Modified Sine Wave Converter

[engnrsrule]

The inverter is prevented from simultaneously connecting while any other 110v source is connected, by means of the 2 bus transfer switches. Only one 110v source ( shore power, generator, or inverter can connect to the 110 distribution bus, and power to the battery charger is only connected if shore tie or generator are connected. The the transfer switches isolate both hot and neutral, though they are connected to common ground.

[Nic7320]

That's why I recommended the Multiplus, it handles everything. Otherwise, you need to add an ATS, a bonding scheme, and handle a lot of electrical safety issues.

Small loads running on small inverters can be treated separately, but somewhere you need a main power system.

[avanti]

Originally Posted by Nic7320

That's why I recommended the Multiplus, it handles everything. Otherwise, you need to add an ATS, a bonding scheme, and handle a lot of electrical safety issues.

All of the high-end marine inverters have such features. There are several excellent ones. We have an Outback 2800, which is very satisfactory.

[eric1514]

Originally Posted by GeorgeRa

I followed the installation manual from Mornigstar. The Morningstar AC out is floating, I picked one of these two AC wires and bonded to the ground, it became neutral. Both outlets are GFCI. I only use either shore/1000W Magnum or Morningstar 300W. I think, accidental turning both wouldn't cause a safety problem. Galley's GFCIs green indicators show me which AC circuit is on, Morningstar or Magnum/Shore.

This is well known source for RV safety. https://www.amazon.com/No-Shock-Zone.../dp/0990527913

His video about generators bonding

So I watched this video and it was very interesting but I'm afraid I still don't get it. I have an older Champion generator I use around the house now and then. In fact, I used it today. I brought it out to exercise it and I tested it with one of those 3-light testers and it read open ground. I was going to make one of those bonding plugs but the generator only has one 20 amp 115v output so I said the heck with it and plugged in my angle grinder (which only has a two prong plug) and got to work. I've done this countless times before and have run an extension cord into the house to run things during a power outage. What's the big deal?

[Nic7320]

The deal is that it's not the safest way to operate.

Yes, it can be done without bonding and in truth, without even a ground. Early electrical systems did just that.

Sometimes a floating system is safer than one tied to ground but more often it's not. That's what's happening with your floating ground, it has no connection to the frame of your generator. But your generator isn't staked to an earth ground either, so... well, you can run it that way.

When you don't have a good ground, that's a good time to use a GFCI. They don't actually need a ground, they test for any difference in currents on the hot and the neutral wires.

Your bond is important because it keeps everything within a voltage range. Additionally, it provides a pathway when things go wrong. Lightning, for example, wants to find a path to earth ground. Without a neutral to earth bond, it has to arc across something else, rather than flowing through a metal strap.

So all these measures increase safety: electrical safety grounds, proper power and current ratings, proper insulation, good quality plugs and cords, surge protection, undervoltage and overvoltage protection, open ground detection, GFCIs, AFCIs, tracking distances on circuit boards and so on.

Then list gets longer when things are U.L. rated. And some CSA and EU standards are more stringent. Take a look at all the safety features designed into an EU electrical plug, and ours will look downright primitive.

You can drive on bald tires and get away with it... for a while. Same with electrical safety. But sooner or later it's going to get you, or someone you care about.

[Nic7320]

Originally Posted by eric1514

... I have an older Champion generator I use around the house now and then. In fact, I used it today... and plugged in my angle grinder (which only has a two prong plug) and got to work.What's the big deal?

Sometimes I can be too theoretical, so I'll throw out a real world example.

Your gen set's been sitting outside and has a little water in it. You don't know this, because it starts up just fine and runs like the day it was new. But once it runs a while, some water splashes up against the generator's windings and now the frame is HOT.

And now you go run your ungrounded grinder and it works just fine. But little do you know, it's been accumulating dust from the brushes up against its case and it's got a path to Neutral.

