Ground and Neutral Wires

[sensij]

How is this thread turning into a @#$%show?

my meter is not of the type Sunking is describing, and does not require a ground. Also, the only loads I've been able to detect in the reverse direction (feeding into the meter) draw equal current on both legs of the 240 V supply, supporting Sunking's belief that the inverter's internal loads will run on 240 V, not 120 V. The loads I have been able to see are associated with the startup and shutdown of the inverter each day. So far, the wattage when it is fully settled into night mode is below the detectability of the meter, although I will attempt to reconfigure it to get a better measurement. It is possible to turn the screen on at night, so I don't think it is depending on the presence of DC power from the array to operate.

If the goal is to answer "what is the purpose of the neutral in a GTI", I'm not sure we have made any progress toward figuring it out for the last couple pages of this thread.

[foo1bar]

Correct but that does not take 120 volts to do that. Just as easily, less expensive and less complicated to do at 240.

I disagree - I think it's likely less expensive at 120V.
There are many high volume (inexpensive) 120V to DC power supply.

As far as "complicated" - it's the same or less, since you're starting with a voltage that's closer to the 12V and 5V DC that is needed.

[Sunking]

I know mine gets power for it's electronics from the grid - even with no panels connected (or it's real dark outside) if I push the button, the backlight lights up and it tells me "Night mode".

Correct but that does not take 120 volts to do that. Just as easily, less expensive and less complicated to do at 240.

[Sunking]

No, the voltage is measured L1-N and L2-N. There is no ground reference provided. I just had another post go to moderation because I included the link, so just look up EKM Meter and you will see what I am using.

---Mod Note: Approved....

Sensi in any meter can or cabinet N-G are bonded together. By law and design Watt Hour meters must use a Ground Reference for Grounded systems, or Phase to Phase Reference for Open Delta.

[foo1bar]

Actually, some GTIs power their electronics entirely from the DC side. They shut down completely when the PV goes away, even if the grid remains.
Once the DC input gets high enough they wake up and try to qualify the grid input for connection.

I know mine gets power for it's electronics from the grid - even with no panels connected (or it's real dark outside) if I push the button, the backlight lights up and it tells me "Night mode".

[inetdog]

I believe the requirement is because of the anti-islanding circuitry - if L1-N or L2-N get out of bounds, it has to shut down.

But I wouldn't be surprised if the ethernet, cpu, LCD, etc are powered by a 120V supply - of course they should only draw 1 or 2 watts So may be hard to measure...
If you disconnect the solar input and turn on the LCD backlight you should see the power draw for it - and if you can see each leg separately, you could probably tell whether it's 120V or 240V powering the tiny DC power supply for those guys. Might be hard to measure though - possibly will only be measurable with the backlight on.

Actually, some GTIs power their electronics entirely from the DC side. They shut down completely when the PV goes away, even if the grid remains.
Once the DC input gets high enough they wake up and try to qualify the grid input for connection.

[foo1bar]

I have CT's on both legs of my SolarEdge inverter's output, and whatever current it draws at night is equal on both. As far as I can tell, there is no 120 v load that uses the neutral conductor, so I can't offer any insight into why it is required.

I believe the requirement is because of the anti-islanding circuitry - if L1-N or L2-N get out of bounds, it has to shut down.

But I wouldn't be surprised if the ethernet, cpu, LCD, etc are powered by a 120V supply - of course they should only draw 1 or 2 watts So may be hard to measure...
If you disconnect the solar input and turn on the LCD backlight you should see the power draw for it - and if you can see each leg separately, you could probably tell whether it's 120V or 240V powering the tiny DC power supply for those guys. Might be hard to measure though - possibly will only be measurable with the backlight on.

[sensij]

The non-socketed meters are generally used when it is not necessary to seal the connections to prevent unauthorized access. Although they do support sealing too.

Yes, the covers of the terminals are lockable, and there is a thin wire that will break if the device is opened from the backside. I put the meter in myself and have no authority that requires it, so I have full control over how it is set up and whatever data can be extracted from it. I'll be reconfiguring the pulse outputs to get 0.625 Wh resolution soon, which will give much better resolution for the low power consumption overnight. Another wrap or two through the CT may still be required to pick up all the idle mode consumption though.

[inetdog]

I am not using a socket meter.

http://www.ekmmetering.com/

The non-socketed meters are generally used when it is not necessary to seal the connections to prevent unauthorized access. Although they do support sealing too.

[sensij]

No, the voltage is measured L1-N and L2-N. There is no ground reference provided. I just had another post go to moderation because I included the link, so just look up EKM Meter and you will see what I am using.

---Mod Note: Approved....

[Sunking]

Huh? My meter measures and reports voltage referenced to neutral on both legs, and reports the power (and direction of current) on each leg individually. By measuring the current on both legs (and finding them equal), I have sufficient data to see whether or not there are 120 v loads, right?

Ground Not Neutral. If there is a problem with your neutral it will show up big time when you measure L-G. If you see 110 volt on one leg, and 140 on another, you had better call your POCO immediately and shut off you mains ASAP. You should hear the brakes squealing before you hang up reporting it. It means you lost your Grounded Circuit Conductor between transformer and your service disconnect point or really poor connection in your meter box.

Utilities have bought many TV and Refrigerators doing that, and a few house fires.

[sensij]

Absolutely. No compromises there.
But the meter sockets for utility power meters of the residential and small commercial type do not even have a terminal jaw in the meter base to connect the neutral to the meter itself. So if you are using a revenue grade meter that is interchangeable with POCO meters, it will not use the neutral as a voltage
reference.

You can still tell if there are any unbalanced line to neutral loads without measuring either voltage or current at the neutral.

I am not using a socket meter.

http://www.ekmmetering.com/

[inetdog]

Huh? My meter measures and reports voltage referenced to neutral on both legs, and reports the power (and direction of current) on each leg individually. By measuring the current on both legs (and finding them equal), I have sufficient data to see whether or not there are 120 v loads, right?

Absolutely. No compromises there.
But the meter sockets for utility power meters of the residential and small commercial type do not even have a terminal jaw in the meter base to connect the neutral to the meter itself. So if you are using a revenue grade meter that is interchangeable with POCO meters, it will not use the neutral as a voltage
reference.

You can still tell if there are any unbalanced line to neutral loads without measuring either voltage or current at the neutral.

[Sunking]

+1
By measuring current in all but one of the leads you know all of the currents, since they must sum to zero.

Dave they do not have to Sum Zero. That would be a very rare event in a single phase service to your home to be equal in bolt legs.

PT = P1 + P2

Poly Phase PT = P1 + P2 + P3.

Voltage in both is referenced to Ground, and current is CT. You could make an argument Neutral and Ground are the Same point in the meter cabinet or can because that is where N-G are bonded together. That is required by utility regulators so you do not pay for power loss between the transformer and you demarc. But at no point is Neutral current metered.

But a GTI uses your utility Transformer to derive the Neutral. A GTI is not capable of doing that. Got me stumped what they are doing. Gotta be a reason, but beats me for now.

[sensij]

Huh? My meter measures and reports voltage referenced to neutral on both legs, and reports the power (and direction of current) on each leg individually. By measuring the current (and power) on both legs and finding them equal, I have sufficient data to see whether or not there are 120 v loads, right?