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Guest Message by DevFuse

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Dish far from house ground


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68 replies to this topic

#41 ONLINE   jimmie57

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Posted 20 October 2012 - 05:22 AM

Where is that rule from? I haven't seen it mentioned elsewhere yet.


I am not an electrical guy but doesn't electricity go to ground to the shortest distance ? Would that just be common sense that the ground wire should be the shortest wire since you do not want this unwanted electricity in the other wires ?

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#42 OFFLINE   veryoldschool

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Posted 20 October 2012 - 08:54 AM

"17 AWG copper clad steel" is extraordinarily specific. Of course it was from satellite company lobbying. Which came first, 17 AWG copper clad steel messenger cable, or that exemption in the NEC?

The 17 AWG cable will act like a fuse, with a direct strike, which is exactly why 10 AWG or larger copper is specified.

The 10 AWG requirement comes from the part of the code addressing TV & Ham radio masts.
It doesn't make any direct reference to a small dish, though it does mention an LNB and a motor, which would be the 2 or 3 meter BUD.
These normally are much higher than the < 1 meter dish, that normally is only 3'.

You seem to think this comes from "lobbying", while I look at it as a "common sense" application.
A.K.A VOS

#43 OFFLINE   P Smith

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Posted 20 October 2012 - 09:10 AM

"17 AWG copper clad steel" is extraordinarily specific. Of course it was from satellite company lobbying. Which came first, 17 AWG copper clad steel messenger cable, or that exemption in the NEC?

The 17 AWG cable will act like a fuse, with a direct strike, which is exactly why 10 AWG or larger copper is specified.


Don't assume the 10 AWG will not vaporized during direct strike.
1/2" copper wire (rod) will be destroyed too in such case.

#44 OFFLINE   harsh

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Posted 20 October 2012 - 12:49 PM

Water meter is in the middle of the front yard, about 60 feet out, centered. Doesn't help me figure out the pipe entrance.

Unless your house was moved from somewhere else, it suggests that the water entrance is on the street side -- probably directly in from the meter.

The water pipe doesn't make a good ground because, AFAIK, it's not bonded to the house ground, and there could be a difference in potential.

Good and code are two different things. Of course if the pipe is plastic, it doesn't matter where it comes in.

Why is a 17 AWG carrier wire adequate for connecting the dish to the Antenna Discharge Unit, according to the NEC?

As I explained above, it is good enough because the wires it is protecting your home from are smaller gauge. It will theoretically outlast the center conductor of an individual cable when it comes time to go fusible link on you.

The major failing your having in understanding this is that the grounding is not designed to sink a lightning strike. It is simply to discharge static and lower voltages that build up for more conventional reasons.

Too often we enjoy the comfort of opinion without the discomfort of thought. -- JFK


#45 OFFLINE   P Smith

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Posted 20 October 2012 - 01:08 PM

Unless your house was moved from somewhere else, it suggests that the water entrance is on the street side -- probably directly in from the meter.Good and code are two different things. Of course if the pipe is plastic, it doesn't matter where it comes in.As I explained above, it is good enough because the wires it is protecting your home from are smaller gauge. It will theoretically outlast the center conductor of an individual cable when it comes time to go fusible link on you.

The major failing your having in understanding this is that the grounding is not designed to sink a lightning strike. It is simply to discharge static and lower voltages that build up for more conventional reasons.

That is the key to get it done right.

#46 OFFLINE   Neurorad

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Posted 21 October 2012 - 06:59 AM

It appears to me that the 'mast' can be grounded with 17 AWG copper clad steel, run back to the bonded ADU, but every cable coming into the house must also be bonded (coax) with 10 AWG copper, per NEC.

Perhaps I should take a closer look at what the NEC says about my electric pet fence and irrigation system. Neither of those are bonded, and both were 'pro installed'.

I'm MUCH more likely to pick up a nearby surge from those systems. I don't think a small wall amount dish could even get a surge.

I wonder if I could hire a knowledgeable electrician or engineer to figure those out. I need to get a whole house surge protection device ASAP, at a minimum.
Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha

#47 OFFLINE   P Smith

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Posted 21 October 2012 - 09:45 AM

I would find such man, but who is open to get thru all your concerns and discuss accepting your knowledge of NEC requirement.

