Victron Quattro Possible Ground Loop / New Installation

OffGridVoltage

Hi AC Power guru’s…..

I know this topic has been done to death, and I have been reading posts till my eyes are bleeding… But I can’t find a definitive answer to my specific question. Most posts relate to boating with shore power anomaly’s, RV Vans with their chassis dilemmas or complicated multi-phase setups with GFCI issues….

There appears to be conflicting opinions on this diverse topic, so here is my question to make my newly installed off-grid back-up circuits safe and get my head around Earth / Neutral bonding once and for all ????

Pics >>

https://drive.google.com/drive/folders/1V5DpOiQ9YKiNiYQlBGjUrMsqIAmLxUUY?usp=sharing

From looking at the NON attached pics and diagram, this is how my newly installed and fully compliant system is right now, prior to the connection of any domestic mains supply or AC generator input. Due to my very limited solar array and allusive Winter sunshine here in the Mountains of South Eastern Australia…. I’m wanting to supplement this stand-alone system with some power from my existing domestic supply to charge my battery’s when they are critically low. This new stand-alone system supply’s my fridge, two water pumps and my home lighting only. (see below for system specs)

My questions are as follows:

1. Should the Earth/Neutral bond strap in Distribution Board #2 (DB-2 >> see pic #3) be connected at all ? Or should the E/N bond be controlled by, and within the Quattro only ? (with respect to the Quattro's own ground relay functioning)

2. When my domestic supply power (DB-1 Main Board) is connected to the Quattro (AC in 2), should the loads on DB-2 obtain their E/N bond from the power source (i.e. DB-1 Main Board) and NOT locally from DB-1 via it’s E/N bond strap ? (assuming the Quattro’s Earth Relay opens as it should whilst it is connected to AC power on it’s AC input, and it’s own E/N bond is disconnected also)

3. Should I include the Earth wire at all from my domestic supply (DB-1 main Board) when supplying the Quattro with power (AC-in 2) due to the fact that both DB-1 Main Board and DB-2 both have separate Earthing Rods (approx. 15 metres apart) ? (my instincts say ‘absolutely YES’ but I need this confirmed)

4. Should the earth wire on the output of the Generator be connected to the Quattro AC-in 1 also ? Or left as it is now with it’s output Earth and Neutral and Active connected to DB-2 first (via circuit breaker) and then only Active & Neutral cables going into Quattro AC-in 1 ? (see pic #2) i.e. When system is running on Generator AC, shouldn’t the Power Source (Generator) dictate the E/N bond and NOT the DB-2 ? (assuming again the Quattro’s Earth Relay opens between it’s Earth & Neutral whilst the Generator AC is present on AC in 1) and (I've determined my Generator does NOT in fact have it’s own internal earth neutral bond)

5. Finally, from looking at my beautiful diagram, where would you expect to see RCB units installed ? At present, the only RCB’s within DB-2 are on the output loads. Am I right in assuming there should be an RCB (RCD / GFCI / RCCB) between the output of the Inverter and DB-2 ?

Much thanks in anticipation of any light you could shed on this, and avoid my sleepless nights laying awake pondering earths, neutrals and electrified things….. ????

System Specs: (see pic #1)

Quattro II 230v 48v/5K/70

2.64kW PV 3S2P

2x BSL LiFePo4 48v Connected via CAN-Bus)

Cerbo GX

Victron MPPT 150/60 (connected via V.E Direct)

BB.

Oh boy... Grounding is probably one of the most complex set of Q&A we have here. And add that different regions in the world seem to have different ideas about what is "proper grounding".

I try to break it down to basics... What is it we are trying to do. For example:

Just to be clear, this is your home, and not an RV/Boat/etc.? Much of the relay based grounding is for Boat/RV installations where you have multiple power sources. Shore power which generally is Earth+Neutral bonded at the shore facility. And there is an AC inverter--Which can be configured for E+N bonding, and a Genset which may have E+N bonding.

The big issue is that shore power E+N bonding and combined with E+N bonding in the RV (example)--End up with two E+N bonding locations, and have "parallel" current flow in both E and N wiring. The E (green wire) circuit should never be carrying power, but should only carry current if there is a short circuit in the system--Which will "trip" and over current device (circuit breaker). "Single" point E+N bonding in the overall system is to prevent these parallel current paths (in E and N wiring). Also, having Shore+RV E+N bonding will "trip" RCD (GFI/GFCI in North American terms) because there is "unequal current flow" in Hot+Neutral wiring at the Shore Power RCD protected outlet (GFI protection is typically required in outdoor/wet area locations). So RV E+N bond must be lifted.

