| Author | Message | ||
| ChuckMC9 (Chucks)
Rating: |
Well, I thought I'd researched this, but in a recent thread, Phil states, "I still recommend that you never connect AC house electrical ground to chassis vehicle ground. You're only asking for trouble if you do." I have just yesterday mounted both my main disconnect and load centers directly to the bay wall, which due to the ground bar inside each, now makes a ground connection directly to the chassis. In George Myer's book, "Designing Electrical Layouts for Coach Conversions," he states, "The only connection between the metal shell of the coach and the safety ground system required by the NEC is at the main distribution panelboard." I have read several places that the genset should be grounded to the frame, but I seem to remember that this whole area is controversial. Any thoughts on this, or should I tear out my main & load center and mount on wood? Please tell me I don't have to do that!  I am *not* discussing the neutral/ground issue, which is another topic entirely. I am speaking of the GREEN wire only! | ||
| Sean Welsh (Sean)
Rating: N/A |
Chuck, I'm going to post this in that other thread too: You *must* connect your AC ground to the chassis at the main distribution. It is required by code, required by law, and extremely dangerous if left undone. Connecting the chassis and the ground system ensures that they are always at the same potential, and any accidental short of a hot wire to the chassis can not result in dangerous voltage appied to something you might be touching. BTW, this is also the reason you must connect ground and neutral whenever running on a internal power source (inverter or generator) -- to ensure that any fault current on the ground system can return to its source, complete the circuit, and trip the protection device. You did it right -- don't worry about it. -Sean | ||
| ChuckMC9 (Chucks)
Rating: N/A |
Sean, thank you *very* much for your informed answer. I'm out at the coach now and it's a relief to have your confirmation in what I'd researched and knew intuitively. ...more soldering awaits! (Dat six gauge takes awhile! ) | ||
| Sojourner (Jjimage)
Rating: N/A |
It possible some careless RV camp ground may have poor neutral grounding. Maybe what Phil is referring to but by all mean do what Sean posted. For your family safety always check coach’s ground to earthly ground w/meter after power plug hook-up. If earth is dry then probe 12” or more of clean “coat-hanger” wire. There should be no voltage with load on. I am sure this not common problem but it can happen. It has happen in houses. FWIW Sojourn for Christ, Jerry | ||
| Jerry Liebler (Jerry_liebler)
Rating: N/A |
For code compliance, the chassis must be connected to the green wires at the panelboard as an absolute minimum. But it must also be connected at many other places too, wherever a metalic box or metalic conduit containing ac wiring is mounted to the chassis, like outlets in the bays, electric water heaters etc. Regards Jerry 4107 1120 | ||
| FAST FRED Rating: N/A |
The big problem is that on many campsites the green wire has high resistance so does not do the job properly. While the red or black (assuming 2 leg 120V for "240" service) carries the power and the white is SUPPOSED to be the return at zero volts , many times either the batt charger or inverter will leave some current on the White(not zero). The posibility of a DC wire coming in contact with a live AC wire in the coach always exists. As does the aging of the insulation on motors in fridges, Air cond , freezers , and washing machine motors. Also some RF protection /supression will also leave a voltage on the white wire. Worst from an elecrtocution is the use of old (1990's) house ranges where the old 3 wire is still in use and the white and green are combined at the range. AS our coaches are insulated from the ground , even in the rain wet tires don't ground much , any juice in the shell will be looking for the easiest path out. AS we are mostly sea water , which conducts electric verry well, WE could become the ground path ,and it only takes milliamps to kill. A boating accident where a kid was electrocuted in fresh water has brought the marine industry to advise using GFI for the entire coach. It is assumed that a simple industrial style monitor to oversee the line voltage on the Ground Green line would require a Knowledgable understanding on the bart of the boater ...FAT CHANCE. SO the use of GFI for the entire vessel (or camper) is recomended. Some sources are, www.bender.org www.controlab-pulsar.com and www.nktechnologies.com The Euros already have stds for this type of instalation , (it may never be an RVIA requirement), but its sure nice NOT to electrocute someone that touches the coach. FAST FRED | ||
