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Author Topic: CATV/RV Grounding Issue  (Read 1745 times)

Mike Sokol

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CATV/RV Grounding Issue
« on: March 04, 2017, 07:13:21 pm »

This is the sort of question I regularly answer on my NoShockZone blog about RV electricity. Take a look a see if you can guess what's causing the issue. I'm pretty sure I already know so we'll compare notes in a few days after I formally answer this.


"Vance Cowley
CATV/MATV Installer

I maintain a cable TV distribution system at an RV park. I suspect an RV had an AC electrical problem that found its way into the cable TV system. The RV was parked before the first pedestal that the cable TV tap burned up. The cable  tap and coax wiring for 4 pedestals literally burned up, the center conductor vaporized. We found one RV, 3rd one in line,  where the wiring in his trailer is completely melted and the plastic mounting plate at the pedestal had been on fire.

As far as I know the connectors for the TV system at the pedestals do not run through ground blocks, older system. How can I prevent this from possibly happening in the future? Is this a floating ground issue?

Just before this incident owners in these 4 pads were complaining about being shocked when they touched the outside of their trailers. A non contact voltage probe was used to identify RV that was causing the problem. The non contact probe illuminated 4 feet away from the problem RV. The trailer was disconnected and the problem with the outside shock went away. The RV owner was asked to have an electrician look at his trailer before reconnecting the power plug to the power pedestal. No information on what was found."

Keith Broughton

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Re: CATV/RV Grounding Issue
« Reply #1 on: March 05, 2017, 07:23:39 am »

This is the sort of question I regularly answer on my NoShockZone blog about RV electricity. Take a look a see if you can guess what's causing the issue. I'm pretty sure I already know so we'll compare notes in a few days after I formally answer this.


"Vance Cowley
CATV/MATV Installer

I maintain a cable TV distribution system at an RV park. I suspect an RV had an AC electrical problem that found its way into the cable TV system. The RV was parked before the first pedestal that the cable TV tap burned up. The cable  tap and coax wiring for 4 pedestals literally burned up, the center conductor vaporized. We found one RV, 3rd one in line,  where the wiring in his trailer is completely melted and the plastic mounting plate at the pedestal had been on fire.

As far as I know the connectors for the TV system at the pedestals do not run through ground blocks, older system. How can I prevent this from possibly happening in the future? Is this a floating ground issue?

Just before this incident owners in these 4 pads were complaining about being shocked when they touched the outside of their trailers. A non contact voltage probe was used to identify RV that was causing the problem. The non contact probe illuminated 4 feet away from the problem RV. The trailer was disconnected and the problem with the outside shock went away. The RV owner was asked to have an electrician look at his trailer before reconnecting the power plug to the power pedestal. No information on what was found."

Bad wiring on one trailer created a "hot skin" condition and that was fed into the shield of the CATV system.
With the CATV cable floating. no cct breaker action happened and the cable shieled was "hot"
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Mike Sokol

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Re: CATV/RV Grounding Issue
« Reply #2 on: March 05, 2017, 07:36:41 am »

Bad wiring on one trailer created a "hot skin" condition and that was fed into the shield of the CATV system.
With the CATV cable floating. no cct breaker action happened and the cable shieled was "hot"

You still have to account for why 4 other RVs were affected by a single RV plugging in. And what was the wiring failure in the first RV that caused the hot-skin condition? Also, was it a high-, medium-, or low-impedance failure. This is closely related to distributed power issues in pro-sound systems, so it's good study.

Mike Sokol

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Re: CATV/RV Grounding Issue
« Reply #3 on: March 05, 2017, 07:46:59 am »

Here's a few more hints that may or may not be relevant to this problem....

Some older campgrounds didn't have "grounded" wiring for the campsite pedestals, so they just added a grounding rod to each outlet pedestal.

Many campgrounds use daisy-chained wiring with 4 to 8 campsites hooked onto a single feeder cable.

RV's are required to maintain separated neutral and ground wiring internally, and be only bonded by the connection they're plugging into for shore power.

Many older RV owners like to DIY their own RV wiring.

