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Grounding 101

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Old 03-30-2015, 04:57 PM   #1  
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Default Grounding 101

I'm starting this thread hoping smart people jump in. Lately, I have seen a lot of antennas mounted on rooftop tripods. Generally, a bundle of wires runs down the mast, across the roof, then down the side of the house. Is this ok?

My understanding was that the grounding wire should be as straight as possible to provide an easy path from antenna to ground. What happens when the wire bends at the edge of the roof?

I have never seen a lightning strike up close. Would it damage the shingles and other wires (coax) if bundled and laid across the roof?
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Old 03-31-2015, 06:48 AM   #2  
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Grounding an antenna does not protect it from lightning. It only helps bleed off any static and keeps spikes and surges out of your television.

Bleeding off that static does help with lightning, but it is not a lightning arrestor.
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Old 03-31-2015, 10:28 AM   #3  
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The main purpose to ground an outdoor TV antenna is to protect those inside the building from any possibility of a lightning strike from getting inside.

Proper grounding of any outdoor antenna structure is a must, it is a very important safety issue, one it helps protect from a stray spike from getting to those inside, and two it helps the antennas performance.

Just grounding the coax shield with a ground block will not keep the lightning from traveling down the center conductor, only an in-line gas discharge device will do this.

If in a lightning prone area then proper lightning rods should be used, these must be installed by a pro.

Lightning will take the path of least resistance to the ground, the 12 gauge or 10 gauge copper ground wire will help, but if the strike is a big one it will vaporize the ground wire along with anything else attached to it, but the best protection is a direct heavy gauge copper wire to an earth ground rod.

I have been inside a radio control room during a massive hit on the radio tower, the tower was a 100 foot aluminum structure, after our eyes recovered to where we could see again, what remained of the tower was a mass of melted aluminum and copper with stray bits of steel sticking out.

The new tower was rebuilt using steel.

After a direct hit on a TV antenna all that may survive is the steel mast and some parts of the coax and ground system, the ground wire should be supported off the roof if the roof is of a wooden construction, how you do this is up to you.

But the ground blocks and gas discharge device need to be located somewhere before the coax goes inside the building.

You also should follow any local electrical codes for proper grounding however ridiculous and archaic they may be.

Remember, lightning will go where it wants to, will hit anything it wants to and when it wants to, ground systems try and keep it away from you.
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Old 06-17-2015, 07:33 PM   #4  
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Default Leakage Current Hazard

Grounding is a very controversial topic, with many conflicting opinions, and a lot of people put up an antenna without following NEC guidelines.

If you want to go by the NEC rules, the guy who has the final say is the local electrical inspector, who the NEC calls the AHJ, Authority Having Jurisdiction. Some AHJs are more friendly than others. A local electrician would know about the inspector in your area.

Article 90.4

Quote:
The enforcement of the NEC is the responsibility of the authority having jurisdiction (AHJ), who is responsible for interpreting requirements, approving equipment and materials, waiving Code requirements, and ensuring equipment is installed in accordance with listing instructions.
The NEC requires that the mast and the coax shield of an outdoor antenna be grounded by separate connections to the house electrical system ground. It does not require that an attic antenna be grounded.

The NEC requirements are certainly valid, but from personal experience you should at least ground the coax with a grounding block (for attic and outdoor antennas) for your own personal safety because all AC operated equipment has leakage current, even when it is operating properly. Just because you can't feel it, doesn't mean it isn't there.

A 2-wire polarized plug power cord does not ground the equipment, it only ensures that the neutral of the equipment is connected to the neutral of the power system and the hot wire is connected to the switch.

Another reason for grounding the coax is to reject interference.

I have made many tests of equipment leakage current using my Simpson 229 Leakage Current Tester. I bought it because I had three close calls with electrical shock and I thought the expense of the tester was well worth it.



When I was calibrating the signal strength scale of an Apex DT502 to send to a friend, I had many pieces of equipment connected to AC:
2 Apex DT502s
2 Audiovox PLV16081 8" TVs used as monitors for the CECBs
1 Sony KDL22L5000 TV
1 CM 0747 preamp power supply/inserter for original 7777
1 AC adapter for Sadelco signal level meter
1 AC adapter for RS preamp

During the tests I noticed a problem that I have seen before but couldn't track down until recently. When I touched a ground and the case of the equipment I felt a mild shock. My Fluke 25 DMM gave a reading of 58VAC. I hooked up my Simpson 229 Leakage Current Tester and found that the voltage reading was 40 volts and the leakage current was about 200 microamps; not enough to be dangerous but enough to give a tingle. (The difference in the voltage readings is because the input impedance of the two meters is not the same.) The reading of about 200 microamperes that you see in the above photo is the actual leakage current that I felt when I was shocked. It was not strong enough to be lethal, but it certainly got my attention. GFCIs are designed to trip at 5 mA, which is 25x as strong.

