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Author Topic: Recommended wire size for equipment to ground buss bar?  (Read 1165 times)

K6BRN

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Re: Recommended wire size for equipment to ground buss bar?
« Reply #15 on: March 10, 2020, 01:36:40 PM »

Hi Floyd (K8AC):

Quote
If you're grounding everything together with heavy braid to try and solve RF problems, I think you'd be more successful if you spent some time determining the cause of "RF in the shack".

I have to agree with Neal (N6YFM).  I also live on a very compact Beach Cities lot in SoCal and a comprehensive grounding system solved the vast majority of my RFI issues.  Yes, I also had to place my antennas carefully to avoid near field RFI, but my ability to do so was limited, as is Neal's.  Same thing with RF radiating from coaxes just 10 feet away from neighbor's homes and RFI radiating INTO my receivers from inverter drive washer/dryer/AC and solar converters.

First step was to solidly ground every coax shield at the QTH entrance using Alpha Delta arrestor blocks and a cluster of 10 ft copper ground rods - due to relatively poor soil conductivity (and use an RF choke near the resonant antennas feed points)

Second step was to run a dedicated 4-gauge ground wire from the (nearby) house power entrance ground to the coax ground rod cluster.

Third step was to run dedicated 120/240 VAC power and ground to QTH "shack" area, exactly parallel to 4-gauge ground wire.

Fourth step was to individually ground each piece of equipment to an inside copper grounding buss bar using heavy braid, and to the outside ground rod, which was very close by (about 3 feet). 

The use of dedicated, equal length ground lines for both ground rod cross strapping and power ground made resulting ground loops VERY short, and therefore of no consequence.  Connecting all equipment to the same ground bar within the shack, and making the connection runs very short with a great deal of conductor "skin" area equalized potential across all equipment, eliminating RF "bite" and computer/rig crashes as well.

Yes, I also made liberal use of ferrite chokes where potential problems could occur.

End result:  No more RFI complaints from neighbors, XYL and kids, even operating at 1KW, on any band.

This was quite a bit of work, but very much needed at my CA QTH, which also has 7 antennas.  Neither of my other QTHs have needed this comprehensive a grounding system to control RFI, and each only has 2 antennas @500W max, though one also has dedicated power/ground lines (I highly recommend this).  So what is needed really depends on location and installation quirks.  Need to do some experimentation at each site to determine need.

Brian - K6BRN
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WB6BYU

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Re: Recommended wire size for equipment to ground buss bar?
« Reply #16 on: March 11, 2020, 09:23:42 PM »

Quote from: K6BRN

... a comprehensive grounding system solved the vast majority of my RFI issues...



You must have horrific common mode current problems to require that much of a
ground system!

What are you using for antennas - end-fed half-wave antennas that rely on the coax
for a counterpoise?  OCFDs designed to use the coax shield as a radiator?

Whatever it is, it sounds like fixing your antenna to reduce the common mode current
would have been easier and less expensive than all that grounding.

K6BRN

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Re: Recommended wire size for equipment to ground buss bar?
« Reply #17 on: March 12, 2020, 12:36:27 PM »

Hi Dale (WB6BYU):

Quote
You must have horrific common mode current problems to require that much of a
ground system!

No, not really.  I just live in a very dense urban neighborhood where any leakage into or out of my station can be problematic.   That's not a problem you seem to have to deal with based on a map of where your QTH is supposed to be.  Very rural.

BTW - as I've said, all of my antennas are resonant - see my QRZ page for a list.  Common mode current is very low, as would be expected with this arrangement, and pretty much irrelevant with a grounded coax and RF chokes.

And... do I REALLY need to defend puting in a good grounding and emissions/noise control system?  I hope not!

Regarding cost - when I redid my antenna suite about five years ago I decided to do it once and do it right.  That included shack power and ground.  The cost of doing it poorly was just a few percent lower that doing well.  Easy decision.  Frankly, the cost was trivial, anyway.  But I do recognize that cost is relative to means.

