Bus Electrical (house) problems

[eagle19952]

I too would like to thank Mike for chiming in, Thanks Mike !!
I emailed some questions to him last year and was grateful for a timely response.

Mike, I don't have time right now do draw a schematic, but what would happen if the ground on the plugin at the campground isn't solid, then you have a fault from the hot side to a a device's ground?  Would the 120v hot leg not try to find the path of least resistance?  Is it not very possible that the current could back feed through the 12v ground wires? 

[jmsokol]

Been in some high end newer campgrounds that the neutral and earth grounds were connected(not correct) at the pedestal. Why?? the person that did it was not educated. Best to ck yourself.. you should have no continuity between the 2.  One tip in anything bus -metal bldg --I have a habit of first touch with back of fingers;if you complete ground your fingers will contract away from object.  Not to be used to test earth ground! Just a old habit from the past when things were much worse.  Just a little trivia.  Bob

Actually, you SHOULD read continuity between the Neutral and Ground at the pedestal. It should NOT be bonded internally at the pedestal. Rather, the Ground and Neutral are bonded together back at the service entrance panel. However, NEVER connect a meter in OHMS mode across any receptacle/plug contacts since the slightest voltage there will blow up the meter, or at least its internal fuse.

I just produced a video review of the Amprobe PK-110 test kit which details how to test 20, 30 and 50 amp outlets on a campground pedestal for correct voltage, H-N polarity, and  Ground. This has not been officially released yet, but it has been vetted and approved by Amprobe's engineering group. See below:

http://www.youtube.com/watch?v=W5pLlZm8O84#

Mike Sokol

[bevans6]

Been in some high end newer campgrounds that the neutral and earth grounds were connected(not correct) at the pedestal. Why?? the person that did it was not educated. Best to ck yourself.. you should have no continuity between the 2.  One tip in anything bus -metal bldg --I have a habit of first touch with back of fingers;if you complete ground your fingers will contract away from object.  Not to be used to test earth ground! Just a old habit from the past when things were much worse.  Just a little trivia.  Bob

I would think the pedestal is the source of neutral/ground bond for the bus, so you should absolutely have continuity between neutral and ground at the pedestal.  The question would be would that bond be provided locally at the pedestal, or carried back to the main panel.  The pedestal should be served with a three or four wire cable and the neutral-ground bond should be at the main panel, I would expect, although there is an argument for locally bonding.  In Canada sub-panels in outbuildings are locally grounded and bonded to neutral in most cases.  I test every connection to a pedestal with a test plug device, every one so far has offered me a bonded ground and neutral.  Mind you I probably have stayed in less than a few dozen campgrounds.

Brian

[jmsokol]

Mike, I don't have time right now do draw a schematic, but what would happen if the ground on the plugin at the campground isn't solid, then you have a fault from the hot side to a a device's ground?  Would the 120v hot leg not try to find the path of least resistance?  Is it not very possible that the current could back feed through the 12v ground wires?  

In that instance, the entire chassis/skin of the RV will be AC voltage biased above earth potential. But because EVERYTHING is at the same voltage, there's no current flow back into the DC systems. Seems counter-intuitive, but that's how it really works. But I don't say this from theoretical book diagrams. I build the tests and demonstrations myself and take readings so I understand how improperly wired systems misbehave and how you troubleshoot them. Here's a video of me opening the 120-volt ground on a 40-ft RV and biasing the entire thing with up to 120-volts AC. Nothing was damaged, but it is highly dangerous to anyone standing on the ground and touching anything metal on the RV. See below:

http://www.youtube.com/watch?v=Y8h64X33aKg#

[digesterman]

Thanks Mike for valuable input, I admit I have little to no patience when it comes to explaining the obvious, I am thankful that there are people like you around that not only have the knowledge but the ability and desire to explain it to the masses.

I have read your articles before, as you know there are not many to be found concerning RV's. I tend to trust the professional convertors that have installed 100's if not thousands in their conversions without problems (well maybe I should retract the "without problems"), not all do it perfectly as know.

P.S.  Did you have any input in the 2014 NFPA 70 (is it article 514? memory left me long ago) concerning the wiring of RV's.

[mung]

Eagle, didn't mean to miss your question on the planes and boats.  Well most planes don't have 120v except for new airliners that use inverters to get that.  Now lets talk about boats.  Hmm, so first of all, the water makes a very good ground and because of that, there is a huge issue with galvanic corrosion.  But more to the point of 120v service to a boat, well since my boat is GRP (glassed reinforced plywood) how exactly would I tie my 12v or my 120v to the chassis?  fiberglass and plywood doesn't make a very good conductor.  So all of my 12v and 120v have home runs and the two never meet.  So, why is this 100% common on boats and really the only way to connect your electric, but not common on buses and RVs?  Kind of interesting isn't it? 