Now it's beer-thirty and the game is on, so it's time to take a break. You turn off the grinder and reach over to turn off the generator, and Zzzzzzzzzappppp... somehow you can't let go and after a few very painful seconds of this, your heart stops beating. Or the opposite happens, it kicks your muscles into superhero mode and it throws you across the lawn. Both can happen, but this is actually better, because it disconnected you from the circuit.

So the first short circuit in the gen set had no place to go, it just charged the frame and created ONE problem. It wasn't until you plugged in a tool that had ANOTHER problem and reached from one potential to the other that you became the pathway for current.

A grounded system would have shunted all that current to the safety ground wire and hopefully trip a breaker, if it's a low enough resistance short. (Notice I said it's just water and carbon dust, and those aren't very low resistance, so maybe it doesn't trip.) But without a ground in the circuit, it won't even know there's a problem.

BTW, is this a double insulated grinder manufactured with a two pin cord, or metal case one with the ground pin cut off?

[GeorgeRa]

Originally Posted by Nic7320

.........................
BTW, is this a double insulated grinder manufactured with a two pin cord, or metal case one with the ground pin cut off?

Good point, with two pin cord tools you don't need GFCI.

[Nic7320]

With a 2 pin cord, you don't need a Ground pin connection.

A GFCI is still useful. It only looks at the hot and neutral by running both wires through a small toroid, and if the currents don't match, then it sends a signal to shut off the power.

So it protects a lot of other fault cases, but in this case, a double insulated tool doesn't have a case, so that's a case where the tool was designed to be safer

Problem is not everything is double insulated.

[GeorgeRa]

Originally Posted by Nic7320

With a 2 pin cord, you don't need a Ground pin.

A GFCI is still useful. It only looks at the hot and neutral by running both wires through a small toroid, and if the currents don't match, then it sends a signal to shut off the power.

So it protects a lot of other fault cases, but in this case, a double insulated tool doesn't have a case, so that's a case where the tool was designed to be safer

Problem is not everything is double insulated.

Practically, what could cause in/out flow difference and how it would impact safety?

[Nic7320]

Booster brought up another possibility that is a bit worrisome.

If an inverter has an internal short from hot to its metal case, and there's a GFCI on the inverter's output, chances are it WON'T trip the GFCI. Because the short is before the GFCI, not after it. Only if the fault current somehow messes with the hot or neutral output wires will the GFCI see a fault.

But a properly bonded safety ground connected to the case should catch the short circuit fault current and protect the user. Hopefully it will trip something on the DC side when excessive current flows and the DC input power goes way up.

Without a ground, there's just no good solution to this, other than a good design layout and good insulation on the transformer.

[Nic7320]

Originally Posted by GeorgeRa

Practically, what could cause in/out flow difference and how it would impact safety?

An unintentional pathway of current. Like water. Or a short circuit to something where the current didn't return the way it is supposed to.

So the flow difference might be current going -- through you.

But what it won't protect is if you touch both hot and neutral. That's no different than any load that's supposed to get power.

And speaking of unintended short circuits, this week I had a fuse holder melt on my solar charger. I'm lucky it didn't short to ground, because the Tesla battery has over 1000 Amps behind it and requires 300 Amps to blow the ANL fuse. It was my mistake, and not unlike Apollo 13 where they upgraded something but didn't upgrade something else. New and much better fuse holders got delivered today.

[Nic7320]

If you'd like to see how well bonding works under extreme conditions, look at this short video:

https://www.youtube.com/watch?v=Fyko81WAvvQ

Dr. Megavolt and I disagree on whether this is due to "skin effect." Skin effect is why high frequency currents tend to travel more in the outside of a solid wire, but his chainmail suit is thousands of times more conductive than the human body at any frequency, so it conducts better due to nothing other than stainless steel's resistance being much lower than he is. It also works better at DC where the frequency is zero, because inductance is no longer involved. By the way, both he and his wife used to ride under the Tesla coil on bicycles at the same time.

