Continuous

[iwire]

What should the electrician do?

Follow the NEC and stop thinking a connection to dirt is going to control Mother Nature.

 

[don_resqcapt19]

...
A case study. A service panel was grounded to the grounding rod right below it, and a cold water pipe 10 ft away from the grounding rod. A gas pipe is 3.5 ft away from the grounding rod was bonded to the rod. Lightning current might find the gas pipe having smaller impedance path, and fried it. What should the electrician do?

So how would you prevent that?

 

[Brian Dang]

I don't know really, but I will research more about the codes. I would try to create a much lower impedance to the dedicated grounding electrode/water pipe as compare to the gas pipe:
1) larger conductor to grounding electrode
2) smaller conductor that permitted, and longer length with some turns (more inductance). This will ensure a higher impedance.

 

[iwire]

I don't know really, but I will research more about the codes. I would try to create a much lower impedance to the dedicated grounding electrode/water pipe as compare to the gas pipe:
1) larger conductor to grounding electrode
2) smaller conductor that permitted, and longer length with some turns (more inductance). This will ensure a higher impedance.

And yet unless you teach electrons to only go where you want them you will still have current flow on the gas line.

Although people love to say 'electricity follows the path of least resistance' that is misleading as electricity also follows the paths of higher resistance.

 

[Brian Dang]

And yet unless you teach electrons to only go where you want them you will still have current flow on the gas line.

Although people love to say 'electricity follows the path of least resistance' that is misleading as electricity also follows the paths of higher resistance.

Current does flow to the higher impedance path but it's smaller i = v/R, and hopefully smaller current won't blow the gas pipe up.

 

[Brian Dang]

What prevents the code to say something like “bonding the gas pipe to EGC” instead of “bonding the gas pipe to grounding electrode”?

I would think grounding the water heater gas pipe to the tank’s cold water pipe is better (far distance from the GEC), since it has much less chance for lighting current dumps on it.

 

[roger]

What prevents the code to say something like “bonding the gas pipe to EGC” instead of “bonding the gas pipe to grounding electrode”?

The code says exactly that, read the next to the last sentence of 250.104(B)

Roger

 

[iwire]

Current does flow to the higher impedance path but it's smaller i = v/R, and hopefully smaller current won't blow the gas pipe up.

I think if you run some realistic numbers you will find little change as both paths are already relatively low resistance.

 

[Brian Dang]

The code says exactly that, read the next to the last sentence of 250.104(B)

Roger

All I see in this article is bonding to a grounding electrode:
http://ecmweb.com/code-basics/gas-pipe-grounding-legal
“Metal gas piping: NEC Sec. 250-104(b) and NFPA 54 [Sec. 3.14(a)]. Sec. 250-104(b) of the NEC and NFPA 54, Sec. 3.14(a) requires you to bond the aboveground portion of a metal gas piping system to a grounding electrode system for safety reasons. NFPA 54, Sec. 3.15 does not allow you to use aboveground portions of a metal gas piping system or its components as a conductor in electrical circuits.”

I don't have NEC book.

 

[Brian Dang]

I think if you run some realistic numbers you will find little change as both paths are already relatively low resistance.

It's hard to simulate, calculate or measure the impedance at lightning current frequency, but we know a perfectly straight conductor at some length will behave more like an inductor at very high frequency current.

The impedance at lightning frequency of the same metal piece will be many times higher than its measured resistance.

 

[don_resqcapt19]

Current does flow to the higher impedance path but it's smaller i = v/R, and hopefully smaller current won't blow the gas pipe up.

Other than with CSST, can you cite incidents where that has happened?

 

[don_resqcapt19]

All I see in this article is bonding to a grounding electrode:
http://ecmweb.com/code-basics/gas-pipe-grounding-legal
“Metal gas piping: NEC Sec. 250-104(b) and NFPA 54 [Sec. 3.14(a)]. Sec. 250-104(b) of the NEC and NFPA 54, Sec. 3.14(a) requires you to bond the aboveground portion of a metal gas piping system to a grounding electrode system for safety reasons. NFPA 54, Sec. 3.15 does not allow you to use aboveground portions of a metal gas piping system or its components as a conductor in electrical circuits.”

