Grounding OTA Mast (Again)

[ckeays]

Hi Guys,

I realize this question has been asked a million times, but here goes:

My OTA antenna is mounted on a 5' mast, on a tripod at the peak of my roof.
(My roof is 30' from the ground)

I have a 3 year old 2 storey home with a very steep roof pitch.

I chose to run the coax cable neatly under the shingle cap (at the ridge of the roof).
The cable goes into the attic and down a conduit (central vac pipe) that the builder installed.
This conduit goes from the attic directly through both levels of my house then to the basement where the panel is located.

I did not want to run the cable down the hip and then beside the downspout or down the brick for many reasons mainly for appearance.

If I run the ground cable along the top of the roof to the closest point where I can bring it down, the ground cable length will be 40 to 50 feet long.

I was thinking of running the ground wire to the panel where the main ground block is located or from the panel back outside the house to a ground rod.

If I run the ground wire down the conduit (in the same path as the coax) the ground wire will be 80 - 90 feet long. Is this acceptable or should I just forget about grounding it?

I can post pictures of installation if requested.

Any suggestions?

 

[harshness]

If you're not going to do it right, don't bother. Note that grounding the mast is done primarily to bleed off static charge generated by wind blowing across the elements.

The one and only way to ground the mast is to run a wire to a bonding point (not just any old metal you can find).

 

[FaT Air]

The minimum that I would do is a 4 turn loop in the coax as soon as it enters the attic. Then a coax ground block at the service panel. Ground block tied into the electrical ground there. Then another 4 turn loop of coax as the coax leaves the ground block to the connected TVs and/or DVR, Make the loops about 4 to 6 inches across. The static charge from winds across the antenna will discharge through the coax shield to the ground block, to the electrical ground.
Trees taller than the antenna height sometimes provides a 'cone of protection' so if they are close enough that may minimize the chances of a strike. YMMV.
To really ground the mast and antenna I'd find the most direct path between it and the ground used by the electrical on the exterior of the home (sorry, but that's the 'universal 'code' AFAIK.
I would NOT run the ground wire through the house. The purpose is to keep a strike outside.
Make corners 'gentle' in the ground wire. No sharp 90 degree corners.

 

[ckeays]

The one and only way to ground the mast is to run a wire to a bonding point (not just any old metal you can find).

Yes but is 90 feet too much for the ground cable?
I am wondering if it is sufficient to just ground the coax through a grounding block to the grounding bolt on my meter base.

 

[ckeays]

The minimum that I would do is a 4 turn loop in the coax as soon as it enters the attic. Then a coax ground block at the service panel. Ground block tied into the electrical ground there. Then another 4 turn loop of coax as the coax leaves the ground block to the connected TVs and/or DVR, Make the loops about 4 to 6 inches across. The static charge from winds across the antenna will discharge through the coax shield to the ground block, to the electrical ground.

Thanks for your response. What about grounding to an outlet using a coax ground block?

To really ground the mast and antenna I'd find the most direct path between it and the ground used by the electrical on the exterior of the home (sorry, but that's the 'universal 'code' AFAIK.
I would NOT run the ground wire through the house. The purpose is to keep a strike outside.
Make corners 'gentle' in the ground wire. No sharp 90 degree corners.

I am afraid that is impossible if I want to make it look good.
My roof is very high, and the ridge (horizontal roof peak) is only about 6 feet long.
So in order to get to the perimeter, I would have to run the wire directly over top of the shingles for about 25- 30 feet.
I guess I have no choice.

I have a roll of 12 guage ground wire. Would this be ok if the length is 50 feet?

Thanks for the advice.

 

[FaT Air]

What about grounding to an outlet using a coax ground block?

If that's all you have available I'd use it.
Don't forget the loops. They''ll filter out most, if not all, induced pulses from near strikes.

I have a roll of 12 guage ground wire. Would this be ok if the length is 50 feet?

Don't see why not.

 

[fred555]

What about a lightning arrestor in addition to a grounded mast?
I use one of these:



http://www.solidsignal.com/pview.asp?p=859902&d=Wilson-Electronics-859902-0-3-GHz-Lightning-Protector-(859902)&sku=813986003237&q=lightning arrestor

 

[FaT Air]

Those are "N" connectors. RG8 usually. 50 ohm usually.
Think a normal TV ground block with a loop of coax on the TV side will be just as effective. That worked wonders on the 300 ft towers and their radios I maintained in the ND oil patch back in the 80's,
I do that here with the TV ant. and sat dishes. Haven't lost any equipment to lightning, but a tree within 50 ft of them took a direct hit a few years ago, and is no longer.

 

[fred555]

Those are "N" connectors. RG8 usually. 50 ohm usually.
Think a normal TV ground block with a loop of coax on the TV side will be just as effective. That worked wonders on the 300 ft towers and their radios I maintained in the ND oil patch back in the 80's,
I do that here with the TV ant. and sat dishes. Haven't lost any equipment to lightning, but a tree within 50 ft of them took a direct hit a few years ago, and is no longer.

Sorry I posted the wrong one. Good catch. This is the one I installed, I figured .2 db loss what the heck:

http://www.solidsignal.com/pview.as..._term=859992&gclid=CNih5Y_lsswCFRFahgodql0OZw

I did the loop too. I figured an insurance company could not argue a claim when there was a real honest to goodness arresetor in the line. The wife wanted no ambiguities as far as insurance goes.

EDIT: It looks like the arrestor is not really required by code for coax:

Antenna discharge unit
The NEC requires that each lead-in conductor from an outdoor antenna be provided with a
listed antenna discharge unit (ADU) unless the lead-in has a continuous shield that is properly grounded (figure 3) [par. 810.20(A)]. The term lead-in refers to any cable or conductor from the antenna system including coaxial cables, waveguides, rotator control cables, and powering conductors and cables for mast- or tower-mounted amplifiers and other outdoor electronics associated with the antenna system.

Thanks! I guess I will not worry about an expensive arrestor next time.

 

[FaT Air]

Not required, but is an optional 'extra'.

 

[harshness]

What about grounding to an outlet using a coax ground block?

Understand that a coax ground requires much the same bonding that a mast ground requires and both the mast and the cable are supposed to be grounded independently (10 gauge on mast and 17 gauge on coax). IIRC it used to be 17ga on the mast as that's what the carrier wire on coax was for.

An outlet is NOT a bonding point. The hard part is that all grounding must be done BEFORE cables or wires enter into the structure. Perhaps not obviously, this includes the ground wire itself (the ground wire can't come from inside).

The Mike Holt website has lots of pictures and what most consider to be authoritative interpretations of the NEC. There's also a couple of YouTube videos from Mike Holt that talk about the issues with nomenclature and now the NFPA has tinkered with the NEC. There's also the concept of an Antenna Discharge Unit brought up in one of the videos that is somehow different from a grounding block but is required on the coax itself.



Again, there is a big difference between protection from static electricity and lightning (though lightning may be "attracted" to static electricity).