Inverter Overloading

[JohnD]

When using an onboard AC power source such as a generator or inverter, the power source neutral has to be bonded to ground. When using shore power, the ground and neutral can’t be connected within the RV.

This bonding switching is generally handled by the ATS wiring. If the neutrals weren’t switched, the neutral would always be connected to ground inside the RV. Shore power has the neutral and ground bonded in the panel. Adding another bonding point results in the ground wire carrying part of the neutral current. Not good.

If the output of the inverter has its ground and neutral bonded internally, if you connect shore power neutral to inverter neutral, there will be problems.

Okay, that is quite interesting. Assuming all that is correct, I think that the manual switch diagram that I have is incorrect and that much of what I assumed in the previous post is wrong. If I understand you correctly, as long as there is shore power, the breaker panel neutral should come from shore such that the ground is bonded to neutral at the shore. If there is no shore power, then the breaker panel neutral should come from the inverter, such that the neutral and ground are bonded at the inverter. Does that sound right?

[Jkwilson]

Okay, that is quite interesting. Assuming all that is correct, I think that the manual switch diagram that I have is incorrect and that much of what I assumed in the previous post is wrong. If I understand you correctly, as long as there is shore power, the breaker panel neutral should come from shore such that the ground is bonded to neutral at the shore. If there is no shore power, then the breaker panel neutral should come from the inverter, such that the neutral and ground are bonded at the inverter. Does that sound right?

I think so. Every AC power source ground and neutral should be bonded once and only once. Shore power is bonded before it gets to you, so your ATS and wiring needs to accomplish two things regarding ground neutral bonding. Bonding the ground and neutral of other power sources when they are in use, and not bonding the ground and neutral of shore power at any time.

This is commonly done wrong even at GD.

[ncitro]

JohnD

Over the summer I replaced my Magnum inverter with a Victron Multiplus (mainly to get a unified interface with my solar controller and battery monitor, but also to get power assist). The SPS was backordered at that time as well. I was under the gun, so did my install without it. I moved basically everything to the inverter phase in my panel except the factory converter (still there as a backup), water heater and fireplace. Everything else is on the inverter phase (including both AC units). I have had everything running and am well below 50 amps on that phase so no issue there. The only downside is since not everything is going through the Multiplus, I have to manage the power assist feature somewhat manually. Basically the total current use it is showing does not include the fireplace or water heater. This is generally not an issue since if I am that short on power I am running the water heater on gas, and if I am running the fireplace I am not running the AC units.

Standard disclaimer that I am not a professional, and make no promises of this working for you.

That all said I had to deal with the neutral issue as well. I used a 12 inch metal enclosure and brought the line cord into it. In there I used insulated terminal strips to split out the phases. One phase went directly into the factory breaker panel. One phase went to the Multiplus and then out of that into the other side of the factory breaker panel. I bonded the ground to the box, and then fed a ground out to the Multuplus and the factory panel. The neutral I split (but did not tie to the ground) and sent one leg to the Multiplus and one leg to the factory panel. For good measure I also brought the neutral out of the Multiplus back into the enclosure and tied it to the other neturals as well.

I did a ton of research about the best way to do this, and found some posts on the Victron boards from Victron that said there was no issue with tying the input and output neturals together. I can say that when I connect the rig to a 15 amp GFCI outlet via a dogbone adapter that it trips the GFCI. I suspect this has something to do with the power assist coming on and the neutral current not matching up.

I wired it in this way so that down the road if I got a SPS it would be easy to pull the wires out of my enclosure and put them into the SPS, but in practice it has worked well so far this year.