The main take-away here is that IF everything you come into contact is bonded at the same potential, there is no shock hazard. That's how grounding works. Anything you touch should be at zero volts. And it's also why a bird can sit on a 16,000 volt wire. It only sees 16,000 volts on one leg, and 16,000 volts on the other leg, so the difference between the bird's legs is also ZERO.

But he did get plasma burns on his feet once. Something he didn't mention.

[eric1514]

Originally Posted by Nic7320

...

BTW, is this a double insulated grinder manufactured with a two pin cord, or metal case one with the ground pin cut off?

Thanks for your answers. Very helpful,

The grinder and the jigsaw I used first both came from the factory with 2-prong cords.

Next question. There's a stud protruding from the faceplate of the generator with a ground symbol next to it. If I attached a wire to it and then to a rod pounded into the ground, would this serve the same purpose as the bonding plug?

[booster]

Originally Posted by eric1514

Thanks for your answers. Very helpful,

The grinder and the jigsaw I used first both came from the factory with 2-prong cords.

Next question. There's a stud protruding from the faceplate of the generator with a ground symbol next to it. If I attached a wire to it and then to a rod pounded into the ground, would this serve the same purpose as the bonding plug?

No it wouldn't. It would give you a better ground with earth reference, though, rather the having the chassis of the generating floating the ground in relation to earth.



Double insulated tools have proven to be very safe from all I have seen and heard. I can't recall ever seeing anyone seriously hurt by one. That said, you always can up with some series of problems and odd circumstances that might create an increased risk, but that appears to be very rare with them.

[booster]

Aside from complex and hard to understand physics and electrical theories, there is on thing that has not been mentioned in the whole mobile power stuff.


First off, no matter how much stuff you do, there is likely always going to be some way that things could go wrong and be a hazard in a vehicle that does not have an earth ground and the body is used for ground buss.


The worst scenarios, I think, are anything to do with getting a hot skin on the van as that puts a person in a particularly dangerous position of being standing on an earth ground with voltage potential to the ground easily being touched on the body. As soon as you start using hardwired inverters that use the van body for ground those issues get more likely. This is also the area where novice installers or owners that put in a hardwired unit are the most likely to be able to make errors. We have seen repeated installs of inverters of unknown bonding tied up parallel with shore power outlets which is not a good thing. I think this discussion that drifted to bonding is good example of the level of non and inaccurate understanding of bonding that the general population has, including some RV techs.


If things like explanations get too complex and convoluted, common sense rules and suggestions can be lost in the fog, so nothing gets improved due to information fatigue. We have seen on this forum over and over again how that happens. How many readers actually want to know all the theory behind why the bonding rules say, simply, "one and only one bond and it must be at the power source". The implementation of that one line can be fairly easily explained or what can be done to an existing install can be given very basic ways to correct it.


All the above is why I think that for occasional, low power, user installs of a standalone, isolated from the chassis, inverter is probably the most easy to make safe, unless the inverter itself is inherently dangerous. If anything you are plugging in has a 3 prong plug on it, don't get a two prong only, and make sure it is bonded. For added safety be a bit, get one with built in GFCI outlet. Plug it into a 12v accessory outlet of adequate 12v DC power and be done with foray into the AC wiring and it's related issues. An inverter that doesn't have to deal with shore power at all makes like a lot easier.



Incessant "whataboutism" seems to be clouding things up by scaring folks about obscure possible issues with a one in a trillion odds to not addressing the issue with a one in a hundred odds of going bad.

[avanti]

Originally Posted by booster

If things like explanations get too complex and convoluted common sense rules and suggestions can be lost in the fog, so nothing gets improved due to information fatigue.

This is exactly why formalized building codes are so profoundly important. As I said before, almost every one of the seemingly arbitrary, often ridiculous-sounding rules that comprise the Code was motivated by some prior tragedy. They are written by committees of professionals who do their best to keep both theory and field-practicality in mind.