I then started unpluging each piece of equipment and noticed that the leakage current went down each time. The boxes have 2-wire cords so I grounded the coax shields at the splitter and the leakage current went to zero. With so many pieces of equipment connected to AC the normal equipment leakage currents were additive.

Most of the pieces of equipment use switchmode power supplies, which have more normal leakage current than the transformer power supplies for the signal level meter and RS preamp.

Even a good quality energized 3-wire extension cord will have some normal leakage current from the hot conductor to the ground and neutral conductors without any equipment being connected to it.

Since I was able to feel a leakage current of about 200 microamperes, my threshold of perception is considerably less than the mean value of 1.067 mA measured by Charles F. Dalziel as described in the 229 manual.

http://www.tequipment.net/assets/1/2...9-2_manual.pdf
for a DIY leakage current tester
http://www.repairfaq.org/sam/safety.htm#saftes
http://www.mdsr.ecri.org/summary/det...px?doc_id=8285

Here is another case of a leakage current problem:

http://www.digitalhome.ca/forum/81-o...ml#post1457594
Attached Images
File Type: jpg Test Setup.jpg (176.4 KB, 4 views)

Last edited by rabbit73; 06-18-2015 at 04:54 PM..
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Old 06-17-2015, 08:43 PM   #5  
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Here are two grounding diagrams:





According to Article 810, the last time I checked, the mast can be grounded with 10 gauge copper or 17 gauge copper-clad steel. However, the coax grounding block must be connected to the house electrical system ground with 10 gauge copper wire.

If you use a separate ground for the mast, it must be bonded to the house electrical system ground with 6 gauge copper wire.

There are some threads about grounding and surge protection. Among to more intelligent comments are those made by westom.
Cables and Surge Protector
http://www.highdefforum.com/cables-c...protector.html
Surge protectors
http://www.highdefforum.com/flat-pan...rotectors.html
Surge protectors question
http://www.highdefforum.com/cables-c...-question.html
line conditioners
http://www.highdefforum.com/flat-pan...ditioners.html
Run bare antenna ground wire thru attic -good idea?
http://www.highdefforum.com/local-hd...good-idea.html
Direct TV & grounding
http://www.highdefforum.com/directv-...grounding.html
best lighting arrestor for outside antenna?
http://www.highdefforum.com/local-hd...e-antenna.html
Attached Images
File Type: gif NEC Grounding.gif (16.5 KB, 72 views)
File Type: jpg GROUNDING Wendell R Breland.jpg (82.0 KB, 71 views)

Last edited by rabbit73; 03-27-2016 at 08:09 AM..
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Old 06-23-2015, 03:07 AM   #6  
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Quote:
Originally Posted by rabbit73 View Post
The NEC requirements are certainly valid, but from personal experience you should at least ground the coax with a grounding block (for attic and outdoor antennas) for your own personal safety because all AC operated equipment has leakage current, even when it is operating properly. Just because you can't feel it, doesn't mean it isn't there.
Attic antennas need to be grounded? Can you explain that, please?
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Old 06-23-2015, 04:59 AM   #7  
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He didn't say it was required by code, he said it may be beneficial for your personal safety.
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Old 06-23-2015, 06:35 PM   #8  
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Originally Posted by projectsho89 View Post
He didn't say it was required by code, he said it may be beneficial for your personal safety.
I want to hear what he thinks about that. I carefully grounded my roof antenna, but my attic antenna is not grounded at all. Safety matters to me...but not much.
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Old 06-23-2015, 09:05 PM   #9  
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I want to hear what he thinks about that. I carefully grounded my roof antenna, but my attic antenna is not grounded at all. Safety matters to me...but not much.
projectsho89's interpretation of what I said is correct.

