1979 42' Grand Banks Electrical System

[CharlieJ]

@TomJRH #30:

So both neutral and ground wires have common termination.

If I am interpreting the photo and your explanation correctly, you have neutral and safety ground landed on the same bus. If that is correct, please note that in the USA, there should only be a neutral to ground (N > G) bond at AC sources: generator output; inverter or inverter/charger when inverting and the secondary of an isolation transformer.

Any other N > G bond will cause a leakage of AC into the water. That condition is what I am trying to correct on the subject boat.

 

[SteveK]

No, both bars have a common ground. If you look closely at the second picture you can see the red jumper connecting the two bus bars. I chose two bars to accommodate the various size wires. I also have a galvanic isolator to isolate the boat from the dock pedestal.

The galvanic isolator is being bypassed by the bonding ground to the neutral on the same buss.

 

[SteveK]

@TomJRH #30:


If I am interpreting the photo and your explanation correctly, you have neutral and safety ground landed on the same bus. If that is correct, please note that in the USA, there should only be a neutral to ground (N > G) bond at AC sources: generator output; inverter or inverter/charger when inverting and the secondary of an isolation transformer.

Any other N > G bond will cause a leakage of AC into the water. That condition is what I am trying to correct on the subject boat.

Bolded assumes that AC ground is bonded to DC ground. Is it?

 

[Comodave]

No, both bars have a common ground. If you look closely at the second picture you can see the red jumper connecting the two bus bars. I chose two bars to accommodate the various size wires. I also have a galvanic isolator to isolate the boat from the dock pedestal.

I see maybe a yellow jumper between the two bus bars, is that what you mean. You said red, red shouldn’t be on a ground bus bar.

 

[diver dave]

The very first shore power plug in for me had a reverse N-L situation. The boat yard, at the actual survey, had a GFCI receptacle wired wrong.
This is one big reason to not connect Earth and Neutral anywhere on the boat.

 

[TomJRH]

Sorry about color, it is yellow. I am not an electrician and had the busses professionally installed. I am a little confused by all this. If the AC neutral and ground are connected to the engine and the DC neutral is connected to the engine via a combined wire or separately, what is the difference? I am assuming that the engine is ultimately the ground. Grand Banks originally only provided a single bus for all grounds/neutrals for AC and DC from what I can tell.

 

[SteveK]

Tom. DC negative is ground. AC ground (green) and DC negative are connected to keep you safe inside the boat in case AC (black or red) happens to touch a DC ground point like the engine block so it can trip the breaker.
AC ground (green) and AC neutral (white) do not connect anywhere in the boat except if you are using an inverter for AC power. Inverter has built in auto switch. Otherwise AC ground and neutral are only connect on the dock pedestal or meter room.
Further if N & G are connected then a galvanic isolator is bypassed to the dock for stray current.

Stray current in the water around a boat can be caused by the AC protection bonding AC & DC ground when that ground is then bonded to the boat bonding system of thru hulls, shaft and zinc.

 

[TomJRH]

Thank you for such a clear and concise explanation. If I understand correctly all AC ground and neutral wires should be on a separate bus that is grounded back to to the dock pedestal. All DC grounds should be on a bus that is grounded to only to the engine, etc. That makes good sense but it still leaves me with the question what is proper wiring for AC ground and neutral when generator is powering the boat?

 

[SteveK]

Thank you for such a clear and concise explanation. If I understand correctly all AC ground and neutral wires should be on a separate bus that is grounded back to to the dock pedestal. All DC grounds should be on a bus that is grounded to only to the engine, etc. That makes good sense but it still leaves me with the question what is proper wiring for AC ground and neutral when generator is powering the boat?

NO
all ground on separate buss. All neutral on separate bus. Never the two on the same buss.
The generator should have built in neutral ground bonding, that you will need to find from the brand installed.

 

[TomJRH]

I will be back on boat next month and will check out what I have. I think that the two bus bars that I had installed must be all DC grounds but I want to be sure.
Thanks for your explanation

 

[CharlieJ]

@TomJRH

That makes good sense but it still leaves me with the question what is proper wiring for AC ground and neutral when generator is powering the boat?

For better understanding, first re-read post#31.

When on genset, the required N>G bond is at the genset output. The source selection device has switched to genset and the N>G on shore is isolated. When on shore power, the required N>G is on shore and the genset N>G is isolated by the source selection device.

One N>G at the active source.

 

[TomJRH]

Thank you for reply. Think I got it, finally.

 

[ronobrien]

New wire

I know that this is no help, but I bought a GB36-1973 last fall and after looking at the wiring, it will all be coming out as part of a 2 year refit. Best of luck on yours.

 

[CharlieJ]

@ronobrien #43

Right answer!

This boat is getting:
> new AC panel board for house loads
> repurposed BS panel for A/C
> proper N busses (1 for each shore power service)
> proper G bus
> new wiring to support the above
> Blue Sea ELCI on each shore power service
> new Victron 3kW MultiPlus inverter/charger
> new AC source selector switch
> a clean electrical bill of health!!

 

[ronobrien]

You have just cleared up a number of concepts for me. Thank you. I am familiar with AC as a building contractor and with DC as a former truck mechanic. It is the interface that can get confusing. Could you recommend a book (or site) for reading up on the subject?
Thanks again.

 

[CharlieJ]

@ronobrien

I highly recommend Nigel Calder's "Boatowners Mechanical and Electrical Manual 4/E Hardcover – July 2, 2015". Available on Amazon. I recommend the hard cover version over the Kindle as you will be making notes as you study.

 

[ronobrien]

Appreciated!!

 

[TomJRH]

Googled "Boatowners Mechanical and Electrical Manual" PDF and found a free download. Large file but well worth downloading. Excellent information.

https://www.engineerrefe.com/boatowners-mechanical-and-electrical/