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Inverter and a plug point


Freddievanleeuwen

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Hi everyone. So I have an interesting question. I have a 3kv inverter that runs a few few plugs completely seperate from Eskom. Power comes from 2 x solar panels and feeds 2 x 120ah batteries. It's running as expected with no issues. Can I use the AC in on the inverter, connect it to a 3pin plug and plug it into a plug point that is on eskom power?

I saw a guy in America that does this with his installations.

 

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8 minutes ago, Freddievanleeuwen said:

Hi everyone. So I have an interesting question. I have a 3kv inverter that runs a few few plugs completely seperate from Eskom. Power comes from 2 x solar panels and feeds 2 x 120ah batteries. It's running as expected with no issues. Can I use the AC in on the inverter, connect it to a 3pin plug and plug it into a plug point that is on eskom power?

I saw a guy in America that does this with his installations.

 

When this was being done with generators its was referred to as a "suicide cable" for good reasons.

The short answer is no, you cant do it safely. Backfeeding into a socket eliminates earth-neutral bonds so no earth leakage.

There are so many reasons why its a bad idea.

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39 minutes ago, Freddievanleeuwen said:

Hi everyone. So I have an interesting question. I have a 3kv inverter that runs a few few plugs completely seperate from Eskom. Power comes from 2 x solar panels and feeds 2 x 120ah batteries. It's running as expected with no issues. Can I use the AC in on the inverter, connect it to a 3pin plug and plug it into a plug point that is on eskom power?

I saw a guy in America that does this with his installations.

 

You have multiple problems here. 

1) a greater load on the batteries. They will deplete more rapidly. 

2) safety. Intersting things are going to happen when the grid power comes back. You certainly can't just leave it connected all the time. 

3) it may be possible that your system puts power out onto the grid during an outage. A big no-no

Rather get it wired into the DB. This gives you some mitigation against (1) as you decide what gets backed up. 

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Looks like the posters missed a crucial bit of info: the user wants to plug the AC IN of the inverter to a plug point. That is acceptable, as long as a couple of conditions are met:

  • The inverter may not export back to the plug - (like the suicide plug comment above - apart from the obvious danger, doing so also bypasses your RCD)
  • The inverter must not draw more current than the plug can supply. In SA a plug can supply 16A, which is enough for the 3kW requirement, but depending on the inverter and settings, it might require more. For instance, say you have 2kW of load and you want to charge the batteries at 2kW.

Then on a separate note, the plugs you have on the output probably don't have any earth leakage protection (like most inverter trollies) but that is a sizeable topic on it's own.

 

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30 minutes ago, Bobster. said:

You have multiple problems here. 

1) a greater load on the batteries. They will deplete more rapidly. 

2) safety. Intersting things are going to happen when the grid power comes back. You certainly can't just leave it connected all the time. 

3) it may be possible that your system puts power out onto the grid during an outage. A big no-no

Rather get it wired into the DB. This gives you some mitigation against (1) as you decide what gets backed up. 

Keep in mind the solar system runs completely separate from the grid. There's absolutely no connection between the two.

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3 minutes ago, P1000 said:

Looks like the posters missed a crucial bit of info: the user wants to plug the AC IN of the inverter to a plug point. That is acceptable, as long as a couple of conditions are met:

  • The inverter may not export back to the plug - (like the suicide plug comment above - apart from the obvious danger, doing so also bypasses your RCD)
  • The inverter must not draw more current than the plug can supply. In SA a plug can supply 16A, which is enough for the 3kW requirement, but depending on the inverter and settings, it might require more. For instance, say you have 2kW of load and you want to charge the batteries at 2kW.

Then on a separate note, the plugs you have on the output probably don't have any earth leakage protection (like most inverter trollies) but that is a sizeable topic on it's own.

 

So the inverter runs at most on a 30% load. The panels supply enough so it will be just for an emergency top up when the batteries are about to run out. The solar has earth leakage and earth wire to the ground with a copper rod.

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2 hours ago, Bobster. said:

My apologies if you mean connecting the AC input of the inverter to a wall plug. That's not a suicide plug.

I misunderstood that one too, you definitely can run the input off a wall plug as long as the charging amps are lower than 16A.

My mate ran his Sunsynk 5kw off a normal plug(live stripped out for CT clamp) and the end of an extension cable so he could plug in tv etc until it was installed. It worked fine aside from the plug shocking you if Eskom was out.

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1 hour ago, RocketBoy said:

I misunderstood that one too, you definitely can run the input off a wall plug as long as the charging amps are lower than 16A.

My mate ran his Sunsynk 5kw off a normal plug(live stripped out for CT clamp) and the end of an extension cable so he could plug in tv etc until it was installed. It worked fine aside from the plug shocking you if Eskom was out.

Yeah it is exactly the same as if you're connected to DB (same power source I mean) I am thinking to remove the earth wire and just run the N and Live. Not sure what you mean by "live stripped out for CT clamp"

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There is also the issue that inverters leak small current to earth via the EMI capacitors, and the household plug is likely to be earth leakage protected. So you might get nuisance trips of the RCD. However, a 3 kW model is smaller than a 5 kW model, so it might cause less leakage to earth.

48 minutes ago, Freddievanleeuwen said:

I am thinking to remove the earth wire and just run the N and Live.

I'd think long and hard about that. The leakage current I mentioned would then flow through some other path, possibly through people touching the metalwork of appliances. That sort of current should not ordinarily be fatal, but it can be nasty. Check the potential of the inverter chassis with respect to a known-good earth with a multimeter; you may find some 90 VAC if you don't have a good earth.

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40 minutes ago, Coulomb said:

There is also the issue that inverters leak small current to earth via the EMI capacitors, and the household plug is likely to be earth leakage protected. So you might get nuisance trips of the RCD. However, a 3 kW model is smaller than a 5 kW model, so it might cause less leakage to earth.

I'd think long and hard about that. The leakage current I mentioned would then flow through some other path, possibly through people touching the metalwork of appliances. That sort of current should not ordinarily be fatal, but it can be nasty. Check the potential of the inverter chassis with respect to a known-good earth with a multimeter; you may find some 90 VAC if you don't have a good earth.

I think I might just stay away from it altogether. Thanks for the info.

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