Technical > Home Improvement > Grounding / Bonding question

reply to UHF

Re: Grounding / Bonding question

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.

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
--
The difference between genius and stupidity is that genius has its limits.

reply to UHF

reply to pende_tim

reply to Splitpair
Hi Wayne,
What is the "MBG" in the above pictures?

reply to pende_tim

reply to pende_tim

reply to pende_tim

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

reply to Splitpair
Exactly what I had in mind. Have some T&B crimp on lugs like the ones in your pic.

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.