Dangers using Auto Transformers and 230V Inverters in North America

Good video Ian. That is a massive safety hazard if not dealt with. Update: Signature solar sells a US version of the 5000ES, which is called the 5000US. The growatt america site has not even updated their marketing materials to reflect this change. The also added a schematic for running the inverter safely. I personally will stick to inverters that do not require an external autotransformer, but there seems to be a safe way to accomplish it. Growatt needs to update their marketing material though, because if someone buys a 5000ES on ebay, and a 5000ES from signature solar, and parallel them, you will create 120V on the ground on the case of one of the inverters. This could be very dangerous, and people would think that they are getting the same exact inverter, when in fact, they are not. Signature solar added an update to their listing to reflect this issue.

Here is a suggestion from the Internet for all those wishing to use a 5000ES or similar: 1. Study the teachings of Mike Holt until you realize that grounding rods are not the same as 0V, do not make things safe on their own, and that the only thing that really matters are “grounding conductors” (a.k.a. the ground wires) that carry current back to the source in the event of a live wire energizing a metal case. This "grounding conductor" return path creates a short circuit that will trip the breaker, which is what keeps us safe. 2. On the inverter input connect the grid's L1, L2, and “ground”. The case of the inverter can be grounded to the grid ground (likely already is). In the event that L1 shorts to the inverter case the current will return to the grid over the grounding conductor. 3. On the inverter output connect L1 and L2 to the autotransformer, connect the “ground” output to the case of the autotransformer. In the event L1 shorts to the autotransformer case current will return to the grid via the grounding conductor. 4. Connect the output of the autotransformer L1, L2, and N to a critical loads panel. Do NOT connect a ground from the critical loads panel to the autotransformer or to the grid ground in any way. See the next step for why. (Think of the autotransformer as the grid transformer for your critical loads panel.) 5. Bond the critical loads panel “ground” bar to N. This creates a “grounding conductor” path back to the “source”, which is the autotransformer for everything connected to the critical loads panel. [You may be tempted to drive a new grounding rod for this new grounding circuit you are creating. See #1.] 6. Pray to your grounding god Mike Holt. Disclaimer: I don’t know if I’d do this, and you shouldn’t without doing your own research, but let’s discuss it.

This guy knows his stuff especially for outside US. A real isolation transformer is highly recommended for isolation.

Excellent point and also helpful tips on how to deal with this issue. I have the 5000es ( purchased from you) but never connect to grid. I have multiple isolating transformers for my 120v loads. Use solar only for charging & chassis ground connected to metal of building and ground rod

Ian is so on it his game is real unlike so many other vendors out there that will say and do practically anything to make a sale and give you no follow-up service. Thank you sir hope to be making another purchase from you soon.

High frequency 230/240V inverters have no transformer on the output. Therefore Neutral and Ground will be connected, if not within the inverter but at the house power panel. Remaining L inverter output has 230/240V potential relative the N/Ground. To derive the 120/240V split phase US system from it an isolation transformer is needed. The auto-transformer will not work because it only works as a voltage divider but does not remove the N/Ground to L relationship. With an isolation transformer that takes 240V on the input and has 120/240V on the output, the middle output terminal can be connected to N and all is save afterwards. Low frequency inverter uses an internal isolation transformer to step up the battery voltage to 120/240V. Middle output terminal can be directly connected with N. 230/240V HF inverter can run 240V devices like A/C or pool pump but no 120V to N voltage will be available. Check out Genetry Solar for reasonable LF inverters.

One possible solution for those who are desperate to use their existing Auto Transformer and EU inverters, unbond the ground like Ian did and then wire the AT only during inverter mode, bypass AT during grid mode. This can be achieved by using additional bypass relays or by rewiring the inverter output at the PCB itself and use the internal inverter bypass relay. I don't see any other solution using AT. Complicated solution though. And Ian's very right about the pole transformer and the AT back feeding each other, will heat up those long house wiring, power loses, and many other problems. Signature solar selling unbonded ground 5000ESs is definitely not a solution. I think it's better to stick to LV split phase inverters for the US.

Try the same measurements with the inverter on and measure voltage instead of resistance to the ground. My MPP solar inverter does not have the ground and neutral bonded internally.

Thanks so much for finally bringing up this problem. Long ago, I bought an MPP-5048MG directly from MPP Solar. Its neutral and ground are still bonded internally, as you said, and its single phase was at 240VAC with respect to them. So I used it as an off-grid system only and connected a grounding bare wire going all the way to the main panel to seek the earth rod. My Hybrid inverter and its subpanel are therefore both grounded but the distance is quite far, about 40 feet, so I probably need a closer earth grounding rod. I left the neutral from my toroidal auto-transformer floating to get my split phases to read 20VAC with respect to its neutral and 240 vac with respect to each other. So far I'm not getting zapped touching any of the enclosures. But you're right about removing that internal bonding screw to disconnect the hybrid inverter's neutral from its the ground and chassis. I agree and will do it, because it will allow me to bond my toroidal auto-transformer neutral to the grounding bus inside the subpanel without creating a short. Moreover I will connect that ground bus to a closer earth grounding rod about 6 feet away from it according to NEC codes in CA. Once done, all cables coming from this subpanel will carry a ground wire that actually will protect people from electrical shocks should one of the phase get loose inside any metal enclosure or appliance. I'll insert a piece of mica sheet underneath those PC boards to prevent arcing, just in case.. I'll probably need to disconnect my grid's bare wire grounding then, so that the solar system is now completely independent of the main utility panel and avoid creating a ground loop.

