Ground Question

[SCPD]

A big Coyote's Smile, PRC.....
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I had to put that disclaimer "...for what it's worth..." behind my EE credentials since I have had very little formal training in lightning-- and grounding -in school. I am probably like most- for what I know has been hard learned thru painful experiences.
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For that matter, I am surround'd by fellow engineers who also fall woefully short of the pretend "experts-in-all-things-electronic" that those outside my lab think us. What looks so good in the textbooks on this grounding subject has proved sour notes when played in the School of Hard Knocks....
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Earlier this summer (spring?) I mention in here what lightning was want to do- it's blasting a hole thru the side of an equipment hut rather than follow the carefully design'd (by engineers, no doubt... ) ground-strap path, innocently to earth. Fortunately it didn't take out any equipment, but it made a jolly mess out of that hut's wall and miraculously did not blow up the large propane tank into which it decided to end its career-- (though it stripped that tank's paint away as through as if it had been sandblast'd- leaving it a shiny steel.)
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The "Hard Knock's School" never stressed the inherent impedence resistance of even a slight loop in a ground strap at the frequencies seen in a mega-lightning bolt.... or so we reasoned at the time (and correct'd??)
I mention'd this to a NASA engineer, whose job it is to protect the giant lightning rods (also known as rockets on the launch pad) from strikes... He said we should have known better than to have anything even approaching a loop in the grounds straps.
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"Look at them all as just big RF chokes"... he said.
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......................I could only smile-
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..... "I must have missed that lecture..."
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....................................CF
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I later realized that this discussion seems to be revolving around two different subject- the ground requirements for AC power and, though connect'd, a different field of surge and lightning protection. The two are related.... but what works for household AC systems should not be confused with what is necessary for lightning protection.
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[wyShack]

The only safe way to handle this is either rewire the house or use an isolation transformer in the shack. You can buy a dry type isolation transformer (I would suggest you oversize it to allow for future equipment). Ground the 'shack' side of the transformer to your ground system (and the case). You now need to follow code for a separately derived 'system' including separate ground. If everything in the 'shack' is on the same fuse/breaker' and the shack is on its own circuit, I would put the transformer at the panel. Otherwise DO NOT have anything (even a wall wart) 'cross connecting' the systems-if you do the difference in ground potential between your ground and whatever ground is on the utility side will appear on your equipment as a DC voltage (which under fault or lightning conditions could be several hundred volts for a short time). That is a good way to 'kill' most solid state equipment.

Back when cable TV was new, the cable company would run their own ground and the next storm would take out the TV tuner-lesson learned and why the NEC requires ground rods be bonded together except for separately derived systems which have to be isolated form each other. By isolated I mean no wires between (phone and data network cables are included and cannot bridge the isolation) the two systems.

May be your only feasible solution.

 

[RFI-EMI-GUY]

The only safe way to handle this is either rewire the house or use an isolation transformer in the shack. You can buy a dry type isolation transformer (I would suggest you oversize it to allow for future equipment). Ground the 'shack' side of the transformer to your ground system (and the case). You now need to follow code for a separately derived 'system' including separate ground. If everything in the 'shack' is on the same fuse/breaker' and the shack is on its own circuit, I would put the transformer at the panel. Otherwise DO NOT have anything (even a wall wart) 'cross connecting' the systems-if you do the difference in ground potential between your ground and whatever ground is on the utility side will appear on your equipment as a DC voltage (which under fault or lightning conditions could be several hundred volts for a short time). That is a good way to 'kill' most solid state equipment.

Back when cable TV was new, the cable company would run their own ground and the next storm would take out the TV tuner-lesson learned and why the NEC requires ground rods be bonded together except for separately derived systems which have to be isolated form each other. By isolated I mean no wires between (phone and data network cables are included and cannot bridge the isolation) the two systems.

May be your only feasible solution.

Lets say he has an old house with knob and tube, or two conductor romex. No metallic conduit. Probably best to rewire.

But an isolation transformer,for the shack in my opinion, is impractical because there will inevitably be cross connection of TV, phone and network wiring throughout the house so the potential for differential currents cannot be escaped.

I had a house built in the 60's in the midwest and it had metallic conduit. The three prong outlets got their protective ground return from the conduit. I also had a house built in the 40's in Miami with conduit and two prong outlets. However the rubber coated wires were a disaster. The conduit made it easy for the electrician to pull in all new home runs of three conductors. A new breaker panel and utility furnished 150 A service upgrade set me back $1700 (In 1986 money).

