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Help with suspected common neutral


Halcyon
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I have been having an issue with an inverter where we suspect a common neutral between backup circuit and non-essential circuit.  Am I correct in saying that a test light bulb should not light up if placed on inverter output live and Eksom neutral bar with grid switched off at 63 amp breaker if all is well ?

 

 

 

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2 hours ago, Halcyon said:

Am I correct in saying that a test light bulb should not light up if placed on inverter output live and Eksom neutral bar with grid switched off at 63 amp breaker if all is well ?

You a correct from my little experience and the earth leakage should also trip if it is mixed

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Thanks Quat, @Richard, please see attachment.

We have modelled our wiring of inverter and DB on this diagram.  The issue is the load power on the inverter is influenced, well on the monitoring screen at least, by  non-essentials switching on and off.  A continuity and resistance test have disproven a common neutral between back up circuit and non-essential circuit however I decided to try the light bulb test today. A 5W light bulb lights up between non earth leakage eskom neutral-bar and inverter live when grid is switched off at 63 amp breaker.  Common neutral somewhere?

IMG_0442.jpg

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The only thing i can think of with my limited knowledge, is do you have a crossover switch installed or a bypass switch installed?

With a crossover the bulb should not light up but with a bypass switch, if it set to bypass it will light up the bulb.

My setup is a bit different from Main to Sub BD with Earth Leakage to CB is than wired to bypass switch and inverter, from inveter to CB out to essentials and bypass switch, Main DB split into 2 left non-essentials with own neutral and right essentials with it's own neutral

Hope it all makes sense and helps

Edited by Quat Allah As Shams
typo
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8 hours ago, Halcyon said:

A continuity and resistance test have disproven a common neutral between back up circuit and non-essential circuit

I don't know much about your inverter and how you did the continuity test (probably with C/O switch in the off position) but have you ascertained that the inverter AC-in neutral and AC-out neutral are not bonded?

8 hours ago, Halcyon said:

A 5W light bulb lights up between non earth leakage eskom neutral-bar and inverter live when grid is switched off

As you troubleshoot, just know that a 5W bulb current draw of 20mA at 240VAC will most likely not trip an ELCB (RCD/RCCB) rated at 30mA leakage current on its own. i.e. with no other load connected to the backup sub-panel.

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12 hours ago, Halcyon said:

We have modelled our wiring of inverter and DB on this diagram.  The issue is the load power on the inverter is influenced, well on the monitoring screen at least, by  non-essentials switching on and off.  

Where are the non-essential loads connected?

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1 hour ago, Richard Mackay said:

Where are the non-essential loads connected?

Hi Richard, Non-essentials loads are in the main DB section per diagram, Stove, Geysers, Outbuilding before E/l on non E/L neutral bar and one plug circuit, pool on E/l and on E/L neutral bar. Backup circuit is on Sub DB per diagram, lights on non E/l neutral bar and plugs on E/L neutral bar.

Edited by Halcyon
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3 hours ago, Kilowatt Power said:

I don't know much about your inverter and how you did the continuity test (probably with C/O switch in the off position) but have you ascertained that the inverter AC-in neutral and AC-out neutral are not bonded?

As you troubleshoot, just know that a 5W bulb current draw of 20mA at 240VAC will most likely not trip an ELCB (RCD/RCCB) rated at 30mA leakage current on its own. i.e. with no other load connected to the backup sub-panel.

Hi Kilowatt, I am still learning about inverters so not too sure what you mean by bonded?  What I do know is that when grid is live, The inverter grid input connects Eskom live and neutral with the inverter load output live and neutral.  When grid goes down inverter disconnects this connection.  The inverter is a 5kw Sunsynk Hybrid inverter.

Yes, for continuity test I switched off 63amp breaker and also isolated inverter with MCB in Sub DB and tested between essential and non essential neutral bars in the DB (buzzer made no sound).   My electrician did a resistance test following same approach and told me no common neutral.