| Sean Welsh (Sean)
Rating: N/A |
Fred, I agree with much of what you said, but this statement: "While the red or black (assuming 2 leg 120V for "240" service) carries the power and the white is SUPPOSED to be the return at zero volts , many times either the batt charger or inverter will leave some current on the White(not zero)." is incorrect. The neutral (white) wire will almost always carry significant current. The current will be the difference between the black and red "hot" currents. If either hot side is "empty," the neutral current will be equal to the current on the in-use hot. The only time the neutral current is zero is if the two hots are in complete balance. Real-world, this is never, except on a device that doesn't use neutral (e.g. a 240-volt cooktop). Balancing loads between the two sides is difficult at best. Plus, in practice, many coaches routinely use only one side of the power. -Sean | ||
| fairtaffy Rating: N/A |
Ok my 25 cents worth. If my breaker box is in the bedroom, I should run a ground to the frame or body of the bus? Then the white neutral is just fine with the seperate bar in the box. | ||
| FAST FRED Rating: N/A |
The problems come when any juice is placed on the Green wire. Its suposed to be the safty line and have a short or fault kick the breaker or fuse. But IF the white and green touch. the return volts , not at zero , will go thru both the white as designed AND the green , which is also the outside of the coach. Some say electric seeks the shortest path, but thats NOT correct. Anyone who has placed 2 different sized resistors in a parallel circuit knows that BOTH carry some juice , not just the larger. The game is to NOT be exposed to 120v at a fraction of an ampere that may be flowing thru the green line , that may be poorly maintained by the RV park.100ma can cause cardiac arrest. BIG whole RV GFI seems the easiest , and not too dificult to retro fit into most coaches with a schematic. FAST FRED | ||
| niles steckbauer (Niles500)
Rating: N/A |
FF - I believe that electricity seeks (or more correctly flows) the path of least 'resistance' - As to the big RV GFI , I agree, if you think about it, our vehicle when hooked to a land line is one huge out door appliance and would be required to be on a GFI if it was a 'permanent' fixture and done to NEC - probably not a bad idea to retrofit all PP to GFI's as it has been determined that due to the baby boomer retirement party approaching, the number of full-timers and seasonal RV'ers will increase 5 fold in the next 15 to 20 years - since a good portion will be novices, it leaves a huge possibility for accident and injury on the inexperienced and unaware - Niles | ||
| John that newguy Rating: N/A |
Grief, Niles.... Every time weepers demand the gubberment -require- things be done in the name of safety, it costs us a thousand times more than we'd spend doing it ourselves.. The price of campgrounds sends us to Wally-World and the Flippin'-J for an overnight stop already... I guess we'll have to make reservations there, if that neat "requirement" is legislated. If my favorite hide-a-way is required to spend a few mil for electrical engineering and installation of GFI crap, they'll have to charge as much as that KOA down the street.. If a guy's worried about the electrical hazards at any campground (as he should be), let him go buy that engineering for his own RV, and let the rest of us test as we always have... Jeesh. | ||
| niles steckbauer (Niles500)
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http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3833660670&category=104232 JTNG - not a couple mil $ - this would handle 95% of campsites in NA - relatively cheap expense for the amount of safety afforded dontcha think ? Niles | ||
| John that newguy Rating: N/A |
I can see the old mom & pop rv parks using those 50 amp breakers in their old 20 amp systems... Niles..... Absolutely nothing is better, than to teach people to test before they use. I've had GFI units fail with sparks going every which way after running over an extension cord.. Why lull people into a false sense of security, when using good common sense and a bit of paying attention, will be the real life saver.... Those devices are like all the rest of the "safety" items the lobbyists push the gov to legislate the "requirement" of ... It's all 'bout the $$$ and less about the true benefits. (well...... that's my opinion, anyway) | ||
| niles steckbauer (Niles500)
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........ just assumed that ma 'n pa would put a 20 Amp GFI in place of a std 20 Amp ........ sorry .......... I'll splain myself ........ HEY (((((MA))))) AND (((((PA))))) JUST SAY NO TO OVERLOADING YOUR PANEL P.S.- Don't put the well next to the septic tank | ||