Some campgrounds use DIY guys to rewire or add power pedestals at each campsite. They often have no electrical wiring training. 

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Re: CATV/RV Grounding Issue
« Reply #4 on: March 05, 2017, 11:18:50 am »

I should have added to "no cct breaker action" was due  to no ground .
What we don't know is, were the other RVs plugged into a same pedestal or was this problem spread out through the camp ground.

The original fault would be a wiring defect that brought hot side of AC to chassis of the RV. Hard to say where that happened.
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Mike Sokol

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Re: CATV/RV Grounding Issue
« Reply #5 on: March 05, 2017, 12:25:35 pm »

I should have added to "no cct breaker action" was due  to no ground .
What we don't know is, were the other RVs plugged into a same pedestal or was this problem spread out through the camp ground.

Since it's generally one RV per campsite, and one Pedestal/Outlet per campsite, it's safe to assume these four RVs were spread across four campsites on four different pedestals. All the pedestals in a campground section are generally daisy-chained together.

Quote
The original fault would be a wiring defect that brought hot side of AC to chassis of the RV. Hard to say where that happened.

Yes, that's most likely the cause. I've seen shorts like this created with wiring laying across sharp metal struts in the chassis of the RV, or wiring that's been pinched between the floor and a metal support beam, or even by a screw drilled into the wall which pierces a wire run. That's a low-impedance/high-current fault which will have full circuit breaker amperage available for the fault current.

An example of a mid-impedance/mid-current fault would be an electric hot water heater with a leak in the heater element. That will provide about 1 to 2 amps of current to the chassis.

A high-impedance/low-current fault would be an appliance with a leaky transformer plugged into an interior outlet in the RV. Leakage can be anywhere from a few mA up to a few hundred mA. Some will trip a GFCI, while others won't.

Everything plugged into an outlet exhibits SOME leakage to their chassis. For instance, a Crown iTech amp will leak up to 3 mA and still pass final testing. A common Surge-Strip will leak 1 to 2 mA. A double-insulated piece of gear will have to have less than 1 mA leakage (IIRC less than 0.7 mA) to pass UL listing.

But this all begs the question. How does ONE RV with a wiring problem that creates a line-to-chassis fault-current affect several OTHER RVs in the same wiring loop. And how do they all get a "hot-skin" voltage?

Hint: I call this a "Reflected Hot-Skin Voltage".

John Roberts {JR}

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Re: CATV/RV Grounding Issue
« Reply #6 on: March 05, 2017, 12:38:08 pm »

RPBG?


JR
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Re: CATV/RV Grounding Issue
« Reply #7 on: March 05, 2017, 01:09:47 pm »

RPBG?

Probably not. Here's another hint. I've seen a few campgrounds where all the pedestals in a section had their EGC "grounds" connected together, but there was a lost connection back to the service panel's Neutral-Ground bonding point. So any voltage induced on one pedestal's ground wire would be "Reflected" to all the other pedestal "ground" wires in the area. So this becomes a floating ground wire interconnecting several pedestals and the RVs connected to them. Any single RV with a line-to-chassis leakage will induce a voltage on its ground wire, which then shows up at multiple RVs at several other pedestals in the area. Of course, if the daisy-chained EGC wire was actually "Bonded" back to the service panel, then NO voltage would be possible on an RV chassis. In a properly bonded EGC the fault current would sink back to the bonding point. If it was a high-current fault, it would trip a 20-amp circuit breaker. If it was a mid-current fault, it would just dump a ampere or two into the service panel bond and we wouldn't know about it. If it was a low-current fault, no problemo since that's what the EGC is supposed to deal with.

Now, think about what happens when you have four RVs connected together via a common EGC ground wire that's not bonded at the service panel. When you hook up a CATV wire that ties the chassis back to the service panel, and plug in a single RV with a direct line-to-chassis short, you can dump ten's of amperes of current through the CATV wiring. I've seen this a bunch of times and it always mystifies the local electricians.

So the next question is, how do we test for this sort of fault at a campground?

