UHF
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join:2002-05-24
clubs: | reply to UHF
Re: Grounding / Bonding question
Decided not to bond to the breaker panel for the time being. Got the antenna protected now at least, and cleaned up a lot of other cables for TV/Satellite that were driving me crazy. |
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UHF
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join:2002-05-24
clubs: | reply to Splitpair
Exactly what I had in mind. Have some T&B crimp on lugs like the ones in your pic. |
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pende_tim
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Andover, NJ
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1 edit | reply to Splitpair
Hi Wayne,
It looks like the are really implementing the single ground point.
The tower is grounded to a ring on the right and that should take the hit from a lightning strike. There is only a single point connection between the right side ring and the left side ring just under the ice breakers so there will be no appreciable current circulating through the loop on the left causing any voltage drop in that loop. That will keep the MGB and the AC/Telco ground points at roughly the same potential.
Yes the site potential can rise during a strike, but as you point out, it does not matter as long as everything rises together. By having only one connection to the fault current path everything rises together.
It is the voltage difference that makes current flow and bad things happen.
Tim |
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UHF
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| reply to pende_tim
said by pende_tim  :In order to eliminate ground loops for lightning protection, all the grounds back into the house should be arranged in a "star" configuration. Ah, yes, there was the reason I asked about this. My ground bar is about 4' from the main building ground rod, but I haven't connected anything to it yet. I may move it so it's at the main ground rod, then I can make it so it's a 'star' ground. |
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Splitpair
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join:2000-07-29
Cow Towne
 ·T-Mobile US
| reply to pende_tim
said by pende_tim :Hi Wayne, What is the "MBG" in the above pictures? Main grounding bar.
»Grounding and Bonding. More than you will ever want to know.
Wayne
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If you cannot fix it with a buttset and some beanies you ain't a technician.
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Splitpair
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Cow Towne
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| reply to pende_tim
said by pende_tim :They don't use single point ground systems? Wow. They must be using some pretty stiff isolators between the various systems. Tim Not really the system works by floating all components to the same level be it zero or tens of thousands of volts. As long as everything is equal there is not current flow between components therefore no damage. Simular to a bird sitting on a primary yea he's charged to 7.6 Kv but un-injured as there is no flow.
Wayne
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If you cannot fix it with a buttset and some beanies you ain't a technician.
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pende_tim
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Andover, NJ | reply to Splitpair
Hi Wayne,
What is the "MBG" in the above pictures? |
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pende_tim
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| reply to Splitpair
said by Splitpair :said by pende_tim :In order to eliminate ground loops for lightning protection, all the grounds back into the house should be arranged in a "star" configuration. Tim That is not how we do cell sites and many times they have engineered ground systems. Wayne They don't use single point ground systems? Wow. They must be using some pretty stiff isolators between the various systems.
The ground rods can be set in any configuration as long as they are interconnected but the ground connection to the electronics and mains power neutral & ground should be connected to a single point off the ground rod system.
In a former life, I was chief engineer in a HV test facility so this advice comes not just from "the theory" but from personal experience (and some blown instrumentation).
Tim
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The difference between genius and stupidity is that genius has its limits. |
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Splitpair
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Cow Towne
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3 edits | reply to pende_tim
said by pende_tim :In order to eliminate ground loops for lightning protection, all the grounds back into the house should be arranged in a "star" configuration. Tim That is not how we do cell sites.
Wayne
--
If you cannot fix it with a buttset and some beanies you ain't a technician.
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Splitpair
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Cow Towne
·T-Mobile US
| reply to UHF
said by UHF :And as far as bonding the strap to the neutral bus, can I simply attach it to the side of the panel, with paint removed, etc? Here's an example of one way to do so.
Wayne
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If you cannot fix it with a buttset and some beanies you ain't a technician.
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pende_tim
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| reply to Splitpair
Hi Wayne,
I would not do the grounding exactly the way you show it in your picture.
In order to eliminate ground loops for lightning protection, all the grounds back into the house should be arranged in a "star" configuration.
Based on your picture, all the grounding points to the house should tie back to the single point on the right called "building ground". This would be the center of the "star" configuration. The "panel bond" and the radio shack grounds should be separate runs back to this point and not be just a pick off of the run back to the radio shack.
If possible, I would tie the Antenna SPD to this point also.
The reason for this is that if the Antenna SPD takes a hit, the surge will travel to all ground points through all paths. Since the Breaker panel also provides a parallel path back to the ground rod on the right, there will be current passing through it and an associated voltage drop due to the impedance of the conductors. ( It is the inductive reactance of these paths that generates the majority of the voltage spike due to the fast rising wave front of the lightning. ). Even though the distance may be short, the generated voltage drops can be extremely large.
Assume ( using some general numbers here ) the antenna gets hit with 1,000,000 volt strike and the wire distance between the tip of the antenna antenna and the earth point is 100 feet. That 1,000,000 volts will be almost equally spread out as a voltage gradient over the 100'. That results in a voltage drop of 10,000 Volts/foot along the conductor. The voltage gradient is spread almost equally along all the conductors because the inductance of wire is almost independent of wire gage. A quick tip: for lower impedance, run several smaller parallel wires.
So if you have two points going back into the house that are in the path of the return current (ie. not connected to the center of the star) they will be at a difference in potential of 10,000 Volts X the number of feet the connection points are separated.