Best Regards,

Brian - K6BRN
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WB6BYU

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Re: Recommended wire size for equipment to ground buss bar?
« Reply #18 on: March 13, 2020, 08:38:34 PM »

Quote from: K6BRN

...That's not a problem you seem to have to deal with based on a map of where your QTH is supposed to be.  Very rural...



It used to be when we lived out in Yamhill County, with about 3 houses within a
quarter mile of the house.  Now, however, we've moved to a suburban 90' square lot
where the neighbors (and their noisy devices) are much closer.

But the point of my post was that none of the hams I've known, even those
who run full legal limit (or more!), have needed such an extreme grounding
system to eliminate problems.  It's not that I'm against hams grounding their
stations if they want to, or if it serves some specific purpose, but from an
engineering perspective I'd rather understand and fix the root cause of the
problem rather than apply folklore solutions and hoping that they work.

So let me pick a couple items you mentioned and see what clues they might
give use...

Quote

First step was to solidly ground every coax shield at the QTH entrance using Alpha Delta arrestor blocks and a cluster of 10 ft copper ground rods - due to relatively poor soil conductivity (and use an RF choke near the resonant antennas feed points)

Second step was to run a dedicated 4-gauge ground wire from the (nearby) house power entrance ground to the coax ground rod cluster.


These are both good practice (and the second is required by building code in
most places).


Quote

Third step was to run dedicated 120/240 VAC power and ground to QTH "shack" area, exactly parallel to 4-gauge ground wire.

Fourth step was to individually ground each piece of equipment to an inside copper grounding buss bar using heavy braid, and to the outside ground rod, which was very close by (about 3 feet). 



Let's consider the overall situation.  Ideally your antennas should be
the only source of RF radiation.  If the neighbors devices are picking up
a signal radiated from the antenna, then no amount of grounding
in your station should make any difference, unless it reduces the radiated
power, or changes the current distribution on the radiating conductors.

The same, of course, goes for picking up noise from the neighbors' devices
on receive.

So the question then is, what is allowing the RF signal go transfer to the
neighbors if it isn't radiation from the antenna (because in theory that
hasn't changed)?  It must be radiation from another part of the system, or
via conduction.  And why would changing the power wiring make a difference,
unless that was somehow either radiating or conducting an RF signal?

You had mentioned "leakage from the coax" in a prior post:  why would
grounding the station reduce that?  Besides, I'm assuming you used
reasonable quality coax, and not the cheap stuff with only 60% braid coverage.

How much power might be radiated from such leakage?  We can set an upper
limit  by looking at the loss figures for the coax, since the leakage must be
considered as part of the cable loss.  If we assume 50' of Belden RG-213 on
40m, the cable loss is about 0.23 dB.  At 1 kW output, the total power loss
is about 30 watts, and that due to leakage likely is much less that that.  To
get another estimate, consider using RG-214 instead, which has a double shield
that should reduce the leakage.  Turns out that the loss in that case is 0.245 dB:
it actually went UP when we added more shielding.  (That's probably because
the added shield forced a reduction in the inner conductor size to maintain the
impedance with the same outer diameter to fit a PL-259 plug.)  But that would
tend to confirm that the actual "leakage" from the coax is a relatively small part
of the total rated loss - perhaps 0.01 dB, for a total leakage power of 1 watt
over a 50' run at 1 kW input.  That hardly seems likely to account for the differences
you are describing.

Now, let's consider the need for separate power runs.  Sure, one way that a transmitter
can interfere with nearby equipment is by RF getting on the power wiring through the
power cord, and getting distributed from there to the other devices.  This actually isn't
that uncommon.  Of course, you also could have voltage regulation problems on an
undersized supply line, especially trying to run an amp on a 15A or 20A circuit along
with other equipment:  that can manifest itself as lights dimming when you key up,
and possibly could cause various symptoms in consumer equipment (especially on
SSB).  But assuming your power drop was properly sized to start with (and size
doesn't appear to be the only problem if the layout of the cabling also made a
difference) then a more likely explanation is that RF was getting into the power
line somehow from the case of the rig, typically onto the AC ground wire.  If that
was the source, then filtering the AC power cord should have fixed the problem.