John Roberts {JR}

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Re: CATV/RV Grounding Issue
« Reply #8 on: March 05, 2017, 02:40:32 pm »

Probably not. Here's another hint. I've seen a few campgrounds where all the pedestals in a section had their EGC "grounds" connected together, but there was a lost connection back to the service panel's Neutral-Ground bonding point. So any voltage induced on one pedestal's ground wire would be "Reflected" to all the other pedestal "ground" wires in the area. So this becomes a floating ground wire interconnecting several pedestals and the RVs connected to them. Any single RV with a line-to-chassis leakage will induce a voltage on its ground wire, which then shows up at multiple RVs at several other pedestals in the area. Of course, if the daisy-chained EGC wire was actually "Bonded" back to the service panel, then NO voltage would be possible on an RV chassis. In a properly bonded EGC the fault current would sink back to the bonding point. If it was a high-current fault, it would trip a 20-amp circuit breaker. If it was a mid-current fault, it would just dump a ampere or two into the service panel bond and we wouldn't know about it. If it was a low-current fault, no problemo since that's what the EGC is supposed to deal with.
That reminds me of my kitchen before I added a ground wire back to my panel. The ungrounded 3-wire outlets and power drops connected all the appliance chassis grounds to each other but the whole shebang was floating.

A bad overvoltage clamp device in a faulty power strip energized my entire kitchen appliances through the common ground (only low mA but enough to feel).
Quote
Now, think about what happens when you have four RVs connected together via a common EGC ground wire that's not bonded at the service panel. When you hook up a CATV wire that ties the chassis back to the service panel, and plug in a single RV with a direct line-to-chassis short, you can dump ten's of amperes of current through the CATV wiring. I've seen this a bunch of times and it always mystifies the local electricians.

So the next question is, how do we test for this sort of fault at a campground?
Line to ground through a 20A fuse. If the fuse doesn't blow, Houston we have a problem.

JR
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Mike Sokol

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Re: CATV/RV Grounding Issue
« Reply #9 on: March 05, 2017, 02:52:53 pm »

That reminds me of my kitchen before I added a ground wire back to my panel. The ungrounded 3-wire outlets and power drops connected all the appliance chassis grounds to each other but the whole shebang was floating. A bad over-voltage clamp device in a faulty power strip energized my entire kitchen appliances through the common ground (only low mA but enough to feel). Line to ground through a 20A fuse. If the fuse doesn't blow, Houston we have a problem.


Exactly right. And this is the same sort of thing that can happen in a distributed power system for sound systems. If there's a failure in the EGC Ground back to the Service Panel's bonding point, any single piece of gear with a significant line-to-chassis fault current will energize the chassis of everything with a ground plug. Then if you touch the mixing console, amp chassis or microphone and an earth-grounded object at the same time, your body will be in the middle of the fault path. If it's a low-current fault, then you feel a tingle. If it's a mid or high-current fault and your hands are wet, that's when you can die.

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Re: CATV/RV Grounding Issue
« Reply #10 on: March 05, 2017, 03:17:12 pm »

One of my electrical inpsectors points out that an inspection is only a point in time.

OSHA has a concept called "assured ground conductor testing".

Considering the wear and tear and constant connecting/disconnecting of "electrical systems" of unknown condition that have the potential to affect other campers, it would seem to make sense for campgrounds to do regular (end of season and start of season??) testing of grounding systems and bonding.  Of course, not many businesses are looking to spend money to prevent things they do not understand.
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Re: CATV/RV Grounding Issue
« Reply #11 on: March 05, 2017, 03:42:30 pm »

One of my electrical inpsectors points out that an inspection is only a point in time.

OSHA has a concept called "assured ground conductor testing".

Considering the wear and tear and constant connecting/disconnecting of "electrical systems" of unknown condition that have the potential to affect other campers, it would seem to make sense for campgrounds to do regular (end of season and start of season??) testing of grounding systems and bonding.  Of course, not many businesses are looking to spend money to prevent things they do not understand.

To paraphrase someone else (read it from Nathan Lively's little book on audio)  "electricity is difficult to explain because it's invisible."

