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Old 07-04-2013, 08:12 AM   #41
Bus Crazy
 
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Location: Upstate NY (Mohawk Valley)
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Re: RV Electrical Safety

Quote:
Originally Posted by jmsokol
. . . . According to safety literature, you're supposed to maintain a 14-foot distance from high-tension power lines. Those are the big boys that can have up to 250,000 or even 500,000 volts and be at least 28 feet above the ground.
We have the 500,000 volt lines between Canadian Hydro and the Big Apple running through the area, though my contact at the control center says they only run about (375,000?) because the sub-stations can't handle the rest. The conductors are more like 180 feet up at the supports with some sag in the middle. The lines ran about 1/4 mile from my last house, and go behind my boss' back yard.

He said the towers behind him came down in a storm a month or two ago, and were back up in HOURS. Don't go near THOSE downed wires!
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. . . a quick thinking police officer called to the scene had a AED (Automated External Defibrillator) in his cruiser . . .
FYI State patrols here have AEDs in 100% of marked cruisers and 100% of offices, with 100% CPR/AED training for both sworn members and civilians.
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Old 07-04-2013, 09:18 AM   #42
Mini-Skoolie
 
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Re: RV Electrical Safety

Quote:
Originally Posted by Redbear
Quote:
Originally Posted by jmsokol
. . . . According to safety literature, you're supposed to maintain a 14-foot distance from high-tension power lines. Those are the big boys that can have up to 250,000 or even 500,000 volts and be at least 28 feet above the ground.
Here's a really excellent paper about working around high voltage power lines by the Bonneville Power Administration.

http://transmission.bpa.gov/lancom/Livi ... _11-07.pdf

I've talked to the lead engineer at BPA, and discussed at length the induced voltages that can occur when you park an RV directly under a high-voltage power line. They say that the 14-ft minimum distance limits these inductively induced currents to less than 5 mA, which isn't dangerous. But the open circuit voltage can reach perhaps 10,000 volts, enough to continuously light a spark plug attached from the bumper of your RV to a ground rod. I know of several campgrounds that put their dumping station right beneath a set of high-voltage lines, and if you touched your RV and the metal water faucet at the same time it felt like you were getting a shock from the faucet. But in reality you were getting a shock from your RV by the induced voltage from the overhead power lines and the water faucet was grounding you. Now, it's not supposed to be harmful (as in fatal) but can feel like grabbing your lawn mower spark plug while it's running. Not fatal, but boy does it hurt. I think that placing an RV dump station directly under a high tension power line is probably a violation of most local electrical codes, so this is something to discuss with your campground association (if you belong to one).

Mike Sokol
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http://www.noshockzone.org
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Old 07-04-2013, 05:48 PM   #43
Bus Crazy
 
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Re: RV Electrical Safety

Mike, I'm curious to know why you haven't made any mention of using a digital volt meter in addition to or instead of the non-contact sensor for verifying pedestal connection. My limited experience has been that a DVM probe stabbed into the soil is plenty of ground for the small current the meter will pass, and I get very nearly the same reading line-neutral, line-ground, and line-soil. In fact I just went out and tested on some gravel outside the house; I was surprised how well the DVM worked just touching a probe to a rock. Patches of dry or wet soil on top of the gravel were nearly as good as direct to the soil. Is the lack of mention primarily because many in the intended audience won't know how to use a meter nor how to understand what the measurement is (or isn't) telling them?

If a person wanted to be really sure that the ground in their hookup is reliable one could intentionally measure the voltage while running a load (a resistance, probably an incandescent lamp or heater) into the ground conductor instead of the neutral. If the voltage didn't hold near nominal it would indicate a high-impedance (ie faulty) ground connection. What do you think of that? Too much like EE work for the average vacationer I suppose, but based on the horror stories, maybe it's worth going prepared for such in my own bus.
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Old 07-04-2013, 06:33 PM   #44
Mini-Skoolie
 
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Re: RV Electrical Safety

Quote:
Originally Posted by family wagon
Mike, I'm curious to know why you haven't made any mention of using a digital volt meter in addition to or instead of the non-contact sensor for verifying pedestal connection..
I have indeed written about that technique on a number of other forums, and published an article in RV Technician Magazine on the proper technique. For anybody used to working on hot circuits it's pretty easy. But I've found that casual RV owners are pretty bad at poking one sharp probe through the rust or paint on a hitch or lug nut, and the other probe onto a screwdriver stuck in the ground. Perhaps if I create a video to show how to do this safely it would help since I worry about a newbie having one hand on a grounded screwdriver and the other near a potential 120-volte hot skin.