[JohnD]

JohnD

Over the summer I replaced my Magnum inverter with a Victron Multiplus (mainly to get a unified interface with my solar controller and battery monitor, but also to get power assist). The SPS was backordered at that time as well. I was under the gun, so did my install without it. I moved basically everything to the inverter phase in my panel except the factory converter (still there as a backup), water heater and fireplace. Everything else is on the inverter phase (including both AC units). I have had everything running and am well below 50 amps on that phase so no issue there. The only downside is since not everything is going through the Multiplus, I have to manage the power assist feature somewhat manually. Basically the total current use it is showing does not include the fireplace or water heater. This is generally not an issue since if I am that short on power I am running the water heater on gas, and if I am running the fireplace I am not running the AC units.

Standard disclaimer that I am not a professional, and make no promises of this working for you.

That all said I had to deal with the neutral issue as well. I used a 12 inch metal enclosure and brought the line cord into it. In there I used insulated terminal strips to split out the phases. One phase went directly into the factory breaker panel. One phase went to the Multiplus and then out of that into the other side of the factory breaker panel. I bonded the ground to the box, and then fed a ground out to the Multuplus and the factory panel. The neutral I split (but did not tie to the ground) and sent one leg to the Multiplus and one leg to the factory panel. For good measure I also brought the neutral out of the Multiplus back into the enclosure and tied it to the other neturals as well.

I did a ton of research about the best way to do this, and found some posts on the Victron boards from Victron that said there was no issue with tying the input and output neturals together. I can say that when I connect the rig to a 15 amp GFCI outlet via a dogbone adapter that it trips the GFCI. I suspect this has something to do with the power assist coming on and the neutral current not matching up.

I wired it in this way so that down the road if I got a SPS it would be easy to pull the wires out of my enclosure and put them into the SPS, but in practice it has worked well so far this year.

ncitro Jkwilson

Thank you for sharing this Neil. Interestingly, I just found a design on the internet that uses a Magnum MSH3012RV instead of the Victron Multiplus (which sounds like it might be what you just switched from). It appears as though the Magnum handles the Split phase/single phase internally. It has 240 input and 240 output, and sends Shorepower L2 to the breaker box when split phase, and Inverter output to L2 otherwise. L1 in the breaker box is always connected to Inverter AC output L1. No external SPS necessary. Additionally, it performs a Neutral to Ground Safety feature as shown below.


Edit for question. Does anybody know if Victron Multiplus has this feature?

[ncitro]

ncitro Jkwilson

Thank you for sharing this Neil. Interestingly, I just found a design on the internet that uses a Magnum MSH3012RV instead of the Victron Multiplus (which sounds like it might be what you just switched from). It appears as though the Magnum handles the Split phase/single phase internally. It has 240 input and 240 output, and sends Shorepower L2 to the breaker box when split phase, and Inverter output to L2 otherwise. L1 in the breaker box is always connected to Inverter AC output L1. No external SPS necessary. Additionally, it performs a Neutral to Ground Safety feature as shown below.


Edit for question. Does anybody know if Victron Multiplus has this feature?

Yeah I had the 2812 I think, so it would switch split phase but only at 30 amp. For that setup I ran my shore power into a new 50 amp panel and split out my non inverter loads (both AC units, water heater and I think maybe the fireplace) and fed the inverter with a 30 amp 220 breaker. Went out of the inverter to the rigs stock panel with all the other loads on it.

This system worked flawlessly, but had no power assist. Once I got the Victron I needed to deal with its lack of split phase switching, but I gained the power assist. Worth it imo, but either you need to get the AMSolar Smart Phase Selector (backordered as you know) or deal with the other phase somehow. I did my install in June I think, and have had two long trips on it with no trouble, but not a super intense stress test.

[gbkims]

Edit for question. Does anybody know if Victron Multiplus has this feature?

It has the Neutral switching. Describes it in Service Manual section 2.3 and Appendix.B block diagram at end of the manual.
https://www.victronenergy.com/upload...4xx)-EN-ES.pdf

Mortons on the Move showed a manual transfer switch wired to a MP switching L1, L2 and Neutral.
https://mortonsonthemove.com/solar-p...-the-inverter/

Magnum manual is more user friendly than Victron I think.
The Magnum MSH3012RV 120/240 feature is nice.