If this were a water or sewer leak the campground owner would *probably* fix it because the failure is obvious and the fault is certain in its causality.  In the case of the electrical problem I can see an RV campground owner saying "it's YOUR camper/appliances/accessories and not MY electrical service" and the typical RV owner would be totally unequipped to respond.  Hell, even many licensed electricians would be unable to adequately define and locate the fault(s).

When it comes to infrastructure my take (as a recent RV owner) is that most campgrounds are slums.  The landscaping may be pretty, the pool may be clean but the key service every unit needs is the most suspect because it's invisible and the RVers don't have the knowledge base to effect a change from campground owners.
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Mike Sokol

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Re: CATV/RV Grounding Issue
« Reply #12 on: March 05, 2017, 03:52:24 pm »

If this were a water or sewer leak the campground owner would *probably* fix it because the failure is obvious and the fault is certain in its causality.  In the case of the electrical problem I can see an RV campground owner saying "it's YOUR camper/appliances/accessories and not MY electrical service" and the typical RV owner would be totally unequipped to respond.  Hell, even many licensed electricians would be unable to adequately define and locate the fault(s).

It would only take a Ground Impedance Tester such as an Amprobe INSP-3 or SureTest Analyzer and a few 50-amp and 30-amp adapter plugs to test every pedestal once a year for ECG ground continuity. But that's $400 worth of gear and 5 minutes per pedestal to test. And then you know about and have to fix the offending receptacles. I've suggested this test procedure to the RV industry governing boards many times, but they don't want to hear about anything that suggests someone could be shocked, and they certainly don't want to tell any campgrounds that they should test their pedestal receptacles. But I keep working on them...  ;)

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Re: CATV/RV Grounding Issue
« Reply #13 on: March 05, 2017, 04:02:50 pm »

It would only take a Ground Impedance Tester such as an Amprobe INSP-3 or SureTest Analyzer and a few 50-amp and 30-amp adapter plugs to test every pedestal once a year for ECG ground continuity. But that's $400 worth of gear and 5 minutes per pedestal to test. And then you know about and have to fix the offending receptacles. I've suggested this test procedure to the RV industry governing boards many times, but they don't want to hear about anything that suggests someone could be shocked, and they certainly don't want to tell any campgrounds that they should test their pedestal receptacles. But I keep working on them...  ;)

When Grandma gets electrocuted while boarding her Monaco and there is a multi-milion $$$ lawsuit, the RV campground industry will finally acknowledge that there is far more maintenance to do than mowing the grass, cleaning the pool and keeping the laundry room open.

But nothing will happen until - as we used to say in college debate - there is blood on the flow sheet.  Without victims with pictures, names and surviving family then nada, zilch, nothing will be done by the *industry* to fix the problems.  When you factor in that many RV camps are in places with non-existent Code enforcement or that have been "grandfathered in" since Edison built his first power plant, it will take a significant loss of life.
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Mike Sokol

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Re: CATV/RV Grounding Issue
« Reply #14 on: March 05, 2017, 04:24:42 pm »

When Grandma gets electrocuted while boarding her Monaco and there is a multi-milion $$$ lawsuit, the RV campground industry will finally acknowledge that there is far more maintenance to do than mowing the grass, cleaning the pool and keeping the laundry room open.

I thought the death of this 3 year old boy from an hot-skin electrified Airstream in the family backyard would move the industry, and I even did a video about it and posted the link on a thread here: http://forums.prosoundweb.com/index.php?topic=150445.0

As soon as Airstream figured out his death was from an improperly maintained electrical outlet, they felt they were off the hook and refused to comment about it. The RV industry all about avoiding litigation, and they've asked me numerous times not to email them about any electrocutions since that would be discoverable if there were any lawsuits due to a death. They're kind of scared about who I might blame.

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Re: CATV/RV Grounding Issue
« Reply #15 on: March 05, 2017, 07:21:48 pm »

This begs another question.  Arriving at a new camp ground and standing plug in hand, what do you do next.  I am picturing pooring water on the ground and pressing a large screw driver into the ground and metering from ground to each conductor to find, hopefully, one hot wire. Then challenge that finding with a load such as a 100 watt bulb.  Next would be the challenge of finding which of the remaining two is the common.  Last. I think I would ignore the ground and drive my own ground rod or use the bed of nails ground.