I'll post a schematic later tonight of my high-current/low-voltage test for checking the RV's safety ground impedance from the chassis to the shore power connection. Pretty simple, yet very safe for even the casual user. And it tests every part of the safety ground circuit, from the chassis connection all the way back to the shore power plug and any adapters (one of the key ground failure points). In the meantime, let's be safe out there.

Mike Sokol
mike@noshockzone.org
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Old 07-08-2013, 07:35 AM   #45
Mini-Skoolie
 
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Re: RV Electrical Safety

Quote:
Originally Posted by jmsokol
I'll post a schematic later tonight of my high-current/low-voltage test for checking the RV's safety ground impedance from the chassis to the shore power connection. Pretty simple, yet very safe for even the casual user. And it tests every part of the safety ground circuit, from the chassis connection all the way back to the shore power plug and any adapters (one of the key ground failure points). In the meantime, let's be safe out there.
So here's my latest test gadget for checking safety ground continuity on a RV. Note that this is used on an UNPLUGGED RV, and the brake light bulb provides about 2 amps of 12-volt DC as a test current. The beauty of this test is that it's low enough voltage not to harm you if something goes wrong, yet it provides enough current to find any loose or corroded connections between the frame of your RV (skoolie) and the ground pin on your shore power cord, including any dogbone or pigtail adapters you might be using. It also allows you to easily see any intermittent open circuits by flexing all wires and connectors while watching the bulb. Be aware that a brake light bulb will get quite hot rapidly, so my plan is to use a cheap trailer brake or side marker housing rather than allow the bulb to lay on a carpet or vinyl floor.



You really don't need the DMM (Digital Multi Meter) for this test, but that would be the gold standard. By measuring the voltage across the battery, them comparing it to the voltage across the bulb, you'll quickly determine if you have a solid internal safety ground connection. Note again that this is used on an unpowered RV, and will do nothing to test the impedance of the safety ground connection on the pedestal outlet. That's an entirely different test, and a bit more dangerous to DIY since there will be 120-volts involved. But I may try to design a safe version of that as well.

Mike Sokol
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Old 07-08-2013, 12:40 PM   #46
Mini-Skoolie
 
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Re: RV Electrical Safety

Also, NEVER stand in the water or a puddle while plugging in a battery charger for your bass boat or RV.

http://www.kare11.com/news/article/1030 ... ne-Co-lake

Two men were shocked in Big Lake MN over the last week while plugging in their bass boat, and there's no news as to their recovery. While it seems obvious that you shouldn't be standing on the wet ground or a puddle and playing with an extension cord, I've actually found a number of ungrounded outlets powering battery chargers in a hotel parking lot during a fishing tournament. Remember, the negative terminal of your battery is supposed to be bonded to the frame of your boat. So if there's a missing safety ground (broken off ground pin on an extension cord) or improperly grounded outlet, then a boat on a trailer can get the same sort of hot-skin condition as any RV. The hot-skin test is the same. Either measure from the chassis/skin of the boat to an earth ground using a DMM, or use a Non Contact Voltage Tester such as a Fluke VoltAlert to test for voltage.

Also, as I noted in an earlier posting here, if the boat is in fresh water the danger of shock-drowning grows since a voltage gradient can reach out from the boat 100 feet or more. Anyone swimming in the water towards a boat or dock with a hot-skin condition will lose control of their muscles the closer they swim towards the dock/boat, eventually losing the use of their arms and simply drowning without signs of electrocution. NEVER swim or get in the water around an electrified boat dock or any boat plugged into an extension cord for shore power or battery charging. It's just too dangerous and not worth the risk.