I don't have NEC book.

So you are telling us about the code and you don't have a code book?

250.104(B) Other Metal Piping. If installed in, or attached to, a building or structure, a metal piping system(s), including gas piping,
that is likely to become energized shall be bonded to any of the following:
(1) Equipment grounding conductor for the circuit that is likely to energize the piping system
(2) Service equipment enclosure
(3) Grounded conductor at the service
(4) Grounding electrode conductor, if of sufficient size
(5) One or more grounding electrodes used
The bonding conductor(s) or jumper(s) shall be sized in accordance with 250.122, using the rating of the circuit that is likely to energize the piping system(s). The points of attachment of the bonding jumper(s) shall be accessible.

Note this is all the NEC requires for gas pipe bonding, no matter what material is used for the gas pipe. The fuel gas code requires more extensive bonding for CSST gas piping.

 

[iwire]

It's hard to simulate, calculate or measure the impedance at lightning current frequency, but we know a perfectly straight conductor at some length will behave more like an inductor at very high frequency current.

The impedance at lightning frequency of the same metal piece will be many times higher than its measured resistance.

Regardless of the source if two paths have relatively low resistance to start with you will not significantly change the current flow by making one path lower resistance if that is even possible.

 

[GoldDigger]

Regardless of the source if two paths have relatively low resistance to start with you will not significantly change the current flow by making one path lower resistance if that is even possible.

No, but you can increase the impedance of one path significantly by deliberately making it longer and with more sharp bends or even loops.

 

[Brian Dang]

So you are telling us about the code and you don't have a code book?


Note this is all the NEC requires for gas pipe bonding, no matter what material is used for the gas pipe. The fuel gas code requires more extensive bonding for CSST gas piping.

Thank you, Don, for the code. This article had omitted the important part -- the choices for a proper bonding the gas piping. Bonding to a grounding electrode is not always a solution.
http://ecmweb.com/code-basics/gas-pipe-grounding-legal

 

[roger]

Brian, as Don points out, you really need to have a current code book to reference when things are pointed out to you. The ECM article you posted is 16 years old.

Roger

 

[don_resqcapt19]

No, but you can increase the impedance of one path significantly by deliberately making it longer and with more sharp bends or even loops.

That is fine, but the type of gas piping more prone to lighting damage, CSST piping, has requirements that result in a lower impedance than what you would have with the traditional gas piping. The use of the EGC is not permitted and a connection using #6 is required.

I doubt, that other than a direct hit, you will find cases showing damage to the traditional iron gas piping from lightning, and there is really nothing you can do about a direct hit. You might be able to prevent a direct hit by the use of a lightning protection system, but short of that, there is not much you can do to prevent damage from a direct hit.

 

[iwire]

No, but you can increase the impedance of one path significantly by deliberately making it longer and with more sharp bends or even loops.

Could we?

Does the NEC allow intentionally increasing the impedance of a bonding circuit?

Is intentionally increasing the impedance of a bonding circuit actually increasing safety or reducing it?

 

[jumper]

Does the NEC allow intentionally increasing the impedance of a bonding circuit?

Interesting question,

While I would have to search further to find a section specifically forbidding such, I would say sections like the following to mean that it is something that would be frowned upon and discouraged IMO.

Electrical equipment and wiring and other electrically conductive ma-
terial likely to become energized shall be installed in a
manner that creates a low-impedance circuit facilitating the
operation of the overcurrent device

primary protector bonding conductor or
grounding electrode conductor shall be as short as practi-
cable. In one- and two-family dwellings, the primary pro-
tector bonding conductor or grounding electrode conductor
shall be as short as practicable, not to exceed 6.0 m (20 ft)
in length.

 

[Brian Dang]

Could we?

Does the NEC allow intentionally increasing the impedance of a bonding circuit?

Is intentionally increasing the impedance of a bonding circuit actually increasing safety or reducing it?

Bonding the gas piping to the grounded water pipe near the interior water heater tank gives a higher impedance to earth ground, as compare to bonding it to the service entrance ground. A good installer should do this way for better lightning protection.