This is incomplete.  Please add to it.
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Mike Sokol

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Re: CATV/RV Grounding Issue
« Reply #16 on: March 05, 2017, 07:37:35 pm »

This begs another question.  Arriving at a new camp ground and standing plug in hand, what do you do next.  I am picturing pooring water on the ground and pressing a large screw driver into the ground and metering from ground to each conductor to find, hopefully, one hot wire. Then challenge that finding with a load such as a 100 watt bulb.  Next would be the challenge of finding which of the remaining two is the common.  Last. I think I would ignore the ground and drive my own ground rod or use the bed of nails ground.

This is incomplete.  Please add to it.

Here's how I do it as a initial test. https://www.youtube.com/watch?v=W5pLlZm8O84

Once you do a quick test of the receptacle with a DMM and a NCVT, then plug in the RV and check for a hot-skin voltage with a NCVT. Checking the RV skin/chassis with a NCVT should find any open grounds since all RVs will have a small amount of leakage current sufficient to raise the hot-skin potential of a floating ground RV to over 40 volts. That's high enough to cause a standard sensitivity NCVT to alert.

The scenario of a non-technical RV owner plugging into a campsite pedestal which they assume is wired correctly is all the more reason that camground receptacles should be tested periodically, possibly yearly.
« Last Edit: March 05, 2017, 08:29:39 pm by Mike Sokol »
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Re: CATV/RV Grounding Issue
« Reply #17 on: March 05, 2017, 10:39:40 pm »

I don't have my 2017 code book yet, but I heard there are changes to GFCI requirements-specifically more 2 pole and 3 pole requirements.  If that applies to campgrounds that should help-at least on new ones (of course the irony here is that new ones that are inspected will be the ones with the GFCIs-but they will also have proper ground systems).

Maybe the most acceptable thing would be a third party rating that included safety as a significant factor.  Safety concerns seem to be fairly well accepted in industrial settings-it would be nice if people would transfer that awareness to their personal life.
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Re: CATV/RV Grounding Issue
« Reply #18 on: March 06, 2017, 01:12:04 am »

The scenario of a non-technical RV owner plugging into a campsite pedestal which they assume is wired correctly is all the more reason that camground receptacles should be tested periodically, possibly yearly.

Semi-related, how many people turn off the breaker on the pedestal before connecting or disconnecting the shore power plug? Seems to me that's a recipe for an arc flash if there's a dead short somewhere down the line (or a lazy camper that doesn't shut off appliances).

Perhaps a combined switch/receptacle could be designed that doesn't allow insertion or removal of the plug when energized? Not sure how you'd make that work with the plethora of different plug bodies out there.

Then you'd have the folks who can't read the label (that says to turn it off) so end up forcing it and breaking something.

Most plug/receptacle combinations aren't designed to be interrupting means.
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Re: CATV/RV Grounding Issue
« Reply #19 on: March 06, 2017, 01:20:22 am »

Semi-related, how many people turn off the breaker on the pedestal before connecting or disconnecting the shore power plug? Seems to me that's a recipe for an arc flash if there's a dead short somewhere down the line (or a lazy camper that doesn't shut off appliances).
The arc flash potential is fairly low in this case due to the long distance these pedestals are from the service panel (a lot of series resistance in those hundreds of feet of connecting wire limits the peak amperage). But many RV owners will pull the plug under load (not switching off the circuit breaker) which eventually causes a lot of pitting on the contacts of the plug/receptacle. This reduces contact surface area as well as increases oxidation of the brass, and that can result in overheating and meltdown of the shore power plug's insulating plastic. 

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Re: CATV/RV Grounding Issue
« Reply #20 on: March 06, 2017, 01:35:26 am »

As to the original question: with modern electrical systems, for someone to be shocked, there is almost always at least two failures involved: the primary failure of the electrical insulation, and the secondary failure of the safety system.

(Usually, what I have termed a "primary" failure happens after the secondary failure. I call it a primary failure not because of chronology, but because the insulation is the primary safety device. The EGC or breaker or GFCI is the secondary safety device.)

