weathervane grounding

[shortcircuit2]

A contractor that I work for is installing a metallic weathervane atop the cupola on the attached garage that we are wiring.

He wants me to run a ground wire to a ground rod for lightning protection.

I'm not sure of the proper way to do this?

Would a #4 bare ground wire to a ground rod be in violation of the NEC in any way?

I was thinking that it must be:

1) A certain size ground wire according to lightning protection rules?

2) Run at least 6 feet from any other wiring method?

3) Run outside of the building only?

4) And the ground rod must be bonded to the building grounding electrode system?

Any guidance would be appreciated...

shortcircuit2

[ October 21, 2005, 06:38 AM: Message edited by: shortcircuit2 ]

 

[bphgravity]

Re: weathervane grounding

You need to get yourself a copy of the NFPA 780.

#4 awg would be just fine

1. I believe only a #6 would be required by the NFPA 780 for this application.

2. yes

3. not required but would be suggested.

4. yes, see 250.106

 

[jwelectric]

Re: weathervane grounding

250.106 Lightning Protection Systems.
The lightning protection system ground terminals shall be bonded to the building or structure grounding electrode system.

This section requires that the electrodes for the Air Terminals is to be bonded to the building ground electrode system.
For information on how to install the lighting rods and the grounding electrode system see NFPA 780, Standard for the Installation of Lightning Protection Systems.

 

[pierre]

Re: weathervane grounding

Shortcircuit2
250.60, 250.106 are the NEC references.

From NFPA 780:
4.2 Masts, Spires, Flagpoles.
These slender structures shall require one strike termination device, down conductor, and ground terminal. Electrically continuous metal structures shall require only bonding to ground terminals.

For some more guidance:
3.9.9 Down Conductors.
Down conductors shall be as widely separated as practicable. Their location shall depend on such considerations as the following.
(1) Placement of strike termination devices
(2) Most direct coursing of conductors
(3) Earth conditions
(4) Security against displacement
(5) Location of large metallic bodies
(6) location of underground metallic piping systems

Remember to try and run your lightning protection conductors as straight as possible, as lightning does not like to travel around corners.

 

[shortcircuit2]

Re: weathervane grounding

Thankyou for the input guys...I need to get a copy of that NFPA 780

I wasn't going to use any strike termination device. Is this really necessary? I connected the #4 ground wire right to the weathervane with a copper pressure lug...

shortcircuit2

 

[bphgravity]

Re: weathervane grounding

The weathervane is the "strike termination device". It will act as a receptor of the lightning flash. The NFPA 780 calls these devices "air terminals". This device connects to the "main down conductor" which terminates at the "ground terminal" which is generally a ground rod.

 

[ron]

Re: weathervane grounding

If you are attempting to provide lightning protection per NFPA 780, an air terminal is required, unless the weather vane is 3/16" thick.
NFPA 780. If you don't want to provide lightning protection, then bonding the weather vane per the NEC wouldn't be required as it isn't likely to become energized.
NFPA 780
4.6.1.2 Metal parts of a structure that are exposed to direct lightning flashes and that have a metal thickness of 4.8 mm (3/16 in.) or greater shall require only connection to the lightning protection system.

4.6.1.3 Such connections shall provide a minimum of two paths to ground.