Re: Inverter/Charger wiring advise


greatketch@...
 


This is a bit confusing...  but I added my second level comments in italics....


---In amelyachtowners@..., <john.biohead@...> wrote :

AC Currents are (almost) never the source of stray current corrosion. To be sure, AC wiring CAN carry DC currents that can be serious sources of stray currents.  This is why AMEL separated the DC Negative from the AC Safety Ground and Bonding system.

RIGHT SO ANY FAULTS IN THE INVERTER, OR DOWNSTREAM EQUIMENT THAT RESUTS IN A DC VOLTAGE OVERLAID ON THE AC WIRING COULD AND WOULD CONTRIBUTE TO A STRAY CURRENT THROUGH THE BONDING SYSTEM...


As with many things with electrics and water... it's complicated.  If such a fault occured, it would show up as a voltage on the bonding system.  Amel's decision to avoid connecting the DC negative with the bonding system is not without its own problems. There is no free lunch...


A couple things about the AC Safety Ground.  It is normally connected to the AC Neutral only at the source of power. This is done so it can provide a low resistance path to carry any leakage current back to the source of power and safely away from people.

SO THE AC SAFETY GROUND ON THE SP CABLE IS CONNECTED TO THE AMEL BONDING SYSTEM. 


Yes.

 

When the generator is running, it connects the AC Safety Ground and Neutral together inside the generator.  RIGHT AND NOW THAT YOU REMIND ME I NEED TO VERIFY THE CONDUCTIVITY BETWEEN THE AC NEUTRAL (BLUE) AND AMEL BONDING (GREEN/YELLOW) WHILE THE GENERTOR IS RUNNING.  WHEN OFF THE TRANSFER SWITCH REVERTS TO SP.  SO WHEN I CHECKED IT I WAS READING RESISTANCE OF THE SP CABLE  UNPLUGGED. 


It can be a little tough to measure by resistance, since you have to measure with the generator running, and small voltages can make the ohm-meter nuts. I checked voltage readings with the generator running between hot and neutral (220V) and between Hot and Safety Ground (220V) and then between Neutral and Safety Ground (~0V) which is what I'd expect.


Same with an inverter.  When it has an external source of power, it passes the AC Safety Ground on through.  When it turns on and becomes the "source of the power" it connects the AC Safety Ground and Neutral so any leakage from the Hot wire has a way to get back to the source of power without going through people.  RIGHT THAT IS EXACTLY HOW THE DEVICE IS CONFIGURED, BUT IT HAS A DISCONNECT TO NOT CONNECT THE CHASSIS GROUND(SAFETY-GROUND/AMEL BONDING) TO THE NEUTRAL.   I WILL CHECK AGAN WHAT THE GENERATOR DOES WHEN ACTIVE.   

 

ONE THOUGHT I HAVE IT THAT THE GENERATOR IS NOT ACTIVE VERY MUCH HOWEVER, THE INVERTER WILL BE POWERED MOST OF THE TIME.  IS THE LENGTH OF TIME THE CONNECTION IS MADE A FACTOR TO CONSIDER?  


I don't see where the time would matter much, it's more a safety issue.


Without a connection back to the inverter when the inverter is the source of power, the AC Safety Ground becomes worse than useless.  If there was an insulation fault that connected the Hot wire to the case of, for example, your microwave, the AC Safety Ground would not be able to drain off that voltage because it could not supply a path for the current back to the source.  In that case the entire bonding system would become charged to the same voltage as the Hot wire with no way for the current to get back to the inverter. Now to put this in perspective, it is very unlikely on the boat that you could find a way to complete that circuit with your body...  but "very unlikely" is not the same as "not possible."

 

UNDERSTOOD.  ONE OF THE DOWNFALLS OF ISOLATING NOT CONNECTING IT.  ON US SUBMARINES WE HAD A SIMILAR SETUP FOR THREE PHASE AC WITH NO GROUND.  POTENTIALLY DANGEROUS TO CREW BUT MORE RESILIENT TO DAMAGE AND ALLOWED CONTINUED OPERATION DOWNSTREAM.  NOT QUITE THE PURPOSE FOR OUR BOATS. 


It's a fuzzy situation where it stops being "safe".  A lot of small inverters have no Safety Ground connection at all.  The expectation being that there is no easy way for a human to put themselves in between the hot and neutral parts of the circuit.  A very different situation than grid power, where the Ground (literally, the earth you stand on) is the return circuit, so any contact with the hot wire is a serious problem.

 

I CERTAINLY INTEND TO THINK A BIT ON THE SET UP BEFORE IMPLEMENTING.  


I don't think what you propose is terribly dangerous, but on the other hand I think it would do nothing to prevent corrosion issues. So any safety loss comes with out a gain.

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