It would initially appear that the EGC is not properly connected in one or more pedestals, and a fault in one RV is backfeeding throughout the CATV shield to the other RVs.

I wouldn't be surprised if the grounding terminal of the receptacle in the pedestal isn't even connected to anything. The wiring is probably a 3-wire bundle either overhead or underground, two hots and a neutral (no ground). The pedestals may be designed with separate neutral and grounding busbars, and the installer didn't jumper (bootleg) the busbars together. If a ground rod was connected, there's no bond to neutral to provide a return path, and if the soil is sufficiently dry, that doesn't provide a good return path, eiter. With no ground wire in the feeders, there is no connection to the service entrance bonding point, or to other pedestals, so the voltage backfeeds throughout the CATV.

If there is a ground rod at each pedestal, but no bond between pedestals, the CATV cable provides a bond through a bonding point (intentional or unintentional) in other RVs.

So you have this condition: hot to chassis fault in RV #1, chassis to CATV shield bond in RV #1, voltage through shield to RV #2 (and 3 and 4), bonding point CATV to chassis in #2, hot skin #2, voltage on EGC of #2 to pedestal, into ground rod at #2. Because the ground rod at #1 pedestal is too high impedance, current flows through CATV shield to ground rod at pedestal #2, accounting for the damage seen in the CATV distribution system.

This shows the importance of having a continuous INTENTIONAL ground path/bond between power distribution points (and appliances such as an RV) to ensure they are at the same potential (as the soil), as well as an INTENTIONAL bond between ground and neutral to provide a controlled return path for fault currents to increase the likelihood of tripping a breaker in the event of an insulation fault.

EDIT: The proper repair is to install a proper EGC from the bonding point at the service entrance to each pedestal, and keep the neutral and ground separate at each pedestal. But if there is no master service entrance -- that is, if each pedestal is considered a service entrance, then bonding the neutral and ground at each pedestal and installing proper ground rods at each pedestal is the way to go. You probably need a ground rod at each pedestal, whether or not neutral and ground are bonded at the pedestal.
« Last Edit: March 06, 2017, 01:46:37 am by Jonathan Johnson »
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Re: CATV/RV Grounding Issue
« Reply #21 on: March 06, 2017, 01:40:30 am »

The arc flash potential is fairly low in this case due to the long distance these pedestals are from the service panel (a lot of series resistance in those hundreds of feet of connecting wire limits the peak amperage). But many RV owners will pull the plug under load (not switching off the circuit breaker) which eventually causes a lot of pitting on the contacts of the plug/receptacle. This reduces contact surface area as well as increases oxidation of the brass, and that can result in overheating and meltdown of the shore power plug's insulating plastic.

Depends on where you are in the park. If you plug in to the first pedestal in the line, and you're near the utility transformer, the arc flash potential could be much higher. But  I do recognize that it's not particularly high, and the pitting damage is a much greater concern -- and equal reason to turn off the power.
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Re: CATV/RV Grounding Issue
« Reply #22 on: March 06, 2017, 08:21:34 am »

To paraphrase someone else (read it from Nathan Lively's little book on audio)  "electricity is difficult to explain because it's invisible."

So true. When I was a controls designer building automated packaging machinery back in the 70's, there was a Mechanical Engineer on my team who I considered to be a genius of mechanical design. He intuitively knew everything about bearings, air cylinders, hydraulic systems, tolerance build up, welding, strength of materials, how to move packages on a conveyor line, etc... He was like a walking Google search engine on anything mechanical before the Internet existed. But anytime I threw a drawing on my proposed wiring diagram on the board he literally froze up. Same for troubleshooting wiring in the field. He said he couldn't understand it because he couldn't see it. Now, I could show him a logic chart detailing what each button or switch was supposed to activate and he was fine with that. And he easily understood any sort of timing chart I drew. But electricity was this big unseen mystery to him. 

Mike Sokol

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Re: CATV/RV Grounding Issue
« Reply #23 on: March 13, 2017, 07:13:00 am »

I finally got some pics from the campground CATV technician. Looks similar to a few XLR cables I've seen burn up. He's offered to send this to me, so of course I want it for demonstration.

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