In a home, you can have the "one" E+N bond in the main panel (in USA) and not need any E+N relays because the Incoming utility power is "floating" (this is actually a lie as at the pole transformer E+N is typically bonded--But is ignored--This ends up being very important for lightning strike energy suppression). And the AC alternator plus the AC Genset have "floating" or NO E+N bonding inside of them for fixed operation. Of course, that means you have to "lift" any E+N grounds in the AC inverter/Genset/etc... (If portable Genset, you would need to reattached the E+N connection for use in a camp ground/job site/non-home/etc. location).

I am a big believer in keeping things "simple". For a fixed home installation, not using the grounding relays and having a single E+N bond in the home's main panel (again in USA), and not bothering with the relay/switched bonding works just fine. You can connect the relay based bonding and functionally ending up with a working ground scheme (i.e., Quatro bonding when it is supplying AC power, generator bonding when Genset supplies power, and utility bonding when running on utility power). But why bother with the complexity and the "what if" questions (what if all your power sources are 'turned off' to work on home/vacation/etc... Which "bonding" is selected, if any. If no bonding, then the home is more susceptible to lightning induced current/voltage caused failures).

Note another "complexity" with Ground Bonding. You probably have a large DC battery bank, and in USA, we would typically have a DC Negative to Earth Ground bond. The AC side of the electrical panel (hot+neutral+earth) wiring may be rated to 100-200 Amperes typically. But a large battery bank may be rated to 300 Amperes or more--Need to make sure that any DC to Earth (metal junction boxes/breaker panels) are rated to carry 300 Amperes and "single point" grounding so that DC current fault does not (for example) get into a 100 Amp rated grounding circuit for the AC wiring side--We can discuss more if needed.

For multiple grounding rods... The "dirt" is not a very good electrical conductor for 50/60 Hz AC current. In the USA a "good" ground rod to Earth connection is typically defined as 25 Ohms or less.  Meaning that "safety earth/ground" wires need to be carried along with Hot+Neutral to all "remote" connections (outlets, well pump, etc.). Ground Rods will not provide a "solid" electrical ground to shunt short circuit current.

V=I*R, I=V/R
240 VAC / 25 Ohms = 9.6 Amps

9.6 Amps is not enough to trip a 13+ Amp breaker/fuse if "using" ground rods only--And no "green wire" ground at a remote location (such as a well pump powered from a home XXX meters away). A short to earth at the well pump will not trip a breaker.

Ground Rods are very useful for shunting lightning current from house wiring to earth because the earth is a "low impedance" conductor (lighting will only follow typical copper conductor less than 10 meters before trying to find an "alternate path" to "dirt".

If you have lightning in your area, then installing surge suppressors between Hot and Neutral and Earth Ground is usually very helpful. Plus other protection (lightning rods on roof, etc.).

Regarding RCD/GFI/GFCI breakers... In the USA, we typically only install GFCI outlets for "wet locations" (near sinks/tubs/outdoor outlets, etc.... I think I have seen "international" codes that may have RCDs installed at the main input breakers (not sure I am correct). 

For me, I would rather have no RCDs when not required (interior outlets, interior ceiling lighting, etc.) as GFCIs do fail (I have replaced a few other the years that have even "spit their springs/buttons out" after 20 years).

If I do have RCDs, I would want to ensure that they are split into several circuits. Such as an RCD to the sink outlets (required by code) and either no RCD for ceiling lighting, or a separate RCD circuit for ceiling lighting so that an RCD trip to the sink outlet does not also kill the kitchen lights too and leave me in the dark.

Another "issue" with RCD.. You can only have an E+N bond on once side of the breaker (usually on the power supply side). If you have an E+N bond on both the power supply side and the RCD load side at the same time, this will generally trip the RCD (looks like an E to N short circuit). The RCD "measures" the Hot+Neutral current going to the loads, and if the current between the H+N wires is different by more than ~0.020 amps, the breaker trips to prevent a ground fault/electrocution event.

Where this "becomes" an issue--For example, many generators include RCD/GFCI breakers and E+N bonding on the Genset plugs--And if connected to a home with E+N bonding (backup Genset power), this will trip the RCD on the genset (need to "disconnect" the Genset E+N bonding to stop RCD false trips).

Is any of this helpful? Sorry it took a few days to answer. Real Life is taking up a bunch of family time right now.

-Bill

Dave Angelini

Hope all is well Bill !   I started to read this one but alot of content and I am swamped now also. Stay Safe !
FRIDAY !