But I think the OP's situation is simpler, his panel is likely grounded, and the wire probably hidden by siding or snaked into the basement or crawlspace and clamped to a pipe somewhere. If not, a careful technician could ground the service using advice given above after reviewing the NEC which is available everywhere.

 

[jonwienke]

The only safe way to handle this is either rewire the house or use an isolation transformer in the shack.

An isolation transformer is a pointless expense given that all grounds are REQUIRED to be connected together anyway. And rewiring the house is probably not necessary. The most likely scenario is that the house does have a ground rod, but it is buried and not visible without doing some digging. Adding an additional ground rod is easy, and won't hurt anything if there already is one.

 

[RFI-EMI-GUY]

An isolation transformer is a pointless expense given that all grounds are REQUIRED to be connected together anyway. And rewiring the house is probably not necessary. The most likely scenario is that the house does have a ground rod, but it is buried and not visible without doing some digging. Adding an additional ground rod is easy, and won't hurt anything if there already is one.

Even if there is none, it wont hurt it to add one. Just kill the main breaker and bond the neutral to the breaker cabinet (assuming that it isn't a sub panel) and attach a ground lead.

 

[wyShack]

While I agree about the issue of cross connection -a isolation transformer will allow for 'multiple' grounding systems-see NEC 250.20.

The problem here is not so much finding (or replacing)the ground rod on the supply side but the fact that by 'working' on the wiring, the electrician is required to bring things up to the 'current' NEC. That may just be the service (likely upgrading to a 100 or 200 amp panel depending on local requirements) or even more updating work to meet current code.The NEC requires any work to be done to current code and when working on older systems this can really open a 'can of worms'. I agree that it is likely best to rewire the whole house for safety and other reasons-I just realize the cost may be prohibitive. If the house is old enough, it likely was wired before a ground was required and therefore the existing wiring has no provisions for a ground connection-just the neutral and hot leads. If so, just grounding at the shack means all the cross connect problems of my earlier post as the 'next' ground is likely at the utility's transformer-which could be hundreds of feet away. An isolation transformer would 'allow' a break in the neutral/ground system and prevent damage to the equipment-but I agree the problem of 'crossing' the grounds would always be a problem.

A similar issue is when using leased phone lines for telemetry in power substations or anyplace wires are run for 'long' distances. In most cases you can use an opto isolator for comm circuits but the key is removing any connection to a 'remote' ground- contrary to popular belief all ground rods are not at the same potential.

 

[jonwienke]

None of that changes the fact that an isolation transformer is unnecessarily expensive, and creates a whole new set of cross-connection hazards. If the OP can DIY, adding a ground rod at the AC service panel and tying that to the antenna ground rods could be done for under $200.

 

[Project25_MASTR]

But an isolation transformer,for the shack in my opinion, is impractical because there will inevitably be cross connection of TV, phone and network wiring throughout the house so the potential for differential currents cannot be escaped.

More people are moving to a single wireless base phone system (except for those who still have fax machines). Ethernet devices have built-in isolation transformers though they don't always work and in my experience aren't something to rely on. The real issues again as you stated, multiple phones and cable TV.

 

[jonwienke]

There's also the issue of whether the walls or floor have any metal components in their construction, which would create a shock hazard if an isolation transformer was installed. And you'd have to be religious about not plugging a vacuum cleaner in one room to clean another, or the vacuum cleaner body would become a significant shock hazard. An isolation transformer would require warning signs and/or strict policies and procedures to prevent people from potential injury while performing normal household tasks that crossed the boundary between the isolated and un-isolated zones.

 

[AK9R]

...Ethernet devices have built-in isolation transformers though they don't always work...

Interesting that you mention Ethernet devices.

Several years ago, a cloud to ground lightning strike hit near my house. The strike induced considerable energy into the cable TV company's RG-6 coax running to my house. That energy flowed into the house and let the magic smoke out of the cable modem which also had a wall-wart power transformer and an Ethernet cable to my computer. No televisions were affected. Some energy continued to flow down the Ethernet cable to my computer and zapped the Ethernet adapter on the motherboard, but no other functions of the computer were affected.

Upon further inspection, I discovered that the RG-6 coming into the house did, in fact, go through a female F to female F grounding block on the outside of the house. However, the ground wire attached to the grounding block was not attached to the nearby ground rod.

Oops. I guess the installer was in a hurry.

 

[NJ9M]

Thanks for all the info. Between this forum and another one I think I've got things figured out.