Both of those symptoms sound to me as though there is RF on the outside of the
coax that not only can radiate (and conversely pick up signals) more than can be
accounted for by "leakage" from the coax, as well as passing from the rig/amp
chassis onto the AC wiring and affecting other equipment that way.  Basically
the outside of the coax is acting like part of the antenna - our old friend, common
mode current
.

Now, I know you say your antennas are all resonant, and (at least some) have RF
chokes near the feedpoints.  I don't question that, but that doesn't say they
can't have common mode current
.  Resonance doesn't matter - in fact, I've
had antennas that had resonances because of common mode current (there
was more current on the coax than on the other antenna wire).

How does this fit with the observed symptoms?  If the common mode current is
from the antenna feedpoint down the coax shield, past the neighbor's house, into
the rig, then out through the ground wire into the AC wiring, it would cause all the
symptoms you are reporting:  running new power wiring can change the current
distribution on the coax, as well as reducing the feedthrough into adjacent devices
on the same electrical circuit.   And in my experience, most radiation from coax is
much stronger due to common mode current than actual leakage from the coax
(except in repeater installations where very high levels of isolation are required).

Oh, but you can't have common mode current because you have RF chokes at the
antenna feedpoints, right?  No, not at all.  Ever seen one of those VHF colinear
antennas that uses parallel tuned circuits between adjacent half wave sections
of radiator?  That same circuit would look like a trap in a standard antenna, but
in that case, because it is added at a high impedance point, it simply provides
the phase shift between sections without impeding the current.  (Well, that's the
theory anyway.  In practice they don't actually work that well.)  The point is that
adding an impedance at a high impedance / low current point on a radiator
doesn't really provide any reduction in current.  And where is the high impedance
point of an end-fed half-wave antenna?  Right at the feedpoint, where folks
typically add chokes and expect them to be effective.  They aren't.


So when I read your initial description of all the things that you did to eliminate
interference in and out of your system, they all just screamed COMMON MODE
CURRENT to me, even without looking at the antennas you are using, because
those are exactly the symptoms that it would cause.

So, yes, by now you've fussed around enough to where you appear to have it
under control, though that might just because you found a lucky length of
power cable that gave a high impedance at the antenna - similar to grounding
the coax 1/4 wave down from the feedpoint.  And, of course, that doesn't mean
you might not still have some common mode current, only that the distribution
along the coax doesn't put maximum radiation at trouble spots.

But if you had solved the common problems at the antenna in the first place,
it would have saved you a lot of work, and you might not have even needed a
ground system (except for lightning protection if that is an issue).


I have no problems with folks grounding their stations, though much of my operation
over the years has been without one (the ground pin of the AC power plug provides
my safety ground).  But grounding isn't a magic cure when the problem is really
something elsewhere that should be fixed at the source instead.


K6BRN

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Re: Recommended wire size for equipment to ground buss bar?
« Reply #19 on: March 14, 2020, 08:44:10 PM »

Dale (WB6BYU):

Whew!  You have even longer posts than I do.  Here are a few replies... if you'd like to discuss this further, PM me and I'll send you my phone number and we can talk - it's the best way to discuss this.

Quote
But the point of my post was that none of the hams I've known, even those  who run full legal limit (or more!), have needed such an extreme grounding system to eliminate problems.

There is nothing extreme about my grounding and CMC choke system.  In fact, it's pretty basic compared to my buddies who are hard core contesters. I'm not.  Perhaps it just seems complex to you?  I mean, like a shack entrance ground, CMCs and ground-loop "free" power ground.  Also, it has few of the advanced lightning protection features found in many Florida and Texas systems which really make things complex.  It's just well done basic grounding and isolation that works - well enough.  So - it's a little surprising none of your buddies or you has seen or done ANY of this.

