The NEC has strict standards for the Grounding Electrode System, and
exactly where and when neutral (ground_ed_ conductor) can be bonded to
ground (ground_ing_ conductor).
It does not limit the number of rods/other that can be used in addition
to the minimums.
Also, additional ground rods/other can be added basically _anywhere_
bonded to a ground lead or equipment chassis. These are simply NOT part
of the grounding electrode system and cannot substitute for any other
grounding requirement.
If you dig a bit there is language about supplemental and supplementary
grounding electrodes. I forget which is which, but one is bonded to the
GES via #6 or larger bonding run, the other is not.
They are both allowed, but _do not do not do not_ replace/substitute for
any required grounding/bonding...You can drive a rod and bond it to the
chassis of a AC powered machine, but this does not in any way remove the
requirement of bonding the chassis to the AC grounding conductor in the
AC feed.
On 7/26/16 17:35, Grant Saviers wrote:
> Jim,
>
> Thanks for your comments. The entrance panels for the two buildings
> have separate meters so they are correctly installed with local bonding.
>
> NEC, if I understand it correctly, does clarify one important point,
> that is that permanently installed outdoor generators can be connected
> to an auxiliary grounding electrode . Even if I didn't have a separate
> electrode the gen frame is bolted to a reinforced 60 sq ft concrete pad.
> So I have 3 code correct grounding electrode connections.
>
> My logic for the tower shed panel bonding was to shunt to the radial
> field a large amount of common mode RFI (S9+40) from PWM 240 VAC mains
> amplifiers driving the rotator 180v DC 1/2hp motors. Even though the
> 16KHz PWM amps are 240v sourced they have a bolted frame connection.
> These amps use IGBT's that switch really fast. I have a shielded
> isolation transformer between them and the panel and balanced 50KHz
> cutoff filters I designed installed on the output of the amps. This
> bonding is not per code, and if there is downside, I'd like to know what
> that is. Fortunately, all this suppresses the rotator moving RFI to
> S1-2 for 20m and above, but I need another 60+ db on 40m. The challenge
> is a filter design that doesn't cause the PWM amp protection circuits to
> trip. This problem is a drift off topic but if others have solved it,
> I'm eager to learn. The configuration is Green Heron controllers with
> remote power amp turning K0XG rings. The rotator cable is inside the
> tower, 16ga twisted pair, not shielded per manufacturer's advice (bad
> advice, they should be shielded). The 180 VDC motors are filtered at
> their frames and can barely be heard on all bands when driven from a
> clean DC source.
>
> Grant KZ1W
>
>
> On 7/26/2016 13:41 PM, Jim Brown wrote:
>> Hi Grant,
>>
>> I won't quote your entire post, but only some key elements that need a
>> comment.
>>
>> On Tue,7/26/2016 11:21 AM, Grant Saviers wrote:
>>> "Ground loops" are an interesting question. The problem is a
>>> "single point ground" is often not feasible and is impossible at my
>>> QTH. My decision was to connect everything together.
>>
>> In general, that's the only right (safe) way to do it.
>>
>>> At my QTH the conductor paths are:
>>>
>>> 1. Buried HV feed to mains transformer which has a Ufer vault ground,
>>> which then feeds
>>> 2. 200a house service with 2 ground rods at entry
>>> 3. 400a shop/shack entry panels with 2 ground rods and bonding to
>>> structural steel
>>> 4. Charger and heater at a backup generator on a concrete pad,
>>> which then feeds back underground to 200a transfer switches at house
>>> and shop, next to mains entry panels
>>> 5. The shop/shack foundation is a perimeter Ufer and the structural
>>> steel is grounded to it, also the main shack ground is to the Ufer
>>> 6. The 3 towers have Ufer bases and ground rod+radial fields
>>> 7. The shack coax entry panel is bonded to the steel structure, coax
>>> is bonded to towers top and for the largest tower to a shed at base
>>> entry panel, all cables are in buried conduits to the shack
>>
>> All of this is REALLY GOOD
>>
>>> 8. Underground control and coax to a 160m wire vertical T with a
>>> ground rod and shunt inductor from 8 elevated 125' long radials
>>> 9. Ethernet, RG6, and control cables are in conduit from shop to
>>> house (not protected at either end - needs fixed)
>>
>> Yes, this is a recipe for destruction, needs serious attention.
>>
>>> 10. The Comcast cable entrance is tied to ground rod at house,
>>> telephone entry is there also, so the house on its own is near single
>>> point grounding.
>>> 11. The equipment shed at the base of the largest tower has the coax
>>> entry panel bonded to the rod and radial field. The shed mains power
>>> panel is also bonded to the radial field.