| Jerry Liebler (Jerry_liebler)
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Fast Fred, I've just pulled into an RV park with my GFCI equipped, properly wired bus conversion. This park has a broken connection in the ground wire to my power pole and the hot is shorted to the ground terminal on my side of the break. Touching the ground terminal on this power pole while standing on the ground is all it takes to kill someone, my GFCI is useless. Fortunately I tested the pole before I plugged in. If a bus is wired properly a tester always used to test before plugging in is a much better investment, and much safer, than a GFCI. Regards Jerry 4107 1120 | ||
| ChuckMC9 (Chucks)
Rating: N/A |
How 'bout a Cliffs notes version for what to do when you arrive at the power pole... For 50A, at the PP, using a meter - No voltage between ground and 'ground' - +-120VAC between each of the two legs and neutral - Neutral = Ground Other info to know, other things to test? | ||
| Jerry Liebler (Jerry_liebler)
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Chuck, Very good, could save some lives. We probably should also verify the integrety of the neutral and ground. To verify the neutral we'll need an unbalanced load, I use a 1500W 120v portable heater between one hot and neutral while measuring the other hot to neutral, the voltage should'nt change but a volt or two when the heater is turned on or off. To verify the ground the neutral side of the load is connected to the ground terminal while the meter is between earth and the ground terminal, the meter should stay very near 0 and if the park has a GFCI it should trip. Regards Jerry 4107 1120 | ||
| John that newguy Rating: N/A |
The telco companies issue a voltage sensor probe. A real handy device that indicates the presence of AC voltage with a simple touch of the probe's carbide point into the metal.. Techs were taught to check every pedestal, pole, guy wire, cable strand, and mobile home side, before doing any work. It's a fairly inexpensive device that's worth it's weight in whatever your estate would pay the beneficiary. http://www.sears.com/sr/javasr/entry.do?sid=I0008300030000100085&pid=03481331000 http://www.safetyemporium.com/ILPI_Site/WebPagesUS/detail.htm?07017 http://www.google.com/search?num=30&hl=en&lr=&newwindow=1&safe=off&c2coff=1&q=ac+voltage+s ensor | ||
| ChuckMC9 (Chucks)
Rating: N/A |
I just remembered that I have a Wiggy! Used it in a prior life decades ago. You can tell some things just by the sound & feel of it. http://www.foxelectricsupply.com/content/products/ProductDetail.asp?qsCatID=26309&qsProduc tNo=69115 ELECTRICITY Principle 1: Electricity is tiny peas. They are hard to see because they are so small and move so fast, however, they are green. Principle 2: The speed of the peas is measured in volts.: The speed of the peas is measured in volts. This can be converted to miles per hour, or furlongs per fortnight if so desired, but volts are nice and tidy. Principle 3: The number of peas is measured in amps. There are so many in a pound, it is inconvenient to weight them. Principle 4: The power the peas have is the number of peas multiplied by their speed. This is just how hard the peas hit. Same principle as getting hit with a water hose. Secondary Idea 1 for Principal 4: Two peas going one speed does the same work as one pea going twice as fast. ( 2 x 1 = 1 x 2) Secondary Idea 2 for Principal 4: Electrical power is measured in watts. What is Watts? Watts = Amps x Volts ( Power companies charge by kilowatt hours or 1000s of watts times hours used. This is defined as work.This distinction is important to engineers but not to real people) Principle 5: The more peas you cram in a pipe, (amps in a wire), the more they rub against the walls. This is resistance and it is measured in ohms. Secondary Idea1 for Principal 5: You can get more electrical work from the same size pipe (wire) if fewer peas going faster are used so there is less rubbing (resistance). Secondary Idea 2 for Principal 5: Rubbing on the pipe (resistance) results in heat. Heat deteriorates insulation. Principal 6: Volts, Amps and Ohms are related. A pack of peas will cram itself into a pipe until the resistance to movement they create by rubbing uses up all their available speed. Number of Peas= Speed / Resistance, or Amps = Volts divided by Ohms. (I=E/R) This is known as Ohms Law and is the basis of all electronics. Use this information to amaze your friends. You now understand electricity. That's all there is to it. Get yourself a tool belt , a bad attitude and a wiggy, and you can be an electrician. Mumble things about potential differentials or power factor and you can pass as an electrical engineer. ( Don't ask what a wiggy is. There are some things we could get hurt for divulging.) http://www.pumpsonline.com/electrical.htm | ||
