Grounding of a satellite dish mast

[gwz2]

Re: Grounding of a satellite dish mast

Pierre,

Good follow-up explanation.
Recently seen a plot with four duplex's ( with about 12 feet between each bldg, in a line along a street. The first and last duplex bldg's had the Electrical Service Entrance (SE) on the far ends of the bldg's and the center two duplex had the SE facing each other across the 12' space. The CATV and the Telephone POE's were on the opposite end of each bldg from the SE. Thus two instances of the CATV and the Telephone POE's were facing each other across the 12' space.
Originally the Telephone drove a 5' Ground Rod for the POE and the CATV which came later drove one Ground rod for each of the face-to-face POE's.
Neither the telephone nor the CATV grounding was acceptable. They, telephone and CATV, finally agreed to use a single ground rod for each of the first two bldg's POE's and install a buried 6 AWG around the rear of each duplex to the SE for the respective duplex.
Then on the second set of duplex's when the CATV came, the installer decided to just bond to the EMT for the Air Conditioner (A/C) which was a about a foot away from the CATV POE. That didn't meet NEC either. They finally meet the NEC 8xx.40 for all four duplex bldg's.

Kept hearing comments similar to " Never had to do that before.".

 

[hbiss]

Re: Grounding of a satellite dish mast

Of course the big question is how did anybody get the Cable Co. and the TELCO to do things right. Here in NY not only do the inspectors not even look for such things but if the grounding is improper (as it usually is) nobody can do anything about it anyway.

 

[gwz2]

Re: Grounding of a satellite dish mast

hbiss,

I am not sure of what happened behind the scene.

I am of the opinion that when the Building Commissioner was alerted that the NEC is for safety ( 90.1(A) and 90.1(B) and 90.5(A) ) and that 800.40 and 820.40 were not being complied-with on the first 4 units of several multifamily buildings, that Certificate Of Occupancy (COO) became a problem on the buildings still to be built.

Again, just an opinion.

The CATV and TELCO are services brougth to the building like the Electric Utility and the NEC requires the (their) equipment to be grounded to the established grounding system, which is usually the electrical grounding system.

I am not sure of "Dish" installations.
Isn't the Dish installation usually the property of the subscriber and then the service is a monthly bill?

If so, then isn't NEC 810.21 the direct responsibility of the property owner or subscriber?

 

[pierre]

Re: Grounding of a satellite dish mast

Jay
I am by no means a Lightning expert, but here is some of what I understand.
The buildup of dissimilar charges which allows lightning discharge can happen even on a grounded surface. An example is when lightning discharges directly to earth, earth is 'grounded', no?
The buildup of opposite charges can happen in many ways, and on all surfaces. That is why lightning will strike a plane, car, tree, side of a building, and people.

My understanding of a 'lightning system' on buildings is to provide a path for the destructive forces of lighning to travel in a relatively safe path to discharge to earth.

Pierre

 

[bennie]

Re: Grounding of a satellite dish mast

A lightning protection system is not capable of withstanding a direct strike. The protection is by attempting to equalize the electric charges, or at least to decrease the potential under the flashover point.

Old Ben and his kite experiment is an example of charge equalization.

 

[Guest]

Re: Grounding of a satellite dish mast

What practical function does this lightning rod serve?
Protecting the State House from Lightning:
The Franklin Lightning Rod


It claims to protect the statehouse from a direct lightning strike. What does it really do?

Also, all the trees at George Washington's Mount Vernon estate are protected by lightning rods. What is their actual function during a lightning strike? Each large heritage tree has a rod and heavy gauge braided copper cable terminating in a driven ground rod.

../Wayne C.

[ September 23, 2003, 12:18 PM: Message edited by: awwt ]

 

[bennie]

Re: Grounding of a satellite dish mast

Lightning protection is not exactly correct, lightning prevention is a more descriptive term.

The lightning rods are electron suckers. They pull the excess of electrons out of the surrounding atmosphere and dump them into the earth. This prevents a high static voltage from developing to a flashover stage.