On your questions regarding why I protect against coax shield currents (and ground loop noise) so heavily:  (this IS repetitive - I said this above)

My CA QTH is a modern home that uses quite a few efficient but electrically noisy inverter driven appliances, from the cental A/C to the washer and dryer and microwave.  Plus, many of my neighbors have extensive solar arrays with distributed inverters.  With seven antennas, my home and very compact 50 x 150 lot are literally (nicely hidden but...) draped in LMR-400UF coax, forming a great (shield) wire web capable of collecting and coupling any noise/RFI from nearby appliances directly into my "shack" and receivers via the coax shield - even from my own transmissions.

A shack entrance ground system for all coax is basic and anchors one end of the RF isolation system. (I'm surprised you've never heard of this!)

At the other end, closer to the antennas are high impedance (at HF) and VERY common CMC RF chokes.  The antennas are ALL resonant, but not perfectly so at all frequencies i use.  Hence, there is some common mode shield current (Yes, Glenn, I KNOW that's not the ONLY cause of CMC).  I've measured it.  About 30 mA in the worst case I found, without this system.  Not a lot.  But my neighbors homes are (at the eaves) less than10 FEET away and they have plenty of home wiring parallel with the coax runs (power/ground/intercom/security cameras...).  And that is enough to trip touch lamps, uspet POE video feeds, etc. easily, or couple into computer speakers on the near side of their house.

These problems are common in dense neighborhoods.  Not so much in more rural areas like yours.  Hence my other two QTHs have very basic safety grounds and RF chokes.  They just don't need more.

But in the before/after comparison of how much these basic steps helped reduce RX noise and TX interference - its pretty dramatic. 

These same steps helped a close friend solve the same problems in his home in a similar neighborhood.  Especially since his "shack" is in the garage right next to the inverter driven washer, the dryer and A/C.  And his GDO stopped having fits when he was on 40M as well.  As I said - these are pretty basic and well known remedies.

So.. your comment regarding antenna proximity...   Not much I can do about directly radiated near-field coupling except move the antennas further away.  But as I said, a LOT of RF was (re) coupled via adjacent antennas and coax runs.  The steps above helped control that problem.  Well enough to keep the peace with neighbors and my own kids and significantly reduce RFI into my receivers.

It's hard to argue with what simply works.  In a very repeatable and predictable way.

But if you'd like to drop in and show me a different and SIMPLER way... I'm all eyes and ears.  You WILL find that the problem is NOT simple when all the antennas are in such close proximity to each other and to metallic objects (like gutters, house wiring and coax).  Near field on 40M is about 65 feet - wider than my lot and near half its depth.  Yet I operate at >1KW from 6M through 160M (OK - NOT where its prohibited).  So controlling coupling ... is a challenge.  And when i rotate the antennas - coupling and SWR ... change.

So... Just how do you justify NOT having an adequate grounding/isolation system in YOUR shack?  (hands on hips, glaring in your direction)  Seems a little irresponsible!   Could cause global warming. The washer must be tripping over itself constantly, especially on 40M and lower!  Does your XYL know?   :)  (Just teasing here, Dale!)

Best Regards,

Brian - K6BRN
« Last Edit: March 14, 2020, 09:04:30 PM by K6BRN »
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WA9AFM

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Re: Recommended wire size for equipment to ground buss bar?
« Reply #20 on: March 15, 2020, 01:36:29 PM »

First, get a copy of "Grounding & Bonding For The Radio Amateur" by Ward Silver, N0AX and give it a read.  An excellent work on electrical, lightning, and RF grounding techniques.

In regard to your operating position, use either 1/2" to 1" flexible strap (either copper or woven) which will allow moving equipment around.  Create a single point ground plain (SPGP) from sheet metal (pick you favorite) with a bus bar; ground ALL your equipment, powered or not, to the bus.  Then ground the bus to your station ground.  Make sure any interface cables are a short as possible and laying flat on the SPGP. 