| Tom Caffrey (Pvcces)
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ChuckMC9, your analogy is interesting. However, there is an error in your Secondary Idea 1 for Principal 4 that should be noted. Where you said "Two peas going one speed does the same work as one pea going twice as fast. ( 2 x 1 = 1 x 2)" is not correct. It would have been correct if you had said "four peas going one speed does the same work as one pea going twice as fast. ( 2 x 1 = 1 x 2)". This is because energy rises as the square of the velocity of a given mass. I don't think it matters in your analogy, because I didn't take it to mean actual speed. I brought it up because so many people would intuitively think it was true. But this notion is important in bus operation because this is the relationship between speed and mass when using your brakes. If you stop from 60 mph, the brakes have to get rid of four times the energy that they would if you stopped from 30 mph. This is also why slowing down for a long downgrade makes it so much easier on the brakes. Isn't this hobby fun? Tom Caffrey PD4106-2576 Suncatcher | ||
| John that newguy Rating: N/A |
Could you repeat that Tom? I left to take a pea.. | ||
| niles steckbauer (Niles500)
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.... if you ever tried to feed a two year old peas ......... you would know that formula ........ and if you ever had to change the diaper later ......... well ....... the velocity, mass thing really kicks in ......... | ||
| Tom Caffrey (Pvcces)
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John that newguy, nah, I'm going to take a pee break! Later. Tom Caffrey PD4106-2576 Suncatcher | ||
| FAST FRED Rating: N/A |
"If a bus is wired properly a tester always used to test before plugging in is a much better investment, and much safer, than a GFCI." The tester will NOT show if the ground is capable of carrying any more current that is required to light the test lamp. Your'e gambeling on the green being usefull. Jerrys method is superb , but not many folks will do it. ""We probably should also verify the integrety of the neutral and ground. To verify the neutral we'll need an unbalanced load, I use a 1500W 120v portable heater between one hot and neutral while measuring the other hot to neutral, the voltage should'nt change but a volt or two when the heater is turned on or off. To verify the ground the neutral side of the load is connected to the ground terminal while the meter is between earth and the ground terminal, the meter should stay very near 0 and if the park has a GFCI it should trip. " So far the only appliance that has given hassles are 12v battery chargers for hobbyist use (10A) or so. ON some of these the case is grounded , and the transformer seems to be grounded to the case too. Easy to check tho before using with an ohm meter to see if there is continuity between the 120v plug and case. A marine practice is to use a clamp ,meter arround the ENTIRE power cable,(not a single wire as usual). FAST FRED | ||
| Jerry Liebler (Jerry_liebler)
Rating: N/A |
Fast Fred, THANK YOU for the complement. Now I'll add a vote for a GFCI. If there is a properly functioning GFCI in the circuit, either in the campground or the RV, the ground integrety is not near as important. Because the GFCI will trip (removing power) if 6 milliamps (a non lethal level) of curent difference is present between the 2 conductors supplying the load, hot and neutral if a 120 volt load or the 2 hots if a 240 volt load. This means the ground only must carry 6 ma not the circuit curent. It is UNSAFE to use any 120 volt appliance that shows continuity between either of the flat terminals of the plug and it's case, either fix it or put it back in the dumpster. Regretably a clamp on meter around all three wires to a 120 volt appliance will not detect many faults within the appliance and is NOT sufficient to assure safety. Regards Jerry 4107 1120 | ||
| ChuckMC9 (Chucks)
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This is a good dialog. Jerry, when you use the heater, did you fabricate a one-leg 'dogbone' to test just one side or the other...or...? Surely you're not working with pigtails out there at the pole? | ||
| Jerry Liebler (Jerry_liebler)
Rating: N/A |
