Re: Inverter/Charger wiring advise


John Clark
 

John,

 

If you are not sure about the status of the AC Safety Ground, you really should have a qualified electrician review your plans. What I write below is based on what I think is a good understanding of the matter, but I wouldn't want to risk your life on it...

UNDERSTOOD  ;)

 

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...

 

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. 

 

 

When your source of power is shore power the AC Safety Ground and the AC Neutral are connected only on shore, never on the boat.  A boat that has no isolation transformer, nor inverter, nor generator would never have the Neutral and Safety Ground connected together on the boat.  AGREED.

 

If your source of shore power comes into the boat through an isolation transformer, the transformer becomes the "source of power" and the AC Safety Ground and Neutral are connected together there.  

 

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. 

 

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?  

 

The inverter case is connected to the AC Safety Ground in the event of a inadvertent connection between the Hot wire and the case so that voltage can be drawn off before it becomes dangerous to people.

 

 

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. 

 

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

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