>>>
>>> Thus, there are a large number of "loops".
>>
>> Of course. The concept of "ground loops" is fundamentally WRONG, and
>> causes us to do dumb things. The ONLY context in which a loop is a bad
>> thing is magnetic induction.
>>
>>> This is probably more complex than most, but I think it is not
>>> uncommon to have loops. Code requires much of the above, and white
>>> (neutral) is connected to yel/grn (earth) at several places.
>>
>> TRAIN WRECK! Good engineering practice, and virtually ALL building
>> codes in NA, require that neutral be bonded to ground ONLY at 1) the
>> service entrance (where power enters a premises); and 2) where a "new
>> system" is established. A new system is established by a transformer.
>> It is NOT established by a feed to another building from the main feed
>> to the premises. The ONLY time there should be more than one bond in
>> two buildings is if 1) the two buildings have their own service (that
>> is, a separate metered connection from the power company; or 2) if the
>> second building is fed from the first, and ground is not carried
>> between the two buildings. This second scheme is no longer permitted
>> by NEC
>>
>> SO -- if you have neutral bonded to ground at more than one place, you
>> need to change that. It's a VERY big deal.
>>
>>> So my strategy was to bury a large ground conductor below the conduit
>>> runs when I could, to tie stuff together. I didn't do this initially
>>> but wish I had as later DC ground resistance measurements showed the
>>> buried wires were about 1 ground rod equivalent at about 100' of
>>> buried bare copper wire (#6). I note that the Andrew lightning
>>> protection guide advises against tying towers to building entry
>>> panels with a separate buried conductor. Rather they let the voltage
>>> surge be equalized on the coax and control wires, I think the theory
>>> is that the differential voltages are less as a result. If my code
>>> knowledge is correct, it requires towers to be bonded to "house
>>> ground", if there is AC at the tower as is true for my motorized
>>> crank ups.
>>
>> NEC requires that the power system ground MUST be carried to all
>> outlets and loads, and it MUST be carried with the phase and neutral
>> conductors (in the same conduit or other cable).
>>
>>> I think my shop foundation Ufer plus structural steel frame makes a
>>> low inductance path from the shack on the opposite corner from the
>>> mains entry and transfer switch panels. The tower foundation Ufers
>>> and rod/radial fields are other "good" low ohms and L grounds with
>>> lots of surface area. The code required pair of mains entry panel
>>> rods are poor grounds in comparison (180 sq ft of concrete per tower
>>> in earth contact vs 0.1 sq ft per rod. 1000 sq ft of concrete
>>> surface in the shop Ufer).
>>>
>>> So if "SPG" means a single point ground at shack entry panel for
>>> coax, control cables, and rigs, then what I have might qualify.
>>> Otherwise, it is impossible to achieve.
>>
>> Yes, that's the real world.
>>>
>>>
>>> An "RF ground" for lightning as the Andrew guide explains is a ground
>>> rod + radials field that distributes the RF energy of a strike over a
>>> large area both capacitively and via conduction.
>>
>> Erase the words "RF ground" from your memory bank -- it is a fiction
>> that has no meaning. Connections to earth, and bonding between those
>> connections is ONLY for lightning safety. The only relationship
>> between those connections and "RF" is to realize that lightning is an
>> RF event, not a DC event, so that the impedance of those connections
>> and that bonding at RF, which is where the energy in lightning is, is
>> what matters.
>>
>>> So the 5 ohm DC ground resistance target has merit as does the radial
>>> wire and ground rod field size. Both are needed.
>>
>> A radial field serves as a low resistance return for antenna current,
>> in place of earth, which is a big resistor. That radial field SHIELDS
>> the antenna from the lossy earth. And from the point of view of
>> lightning protection, if it is bonded to facilities grounds, it
>> provides capacitive coupling to the earth to reduce the impedance to
>> earth at RF.
>>
>>> While buried conductors benefit from the shunt earth conductivity,
>>> the wire inductance limits the useful length of the radials to about
>>> 50ft according to Andrew. The K1TTT analysis shows why tower top and
>>> bottom coax shield bonding is needed and why elevated coax should be
>>> avoided if at all possible.
>>
>> Yes on all counts.
>>
>>>
>>> Fortunately, Western Washington has a very low strike frequency, but
>>> with a tower top 40' above the 110' tree line and on a ridge, my
>>> attention to lightning protection has significantly increased.
>>
>> Lightning enters our premises on MANY conductors -- power line, TELCO,
>> CATV -- as well as antennas.
>>
>>> "There is no such thing as ground" from Vonada's Engineering Maxims.
>>
>> Now we're getting closer to the real world. :)
>>
>> 73, Jim K9YC
>> _______________________________________________
>>
>>
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