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Author Topic: Possible ground problems??  (Read 249 times)
K4JC
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Posts: 76




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« on: June 18, 2007, 06:53:31 PM »

Hi all. I have a problem I've not encountered before, and I've put together a lot of hamshacks. I am running my HF rig, Yaesu quad bander, and a 220 mobile in the shack all using an Astron RS-50M power supply. Occasionally when I go to connect the coax jumpers from the rigs to the feedlines (I always disconnect the feedlines when not in use) I get a small AC shock from the PL-259s. This happens no matter which radio or antenna I am connecting. It isn't always, just once in a while.

The VHF/UHF antennas are all grounded, as is the mounting pole. HF antenna is a Windom. Logistically I have no way to run a proper ground for the equipment. Does this sound like a grounding problem? Would an "artificial ground" such as MFJ carries be a viable solution?

Thanks for any help you can give.
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AA4PB
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« Reply #1 on: June 18, 2007, 07:04:11 PM »

This is often caused by leakage currents in other devices in the house that cause currents to flow in the grounding conductor of the electrical system. The result is that the potential at the ground pin on the outlets is different than that of your antenna ground. This is one reason that the National Electric Code (NEC) requires your antenna ground rods to be bonded to the building's electrical system ground. It helps to ensure that all "grounds" are actually at the same potential.
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KE3WD
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« Reply #2 on: June 18, 2007, 07:06:54 PM »

Probably not AC but static buildup on an antenna with large capture area.  

This can be a real problem in some locations where it is the right and usually dry condx.  

I've heard of some ops being able to bleed off such charge, believe it or not, off of the insulation on the coax wire by wrapping it tightly with several turns of solid copper wire and then attaching a flexible ground to that.  

I think that by far your best approach would be to purchase a good coax switch that also incorporates automatic grounding of nonconnected inputs, like the Alpha Delta or the MFJs that feature such and stop messing around with disconnected coaxes, which can arguably be not as effective assurance against lightning strike as some believe.  The lightning, after all, can reach potentials that will pull it from sky to ground (with electrons actually flowing the other direction) -- the distance between the unconnected coax and any ground potential in your shack is thus a short jump indeed.  

It is also a very good idea to use Polyphaser lightning protectors, one for each antenna line, grounded as per Polyphaser's directions.  Don't let the small size of the Polyphaser devices fool you, and don't make the mistake of thinking that they are equal in technology or performance to the old gas tube or spark gap arrestors either.  Different technology that has proven itself time and again for me.  


.
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KE3WD
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« Reply #3 on: June 18, 2007, 07:09:49 PM »

If you indeed think that it is AC, use an AC voltmeter and measure the potential from point to point.  

If you get any significant reading, more than a few volts AC, by all means suspect something to be amiss with your house electrical bonding system and have a licensed electrician come quick.

If your AC panel bonding ground has become deteriorated or is nonexistant, there might be a situation here where your entire house wiring system may be finding ground potential via any shack grounding you have, especially if you are running a ground rod for the shack or antennas.  


.
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K4JC
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« Reply #4 on: June 18, 2007, 08:42:18 PM »

All good suggestions, and all good possibilities as many of the factors mentioned have come into play here. Conditions have been very dry (serious drought), and it is entirely possible I have a flaky electrical system, as the house is nearly 100 years old and still has signs of the original electrical system (the old screw-in fuse panel is still on the front porch! But long since disconnected...)

Maybe I should have an electrician come in and give things the once over; if nothing else, for peace of mind. If it isn't too expensive, maybe have a dedicated line run just for the radios.
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VA7CPC
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« Reply #5 on: June 18, 2007, 10:27:12 PM »

Get a plug-in  polarity tester at any electrical supply house (Home Depot has them).

If you have currents flowing through the AC ground wire, or mis-connected wiring, it should show them up.

It's always nice to say to the electrician "I _know_ I have a problem".

   Charles
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KE3WD
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« Reply #6 on: June 18, 2007, 11:01:12 PM »

Plug in polarity tester with LEDs on it isn't worth diddly squat in a home that has a fuse box, two-wire AC and possibly pin and tube wiring in the walls.  

What you want to check and test is the AC fuse panels GROUND BONDING.  Properly should be just outside the box mounting clamped to an 8 foot ground rod.  But in many older homes it may be clamped to the copper water pipe, which is considered not so good these days for various reasons.  


.
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N6AJR
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« Reply #7 on: June 18, 2007, 11:07:00 PM »

I picked up a roll of 2 inch wide copper , fairly thing, (like as thick as 3 or 4 sheets of paper) and we tacked this under the rear perimiter of the u shaped work table in the shack. we then ran the same copper from the radio grounds to the continous strip and fastened with a screw and those star washers.  this would give you a common ground for all your gear, and I also ran a wire out to the earth ground ( very close) this feels better iven if I can't prove its better, I like it. it just seems right.
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KB9CRY
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« Reply #8 on: June 19, 2007, 04:12:26 AM »

I'd say that you're just seeing static buildup on your antennas that is being stored and then released when you plug in your coaxes.

You need to install a proper grounding system, a lightning grounding system.  If you can feel the shock or see the flash, think of what it could do to your electronics.

Even if you don't have lightning, this is why everyone needs a properly designed and installed grounding system.

Do a search for grounding on the main forums page.  Go to the Polyphaser and ICE websites and read their technical articles.

You need the following:

Antenna/Tower grounds (you said that you have that).

Single Point Ground

Lighting Arrestors

Shack Ground

Electrical Service Ground

Read up on all these subtopics.
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WA3SKN
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« Reply #9 on: June 19, 2007, 06:49:47 AM »

OK, there are several questions about what is going on here, but the answer to all of them is Ground, Ground, Ground!
Break out a meter and start measuring... antennas to ground, AC to ground, neutral to ground, radio ground to AC ground,ETC.
You will probably determine the cause quickly.  Then you can plan your new and improved ground system around it!

-Mike
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AA4PB
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« Reply #10 on: June 19, 2007, 06:59:13 AM »

I think it unlikely that you would get enough static buildup on a VHF/UHF antenna to cause a spark, especially if they are grounded. The windom perhaps but not to the coax shield if it is grounded.

Leakage currents in the power grounding conductor are not necessarily an indication of faulty wiring and it is not an uncommon situation. What it indicates is the need to bond your antenna grounds to the power system ground at the service entrance panel in accordance with NEC requirements.
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