Welcome to the forum cub570
Quote:
Originally Posted by cub570 
Everything is plugged in through a fairly typical surge strip. I'm thinking at least part of it is that I live in an older house, and all the outlets are ungrounded (2 prong).
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If you mean that your outlets are ungrounded and your pieces of equipment have 2-wire plugs or 3-wire plugs with an adapter, I think I have experienced the same problem.
When I was calibrating the signal strength scale of an Apex DT502 to send to a friend, I had many pieces of equipment connected to AC:
2 Apex DT502s
2 Audiovox PLV16081 8" TVs used as monitors for the CECBs
1 Sony KDL22L5000 TV
1 CM 7777 preamp power supply
1 AC adapter for Sadelco signal level meter
1 AC adapter for RS preamp
During the tests I noticed a problem that I have seen before but couldn't track down until recently. When I touched a ground and the case of the equipment I felt a mild shock. My Fluke 25 DMM gave a reading of 58VAC. I hooked up my Simpson 229 Leakage Current Tester and found that the voltage reading was 40 volts and the leakage current was about 200 microamps; not enough to be dangerous but enough to give a tingle. (The difference in the voltage readings is because the input impedance of the two meters is not the same.) GFCIs are designed to trip at 5 mA, which is 25x as strong. I then started unpluging each piece of equipment and noticed that the leakage current went down each time. The boxes have 2-wire cords so I grounded the coax shields at the splitter and the leakage current went to zero. With so many pieces of equipment connected to AC the normal equipment leakage currents were additive.
Most of the pieces of equipment use switchmode power supplies, which have more normal leakage current than the transformer power supplies for the signal level meter and RS preamp.
Even a good quality energized 3-wire extension cord will have some normal leakage current from the hot conductor to the ground and neutral conductors without any equipment being connected to it.
Since I was able to feel a leakage current of about 200 microamperes, my threshold of perception is considerably less than the mean value of 1.067 mA measured by Charles F. Dalziel as described in the 229 manual.
http://www.simpsonelectric.com/uploa...9-2_manual.pdf
http://www.mdsr.ecri.org/summary/det...px?doc_id=8285
Since your pieces of equipment most likely have switchmode power supplies and they are interconnected through the shields of the cables between them, I suggest that the shields be connected to a ground. This demontrates the advisability of using a grounding block on the antenna downlead.
If you are able to borrow an appliance leakage current tester to see if your equipment is faulty, that would be ideal. It is also possible to assemble an inexpensive leakage current test circuit.
http://www.repairfaq.org/sam/safety.htm#saftes
When setting up your equipment, turn all pieces off and remove their power plugs (or the power strip plug). Connect the cables between them, plug them into AC, and then turn them on.
For maximum safety:
1. Have an electrician install a properly wired 3-wire outlet for your equipment so that the equipment that has 3-wire plugs is grounded.
2. Test all pieces of equipment to be certain that the leakage current of each piece is below 500 microamperes (0.5 mA).
3. Interconnect the pieces of equipment as required.
4. Plug the 3-wire and polarized 2-wire plugs into the outlet strip.
5. Turn the power strip and then the equipment on.
There is another step that really needs to be done between no. 3 and no. 4, which is to ground the pieces of equipment that have 2-wire polarized plugs. This is the "dirty-little-secret" that is not often mentioned, but is important because the normal within-limit leakage current of equipment that has 2-wire polarized plugs is additive when connected together. Even though my Sony Bravia is in a plastic case and has leakage current within safe limits, there exists the potential for leakage from the antenna coax shield to ground.
I did my test setup in the kitchen and had two grounds available to drain the total equipment leakage current of about 200 microamperes: the grounding pin of the 3-wire outlet and a copper cold water pipe (same ground as for electrical panel). Either one reduced the total leakage current to zero.
If a separate ground rod is used to ground the equipment it must be connected to the electrical service ground with no. 6 gauge copper wire as specified by the new NEC guidelines for outdoor antennas. One of the reasons for bonding together the two grounds is to eliminate the possible voltage potential between them.
See also this thread:
Electrocuted by coaxial cable (no joke)
Leakage Current Tests 3.pdf 87.701171875k . file
Edited by rabbit73 - 10/29/12 at 5:51pm
