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Proper grounding 2-wire grid setup

ichernev

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Dec 28, 2022
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Hello,

I'm planning on setting up a grid-tied hybrid system (48V bat + PV). I read through (among other things) the Grounding Made Simpler p1-3 (thanks a lot FilterGuy!), and the manual for the inverter I'm focusing on (Deye Hybrid 5-8kw single phase, manual attached).

A bit of background first: the grid here (somewhere in Eastern Europe) is 230v single phase. It is transported in 3phase and in a distribution box outside the house each property takes one of the phases. The distribution box has a big grounding connector stuck in the ground, and the N is grounded this way. In the end 2 wires (N and L) come in the property, where the N is grounded.

The yellow-green/PE conductor "originates" in the main house panel, where it's bonded to N, and you should install an RCD (residual current circuit breaker) on the L and N lines. It breaks the connection if it finds any current leaking from L to somewhere other than N.

Now the question: according to page 5 of Part 3 of Grounding Made Simpler series, one should avoid having a second grounding rod, because a nearby lightning can induce current between the two rods. In my case, if I stick a grounding rod around the panels to ground them, the battery, and connect to the inverter (more on that in a bit), then a nearby strike can induce a current that will pass right through the inverter (from my rod -> inverter -> PE (N) of grid -> grid-installed rod outside).

According to inverter wiring manual (page 21/22 (bottom of page says 19/20) in attached manual), the N from the grid should not be interrupted when grid is offline (presumably to retain the grounding), but then it says to attach separate grounding to the case ("if the original protective conductor fails"). So how am I supposed to ground the outside of the inverter to something else, other than the grid N, when that would introduce a separate grounding rod I'm trying to avoid.
 

Attachments

  • Deye-SUN-5-6K-SG01LP1-US-SUN-7-6-8K-SG01LP1-US-EU-User-manual.pdf
    7.6 MB · Views: 12
Interesting conundrum...

Several comments

* There have been multiple studies that have shown equipment failures are much higher when they are connected to auxiliary grounding electrodes.

* All of the major Gas/diesel generator manufacturers used to have similar statements.... but they no longer do. The interesting thing is that their warranty costs dropped significantly as soon as they changed their policy.

* I do not know the regulatory policy where you are, but in the States, the NEC allows (but does not require) additional grounding electrodes. Furthermore, the NEC essentially has no requirements for how an auxiliary ground is implemented. If you implement one, you can do it any way you want. You could stick a bare copper wire 100cm into a flower pot and it would meet all the NEC requirements for an auxillary ground. This tells me they don't think auxiliary grounds are useful. I suspect the primary reason they allow auxiliary electrodes is that they say to follow manufacturers' instructions..... and manufacturers say to add them.

* On all inverters I have looked at the AC-output ground, the inverter case, and the AC input ground (If there is one) are all tied together internally. (If anyone knows of one that is different, please let us know).

I can't tell you how to solve the conundrum. All I can do is tell you what I do: I don't use the case grounding screw. I do all the grounding through the AC connections to the inverter. If the AC grounding is done correctly, the case of the inverter is adequately grounded
 
Thank you for the detailed analysis! It's great that manuals are changing in the right direction. I'm not sure if I'll be able to open the case of the inverter (once I buy it) without voiding warranty to check how it's all grounded inside.

On a related topic -- in p1 of the "Wiring Made Simpler" you explain about the importance of grounding for dissipating static charges so they don't build up. Is this still relevant when the EGC goes to N (in main panel) which is then bonded to ground (in distribution panel). Because this means there is 220v on the N line (if there is any load in the house) -- is the static charge able to dissipate over that voltage?
 
I'm not sure if I'll be able to open the case of the inverter (once I buy it) without voiding warranty to check how it's all grounded inside.
For grounding, while the inverter is completely disconnected from everything, measure for continuity between the case, input ground, and output ground. I am willing to bet you will find they are all connected together.

On a related topic -- in p1 of the "Wiring Made Simpler" you explain about the importance of grounding for dissipating static charges so they don't build up. Is this still relevant when the EGC goes to N (in main panel) which is then bonded to ground (in distribution panel). Because this means there is 220v on the N line (if there is any load in the house) -- is the static charge able to dissipate over that voltage?
Yes, this will neutralize any static charge on the AC circuit.

The neutral line does not have 220V on it. When the neutral gets tied to ground at the N-G bond, the voltage of the neutral is clampt at the same voltage of ground. Neutral should be close to zero volts when referenced to ground. It wont always be exactly zero because current on the neutral will creat a voltage on the neutral, but this will typically be no more than a volt or so.
 
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