#48 OFFLINE   Neurorad

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Posted 21 October 2012 - 12:53 PM

My knowledge of NEC requirements are limited, at best. I'm interested in hiring someone more knowledgeable.

I plan on putting a pool in the back yard in the next 5 years, so extending the ground properly to the dish location may not be a big deal, if the pool needs to be bonded to the house ground. Not sure if that is indicated, though, but probably. Any pool experts? ;)
Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha

#49 OFFLINE   bobnielsen

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Posted 21 October 2012 - 04:24 PM

My knowledge of NEC requirements are limited, at best. I'm interested in hiring someone more knowledgeable.

I plan on putting a pool in the back yard in the next 5 years, so extending the ground properly to the dish location may not be a big deal, if the pool needs to be bonded to the house ground. Not sure if that is indicated, though, but probably. Any pool experts? ;)


It was a requirement when I put a pool in 40 years ago and I doubt any requirements have been relaxed since then.

#50 OFFLINE   Neurorad

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Posted 21 October 2012 - 06:17 PM

Cool, thanks for that. I'll have an excellent, bonded ground very close to the dish (but not too close); I think I saw an NEC minimum distance to a pool, somewhere.
Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha

#51 OFFLINE   westom

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Posted 21 October 2012 - 08:33 PM

My knowledge of NEC requirements are limited, at best. I'm interested in hiring someone more knowledgeable.

You are still confusing ground as defined by the NEC (only for human safety) with ground that makes surges irrelevant (for electronics safety). Ground for human safety is often insufficient (due to too much impedance).

For example, a long wire transmitter antenna might have 100 volts on one point. And the same wire might have zero volts on another point. That would not happen with electricity that concerns code. But that is relevant to another electricity that concerns surges. Wire can be electrically different at both ends. Therefore a connection from satellite dish to earth must also be short (ie 'less than 10 feet'). That wire must not have sharp bends. And other factors never found in the NEC. Because those same requirements (low impedance) are irrelevant to human safety.

The term is called impedance. Impedance is irrelevant to how 60 cycle works. And is significant to how surge protection works.

Various requirements both for human safety and for protection means a dish (typically) must have its own earth ground (as wire as short as possible to be both low resistance and low impedance). Those same requirements also say why a coax cable must be earthed (as short as possible) to single point ground before entering the building.

An engineering application note demonstrates these concepts that also apply to your dish (and would be irrelevent to a pool and to NEC):
http://www.erico.com...tes/tncr002.pdf

Another example of different electrical characteristics when earthing for human and electronics safety. An 18 AWG wire (ie lamp cord) is typically considered a 10 amp wire (for human safety). The same wire may conduct a surge current up to 60,000 amps. Due to electrical differences in those two currents.

A 12 AWG wire (often used for earthing communication cables) and the 6 AWG wire (often used for earthing AC electric wires) are both more than sufficient (thick enough) to perform both human and electronics safety. And also should remain sufficiently 'thick' many decades later for both purposes. Those wires are thick enough to provide low resistance. But impedance is mostly defined by wire length. Low impedance means that same wire is typically shorter than required by code.

Edited by westom, 21 October 2012 - 08:48 PM.


#52 OFFLINE   P Smith

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Posted 21 October 2012 - 09:55 PM

The term is called impedance. Impedance is irrelevant to how 60 cycle works


I think NEC definitions must be same as for electromagnetic definitions. Those you are incorrect.
Impedance would be a complex parameter what defined at freq not eq 0 (constant current) and includes resistance, capacitance and inductance.

So, the impedenace is totally relevant to freq 60 Hz (and any AC) , and irrelevant for DC.

#53 OFFLINE   westom

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Posted 21 October 2012 - 10:31 PM

So, the impedenace is totally relevant to freq 60 Hz (and any AC) , and irrelevant for DC.


Put numbers to your summary. When done, impedance for a wire at 60 Hz is almost identical to wire resistance at DC. Parameters for both 60 hz and DC do not explain currents that occur in wires during lightning. Does not even explain why the 10 amp (18 AWG) wire can also conduct a lightning current approaching 60,000 amps.

