Odd advice from Aims tech support

[WilliamC]

Background. I have an Aims 4000w 24vdc to 120/240vac inverter. This is for a battery backup during power outages of critical circuits. Like water-well, refrigerator, and freezer. The 24v battery is the main source of power, and the charge is maintained by a standalone Victron battery charger (not the built in charger in the inverter). I also wired in a generator input to the inverter in case of prolonged outages. The generator is a 4000w 120/240vac Honda generator.
Now for the odd advice. I was told I don’t need a neutral wire from the genset to the inverter. Just the two wires, one for each side of the 240vac. That the generator and inverter would make its own ground. I questioned the advisor specifically and repeatedly about needing 3 wires from the generator or two wires from the generator into the inverter. He was quite clear that only 2 wires were needed.
I have never used this generator input, but the question and concern has remained.

 

[BentleyJ]

If its a low frequency inverter then it has big transformer and the output neutral is derived on the secondary side (load) of the transformer.

 

[seneysolar]

Background. I have an Aims 4000w 24vdc to 120/240vac inverter. This is for a battery backup during power outages of critical circuits. Like water-well, refrigerator, and freezer. The 24v battery is the main source of power, and the charge is maintained by a standalone Victron battery charger (not the built in charger in the inverter). I also wired in a generator input to the inverter in case of prolonged outages. The generator is a 4000w 120/240vac Honda generator.
Now for the odd advice. I was told I don’t need a neutral wire from the genset to the inverter. Just the two wires, one for each side of the 240vac. That the generator and inverter would make its own ground. I questioned the advisor specifically and repeatedly about needing 3 wires from the generator or two wires from the generator into the inverter. He was quite clear that only 2 wires were needed.
I have never used this generator input, but the question and concern has remained.

That is correct.

 

[WilliamC]

If its a low frequency inverter then it has big transformer and the output neutral is derived on the secondary side (load) of the transformer.

This is a low frequency inverter.

 

[WilliamC]

My confusion came from the manual which shows 3 wires for the electric input, which in my case is from the 240 plug of a generator.

 

[seneysolar]

My confusion came from the manual which shows 3 wires for the electric input, which in my case is from the 240 plug of a generator.

Yeah, you gotta read the text, input is hot hot ground, output is hot hot neutral.

 

[WilliamC]

Yeah, you gotta read the text, input is hot hot ground, output is hot hot neutral.

So is the inverter not needing a ground wire on the input side because the output neutral is already grounded in the breaker panel?

 

[Mattb4]

Based on the image you posted for wiring Dual phase (Split phase) it shows both an input ground and an output ground connection. Likely the input ground and output ground are bonded to the inverters chassis. Unless stated in your manual, or based on testing, you will need to have a NG bond in the distribution panel.

 

[Supervstech]

So is the inverter not needing a ground wire on the input side because the output neutral is already grounded in the breaker panel?

Ground and neutral are not the same thing.

The three wires in the picture you showed is hot hot and ground, i dont see a neutral anywhere in the diagram.

The generator is providing two hots.
Ground is a stake into the ground, for imbalances.
It can come from the generator if there is a ground conductor tied to ground, or it can come from the building grounding system, but ground should not be connected to neutral outside your main panel.

 

[SparkyJJO]

My confusion came from the manual which shows 3 wires for the electric input, which in my case is from the 240 plug of a generator.

The top says "single phase,230Vac or 120Vac" and the bottom (which is slightly cut off is "dual phase", "240V split phase"

Neutral input only shows in the single phase diagram, not the split phase.

 

[Supervstech]

The top says "single phase,230Vac or 120Vac" and the bottom (which is slightly cut off is "dual phase", "240V split phase"

Neutral input only shows in the single phase diagram, not the split phase.

Good point, i assumed he knew he had split phase output, and was reading that picture, good call clarifying what he needs to look at.

 

[seneysolar]

So is the inverter not needing a ground wire on the input side because the output neutral is already grounded in the breaker panel?

The top says "single phase,230Vac or 120Vac" and the bottom (which is slightly cut off is "dual phase", "240V split phase"

Neutral input only shows in the single phase diagram, not the split phase.

Yes that's correct, for a generator, no neutral on the input side, just Hot-Hot-Ground.

Then the output terminals have Hot-Hot-Neutral.

The case on the inverter has a ground lug for the earth ground system.

Single phase 120V versions switch the neutral ground bond with the internal transfer switch. The split phase 240v versions don't, as they don't pass through the neutral. You should verify that you have a neutral ground bond while in inverter mode with a multimeter. In this scenario you would not create another neutral ground bond at the panel, just ground the case lug of the inverter to the ground bar in the panel.

 

[Hedges]

Are those images in the manual of terminals inside the inverter, and do the labels on the inverter magically change from ground symbol to "N" when you decide to use "Dual Phase Wiring Mode"?

An inverter certainly could qualify and accept floating 240V input. Older GT PV did that. Some now have optional neutral connection, allowing them to recognize and configure, or they can be explicitly told what to expect. I think newer grid-tie code requires independent measurement of L1 and L2 voltage.

This Aims inverter might not know difference between floating 240V and single phase 240V with one leg (neutral) grounded. It would be in for a nasty surprise if it connected to that.

 

[seneysolar]

Are those images in the manual of terminals inside the inverter, and do the labels on the inverter magically change from ground symbol to "N" when you decide to use "Dual Phase Wiring Mode"?

An inverter certainly could qualify and accept floating 240V input. Older GT PV did that. Some now have optional neutral connection, allowing them to recognize and configure, or they can be explicitly told what to expect. I think newer grid-tie code requires independent measurement of L1 and L2 voltage.

This Aims inverter might not know difference between floating 240V and single phase 240V with one leg (neutral) grounded. It would be in for a nasty surprise if it connected to that.

They use alot of "common" images in their manuals. The split phase versions are labeled accordingly as per the Dual Phase diagram and do not accept 120V input.