[howson]

If $ is not an issue, two MultiPlus' solves the problem with more BBs. Amazing how many setups have that config!

[JohnD]

It has the Neutral switching. Describes it in Service Manual section 2.3 and Appendix.B block diagram at end of the manual.
https://www.victronenergy.com/upload...4xx)-EN-ES.pdf

Mortons on the Move showed a manual transfer switch wired to a MP switching L1, L2 and Neutral.
https://mortonsonthemove.com/solar-p...-the-inverter/

Magnum manual is more user friendly than Victron I think.
The Magnum MSH3012RV 120/240 feature is nice.

Thanks for the links Gene. That settles my concerns about the neutral bonding. However, in the wiring diagrams I have seen, I haven't noticed any devices addressing the underlined earth leakage circuit breakers below. The and/or wording leaves it a bit vague. Any input on that would be appreciated.

Victron Manual
• AC-out-1 (see appendix A) The AC output cable can be connected directly to the terminal block "AC-out". From left to right: “PE” (earth), “N” (neutral) and “L” (phase). The Output Neutral is not bonded to ground. With its PowerAssist feature the Multi can add up to 3kVA (that is 3000 / 120 = 25A) to the output during periods of peak power requirement. Together with a maximum input current of 50A this means that the output can supply up to 50 + 25 = 75A. An earth leakage circuit breaker and a fuse or circuit breaker rated to support the expected load must be included in series with the output, and cable cross-section must be sized accordingly. The maximum rating of the fuse or circuit breaker is 75A.
• AC-out-2 (see appendix A) A second output is available that disconnects its load in the event of battery operation. On these terminals, equipment is connected 5 EN ES Appendix that may only operate if AC voltage is available on AC-in, e.g. an electric boiler or an air conditioner. The load on AC-out-2 is disconnected immediately when the MultiPlus switches to battery operation. After AC power becomes available on AC-in, the load on AC-out-2 will be reconnected with a delay of approximately 2 minutes. This to allow a genset to stabilise. AC-out-2 can support loads of up to 25A. An earth leakage circuit breaker and fuse rated at max. 32A must be connected in series with AC-out-2. Note: Loads connected to AC-out-2 will be taken into account in the PowerControl / PowerAssist current limit setting. Loads directly connected to the AC supply will not be included in the PowerControl / PowerAssist current limit setting.

[JohnD]

If $ is not an issue, two MultiPlus' solves the problem with more BBs. Amazing how many setups have that config!

Money and space are both concerns ;-) I got a chance to visit openrangeowners yesterday to see Mark's setup. That Multiplus is a monster, and I have pretty limited space in my 260RD.

[gbkims]

Thanks for the links Gene. That settles my concerns about the neutral bonding. However, in the wiring diagrams I have seen, I haven't noticed any devices addressing the underlined earth leakage circuit breakers below. The and/or wording leaves it a bit vague. Any input on that would be appreciated.

An earth leakage circuit breaker and a fuse or circuit breaker rated to support the expected load must be included in series with the output, and cable cross-section must be sized accordingly

Usually the installs you see use the existing RV's 50A Main CB in the circuit breaker panel for the AC out of the Multiplus.
Victron's wording lean's toward the world market where Residual-Current Devices (RCD) are used and required. https://en.wikipedia.org/wiki/Residual-current_device
In the USA we tend to have GFCIs for the leakage current wired to the branch circuits.

You can see the MCB/RCDs doing the job of the RV's circuit breaker panel in Victron's system example drawing:
https://www.victronenergy.com/upload...4V-120V-AC.pdf

As to the smart ATS, The 1st gen & 2nd gen ones are Progressive Dynamics ATS (PD52V, PD52DCS) with the L1,L2 jumpers and a 240V relay to sense 120/240v split phase to control the ATS.