Re: Bonding and Solar Power System
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Adam, In my experience, many marine electricians have difficulty explaining this to you. I am not a marine electrician, but let me help you, at least, I hope, somewhat. I really hope that this does not sound like a lecture as all I want to do is share some experience with you which will hopefully cause you to research this issue more.
You wrote, "It seems that these wires should and must be connected to an earthing point." This is probably technically true, but probably only if the DC voltage is above 50VDC. The purpose would be to protect you from an electrical shock. Almost everyone agrees that DC electrical shock protection is not needed below 30VDC. Some solar panel installations have been done in series with potential voltages of 3 panels reaching 70VDC. If a wire chafes against the arch, the arch could potentially deliver an electrical shock if you are somehow grounded. The solar controllers I have seen do not have an Earth connection. BUT, even though there may be some risk from these very remote things unless you are connected to shore power you really do not have any available protection from an Earth circuit. However, this may be a reason to wire solar panels in a parallel circuit rather than in series.
Earth is not Bonding.
Earth is a safety circuit used on AC current systems. An AC "Earth" circuit is used to protect you from an electric shock. It does this by providing a path (a protective conductor) for a fault current to flow to earth, which is literally a copper bar driven into the earth. Earth is also needed in a GFI circuit to switch off the electric current to the circuit that has a fault. Earth is for AC circuits, not DC circuits. In the US earth wires are green. In the EU, and elsewhere earth wires are yellow/green. Amel's bonding system also uses yellow/green wires.
Bonding is connecting all of the items that may be in contact with raw water together and terminating at an underwater anode. The purpose of bonding is to reduce corrosion and electrolysis caused by stray-current and galvanic corrosion. Normally bonding connections are made to all metal items that may be in contact with raw water. Amel takes bonding to the next level and connects even those metal items that are in the freshwater system which are electrically in contact with raw water via the watermaker.
SSB Ground Plane: Amel built your boat with a Ground Plane for an SSB radio. The Ground Plane is connected to boding if you do not have an SSB.
Isolated Ground is used by Amel on main engines and generators, which is a method of disconnecting the 12-volt negative from the engine block.
DC Ground: Circuits powered by batteries do not have an Earth circuit. Batteries do not have a connection to the physical earth. So most DC-powered circuits, especially by batteries, have a floating ground, not Earth. There are 2 DC Ground circuits on your Amel, 12-volt (starting) and 24-volt (house). The negatives of these should not be connected and they should be isolated. Some owners have used a 24-volt to 12-volt converter to charge the starting battery from the house bank. An "Isolated Converter" should be used in this case.
Although American Boat & Yacht Council (ABYC) requires DC Negative, AC Earth, and the Bonding System to be connected as one, I personally think that they are wrong and I know of serious issues caused by the connection to DC ground to Bonding. The Amel Bonding system is connected to the AC Earth circuit.
Back to your arch: I am not sure of a need to connect the arch to Bonding, but I assume that it could be argued that it should be connected for the same reason that Amel, beginning with the 54, connected the masts and rigging to bonding. I assume that this was an effort to reduce corrosion. I personally think that it might have had the reverse effect. I have often noticed the increase in paint bubbling on the rig of 54s and later models and the increase of corrosion of the rails and standing rigging. Some people point to other reasons. I simply do not know, but I believe it is coincidently suspicious.
It is not as simple as some people make it out to be.
I hope this helps.
On Fri, Mar 12, 2021 at 10:09 PM Adam Body <adamgcbody@...> wrote:
This post is a continuation of the recent discussion about the rudder post and galvanic protection system. I have discovered that the two green wires that had been disconnected from Flora's bonding system (at the rudder post) are the earth wires from the solar array/panel frame at the stern and from the solar charge-controller/battery charger. It seems that these wires should and must be connected to an earthing point, so I am at loss as to why they would be disconnected. Was it an oversight? Does anyone have some experience on earthing their solar array frame and the associated controller?