MIke Sokol
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Old 07-08-2013, 02:08 PM   #47
Bus Crazy
 
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Re: RV Electrical Safety

Quote:
Originally Posted by jmsokol
So here's my latest test gadget for checking safety ground continuity on a RV. Note that this is used on an UNPLUGGED RV, and the brake light bulb provides about 2 amps of 12-volt DC as a test current.
That's simple, clever, elegant. I like it.

Quote:
Originally Posted by jmsokol
Also, NEVER stand in the water or a puddle while plugging in a battery charger for your bass boat or RV. Two men were shocked in Big Lake MN over the last week while plugging in their bass boat
That surprises me, actually. Is it common that the output of a battery charger would not be isolated from the input? I'll admit I've never actually looked for a hi-pot rating on a battery charger before... Or maybe it's one of those low-end chargers that are nothing but a transformer and a diode bridge, and it happened that the metal case was connected to the boat and to (faulty) mains neutral or ground..?

Quote:
Originally Posted by jmsokol
Also, as I noted in an earlier posting here, if the boat is in fresh water the danger of shock-drowning grows since a voltage gradient can reach out from the boat 100 feet or more.
Would you mind explaining the circuit theory on that one more? Clearly the idea here is that the boat hull is electrified and that the circuit goes through the fresh water back to the soil somewhere around the supply point, so there's a current flowing down a wire, onto the boat, through the water, back to the soil. A person could swim into the path of that current. But I don't follow how the current is going to pass through the person, at least until such time as they touch either the boat or the bottom of the lake/river. Or is the impedance of the human body lower than that of the water, so that when some length of the swimmer's body is along the path of the current it flows through their body instead of flowing through the surrounding water?

Hazardous.. but fascinating, too.
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Old 07-08-2013, 02:51 PM   #48
Mini-Skoolie
 
Join Date: Aug 2012
Posts: 118
Re: RV Electrical Safety

Quote:
Originally Posted by family wagon
Quote:
Originally Posted by jmsokol

Quote:
Originally Posted by jmsokol
Also, NEVER stand in the water or a puddle while plugging in a battery charger for your bass boat or RV. Two men were shocked in Big Lake MN over the last week while plugging in their bass boat
That surprises me, actually. Is it common that the output of a battery charger would not be isolated from the input? I'll admit I've never actually looked for a hi-pot rating on a battery charger before... Or maybe it's one of those low-end chargers that are nothing but a transformer and a diode bridge, and it happened that the metal case was connected to the boat and to (faulty) mains neutral or ground..?
All modern battery chargers will have some sort of 120-volt line isolation transformers, but all power transformers leak some common-mode current between the "isolated primary and secondary windings". And many modern appliances will be what's known as "double insulated" a fancy term that implies there's an extra layer of insulation between the transformer windings. But as any transformer ages and is exposed to heat/vibration/moisture, this insulation lay will eventually break down, letter LARGE amounts of current flow directly between the primary and secondary windings. This is especially true if your battery charger is left in the rain or takes a bath in the lake, certainly a possibility. If there's a ground pin on the charger's power plug, then those currents are harmlessly sent to earth ground. But if the ground have been disabled (broken off) or plugged into an ungrounded outlet, then a person touching the boat (typically connected to the negative battery terminal) and water at the same time will become the fault current path. Your wet body has a resistance around 1,000 ohms, so Once you have over 20-volts AC, there will now be 20 mA of current flowing though your body, and all your muscles will contract at the same time and paralysis results. Your heart may not be in V-Fib just yet, but that doesn't matter since you can now slip below the water and drown. Most shock drownings are never properly attributed to "electricity" since unless somebody sees you getting shocked, they all assume you just drowned.

Mike Sokol
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Old 07-08-2013, 03:21 PM   #49
Mini-Skoolie
 
Join Date: Aug 2012
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Re: RV Electrical Safety

Quote:
Originally Posted by family wagon
Would you mind explaining the circuit theory on that one more? Clearly the idea here is that the boat hull is electrified and that the circuit goes through the fresh water back to the soil somewhere around the supply point, so there's a current flowing down a wire, onto the boat, through the water, back to the soil. A person could swim into the path of that current. But I don't follow how the current is going to pass through the person, at least until such time as they touch either the boat or the bottom of the lake/river. Or is the impedance of the human body lower than that of the water, so that when some length of the swimmer's body is along the path of the current it flows through their body instead of flowing through the surrounding water?