The NEC was written for electrical professionals, and even they have trouble understanding it. It is often revised based on experience from the field. It was originally concerned with the fire protection (hence its origin with the NFPA) aspects of electrical systems, and grounding to reduce the chances of lightning strikes by shunting the charge buildup on aerial conductors to ground.
https://en.wikipedia.org/wiki/National_Electrical_Code

Perhaps you have noticed the NEC, over the years, has shown an increased concern for personal electrical safety by requiring polarized receptacles, polarized 2-wire plugs, 3-wire receptacles, and more recently GFCIs. I expect this trend to continue.

At this point I feel like a harbinger.

Safety matters to me...a lot, because of my three close calls with electrical shock. The first one was when I was designing a power supply for an electronic flash for photography. That type of power supply contains storage capacitors that store many joules of energy at a high voltage. In my case it was 100 joules at 450 volts DC; a lethal amount.

I broke the rule that says one hand in my pocket and one hand to test the circuit. I had one hand grounded and one had to test the circuit. Well, the hand that was testing slipped and touched 450 volts. Fortunately, I was able to remove my hand and tell you my story.

The second time was when I was using HP test equipment. Someone had connected a power cord that had 3 pins at the equipment end and a 2-wire (non-polarized) plug for the receptacle. When I touched the case of the equipment I felt a tingle, and investigated. I had the medical staff x-ray the end for the equipment and to my horror saw that one side of the line cord was also connected to the grounding pin of the equipment. This meant that there was a 50 percent chance of having the equipment cabinet at full line voltage according to which way the plug was inserted.

The third time was with a soldering gun. Someone had apparently dropped the soldering iron and fractured the plastic handle. Their fix was to tighten the mounting screws which then connected one side of the line to the metal barrel of the iron. When I touched the barrel of the iron to a metal chassis I was repairing, it drew an arc, which alerted me to the danger.

My experience with leakage current, and that of the Canadian (link in post #4) with the converter box were warning signs to be heeded. In both cases the leakage current wasn't lethal, but if the equipment was defective, had been repaired improperly, or damaged it might become lethal.

The text of my leakage current tests is in the next post.

Last edited by rabbit73; 06-23-2015 at 09:21 PM..
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Old 06-23-2015, 09:12 PM   #10  
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Leakage Current Tests of Equipment Used for CECB Calibration

When I was calibrating an Apex DT502 signal strength bar with a SLM (Signal Level Meter) I noticed a slight shock when I touched ground and the equipment case. Because I didn't want to use, or pass on, dangerous equipment I tested the equipment that I was using for calibration with my Simpson 229 Leakage Current Tester.

Apex #1: 22 VAC, 52 A (micoamperes)
Apex #4: 21 VAC, 50 A
Apex #1 & #4 together: 30 VAC, 100 A (note that the leakage currents add)
2 Audiovox PLV16081 8" TV/Monitors: 21 VAC, 24 A each
CM 0747 Power Supply/Inserter for CM 7777, plug inserted correctly: ~1 VAC, ~1 A
CM 0747 Power Supply/Inserter for CM 7777, plug inserted reversed: 14 VAC, 33 A
Sony KDL22L5000 TV: 24 VAC, 52 A
Sadelco 719E SLM with AC Adapter/Charger: ~1 A
Radio Shack 15-1115 Preamp with AC Adapter: ~1 A

Leakage current tests must be made under 4 conditions: power on and off with plug normal, power on and off with plug reversed. With the exception of the CM 0747, all equipment gave the same readings under the 4 conditions. The 0747 has a 3.3 Meg resistor from ground to one side of the line, presumably to drain a static charge from the coax shield , which explains the difference in leakage current readings.

The Apex boxes and the 8" TVs have switchmode power supplies that have higher leakage currents. The AC adapters for the SLM and the RS preamp use a transformer adapter which has good isolation from the AC line.

CONCLUSIONS:

All pieces of equipment tested are safe to use individually as per the guidelines in the Simpson manual and other standards. However, when other equipment is connected, the leakage currents add as demonstrated by connecting the two Apex boxes together. This means that when pieces of equipment that have 2-wire power cords are connected together, even when the polarized plugs are correctly inserted, it is advisable to ground the cabinets and coax. Before I grounded the interconnected equipment that I was using, the AC voltage to ground was 40 volts, and the total measured leakage current was about 200 A.

I originally bought the Simpson tester because of three close calls. One was because of my carelessness, the other two were because of the stupidity of others.