[bobofthenorth]

Eagle, didn't mean to miss your question on the planes and boats.  Well most planes don't have 120v except for new airliners that use inverters to get that.  Now lets talk about boats.  Hmm, so first of all, the water makes a very good ground and because of that, there is a huge issue with galvanic corrosion.  But more to the point of 120v service to a boat, well since my boat is GRP (glassed reinforced plywood) how exactly would I tie my 12v or my 120v to the chassis?  fiberglass and plywood doesn't make a very good conductor.  So all of my 12v and 120v have home runs and the two never meet.  So, why is this 100% common on boats and really the only way to connect your electric, but not common on buses and RVs?  Kind of interesting isn't it? 

First off GRP is "glass reinforced plastic".  I'm not sure what "glassed reinforced plywood" might be unless you are referring to cold molded plywood.

Second, in the marine world, there is a heated debate about the connection of 12 volt grounds and the bonding system for electrolysis prevention but this forum is most definitely not the place to open that discussion.  Boats float in water which is more or less conductive and that introduces a whole new level of electrical complications.  What happens in the boating world has some relevance to what you can or should do on your bus but its not definitive.

[eagle19952]

i give up....
What if your at a dock with shore power in a steel boat that is big enough to land an airplane ?
PS.
Boeing B 737 NG
Primary electrical power is provided by two engine integrated drive generators (IDG's) Which are rated at 90Kva and supply three-phase 115 volt, 400 cycle  Alternating Current

Eagle, didn't mean to miss your question on the planes and boats.  Well most planes don't have 120v except for new airliners that use inverters to get that.  Now lets talk about boats.  Hmm, so first of all, the water makes a very good ground and because of that, there is a huge issue with galvanic corrosion.  But more to the point of 120v service to a boat, well since my boat is GRP (glassed reinforced plywood) how exactly would I tie my 12v or my 120v to the chassis?  fiberglass and plywood doesn't make a very good conductor.  So all of my 12v and 120v have home runs and the two never meet.  So, why is this 100% common on boats and really the only way to connect your electric, but not common on buses and RVs?  Kind of interesting isn't it?  

[mung]

Bob back when my boat was built in England it was marine ply with fiberglass on both sides of it and they called it GRP.  That term has now been changed to plastic, but fiberglass was so new back then that they way over engineered it.

[86102A3]

I think what is important is that when you have metal in any vehicle, it must be grounded to the AC system. The 12v system uses the frames of metal vehicle mainly because it is cost effective, they do not have to run a wire back to the battery. If the vehicle/boat does not have a metal frame they would have to run the wires back to the battery to complete the circuit. Personally I do not like using the frame for the return, it usually is where you find a problem with a bad ground connections.

[jmsokol]

So, if you pull up to a camp site and the pole isn't grounded like it should be, then the wife plugs something in that has a neutral fault, where is the current going to go folks?  Also keep in mind that a bus is all metal vs most RVs which are not.

My 26 ft Airstream is a whole lotta metal.... 

[bevans6]

Trivia - the main reason that car makers went to negative ground electrical systems back in the late 1950's and early 1960's was to make the chassis wiring sacrificial, electrolytic corrosion-wise.  Similarly the reason telephone plant wiring uses negative 48vdc for the battery voltage on the outside plant wiring to your home is to make the wiring the part that doesn't corrode electrolytically.  When your phone goes off-hook an AC frequency is superimposed atop the -48, here it's 350hz and 440hz.  When the phone rings, they impose a 90 volt AC 20hz on top of the -48 volts (so it swings from zero to negative 93 volts, which is enough to give you a good wake up shock, you can barely feel dial tone but I was knocked off a ladder when I was casually holding a tip and ring pair and someone called that number...)

So AC and DC coexist all over the place.   Ontario Hydro used to run digital data signals on top of the high voltage 60hz distribution network.

Brian

[eagle19952]

Further (and then I really do give up), regarding boats in water....

In a properly wired system, current traveling aboard on the hot wire returns solely through the white wire. Because a boat floats in a conductive medium, interconnecting the green and white wires aboard affords current returning to its source—the transformer ashore in this case—through three paths: the white wire, the now-connected green wire, and the water via bonded underwater metal hardware such as the engine/propeller, strainers, and seacocks. Contrary to popular belief, electricity takes all paths back to its source, not just the path of least resistance. This presents a clear hazard to swimmers, and those aboard may also be at risk, depending upon the nature of the fault. Therefore, it is vitally important that the connection between the AC safety grounding wire and the neutral wire occur only at the power source. That means, at the onshore transformer supplying the dock shore cord, or at a generator or inverter—when and only when one of those is supplying power to the vessel.

http://www.proboat.com/demystifying-the-neutral-to-ground-connection.html

[mung]

Yet code says not to run low voltage control wires with 120v or above circuits. 

[eagle19952]

stay safe.

Yet code says not to run low voltage control wires with 120v or above circuits.