Hazardous.. but fascinating, too.
So here's how shock-drowning works in freshwater. Saltwater doesn't behave the same way due to its much higher conductivity. See http://www.qualitymarineservices.net/ for more detailed information and a list of shock drownings.

If you immerse an electrified object (such as a boat) in freshwater, there's not enough water conductivity to actually "ground" the electricity quickly. Think of it was an infinite number of resistors up to 100 feet long extending from the object in a big hemisphere around you. The potential will start at 120 volts near the boat, and gradually taper off to zero volts between 60 to 100 feet away, depending on water salinity and such. Now if you were to put two meter probes in the water about 3 feet apart, you could measure a voltage difference due to this gradient field. If you're way far out from the boat, then you might only read a volt or two between the probes. But come closer to the big voltage divider network (the water) then the same distance between the probes will increase to a lot more voltage. It's a gradual thing, but as you come closer to the energized boat, then the voltage between 3-ft probes will increase to 20 or 30 volts or more. So if your one hand is at 90 volts in the water, and your other hand is at 60 volts in the water, you'll have 30-volts hand-to-hand when you extend them, a little less when your hands are pulled close to your body. Again, a wet human being has around 1,000 ohms resistance, so you now will have 30 mA of current going through your body, and be unable to move your arms. Of course, you'll then just sink and drown.

Of course, if you're in the water and grab an aluminum boat or dock ladder that's not immersed, you'll then take the full 120-volt differential across your body and likely be feeling 100 mA or more current. That's enough for electrocution (death) in a few seconds. But its also possible that a rescuer attempting to pull a shock-victim out of the still electrified water can themselves be shocked and electrocuted. So turn off the dock or boat power first BEFORE jumping in.

Also, most people don't know it, but even plastic water irrigation pipes can carry electricity over long distances. Here's the story of two 14-year old girls who were working in a corn field, and the irrigation pump had lost its safety ground due to a lighting strike. When they stepped in a puddle of "electrified" water and touched a "grounded" corn tassel, they were both electrocuted (killed) http://www.insurancejournal.com/news/mi ... 209869.htm So sad since a simple NCVT such as a Fluke VoltAlert would have easily found that electrocution hazard.

The rule around water is this. Don't swim around boat docks with power outlets or boats plugged into any kind of shore electrical power. And if you ever feel the slightest tingle from anything while you're wet, STOP what you're doing and seek professional electrical help. A hot-skin on an RV is dangerous enough but safe until you actually touch it. But a hot-skin on a boat or dock can extend out many yards from the source and cause a drowning from scores of feet away.

Mike Sokol
mike@noshockzone.org
http://www.noshockzone.org
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Old 07-08-2013, 03:44 PM   #50
Mini-Skoolie
 
Join Date: Aug 2012
Posts: 118
Re: RV Electrical Safety

Quote:
Originally Posted by family wagon
Quote:
Originally Posted by jmsokol
So here's my latest test gadget for checking safety ground continuity on a RV. Note that this is used on an UNPLUGGED RV, and the brake light bulb provides about 2 amps of 12-volt DC as a test current.
That's simple, clever, elegant. I like it.
Thanks.... this is exactly what I built for testing short circuits in the wiring of cars back in my youth. I got tired of blowing fuses looking for the short, so a brake light bulb on a couple of alligator clips let me put it across the open fuse. I could then flex all the wires and if the light came on brightly, there was a short to the chassis. Of course, for a safety ground we WANT a short circuit to chassis ground, so it works in reverse. It also allows you to keep adding on extension cords and dog-bone adapters to find the source of an open safety ground circuit.

Also, for you diode heads out there, this test circuit is essentially one-half of a Kelvin bridge like I used to measure resistor values in nuclear missile guidance systems I was building (no kidding). See http://en.wikipedia.org/wiki/Kelvin_bridge for some brain teasing. Kelvin bridges are really cool since there are separate current and voltage paths for measuring resistance, so any series resistance in the test leads are "nulled out".

Mike Sokol
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