Ben Franklin had a key attached to the wet kite string, this key allowed electrons to build up on the plates of the leyden jar, which is basically a capacitor. The leyden jar would flash over when charge reached the breakdown stage.

The lightning prevention is a shorting effect between the opposite charges.

Florida should investigate my invention of hanging a 4/0 copper from a large balloon

 

[jay80424]

Re: Grounding of a satellite dish mast

Lightning prevention was my understanding as well.

Sorry to get back to the grounding issue, lightning is much more intresting, but one of my questions wasn't answered.

There is a small solid bare copper wire comming out of the service disconnect, I can put a split bolt on that and use it as my ground?

And if I have 2 dishes up there on the roof, I can connect them together and use the single # 10 ground wire?

Thanks alot, you guys have been great. I went to the electrical supply today and bought some split bolts and #10 insulated copper.

 

[pierre]

Re: Grounding of a satellite dish mast

Jay

Yes to the last two questions you asked. I personally would try to connect the 10 AWG to the GEC outside the building if I could.

Pierre

 

[gwz2]

Re: Grounding of a satellite dish mast

That small solid copper wire out of the service disconnect maybe the one mentioned in 250.94(3) FPN No. 1.

If it is then, yes it is for such purposes as your Dish grounding. But you should be sure that the copper "pig-tail" is for that purpose.

For an excellent comment on 'the why's 'of grounding of CATV, Radio and TV, Communications, read the comment following 250.94 in the NFPA NEC Handbook starting on page 205.

 

[orrinc]

Re: Grounding of a satellite dish mast

I understand how to handle grounding/bonding of a satellite dish for a single-family or two-family home.

I am confused about what to do on a multi-story apartment building, with several roof-mounted satellite dishes (and possibly an off-air TV antenna) connected to a distribution system.

I believe that according to 810.21F1a, the shields of the coaxial downlead cables should be attached to the building electrical grounding system on the roof, via grounding blocks near the dish connections.

This would mean that any lightning discharge at the dish or antenna locations would run through the building to the electrical service entry grounding point, probably at the ground floor.

Is this correct, or is there a better way to ground the antennas?

If there is a mast or dish mounting bracket, should it be connected at the same point as the coaxial grounding blocks, or separately?

Finally, in such a multi-family (more than two)application, is the satellite distribution system grounding fall under 810 or 820? Does it matter? (we are not dealing with mobile homes, or one- or two-family homes, so the 20 foot rule apparently does not apply).


Thanks!

Orrin

 

[hbiss]

Re: Grounding of a satellite dish mast

I believe that according to 810.21F1a, the shields of the coaxial downlead cables should be attached to the building electrical grounding system on the roof, via grounding blocks near the dish connections.

No. 810.21(F)(1)(a) refers to the grounding conductor from the masts or dishes. The ground blocks need to be where the cables enter the building- 810.20(B).

This would mean that any lightning discharge at the dish or antenna locations would run through the building to the electrical service entry grounding point, probably at the ground floor. Is this correct, or is there a better way to ground the antennas?

Depends on the building type and construction, certainly building steel is an option. Though allowed, I would limit the length of grounding conductor run within the building. Opt first to run it on the outside if practical.

If there is a mast or dish mounting bracket, should it be connected at the same point as the coaxial grounding blocks, or separately?

I think I covered that above. The grounding conductor from the ground blocks does need to be bonded to the grounding conductor from the mast or dish and if done right they will be.

Finally, in such a multi-family (more than two)application, is the satellite distribution system grounding fall under 810 or 820? Does it matter?

I believe the antennas, masts and dishes would fall under 810 while the wiring from them and that on or within the building would fall under 820.

we are not dealing with... one or two-family homes, so the 20 foot rule apparently does not apply.

Maybe not but the laws of physics still do. If it is possible to do I would heed it.

-Hal

[ July 18, 2005, 08:39 PM: Message edited by: hbiss ]