However, inverter still getting interference from non-essential loads switched on and off.  Then decided to try 40W light bulb from inverter output live with Grid off at 63amp breaker.  No light, but a 5W light bulb lights up.  205V reads between inverter output live and Eskom neutral bar with grid off at 63 amp breaker.  Tested each neutral wire separately on non essential neutral bars.  6 out of 9 wires cause 5w bulb to light up.  I am going to reverse test with inverter isolated at MCB and keep Eskom live.  Am I on the right track to find where common neutral may be?

 

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18 hours ago, Halcyon said:

Am I correct in saying that a test light bulb should not light up if placed on inverter output live and Eksom neutral bar with grid switched off at 63 amp breaker if all is well ?

No. In any correct installation, there will be a path from AC-out neutral to earth somewhere, otherwise the outlet is not safe. It's a matter of where that connection comes from. You need to avoid multiple connections from neutral to earth for residual current detectors to work.

Some inverters link AC-in neutral to AC-out neutral continuously, others only when the inverter proper (the DC to AC converter) is operating.

What model of inverter is it, and is it a hybrid or off-grid type?

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2 minutes ago, Coulomb said:

No. In any correct installation, there will be a path from AC-out neutral to earth somewhere, otherwise the outlet is not safe. It's a matter of where that connection comes from. You need to avoid multiple connections from neutral to earth for residual current detectors to work.

Some inverters link AC-in neutral to AC-out neutral continuously, others only when the inverter proper (the DC to AC converter) is operating.

What model of inverter is it, and is it a hybrid or off-grid type?

Hi Coulomb, it is a Sunsynk 5kw Hybrid inverter.

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7 hours ago, Kilowatt Power said:

As you troubleshoot, just know that a 5W bulb current draw of 20mA at 240VAC will most likely not trip an ELCB (RCD/RCCB) rated at 30mA leakage current on its own. i.e. with no other load connected to the backup sub-panel.

My experience is that a 30mA RCD tends to trip at 20mA, but not at 15mA. The rules say it MUST trip instantaneously at 30mA and MAY trip above 15mA. Of course that means a 5W lamp is going to put you in that no-man's land where you're not quite sure which one it will do. So one way is to actually test it (deliberately place it between live before the RCD and neutral after the RCD). In other words calibrate your test equipment... 😛

 

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18 hours ago, Halcyon said:

Thanks Quat, @Richard, please see attachment.

We have modelled our wiring of inverter and DB on this diagram.  The issue is the load power on the inverter is influenced, well on the monitoring screen at least, by  non-essentials switching on and off.  A continuity and resistance test have disproven a common neutral between back up circuit and non-essential circuit however I decided to try the light bulb test today. A 5W light bulb lights up between non earth leakage eskom neutral-bar and inverter live when grid is switched off at 63 amp breaker.  Common neutral somewhere?

IMG_0442.jpg

The 5w lightbulb does trip the E/l on backup plug circuit as you all suggested.  I have aborted the test as the light bulb lights up on all the non-essential neutrals from Grid live with inverter isolated using its MCB (not what I was expecting).  This is not helping me identify if there is indeed a common neutral causing my issue.

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17 hours ago, Halcyon said:

205V reads between inverter output live and Eskom neutral bar with grid off at 63 amp breaker. 

Is your inverter output voltage rating 230VAC?

What voltage do you get between the following points?

  1. Inverter phase (L) & backup sub-panel neutral (N)
  2. Inverter phase (L) & protective earth (PE) and
  3. Inverter neutral (N) & protective earth (PE)
13 hours ago, Halcyon said:

The issue is the load power on the inverter is influenced, well on the monitoring screen at least

Please explain your observation further. Does switching on a non-essential load increase the power drawn from the inverter e.g. from 250W to 650W?

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8 minutes ago, Kilowatt Power said:

What voltage do you get between the following points?