Don't use the braid from old coax to bond your equipment together; it's not designed for that use.  Once removed from the coax, the braid begins to degrade both physically and chemically.

As Mike Holmes says, "Do it right the first time."

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K6BRN

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Re: Recommended wire size for equipment to ground buss bar?
« Reply #21 on: March 15, 2020, 06:10:03 PM »

Quote
First, get a copy of "Grounding & Bonding For The Radio Amateur" by Ward Silver, N0AX and give it a read.

Good advice!
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W3TDH

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Re: Recommended wire size for equipment to ground buss bar?
« Reply #22 on: April 29, 2020, 01:40:42 PM »

I use 1 inch tinned braided strap to bond all my components. 

Tinned copper braid is nice because of its very large surface area and flexibility. The end for equipment connection can be rolled, inserted into the sleeve of a large terminal lug, and then soldered. Makes for a very tidy connection to an existing equipment ground terminal. You can solder the edge of the other end to prevent fraying, if you like. My bus bar is a 1" section of copper pipe, with copper stand-offs and copper-plated  screws to mount to the studs beneath the drywall. The braids will terminate on the tubing, as will a 3" copper strap coming into the station from the nearby ground rod. I placed a snugly-fitting wooden dowel in the pipe to provide support against crush pressure from clamps, but I'm considering soldering both strap and braids to the pipe, once I have equipment where I want it, (and after removing the dowel). I imagine (and may be quite mistaken) that I can roll the strap tightly around the pipe one and one half turns, secure it with sheet metal screws, and then sweat it with a torch as you would any copper pipe joint. All will be well-prepared and coated with rosin flux. Using 63/37 Sn/Pb (eutectic) solder should reduce the heating required, but it's still a very large "joint," so may need a so-called MAPP gas torch. And suitably placed heat shields while working! If my plumber friend says, "Are you kidding?" and refuses to help, I'll take the hint and stick with just the clamps and sheet metal screws.
I am not saying that you suggested this I am just taking the opportunity to point out that the US National Electric Code (NEC) specifically prohibits any Equipment Grounding  Conductor or Grounding Electrode Conductor connection made only with solder. The reason is that during a high voltage cross fault or a Lightning discharge the solder will melt open instantly and spatter the area with molten solder.

We were looking for a way to terminate tinned copper braid for field day and found a company that makes a copper tab which folds over the braid and is then tightened onto the braid by the attachment hardware. We could not get them quickly enough so we took 1/2 inch copper pipe, shined it up with emery cloth and a wire brush, partially collapse pipe piece in a vise, applied a liberal amount of Copper based antioxidant paste, collapsed pipe piece tight onto the braid with the vise; warning over tightening will sever much of the braid; and then drilled hole for connection stud. Because the connection ends up being air tight corrosion inside of the tab is unlikely. The outside of the tab can be cleaned up as necessary with Emery cloth. If the connecting hardware is brass than regular sized hardware will be fine. If the hardware is Stainless Steel then use fender washers and bell nuts so as to enlarge the connection area to more of the copper terminating tab. If you use flat copper strip brass fender washers are large enough to make a good connection. Do not use normal sized flat washers to connect directly to the conductor without a copper tab.

I believe that rolling braid as tight as you can into the smallest hy press lug it will fit into and then crimping the lug with a tool and die made for that sized of lug would also make a durable airtight connection. Apply copper antioxidant paste to the braid prior to crimping.

--
Tom Horne W3TDH
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KK6WLN

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Re: Recommended wire size for equipment to ground buss bar?
« Reply #23 on: June 05, 2020, 04:26:06 PM »

We were looking for a way to terminate tinned copper braid for field day and found a company that makes a copper tab which folds over the braid and is then tightened onto the braid by the attachment hardware.
--
Tom Horne W3TDH

Could you please pass along the company name or a link for the copper tabs?  Thank you!

Apply copper antioxidant paste to the braid prior to crimping.

Do I need to use the paste on these connections inside the shack also?  Or just outdoor connections?

Thanks guys!  Pete
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