Many years ago a neighbor asked me to help him connect his new TV. He was having trouble because the polarized 2-wire plug wouldn't go into the AC receptacle, so he filed down the wider prong (neutral). I asked him why he hadn't just turned the plug around so that the wider prong would go into the longer slot. He looked at the outlet, looked at the plug, and then looked at me and said: "Oh."

Best regards,
rabbit
January 12, 2010

Last edited by rabbit73; 06-24-2015 at 05:33 AM..
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Old 06-24-2015, 04:32 AM   #11  
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Quote:
and more recently GFCIs. I expect this trend to continue.
Yep, the trend has actually move towards requiring AFCI (Arc Fault Circuit Interrupting) protection.

When I built my house in 2004, I was required to install AFCI in all rooms that were considered sleeping areas (NEC 2002). Now, the requirement for AFCI protection has spread to almost the whole house in that they are required in new construction in every place that didn't already require GFCI protection (NEC 2014).
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Old 06-25-2015, 05:57 PM   #12  
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Originally Posted by wizwor View Post
I want to hear what he thinks about that. I carefully grounded my roof antenna, but my attic antenna is not grounded at all.
Appreciate that grounding for two completely different reasons is being discussed. As noted, electrical code only discusses grounding for human safety. Also ground for surge protection - transistor safety. That ground must meet code requirements for 'human' safety. And then meet additional requirements for 'transistor' safety.

A roof antenna must be earthed so avert damage from direct lightning strikes. Despite another's denial, that is why an antenna is earthed AND why its coax must connect low impedance (ie less than 10 feet) to single point earth ground before entering the building.

A wire bend around the eves will meet human safety codes. And compromises lightning protection. Any way to earth an antenna on a more direct path to earth will increase transistor protection.

Interior antenna is protected by something that is electrically conductive - ie wood. Chances of a direct strike to that antenna are slim. However its coax should be safety grounded downstairs. Then a fault to coax somewhere inside would trip a circuit breaker; not leave an electrically hot antenna in the attic. Safety codes do not explicitly demand it. But it is just good practice.

Code also demands an overhead antenna's earth ground also connect to the electrical earth ground. This is best done with a buried wire from an antenna's electrode to the electrical electrode. That not only meets human safety requirements. It makes a better single point earth ground for all household transistor protection. In practice, however, few actually bury the interconnecting ground wire as required by code.

Appreciate that grounding for human safety has different objectives than grounding for transistor safety. Transistor safety means both meeting and exceeding electrical code requirements.

AFGIs and GFCIs are for human safety; do nothing for transistor safety.
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Old 06-26-2015, 11:10 PM   #13  
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Soon the government will be protecting us so well from ourselves that we will live forever.
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Old 06-27-2015, 08:31 AM   #14  
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Soon the government will be protecting us so well from ourselves that we will live forever.
Zeus will never let that happen. Otherwise we might stop believing in the gods.

Socrates warned us about them gods. Look what happened to him.
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Old 06-28-2015, 05:10 AM   #15  
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Thank you.

Quote:
Originally Posted by westom View Post
Appreciate that grounding for two completely different reasons is being discussed. As noted, electrical code only discusses grounding for human safety. Also ground for surge protection - transistor safety. That ground must meet code requirements for 'human' safety. And then meet additional requirements for 'transistor' safety.

A roof antenna must be earthed so avert damage from direct lightning strikes. Despite another's denial, that is why an antenna is earthed AND why its coax must connect low impedance (ie less than 10 feet) to single point earth ground before entering the building.

A wire bend around the eves will meet human safety codes. And compromises lightning protection. Any way to earth an antenna on a more direct path to earth will increase transistor protection.

Interior antenna is protected by something that is electrically conductive - ie wood. Chances of a direct strike to that antenna are slim. However its coax should be safety grounded downstairs. Then a fault to coax somewhere inside would trip a circuit breaker; not leave an electrically hot antenna in the attic. Safety codes do not explicitly demand it. But it is just good practice.

Code also demands an overhead antenna's earth ground also connect to the electrical earth ground. This is best done with a buried wire from an antenna's electrode to the electrical electrode. That not only meets human safety requirements. It makes a better single point earth ground for all household transistor protection. In practice, however, few actually bury the interconnecting ground wire as required by code.

Appreciate that grounding for human safety has different objectives than grounding for transistor safety. Transistor safety means both meeting and exceeding electrical code requirements.

AFGIs and GFCIs are for human safety; do nothing for transistor safety.
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