  1. Inverter phase (L) & backup sub-panel neutral (N)
  2. Inverter phase (L) & protective earth (PE) and
  3. Inverter neutral (N) & protective earth (PE)

Take at least two sets of measurements with no load and when an appliance causing interference is turned on.

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3 hours ago, Kilowatt Power said:

Is your inverter output voltage rating 230VAC?

What voltage do you get between the following points?

  1. Inverter phase (L) & backup sub-panel neutral (N)
  2. Inverter phase (L) & protective earth (PE) and
  3. Inverter neutral (N) & protective earth (PE)

Please explain your observation further. Does switching on a non-essential load increase the power drawn from the inverter e.g. from 250W to 650W?

Hi Kilowatt

Yes inverter's standard rating is 230V.  It reads less than that, easily down to 203V when in backup mode from inverter output live to inverter neutral.  When grid back on it always matches main grid voltage.

Scenario.  Assume backup circuit load using 600W confirmed by effergy clamp on load output live from inverter.  The inverter UPS load power on screen will read the following under various conditions.

  1. 450W - with all non essentials switched off (I acknowledge an effergy clamp is not always accurate)
  2. 2500 W - Geyser 1 switches on
  3. 185W - Geyser 2 switches on
  4. 950W - At the zenith of solar power production in daytime.

Keep in mind for this scenario created above the effergy clamp maintains the 600W backup circuit reading.

Test results.  used example from 3 above.

  • Before Geyser 2 switched on.  L - N = 230V, L - PE = 230V /231V, N - PE = 0,383V
  • Geyser 2 switched on. L - N = 226V, L - PE = 226/227V, N - E = 0,861V

Let me know if you need any more info?

 

 

Edited by Halcyon
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9 hours ago, Kilowatt Power said:

Take at least two sets of measurements with no load and when an appliance causing interference is turned on.

Some other interesting observations garnered moments ago - DC isolator switched off so no solar power and the gird on so batteries idle. 

Current clamp multi meter used to test current on various wires described below.

Inverter output live = 4,6 amp, inverter output neutral = 3,28 amp

Inverter grid input = 1,90amp, Grid input neutral = 1,36

This seems very odd to me?  surely if no solar and no battery the grid current in and load current out should be very similar?  Should the neutral wires not have an equal current flowing in the opposite direction?   I put clamp around earth wire at inverter and barely any current is flowing through it.

 

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7 hours ago, Halcyon said:
  • Before Geyser 2 switched on.  L - N = 230V, L - PE = 230V /231V, N - PE = 0,383V
  • Geyser 2 switched on. L - N = 226V, L - PE = 226/227V, N - E = 0,861V

These readings look perfectly ok. The 205VAC measured between inverter phase & Eskom neutral with grid off was hinting towards a "voltage divider" circuit between L - N and N - PE.

7 hours ago, Halcyon said:

Scenario.  Assume backup circuit load using 600W confirmed by effergy clamp on load output live from inverter.  The inverter UPS load power on screen will read the following under various conditions.

  1. 450W - with all non essentials switched off (I acknowledge an effergy clamp is not always accurate)
  2. 2500 W - Geyser 1 switches on
  3. 185W - Geyser 2 switches on
  4. 950W - At the zenith of solar power production in daytime.

Keep in mind for this scenario created above the effergy clamp maintains the 600W backup circuit reading.

Considering that you have a true hybrid inverter with combined off-grid and grid-tie capabilities and ample kWp PV array hooked up to the unit then you could be pushing PV power back from the inverter AC-input to non-essential loads in the main DB.

If at all this is the case then no need to worry as what you are seeing as "interference" is the expected behaviour of a hybrid inverter with self-consumption/zero export settings enabled (of course with grid present) 

Regarding self-consumption/zero export configuration, do you have a current transformer (CT) installed on the main DB incomer?