Building codes are not meant to be pedagogical--you are not supposed to think about them, or even to understand them. You are just supposed to FOLLOW them. They are not perfect, and more often than not, you can get away with ignoring any given one without negative practical consequences. But, you can also often get away with playing Russian roulette without practical consequences. The Code represents the accumulated wisdom of almost two centuries of real-world experience. People who think they understand the underlying physics well enough that they can second-guess the Code are fools (this is not a swipe at anyone on this list). Even if they did have such understanding, they couldn't possibly have access to the long, bloody history that lies behind each rule.

"Best practice" is nothing to sneeze at.

Sorry for the rant.

[GeorgeRa]

Originally Posted by booster

……………………………
Double insulated tools have proven to be very safe from all I have seen and heard. I can't recall ever seeing anyone seriously hurt by one. That said, you always can up with some series of problems and odd circumstances that might create an increased risk, but that appears to be very rare with them.

Originally Posted by booster

………………………..
Incessant "whataboutism" seems to be clouding things up by scaring folks about obscure possible issues with a one in a trillion odds to not addressing the issue with a one in a hundred odds of going bad.

Originally Posted by avanti

This is exactly why formalized building codes are so profoundly important. As I said before, almost every one of the seemingly arbitrary, often ridiculous-sounding rules that comprise the Code was motivated by some prior tragedy. They are written by committees of professionals who do their best to keep both theory and field-practicality in mind.
Building codes are not meant to be pedagogical--you are not supposed to think about them, or even to understand them. You are just supposed to FOLLOW them. They are not perfect, and more often than not, you can get away with ignoring any given one without negative practical consequences. But, you can also often get away with playing Russian roulette without practical consequences. The Code represents the accumulated wisdom of almost two centuries of real-world experience. People who think they understand the underlying physics well enough that they can second-guess the Code are fools (this is not a swipe at anyone on this list). Even if they did have such understanding, they couldn't possibly have access to the long, bloody history that lies behind each rule.
"Best practice" is nothing to sneeze at.
Sorry for the rant.

Thank you.

[Bud]

Originally Posted by avanti

This is exactly why formalized building codes are so profoundly important. As I said before, almost every one of the seemingly arbitrary, often ridiculous-sounding rules that comprise the Code was motivated by some prior tragedy. They are written by committees of professionals who do their best to keep both theory and field-practicality in mind.

Building codes are not meant to be pedagogical--you are not supposed to think about them, or even to understand them. You are just supposed to FOLLOW them. They are not perfect, and more often than not, you can get away with ignoring any given one without negative practical consequences. But, you can also often get away with playing Russian roulette without practical consequences. The Code represents the accumulated wisdom of almost two centuries of real-world experience. People who think they understand the underlying physics well enough that they can second-guess the Code are fools (this is not a swipe at anyone on this list). Even if they did have such understanding, they couldn't possibly have access to the long, bloody history that lies behind each rule.

"Best practice" is nothing to sneeze at.

Sorry for the rant.

avanti, your rant can also be applied, describes why it is so so safe to hop on an airliner, while staying out of your bathtub!

Thanks for the rant.

Bud

[booster]

There are good rants and bad rants, and Avanti's is spot on and needed to be plainly stated, as it was.

[eric1514]

This has been a good discussion, as most are on this forum. They always tend to go above my head because this stuff is not how I made a living but I like learning and you all are usually helpful.

On my C, I was going to increase the battery bank and put in an inverter to run the microwave for short periods of time. I thought it would be neet to wire it into all the coach outlets with a transfer switch but I really think that it would have been above my pay grade so I resigned myself to only powering one half of a 110v dual outlet. I would cut the tabs where the screws are in the back of the outlet to isolate top and bottom and power one half with shorepower when plugged in and the other half with the inverter for when no shore power was available. This would neccesitate unplugging the microwave from one outlet to the other but it seems, after reading this thread, to really be the safest way to do this and since this is all I would be using it for, it's not really a big deal to open a cabinet door and move the plug.