Bus Electrical (house) problems

Gordie Allen · October 10, 2014, 08:51:13 PM

So, if I'm not plugged into a shore line and my inverter is supplying 120v through my ac panel, to what should my ac ground from my panel be attached?

eagle19952 · October 10, 2014, 09:12:34 PM

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

Neutral and ground must be bonded together at one and only one point. That point must be solidly grounded to earth.

akroyaleagle · October 10, 2014, 10:10:00 PM

If the neutral and ground get together in your 50amp cord, you will let the smoke out of a lot of stuff!

Gordie Allen · October 10, 2014, 10:49:55 PM

So what I don't understand is, when I'm going down the road (or parked) using my inverter, what makes me "solidly grounded to earth"? (other than gravity

) Does the inverter bond neutral and ground when switched on?

mung · October 11, 2014, 06:23:19 AM

http://ecmweb.com/bonding-amp-grounding/shocking-truth-about-grounding-electrode-conductors

mung · October 11, 2014, 06:26:00 AM

If you do use your chassis for an AC ground, I hope you carry a grounding rod and a sledge hammer with you.

Oonrahnjay · October 11, 2014, 07:13:12 AM

Quote from: mung on October 11, 2014, 06:23:19 AMhttp://ecmweb.com/bonding-amp-grounding/shocking-truth-about-grounding-electrode-conductors

Very interesting, Vern. I had always assumed what they say not to assume!

eagle19952 · October 11, 2014, 08:31:24 AM

think about what you are saying....

Quote from: mung on October 11, 2014, 06:26:00 AM
If you do use your chassis for an AC ground, I hope you carry a grounding rod and a sledge hammer with you.

i think you are failing to remember that the earth ground is a fault ground which is a secondary path to the source..which could be a pole a generator a solar control a windmill or an inverter.
in the event of a fault ( and properly wired) the neutral is what trips the breaker... not the ground.
So. Tell me how that ground rod is going to help you out at sea....or in an air plane.

PS no grounding rod here, 12 years in... I do have a 8 pound sledge that i use to thump tires.
PSS I wsh I was better at penning concepts.

eagle19952 · October 11, 2014, 08:33:52 AM

Quote from: akroyaleagle on October 10, 2014, 10:10:00 PM
If the neutral and ground get together in your 50amp cord, you will let the smoke out of a lot of stuff!

the cord is not the source.

mung · October 11, 2014, 01:00:00 PM

The real issue is that if you have the chassis sharing a common ground with both 12v and 120v sources there is the potential that your 120v source can fry everything on your 12v side. Probably won't happen in most failure modes, but is still well within the possible outcomes of a failure.

eagle19952 · October 11, 2014, 01:23:01 PM

Vern, if every thing is on a common ground, wired properly, the breaker trips, saving any voltages from smoking anything...whether AC or DC.
again where are you putting the ground rod on the boat or plane ?

Quote from: mung on October 11, 2014, 01:00:00 PM
The real issue is that if you have the chassis sharing a common ground with both 12v and 120v sources there is the potential that your 120v source can fry everything on your 12v side. Probably won't happen in most failure modes, but is still well within the possible outcomes of a failure.

jmsokol · October 11, 2014, 01:35:13 PM

Quote from: mung on October 11, 2014, 01:00:00 PM
The real issue is that if you have the chassis sharing a common ground with both 12v and 120v sources there is the potential that your 120v source can fry everything on your 12v side. Probably won't happen in most failure modes, but is still well within the possible outcomes of a failure.

I'm Mike Sokol from No~Shock~Zone which has a number of my bonding and hot-skin articles linked above. Not only am I a Master Electrician and EE, I also have the RVIA handbook in front of me. Every RV built in the USA is designed to have the incoming 120-volt EGC (Electrical Grounding Conductor or Safety Ground) bonded to its chassis, door frames, and all metal structures. And all 12-volt DC vehicle systems have their negative terminals bonded to the same vehicle chassis. Even though it seems like there should be some sort of dangerous interaction between the AC and DC systems, in fact there is no interaction at all. I'm also an expert on electrical failures, and there are no failure modes I can think of that would cause a RV's 120-volt system to "fry" the 12-volt system. So, if you know of one, please post a schematic and current flow diagram so I can evaluate it.

Also as noted, it IS vitally important that the ground and neutral wires inside your RV/Bus are isolated from each other. They will eventually be bonded together, but all the way back at the service panel at the incoming power line, or inside your on-board generator's transfer switch. I also came up with a simple G-N bonding plug for portable generators that fulfills the same function. This is not actually earth "grounding" but G-N "bonding" which fulfills the same function on a floating electrical system powered by an isolated generator such as a Honda EU2000i and similar.

And while its hard to believe, a ground rod will not really "ground" your RV since the earth itself is a pretty poor "ground". A "ground rod" can measure up to 100 ohms to the earth and still pass code. It's really there for lightning protection, not ground fault currents.

I think one of the reasons this is so confusing to most consumers and many technicians is that the word "grounding" and "bonding" are used interchangeably, when they are, in fact, very different things that fulfill very different functions. I've just published a book on RV Electrical Safety for Consumers, and now working on one for RV Technicians. It will include all sorts of additional electrical troubleshooting and wiring information.

bevans6 · October 11, 2014, 01:48:56 PM

Finally a voice of reason. And expertise. And qualifications from actual qualifying places. Saying, I am proud to note, much the same thing I said, but way better.

Nice to have you visit, Mike.

Brian

mung · October 11, 2014, 02:20:24 PM

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?

robertglines1 · October 11, 2014, 02:37:50 PM

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