I would not recommend using this unit unless you fully understand what Ian has stated here in the video, furthermore i would say if you are choosing to remove the ground bond screw you may also wish to dis-assemble the back board from the case and either remove the standoff or install some electronic isolation paper such as fish paper to improve the isolation of the ground. Again, unless you are very well adept in electronics and house wiring, DO NOT ATTEMPT

i believe victron works around this problem by having internal relay inside quattros (and maybe multiplus) for bonding l2 and ground and their autotransformer also has a relay that can be used to bond or not neutral and ground, you can program and activate these relays in various scenarios like bypass or inverting power, does that solution make it safe to use their 230 (euro) models?

Great vide! Would it be possible to discuss a different installation which would be let's say "opposite" to this situation? What would an installation look like if somebody located in Europe with a European solar installation supplying standard 230-240 VAC, 50 Hz who wants to install a US inverter to provide 120 VAC, 60 Hz to standard US outlets?

If you are grid tie, why don't just use L1 and L2 from grid and use the autotransformers for neutral? in other words don't use the neutral that came from grid and let the autotransformers provide the Neutral when is in bypass mode and off-grid mode.

Thanks for posting this danger Ian! Seems many DIYers don't get "ground loops" either. Can't count the number of service calls I've had over the years from residential DIY subpanel installs within barns and out buildings...with mains panel feeds being bonded neutral and connected to separate grounds in outbuilding subpanels. If the distance from mains panel to sub in an outbuilding or other "perceived need" (backup generator in the outbuilding) for separate ground rods at the outbuilding are present, then installing an isolation transformer, 3 pole transfer disconnects, etc (defined as a separately derived system within the NEC) before the subpanel is required. "Well it works, so prove me wrong" mentality of unskilled non-tradesmen respects no published electrical safety/code compliance standards.

Well I was running 3 growatt 5KW from signature solar and there growatt 11.4 kw auto transformer Well what a surprise the transformer crapped out You can only imagine the MESS I’m dealing with down🤮‼️‼️‼️ I had 390volts coming out between the 2 legs I lost my garage door openers , 6 automatic sky lights , a jacuzzi tub , dish washer , gfcI breakers my Kerig My heating and cooling unit and all sorts of light bulbs blew up Thank god my son who’s an electrician was home while I was gone to shut everything down All SS will do is replace my growatt transformer PLEASE people be very careful building a system like this Everything was built just the way signature solar design Sickening Thanks a lot Ian for making everyone aware of this issue I just wish I found it before this huge mess happened 😢

Thanks for the great video Ian. It would be nice if you did a follow up one on what happens if that neutral wire gets lose on the Autotransformer.

This is a problem I have been banging on about since I first found the diysolar forum. The 230v units are less expensive and auto transformers are also relatively cheap compared to a full isolation transformer. So yes, cheaper non approved equipment can indeed make your lights light up and your motors spin just fine no problem. BUT it is a huge safety risk IF/WHEN something goes wrong. Electric shock, blown appliances in your house or if you are lucky just a blown inverter. Ian, I hate that screw removal technique I wish you had not shown that. Is the circuit board now just about not quite touching the frame of the inverter or is it an actual rated gap between the PCB and frame ? That "new" growatt auto transformer is bollocks, it is a hacked up ATS box that has had the contactor removed and the transformer just wired direct. It is being sold as UL approved but that is bullshit. SS say it is done by Growatt but I doubt it. Just spend the money and BUY PROPER equipment for your situation.

Very clear video on neutral bonding issues. Seems like a better solution to "grid tie" without selling power back to the electric company would be to buy a 48v battery bank charger and disconnect ac power from the inverter. Therefore, if you are lacking sun for several days, you can still top off the batteries with the grid. It would be a "partial" grid tied solution.

If the bolt is removed in Europe, it functions so that we can remove the ground to neutral bond in the inverter when we already have a ground to neutral bond in the panel (because ground to neutral bonding can only be done at one point). Even though the bolt is removed, there is no voltage difference between neutral and ground in the inverter because it is combined in the main panel. If used in the US with a setup like in the video, there will be 120v between ground and neutral in the inverter and also in the bonding bolt holes, where the distance between the conductors may only be a few millimeters. The point is that European inverters are definitely not designed for use in the US, they can be tricked, but it could possibly harm the device and its users.

The scariest part of this is I can't follow this and I'm sure I'm not the only person.