Tim
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The difference between genius and stupidity is that genius has its limits. |
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whizkid3
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join:2002-02-21
Queens, NY
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1 edit | reply to UHF
said by UHF :Equipment safety grounds? Wouldn't that be the third wire on the AC? Yes. said by UHF :And as far as bonding the strap to the neutral bus, can I simply attach it to the side of the panel, with paint removed, etc? The ground bus is bolted the cabinet of the panel anyway, and the neutral bonding screw is installed. Provided you use the proper lugs, and no sheet-metal screws - nut & bolt it with washers and a lock next to the nut. I would c-tap it and run a wire to the bus. |
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UHF
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| reply to whizkid3
Equipment safety grounds? Wouldn't that be the third wire on the AC?
And as far as bonding the strap to the neutral bus, can I simply attach it to the side of the panel, with paint removed, etc? The ground bus is bolted the cabinet of the panel anyway, and the neutral bonding screw is installed.
I do have an actual copper ground bar like those used at a commercial tower site with insulated standoff, etc (»store.electrical-insulators-and-···1kt.html) that is being used at the coax entry point. And appropriate Polyphasers. At this point, the only antenna is a wire dipole supported by trees. If I ever get a tower or HF vertical installed I will have additional ground rods installed at the base of those bonded back to the ground bar. |
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whizkid3
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| reply to UHF
said by UHF :I was also planning to run 3" strap from the ground bar into the basement, where it will run right past the breaker panel on it's way to the radio room. Perfectly acceptable (assuming your wire gauges are right). However, you must have equipment safety grounds that run to the ground bus in the panelboard for any ham gear powered from this panel. As well, you should bond the strap that runs from your copper bus to the ground/neutral bus in the panelboard. From that point to the external copper bus, your strap will be part of the grounding electrode system. Tie your antenna and mast grounding system to the copper bus. I would also suggest gas-discharge tube surge arrestors on any coax cable at the point of entry, with the surge arrestors bonded to the external copper bus. If you really want to go all out, construct a copper or aluminum plate grounded and mounted on the wall where the coax lines enter the house to mount bulkhead type gas-disharge tubes to. (Use appropriate surge protection for other type antenna cables, as well.)
said by UHF :Also considering a couple more ground rods, somewhere between 2 and 6. Can never have too many. Two would go south in that picture, and then possibly extending off the two outer rods towards the north, a partial ring around the house. But that's only if I get really ambitious, Why not. For that matter, how about a grounding counterpoise with lightning rods and down-conductors on your masts? |
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UHF
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| reply to Splitpair
Here's a crappy diagram. Ground rod at the meter base, bonded to the panel located directly on the other side of that wall (but in the basement). House didn't show up in the diagram, but the outer two rods are at the corners of the house, bonded with #2 (buried) to the original ground rod.
I'm adding the SPD and ground bar a the location shown, was planning to bond it back to the middle ground rod with 3" strap.
I was also planning to run 3" strap from the ground bar into the basement, where it will run right past the breaker panel on it's way to the radio room.
Also considering a couple more ground rods, somewhere between 2 and 6. Can never have too many. Two would go south in that picture, and then possibly extending off the two outer rods towards the north, a partial ring around the house. But that's only if I get really ambitious, I'm sitting on lime rock so driving ground rods can be an exercise in futility at times. |
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Splitpair
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Cow Towne
·T-Mobile US
1 edit | reply to UHF
said by UHF :I'm installing some ham radio antennas so I've put in a copper ground bar outside where coax enters the house for the lightnng arrestors. You are placing a new ground rod at the antenna grounding bar correct?
Wayne
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If you cannot fix it with a buttset and some beanies you ain't a technician.
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pende_tim
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Andover, NJ
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| reply to UHF
Just make sure you connect in the following order:
Ground bar for antennas to 3 ground rods to electrical panel then to radio shack.
You want the lightning arrestors to discharge to the ground rods first and NOT to the electrical panel. That way all the current will pass directly into earth and the electrical panel will remain at ground potential. If you go to the panel first, the impedance of the copper strap between the panel and the ground rods will put your panel several thousand volts above ground. There may be several ground loops back to earth which could conduct significant amperage and do a lot of damage to the house wiring and attached devices.
Tim
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The difference between genius and stupidity is that genius has its limits. |
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UHF
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clubs: | reply to Splitpair
Thanks, Wayne! |
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Splitpair
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Cow Towne
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2 edits | reply to UHF
said by UHF : Should I just disconnect the #6 running outside and rely on the strap for the grounding conductor? Since your strap is a bond do not disconnect the ground and do bond the panel to the strap.
Wayne
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If you cannot fix it with a buttset and some beanies you ain't a technician.
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UHF
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| Currently my main electrical panel is grounded via three 8' rods bonded with #2 wire, but using a #6 from the rods to the panel. Also a #6 to the street side of the water meter.
I'm installing some ham radio antennas so I've put in a copper ground bar outside where coax enters the house for the lightning arrestors. I'm going to bond this to the three ground rods using a 3" copper strap. My plan is to then bring the 3" strap into the basement and continue it to the radio room.
This strap will pass right by the electric panel. Should I bond the strap to the panel at that point, or just pass it by? My gut instinct is to bond it, but will that meet code with the other wire running out to the ground rods? Should I just disconnect the #6 running outside and rely on the strap for the grounding conductor? |
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