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Old 09-07-2017, 03:00 PM   #21
Bus Nut
 
Join Date: Oct 2015
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Okay, so the setup I am currently working with would have a generator, a battery bank, and shore power.

On the shore power side of things, you're starting with a bond. Most people seem to run the shore power directly into an inverter/charger so that it can charge the batteries while supplying power. In this case, you wouldn't want the inverter to have it built in based on what you are saying.

This means you would have to build in a bond somewhere after the inverter that would only be connected when the inverter is drawing battery power. Is that correct?

Or are inverters that people are using designed so that the bond is only active when there is no input from shore power?

Edit: Also, I second what PNW Steve said. Thank you.

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Old 09-07-2017, 07:07 PM   #22
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I like a book called upgrade,operate and troubleshoot 12v systems written by Harold Barre.
It covers boats/RV's.
Wind,solar,generator systems.
Design/calculations including battery and panel sizing, correct wire sizes, and almost everything for what we are doing except saying school bus.
Mike Sokol is a must watch but the other book has helped me.
Good luck
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Old 09-07-2017, 07:29 PM   #23
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Okay, so I've been reading and thinking about this some more.

It seems like the essence of what is being described is that the breaker box inside an RV should be setup like a subpanel in a house, in the sense that the ground should have a separate buss bar and the neutral should be floating.

First of all, is that correct?

Second, would a setup like what I'm about to describe fulfill the requirement to only have one bond per system...

Let’s say we have shore power, a generator, and batteries. The hot and neutral wires from the shore and generator would first go to a switch to ensure they aren’t both active at once. From this switch, they go to a main breaker. From there they go into the inverter charger. The hot leaving the inverter goes to the actual breakers, then to the outlets. The negative goes to a floating negative buss bar (not bonded to ground or frame) and to the outlets.

The ground wire coming from the appliances goes to a separate buss bar that IS bonded to the frame. From there, one ground goes back to the shore pedestal, one goes to the generator, and one goes to the inverter.

Edit: I'll check out that book, thanks
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Old 09-07-2017, 07:36 PM   #24
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Quote:
Originally Posted by PigPen View Post
On the shore power side of things, you're starting with a bond. Most people seem to run the shore power directly into an inverter/charger so that it can charge the batteries while supplying power. In this case, you wouldn't want the inverter to have it built in based on what you are saying.
Just to make sure we're on the same page, I think what you're describing is a topology like the following. I've put in arrows to illustrate the energy flows.
topology.png
You're right: some inverter-charger devices will offer a built-in ground-neutral bond. It isn't an inherently good nor bad feature; it's the design of the system around it that makes it good or bad.

If we think of only the batteries and the grid-supplied shore power, a built-in automatic bond in the inverter-charger would be really convenient. It'll bond when shore power is disconnected, and open when shore power is connected. Great!

The catch is this: what happens when the shore power cord is plugged to a generator? What provides the ground-neutral bond?

The inverter-charger won't provide the bond: its logic is "if there's power at my ac input, disconnect the bond." The inverter-charger doesn't actually know or test whether the ac input circuit provides a bond. (note: I'm generalizing. It'll be important to confirm by checking the owner/user/installer manuals of any specific device before use.)

The generator may or may not provide the ground-neutral bond. I'm most familiar with the Honda portable inverter generators (EU2000 and EU7000) and know that these from the factory do not provide a bond. It has been reported that other generators do provide a bond. The point is, bonding isn't standardized in the industry and we can't make an assumption.

When considering the portable generator scenario one might say "the automatic bond in the inverter-charger did the wrong thing! It's bad!" I would say just be aware of and understand the issue and plan accordingly.

For the specific case described here (topology as above, inverter-charger with automatic bonding, possibility of plugging shore power to a generator with unknown bonding), here's one simple idea. Several years ago Mike Sokol proposed building a ground-neutral bond plug. Make one and tether it to the male plug end of the shore power cord. Each time the shore power cord is plugged into a power source it'll be there and remind you to ask yourself "am I plugging into a generator? Plug in this bond plug to the generator too, to ensure that the ground-neutral bond is provided."
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Old 09-07-2017, 07:46 PM   #25
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I posted a response right before you.

I was asking if this system would work:

Letís say we have shore power, a generator, and batteries. The hot and neutral wires from the shore and generator would first go to a switch to ensure they arenít both active at once. From this switch, they go to a main breaker. From there they go into the inverter charger. The hot leaving the inverter goes to the actual breakers, then to the outlets. The negative goes to a floating negative buss bar (not bonded to ground or frame) and to the outlets.

The ground wire coming from the appliances goes to a separate buss bar that IS bonded to the frame. From there, one ground goes back to the shore pedestal, one goes to the generator, and one goes to the inverter.

----

But based on what you just said, I'm thinking it would make more sense to have one cord that is either plugged into the generator or the shore pedestal, then using one of those plugs if the generator doesn't have a bond built in.
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Old 09-08-2017, 03:27 PM   #26
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I re-arranged the quote segments a bit.
Quote:
Originally Posted by PigPen View Post
But based on what you just said, I'm thinking it would make more sense to have one cord that is either plugged into the generator or the shore pedestal, then using one of those plugs if the generator doesn't have a bond built in.
It does offer some simplicity, and if a person is going to use a portable generator, it could keep things easy.

If the generator is to be built in, and if the shore power cord is to be stowed near the generator anyway, a person could still use that same process without the extra step of positioning the generator. Or..
Quote:
Originally Posted by PigPen View Post
Letís say we have shore power, a generator, and batteries. The hot and neutral wires from the shore and generator would first go to a switch to ensure they arenít both active at once. From this switch, they go to a main breaker. From there they go into the inverter charger. The hot leaving the inverter goes to the actual breakers, then to the outlets. The negative goes to a floating negative buss bar (not bonded to ground or frame) and to the outlets.

The ground wire coming from the appliances goes to a separate buss bar that IS bonded to the frame. From there, one ground goes back to the shore pedestal, one goes to the generator, and one goes to the inverter.
That's a fairly standard arrangement for an onboard generator setup. It's especially desirable if the generator will be remote startable, or is designed for hard-wire connection, etc.

The wiring all sounds right, including the grounding. The only question remaining is how does the system ensure the ground-neutral bond connects appropriately? Earlier we assumed the inverter-charger connects it when there's no ac at the input (to be verified in the manuals of the specific unit to be used). If the generator provides a ground-neutral bond too, you'd be all set. NOTE: having the neutral switched by the transfer switch is important. It's what prevents the generator's always-on ground-neutral bond from being in circuit when shore power is plugged in.
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