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I'm installing a new antenna mast to hold one or more antennas. The new mast will be strapped on to a chimney near the center of my house. Coax will run down the mast, across the roof, down the side, and enter the house within inches of ground level.

A collection of several ground rods spaced several feet apart (and tied together) is already installed near where the coax enters the house, with one rod being less than a foot from the entry point. The coax will run through a lightning arrester (specifically https://www.dxengineering.com/parts/DMN-SP3000W) at the ground rods.

Since the mast itself will have no ground connection (except what a brick chimney provides), the coax should be the most likely path to ground. Is the lightning arrester sufficient for lightning/static discharge, or should I run a separate grounding wire from the mast down to the ground?

If it's relevant, station ground will come to a single point in the shack and then be a thick copper cable wire back out to the same ground rod system.

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You should definitely ground the antenna to your earth system with a heavy conductor. The coax alone will not cope well with the lightning current. By carrying a share of the current, the earth wire also reduce the voltage transferred to the coaxial cable inner conductor, and hence the load on the lightning protection device.

Better would be a metal cable tray, continuously bonded, carrying the coax and earth cable, and connected to the antenna and earth system.

Grounding your shack at a single point sounds good. The lightning protection device is great.

Note that the LPD does only two things - it provides a solid ground point for the coax shield, and it prevents large differential voltage in the coax. It doesn't scare away lightning, and only makes a difference if it's part of a well designed grounding system.

Remember that all cables entering the shack must be protected - coax you have taken care of, what about power? It should also go through a lightning arrestor at the single earth point. Otherwise a strike on a nearby utility pole could lift the mains up by a few thousand volts, which will travel through your shack to get to your nice earth.

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One definitive answer comes from the National Electric Code Section 810, which requires that both the coax and the mast itself be grounded. However, in my experience, the vast majority of people do not bother.

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