Is your metal chimney grounded ?

[Whitespider]

And, philoshop, your concerns were well founded.
Improper, DIY grounding solutions will in fact likely “create a potentially hazardous condition” and likely increase the resulting damage from a lightning strike or some sort of electrical fault.
If you’re lucky, they may simply be wholly ineffective… if you’re lucky.

 

[CWME]

I have nothing productive to add to the conversation other than to say this is a very interesting thread.

 

[bayard]

doing it wrong

you might be on to something, about grounding it wrong. lightning has hit around my house many times.i mean very close.trees 20 feet away the backyard etc.now my metal boiler pipe is the highest point on the roof .we have never had a house strike? so maybe leave it be.k

 

[Deprime]

Just to clarify, my previous post was just in relation to protection for the structure (i.e. house) from direct strikes. Some of the other grounding that has been discussed provides for dissipation of induced currents. For safety sake, I wanted to make sure that no one was running ground wires through the structure of their home for the sole purpose of direct strike lightning protection. The idea of that is to keep the energy created from a direct strike outside of the structure so as to prevent your house from catching on fire. Consequently, this also provides for dissipation of induced voltages as well.

Deprime,
The reason for the separate ground rod and then bonding it to the service ground is to reduce the “resistance to ground”… that’s also the reason for it to be some distance from the service ground, to increase the dissipation area. The National Electrical Code specifies “not more than 25 ohms of resistance” to earth ground… which is too high for most sensitive radio equipment antenna connections, but more than sufficient for a chimney. It wouldn’t hurt anything to install an additional ground rod for a chimney… but as you state, it must be bonded to the service ground.

You are correct in that a lower resistance to ground is required for protection of sensitive electronics. Most HF setups utilize ground radials to decrease this resistance. My current setup is VHF/UHF and I have not provided a high level of protection for the equipment. My setup is just for the protection of the structure in the event of a strike since I have a 14ft metal pole sticking up on the top of my roof.

Side Note: I know someone who has received a good jolt after coming into contact with two separate grounding circuits (connected to two separate ground rods) that were not bonded to each other. This was due to the difference in electrical potential between the two circuits. Make sure everything is bonded to each other in any grounding circuits as Whitespider has stated!

 

[Whitespider]

Side Note: I know someone who has received a good jolt after coming into contact with two separate grounding circuits (connected to two separate ground rods) that were not bonded to each other.

LOL
That ain't the first time that's happened... and a perfect illustration of what can happen when improper, DIY grounding solutions are used. Your friend (I'm assuming friend) is lucky it was just a jolt, it could have been much worse. Another common one is using the water pipes as a ground for something such as the phone line... and then they get a cordless system that requires the base to be plugged into a 120v outlet... and then every time the phone rings and their hand is on a water faucet they receive a discomforting tickle... LOL

 

[Whitespider]

...now my metal boiler pipe is the highest point on the roof...

Are we talking a wood boiler, or some other "in-building" boiler??

Lightning protection for in-building boilers and boiler stacks may be... well... tricky when it comes to lightning protection. Typically a boiler has some sort of sensitive electronics critical to operation... and a malfunctioning boiler can be darn dangerous, not only to you and your home, but the whole neighborhood. I won't even pretend that I know what is correct, but I have seen lightning protection on boilers and boiler stacks. I suspect that basic grounding wouldn't be enough (and may even be dangerous??), more likely a protection system employing surge/lightning suppressors/arresters would be appropriate... but, again, I do not know. If you did decide to do something I would, in this case, definitely recommend you consult an electrician, maybe even the boiler/boiler electronics manufacturer, and possibly check local code and your insurance company. You may even find out that surge/lightning protection was installed with the boiler, or included in its design and installation.

You are correct in that a lower resistance to ground is required for protection of sensitive electronics. ... My setup is just for the protection of the structure in the event of a strike since I have a 14ft metal pole sticking up on the top of my roof.

Even so, you did lower resistance to earth ground with the additional ground point (rod). You can look at each ground point as a separate resistor (as long as they are enough distance apart), and whenever you have two or more resistors in parallel (bonding them together makes them parallel) total resistance will be something less than the value of the lowest single resistor. The formula for that looks like this...
r = 1/[(1/r1)+(1/r2)]
So, for example, if your service ground was 20 ohms, and your additional ground rod has, say 40 ohms resistance...

• r = 1/[(1/20)+(1/40)]
• r = 1/(.05+.025)
• r = 1/.075
• r = 13.33 ohms of earth ground resistance

Of course we have no idea what the resistance is at your additional ground point, it may be 500 ohms (likely much, much lower), making the total 19.23 ohms... which would hardly be worth the effort.

 

[bayard]

old wood boiler, northland

i have an old wood oil boiler .been there since 1974,no fancy elec. stuff.just a water stat valve.k

 

[steved]

I'm just going to put this little tidbit out there...grounding does not mean you won't get hit.

Further, my folks' chimney was hit back in the late 80s; blew the top three feet right off the chimney. Luckily it didn't get into the house electric service (must have just traveled down the chimney to the basement and ultimately "ground"). You want to know the interesting part of that strike? That was a masonry chimney with a clay tile liner. Not a single piece of "metal" in the entire thing down to the point the stove was hooked in. And the electric pole in the front yard is at least 20 feet higher, complete with a transformer. The insurance paid to have the top rebuilt, and a stainless liner installed...they have not been hit since.

Lightning is unpredictable, and grounding helps; it but does not guarantee a strike won't hit.