Chuck, Using a short piece of 4 conductor 8AWG cord I made up a 50 amp plug to a 4"x4" Plastic conduit box 'test box'. In the box I have a duplex outlet and a 'three way' switch that selects the neutral or ground of the input as the neutral of one of the outlets, the other outlet is the other hot and wired normally. The outlets are labled 'meter' and 'heater(switched neutral)'. BTW I test neutral & ground integrety on 30 amp outlets too, just plug the 30 to 50 amp adapter in first, then the test box plug. Before plugging in the heater, with the three way switch in the 'neutral test' position I make the preliminary meter tests in the outlet with my DVM's probes. The box is plastic so I'm not holding a hot lead if the outlet's wired wrong. I went to all this trouble after reading of a fellow who fried several appliances because of a broken neutral causing serious overvoltage. Regards Jerry 4107 1120 | ||
| John that newguy Rating: N/A |
Jerry- Post a schematic...? (Or get a patent.. This sounds great!) | ||
| Jerry Liebler (Jerry_liebler)
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First, a bit of a disclaimer/confession. My test box does violate the NEC and is a possible fire hazard because it allows connection of a 15 amp appliance to a 50 amp circuit without appropriate circuit breakers or fuses. I basically went cheap and figured it'll be used outside and by me who realizes the hazard that a short in the heater could cause. Now that home depot has plastic boxes that can hold a pair of 15 amp breakers that's the better way to build a test set without the fire hazard but still violates the code in order to test ground integrity. But it'll take two boxes, one holding the breakers and one holding the outlet and switch. Duplex outlets have tabs that must be removed in this application to seperate, electrically, the outlets from each other. The materials should still cost under $50. I have reservations about publishing a schematic that violates the NEC. Regards Jerry 4107 1120 | ||
| Brian Brown (Fishbowlbrian)
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Wow. As Wayne might say, I'm truly "not worthy" of the knowledge freely and graciously given on this Board. Jerry (and all you other gurus who keep posting these gems)… hat’s off! Brian | ||
| Richard Bowyer (Drivingmisslazy)
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Jerry, I do not understand the NEC violation. The protection should be internal to the heater I would think. I believe breakers should protect the wiring between your box and the utility. Richard | ||
| Stan Rating: N/A |
I think the violation is connecting a 15 amp receptacle to a 50 amp breaker although for RV use anything may be legal since you can buy adaptors to go from 50 amp down to 15 amp. | ||
| niles steckbauer (Niles500)
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The inverse would be illegal - going from a 50 amp connection to a 15 amp main breaker - the main service must be equal or greater than the down stream load - Niles | ||
| ChuckMC9 (Chucks)
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Jerry, that's a neato device. If I may pull it all together, - To verify neutral When your switch is in 'normal' position, the meter is on the other leg, connected between hot and neutral, and the voltage shouldn't change but a volt or two when the heater is turned on or off. - To verify ground The switch is flipped, with the meter being between earth and the ground terminal. The meter should stay very near 0 and if the park has a GFCI it should trip. Is this the overall scenario? Thanks again for all your trouble! -c | ||
| Jerry Liebler (Jerry_liebler)
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Chuck, You've got it. But be aware that a short in the heater could cause it's cord to burn as it's really on a 50 amp circuit. Also, verifying ground integrety may technically violate the NEC so don't do it in front of the 'code police'. Regards Jerry 4107 1120 | ||
| Jim Bob Rating: N/A |
Ah, but if the ground integrity is faulty, it IS in violation of the NEC AND it's a life hazard & we need to know that, right?????? Catch 22! Jim-Bob By the way, in the recent Florida hurricane season, we lost every device in our house that had a PC board when the neutral wire was broken at the power pole. Our 120 volt outlets swung from 50 to 200 volts as various devices, turned on or off. Every analog device survived. | ||
| FAST FRED Rating: N/A |
"Every analog device survived." AS did everything that was UNPLUGGED. Surely a simple and cheap method of saving costly equippment during a lightning storm , if no "Brickwall" is installed. Works great for load controll too! FAST FRED | ||
| Jim Bob Rating: N/A |
True Fred. We unplugged the computer, but we didn't shut off the main or unplug everything in the house including the garage door openers. We didn't shut off the main because of the fridge & freezer & security lights & system. Next time we will be more diligent, maybe just shutting most of the breakers off. We also got a little tired or lazy after leaving three times in a month. The last storm got us. Jim-Bob |