60 Hz electricity is from a voltage source. Surges are from a current source. Just another of so many electrical differences. Those so many differences explain why NEC requirements do not define lightning protection.

#54 OFFLINE   veryoldschool

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Posted 21 October 2012 - 10:40 PM

Does not even explain why the 10 amp (18 AWG) wire can also conduct a lightning current approaching 60,000 amps.

Maybe it would for a few nano seconds before it vaporized.
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#55 OFFLINE   P Smith

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Posted 21 October 2012 - 11:58 PM

Put numbers to your summary. When done, impedance for a wire at 60 Hz is almost identical to wire resistance at DC. Parameters for both 60 hz and DC do not explain currents that occur in wires during lightning. Does not even explain why the 10 amp (18 AWG) wire can also conduct a lightning current approaching 60,000 amps.

60 Hz electricity is from a voltage source. Surges are from a current source. Just another of so many electrical differences. Those so many differences explain why NEC requirements do not define lightning protection.

I'm lost here ... :confused:

#56 OFFLINE   westom

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Posted 22 October 2012 - 07:34 AM

I'm lost here ... :confused:

Posted were first year electrical engineering concepts that you must understand before you can dispute or reason any of this. You have assumed impedance at 60 Hz is significant because you have not calculated what that wire impedance is.

Why must the wire connection to earth ground be so short for transistor protection. And can be so much longer for human protection? Even the concepts called voltage source and current source are relevant. Just another reason why NEC requirements do not define earthing also for protection from lightning. And why protection from lightning means both meeting and exceeding NEC requirements.

#57 OFFLINE   Neurorad

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Posted 23 October 2012 - 09:36 PM

I'll ground the dish and mast using 17 AWG copper clad steel, but I probably won't ground the dish properly, if I can avoid it. Direct strike isn't a concern, and not at all concerned with surges from the dish.

I'll ground the pet fence and irrigation system, though, and add the whole house SPD (using a short, straight connection of course). Those are now on my short list, with DirecTV installation, and new WAPs.
Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha

#58 OFFLINE   woodybeetle

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Posted 26 October 2012 - 09:49 AM

SO I have watched this thread unfold and havea couple of comments that are warranted in my opinion.

a. the 1 gauge wire from the dish to ground is not a ground source, it is intended to bleed off static discharge built up in the antenna (LNB).

b. the usage of a 10 gauge wire to bond to the earth ground is designed to minimize near lightning surges, and is normally sufficient.

c. a customer will always read the NEC and decide that he knows what is best, thus installing outside of code.

d. a well trained installer will avoid the install due to the liability it will induce in the future.

Food for thought:

Installed a 22 story MDU, 186 apts in building,

# 6 copper from LNBs to bonded ground, 8 Feet away
# 4 copper from coax to bonded ground plate in first closet, 31 feet from dish
# 8 copper from coax to bonded ground plate every 2nd floor

All ground points installed by electrician and passed city inspections at a cost of approx 3800 dollars for work performd

Lightning impacted(direct strike) adjacent building (140 ft away)

Spent 3 days reinstalling our system, all electronics dead, most of coax scorched on center conductor, roughly 60 DTV set top boxes would not power up.

Point of ingress of the lightning to the satellite system, a ethernet port from the internet provider to our monitoring system, his system was grounded as well.

Satellite Company Insurance claim of 37000
Property insurance claim of 250000+


Moral of the tale, No matter the intention of the installer, mother nature will find a weak point and exploit it.
Daniel D. Corum
DDCESI/Idiot Proof Television

#59 OFFLINE   P Smith

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Posted 26 October 2012 - 10:32 AM

After your morale, would you post practical advise regarding grounding, at least for that mentioned MDU setup.

#60 OFFLINE   Neurorad

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Posted 26 October 2012 - 10:53 AM

Daniel, I agree with you, on every point. I wonder how well the incoming ethernet connection was grounded. Any SPD on that setup?

I hope I get an installer who isn't well-trained. Signed up for DirecTV yesterday, install scheduled.

Does the installer show up with the equipment, or is it shipped to my address? If the installer refuses to install improperly (i.e. does his job well, no criticism here), am I supposed to hand him the equipment, if it was shipped?
Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha




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