Radio Antenna

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chris kennedy said:
810.21 I'm guessing you already read this and there is more to the question.:smile:
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No more intentionally I just posted while opening my book. I have an antenna portion to one of my projects and I want to verify its grounding.

I wonder if 820 plays a role because at a glance it looks like these may ground differently? I may need to ask the technician that?s supplying the antenna what type it is?
 
tryinghard said:
No more intentionally I just posted while opening my book. I have an antenna portion to one of my projects and I want to verify its grounding.

I wonder if 820 plays a role because at a glance it looks like these may ground differently? I may need to ask the technician that’s supplying the antenna what type it is?
Click to expand...

That's a good start. Because this question often comes up, it might be easier to think in these terms:

An "Antenna" is never grounded. It's metallic *base* and the mast (if provided) is bonded to an equipotential grounding system.

The coaxial feed to an antenna has an outer shield (braid or solid) that is in contact with any connectors used with the coax. "Shield grounding" is bonding that coax shield (or connector) to a ground system in as many places as practical, but always at the "top and bottom" of the system. Convenient shield-ground kits are sold at most electrical supply shops. Harger, Andrews, etc have good on-line catalogs for these. If you choose to use shield-ground kits (exposing the outer-braid of the coax v. just bonding the connectors) only use conductive (Cu/Ni etc) bonding grease. Silicon should be used as a dielectric when screwing threaded coax-connectors together. Do use "Coax-Seal" or equivalent rubberized self-sealing wrap to permanetly protect any outside connection.

Wire-only antennas that have no mast still have identical coax shield-grounding requirements as with all antenna systems, including satellite.

A coaxial surge protector (some call these arrestors) must be installed to protect the sensitive receiver-components of all radios with external antennas. Proper shield grounding of the coax *before" the protector is vital.

Even a near-by lightning strike will "charge" an antenna sufficiently to damage sensitive radio equipment. Snow can cause enough static build-up on large antennas to arc-across an open coax-connector.

Finally, NFPA 780 is a must-companion for antenna work.

Good luck,
Jack
 
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oceanaradio said:
That's a good start. Because this question often comes up, it might be easier to think in these terms:

An "Antenna" is never grounded. It's metallic *base* and the mast (if provided) is bonded to an equipotential grounding system...
Click to expand...

Jack,

I'm just grounding the mast, lightning reasons, wouldn't 810.21 apply?
 
Art 810 is the mast.
Art 820 is for the coax.
Both require a bonding jumper to a GEC, if there is a bulding GEC you want to create a single point ground. The 2008 has a requirement for a intersystem bonding termination. Typically the coax shield is terminated to a impulse protector close the entrance into the building, then you would transition to an interior rated coax.
The problem is the titles of art 810 and 820 are misleading, read the scopes to clarify
 
K8MHZ said:
Lot's to learn here:

www.polyphaser.com

NEC requirements in chapter 8 are the barest of minimums. Antennas may require 3 different grounds, RF ground, lightning protection and AC mains safety. Whatever is sought, the ground system of an antenna must be connected to the AC mains system.
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Thanks, the ground I'm talking about is to the existing electrode system and if I did install another electrode it would become a part of this ground system as well.

A technician will be responsible for the antenna furnish & installation, I?m just making sure it?s grounded to NEC.
 
tryinghard said:
Thanks, the ground I'm talking about is to the existing electrode system and if I did install another electrode it would become a part of this ground system as well.

A technician will be responsible for the antenna furnish & installation, I?m just making sure it?s grounded to NEC.
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You were wise to ask about the details. A radio-supplier could install the antenna, furnish his own ground rod (not seeing or asking about a bonded ground system) and technically be done with his work, improper as it is. Both cable and satellite t.v. installers are notorious for this behavor. Their defense is that if lightning attaches to their antenna, the ground rod they furnished would indeed divert most lightning energy safely to earth. What they fail to accept responsibility for, is their isolated ground system will be the cause of multiple system damage when lightning energy enters a structure through power company lines, and exits via sensitive equipment to the isolated ground rod the installer just added. Insurance payouts for lightning damage are into the billions each year, and we all pay for this in our premiums, mainly because of improper installations.

Jack
 
tryinghard said:
Jack,

I'm just grounding the mast, lightning reasons, wouldn't 810.21 apply?
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All you have to worry about is 810.21 and running the bonding conductor from the mast to the nearest GES or water pipe.
 
dereckbc said:
All you have to worry about is 810.21 and running the bonding conductor from the mast to the nearest GES or water pipe.
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I agree but only if the water pipe is an electrode.

Many places the water pipe is simply only a water pipe that is bonded as per 250.104 and not an electrode as per 250.52. :)
 
tryinghard said:
I agree but only if the water pipe is an electrode.

Many places the water pipe is simply only a water pipe that is bonded as per 250.104 and not an electrode as per 250.52. :)
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That is why you have to read, including the references. Since the GES is likely outside and the closest point kind of makes it a NO-BRAINER :grin:
 
dereckbc said:
That is why you have to read, including the references. Since the GES is likely outside and the closest point kind of makes it a NO-BRAINER :grin:
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If I read 810.21(F)(1)b along with 250.52(A)(1) I cannot connect to the water pipe unless it fully complies as an electrode, this is in light of ?as covered in 250.52.?
 
oceanaradio said:
A coaxial surge protector (some call these arrestors) must be installed to protect the sensitive receiver-components of all radios with external antennas.
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This may be a good idea, but is not required by Article 820.
 
Quote:
Originally Posted by oceanaradio
A coaxial surge protector (some call these arrestors) must be installed to protect the sensitive receiver-components of all radios with external antennas.

BarryO said:
This may be a good idea, but is not required by Article 820.
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810.20 Antenna Discharge Unit.
(A) Required. Each lead-in conductor from an outdoor antenna
must be provided with a listed antenna discharge unit.
(B) Location. The antenna discharge unit must be located outside
or inside the building, nearest the point of entrance, but not
near combustible material.
(C) Grounding. The antenna discharge unit must be grounded in
accordance with 810.21.

Now here is where industry standards, whether it be DoD, Motorola, M/A COM, etc, all leave no doubt as to the requirement that a surge-arresting device be installed here, and they don't mince words to leave a reader wondering what an "antenna discharge unit" is. Not to be confused with a grounding-block, usually referred to as a shield-ground, which are required in several locations depending on the height of the mast or tower, and the length of run between the tower and the entrance-point.

Where lightning protection is concerned, the NEC and NFPA 780 must be followed together, and industry goes a bit farther in the details and nomenclature.

Brgds,
Jack
 
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