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3 minutes ago, Kilowatt Power said:

These readings look perfectly ok. The 205VAC measured between inverter phase & Eskom neutral with grid off was hinting towards a "voltage divider" circuit between L - N and N - PE.

Considering that you have a true hybrid inverter with combined off-grid and grid-tie capabilities and ample kWp PV array hooked up to the unit then you could be pushing PV power back from the inverter AC-input to non-essential loads in the main DB.

If at all this is the case then no need to worry as what you are seeing as "interference" is the expected behaviour of a hybrid inverter with self-consumption/zero export settings enabled (of course with grid present) 

Regarding self-consumption/zero export configuration, do you have a current transformer (CT) installed on the main DB incomer?

Thanks. Yes the inverter has a CT clamp which has to be connected to main eskom input live. The inverter has a limiter option to use solar power for backup circuit only or sell excess power to the whole home to zero utility meter or you can set on export mode to sell any excess solar power and reverse meter. 
 

This interference is especially visible at night when the grid is on and no solar power is being produced. This is what is baffling me so much as it does not make sense that the backup load power on inverter screen suddenly jumps up or down when non essentials switch on of off. Especially when a current meter on the backup load cable confirms current has not changed before or after the non essential on or off.  Boggles the mind!

 

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57 minutes ago, Halcyon said:

This interference is especially visible at night when the grid is on and no solar power is being produced. This is what is baffling me so much as it does not make sense that the backup load power on inverter screen suddenly jumps up or down when non essentials switch on of off.

I have a feeling that you have a setting somewhere enabled that allows export to grid at night using stored battery energy. Skim through the user manual for this feature.

Why do I say this? Your Sunsynk inverter is most likely manufactured by Ningbo Deye Inverter Technology Co, the company behind the inexpensive and highly popular SunG GTIL2 solar grid-tie inverter with limiter. These grid-tie inverters are capable of connecting to PV solar, wind or batteries and exporting to grid at night using stored battery energy. The same features could be built into your Sunsynk inverter. 

PS: SunG GTIL2 users have a fairly active Facebook group that you can join and ask specific questions related to your inverter. I hope this helps. 

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4 hours ago, Kilowatt Power said:

I have a feeling that you have a setting somewhere enabled that allows export to grid at night using stored battery energy. Skim through the user manual for this feature.

Why do I say this? Your Sunsynk inverter is most likely manufactured by Ningbo Deye Inverter Technology Co, the company behind the inexpensive and highly popular SunG GTIL2 solar grid-tie inverter with limiter. These grid-tie inverters are capable of connecting to PV solar, wind or batteries and exporting to grid at night using stored battery energy. The same features could be built into your Sunsynk inverter. 

PS: SunG GTIL2 users have a fairly active Facebook group that you can join and ask specific questions related to your inverter. I hope this helps. 

Thank you

I think I inadvertently discovered the issue.  The inverter seems to take the UPS Load power reading from the current on the inverter output neutral and not the live wire. 

The current on the neutral wire corresponds to the backup circuit power displayed on the inverter screen almost exactly.  The "interference power" as non-essentials switch on and off is the power from the current on the neutral wire and not the live wire.

6 hours ago, Kilowatt Power said:

2500 W - Geyser 1 switches on

For my test example 2 - where main geyser switched on I read 3,83 A on inverter output live, but 9,96 A on the output neutral.  ((see attached image - green and orange circle is where I did the current testing). 

I thought current on live and neutral should be the same?  How is this happening?

I then decided to do a current test on the main utility entering the house.  

At time of testing Live = 3,83 A, Earth = 0,75 A and Neutral 2,75 A,  How is this possible?

IMG_0442.HEIC

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I'll go back to the issue of non-essential loads "interfering" with the inveter at night hoping that it will lead to identifying a common neutral if any.

From the main menu, go to Settings -> Grid Setup -> Limiter and post a photo of the screen. It should look like the attached image captured from the manual.

 

 

Sunsync-limiter-settings.png

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