really big surge trying to discharge to ground through a much longer run of 14 AWG would develop an even larger potential at the flex pipe. The potential could be, and apparently is, great enough to puncture the jacket and then discharge to plumbing, other conduit, or other grounded objects that are not already carrying the transient current and are therefor still at the true ground potential (as they are not involved in any ground potential rise caused by high freq current through inductive wiring)

My 2 cents.

Holy crap, Batman! That's some pretty impressive testing you did to say the least.

I do know of a case where a customer's only gas appliance was a manufactured fireplace which used a metallic stack for a flue. This was the home's only metallic roof penetration and it appears that it was struck by lightning. There was not a hole in the CSST, but there were four spots in the 40 foot pipe run to the propane tank indicating areas for concern. The customer removed the gas option for the fireplace and went back to using wood.

You know............This could be a good thing for electricians when you think about it. Make gas distribution indoors illegal which would mean that the electricians get MUCH more business. I like the idea myself even though it's a "pipe" dream.