Shore power grounding

Ok...If I am reading this right, this is how it should be wired: White, Black, and Green from the shore power inlet to the appropriate terminals in the breaker pannel. Green, White and Black from the AC outlets to the appropriate terminals on the breaker panel. Green, White, and Black from the on board charger to the appropriate terminals on the breaker panel. Run a seperate Green wire from the appropriate terminal on the breaker panel to a ground buss bar. Run a Green ground wire from the on board charger case to the same buss bar. Run another Green wire from the same buss bar to the engine ground point or stern drive mounting bolt. Sound right?

 

Yes that sounds fine but as you should already have a ground to the charger you shouldn't need another but no harm if you do. Any other metal parts close by and not otherwise well connected electrically or underwater would also need grounding, tanks, anodes etc. You don't need to ground every floating nut and bolt on the boat just those main parts.

 

I just found this post from a few years back and it kind of points me in another direction. Is this a case of more than one way of doing something?>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>









Electrical work is really pretty simple, but there are concepts you need to understand, that most folks don't. There are several good books on the subject and I strongly recommend you get one or two of them.

I don't like bonding metal components in a boat, though it is a common practice in the USA, it isn't in most other countries. I like isolated systems, for a number of reasons, that aren't necessary to go into here.

Your AC system will "carry the bond" (ground) through the shore power cord. If you generate 120 VAC on board with a genset you will get the same with the internal 3 wire arrangement running throughout the yacht, though depending on the genset manufacture and the installation, you may or may not have a grounding plate installed on the hull. You're best off following the genset manufacture's instructions or having it professionally installed.

Lightening protection will require a ground plate affixed to the outside of your hull. There are complete, commercially available systems that can be installed or you can do it yourself. Typically this is a large gauge wire, possibly having a mast top rod, connected to a ground plate bolted to an underwater location on the hull.

12 VDC from a battery bank is reasonably basic and doesn't need a "ground". Basic 12 VDC work is as simple as bringing the positive and negative (some folks call this negative post a ground, but it's not) legs of a circuit to the device you want to operate. Typically this is done by supplying the 12 VDC to a fuse or breaker panel (AC is done very similarly, though there is an extra wire to deal with, which is a real "ground"), where it's branched off to the different needs. Some of these needs will require switching, indicator lights, relays, etc. Most devices you may buy (new) will show a simple wiring diagram in the installation instructions.

The easiest way to get a handle on this stuff is to make a list of everything you will, or expect you will install, requiring electricity. There will be three lists, a 120 VAC, a 12 VDC and a combo (requires both 120 and 12 volt power, like a portable fridge) each broken down to every switch, relay, light, motor, sending unit, etc. Armed with these lists and your new found understanding (because you got a book or two) you may find it a bit tedious, but very doable work. I enjoy electric work.

The Marine Electrical and Electronics Bible - by John Payne. About 25 bucks new, half used.
Sailboat Electrics Simplified - by Don Casey. About 15 bucks new.

One or both of these books will get you there.

 

Isolation Transformer

I'm not certain what you mean by shore power here, but you're not mentioning the isolation transformer which is a very critical piece of the wiring diagram. The transformer should allow complete isolation of the shore AC system from the DC system of the boat.

A common mistake is to connect the shore power green (earth) wire to the bonding circuit of the boat. You want to be certain that no DC current is allowed through your shore power connection, only AC.

 

I wouldn't agree it's pretty simple when every action has a reaction. I think that's too generalised to understand which isolated system is meant, AC or DC, they both have different requirements! AC can't safely be isolated in most cases and would not comply with standards, DC can be isolated as I've already mentioned before.

If you touch your charger and your engine at the same time without them being bonded, it is quite possible for there to be a potentially fatal voltage between them in certain circumstances! The standards, codes and regulations are there for good reasons.

John Payne's book is ok but as always not everything is 100% correct and he does change his mind on subsequent prints.

 

The OP does not appear to have an isolation transformer although it is advisable. The earth wire must be connected to the AC earth point onboard to carry any fault currents to earth in order for fuses, trips and interrrupters to work.

Ideally the DC supply should be isolated but where AC and DC supplies use a common connection such as the engine then this cannot be avoided but it will have no affect on the AC or DC supplies. Galvanic erosion is not created by AC or DC supplies if this is what you are leading to.

 

I don't understand what you mean by isolated... my meaning is electrical isolation with no earth wires. Physical isolation can work but no point if all is bonded.

 

By isolation I mean no earth wires connected to anything DC.

 

The DC is not the issue, doesn't need an earth as too low voltage, in any event you can't avoid it unless your starter, alternator, engine sensors etc. are all negative isolated from the engine where you already said your charger is bonded to.

I did mention previously about isolating the AC circuits from the DC circuits complete with local bonding but this can't be done if your charger is in close proximity to the engines.