[TowerTalk] Single Point Service Ground Question

Jim Lux jimlux at earthlink.net
Fri Jan 4 13:50:28 EST 2008



-----Original Message-----
>From: Jim Miller <jim at jtmiller.com>
>Sent: Jan 4, 2008 9:41 AM
>To: TowerTalk at contesting.com
>Subject: [TowerTalk] Single Point Service Ground Question
>
>Everything in my house is tied to the single point service entrance as it 
>enters the house.
>
>The ground rod is actually inside the house sticking out of the basement 
>slab directly under the breaker boxes. Cable (after some nagging), 
>telephone, ham antenna feed and of course the grounds for the two fuse boxes 
>all tie there.
>
>It occurred to me that I had never seen such a tie for my propane service 
>however. I just checked outside and the tank, which is 50ft away from the 
>service entrance, has no connection to this single point ground.
>
>The 1000 gallon tank is buried and the service line comes up at the back 
>corner of the house, enters a regulator which is mounted on the entrance 
>pipe which penetrates the foundation. From there it travels across the 
>basement to the furnace. Ground rise potential differences between the tank 
>and the service point ground must therefore transit the basement first on 
>the metallic flexible gas line, then via the furnace electrical circuit back 
>to the box.
>
>I think the National Electrical Code covers all the issues related to 
>grounding. Does it say anything about the grounding of the propane service?

The NEC has the following 250.104 (B) Other metal piping:
"Where installed in or attached to a building or structure, metal piping system(s), including gas piping that is likely to become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor...."

I think a bit revolves around the phrase "likely to become energized".  The "fine print note" also says that a special bonding jumper is not usually required, since the required bonding is achieved by the pipe being connected to the appliance, which is then grounded in the usual way.  We're talking about safety in the event of an internal or external short, here, not lightning potentials, also.

This is from the 2005 NEC.. earlier editions may be different (and might be the ones relevant in your jurisdiction

Jim, W6RMK


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