Connecting AC/DC ground to common rail - ships bond

AlaskaDreaming · 08-04-2016, 10:49 PM

Hi All,

I am a new owner of an old Kadey Krogen (1982 - 42'). I have been working with an electrician to upgrade/update electrical systems and have run into a controversy between the electrician and another shipwright helping install an vacuflush system. It has to do with whether the ac/dc negative buss is tied into the common bonding system of the boat. The electrician says that current North American standards say that they should all be linked. Others are saying that if you do this, and anyone accidentally miswires something on the boat, or a short occurs in a piece of equipment, then you can start to run currently through your thruhulls, etc.. leading to corrosion and loss (some even say you risk sinking your boat).

So- after a lot of reading I can see that there are very different opinions on this ... I wonder, for those with older boats, how did they do this originally in these boats? Any opinions or thoughts on the best way to go? I noticed that most of the thruhulls are connected to green wires that seem to be exiting from the original wiring harness (my boat has had a lot of 'changes' along the way) ... and currently it appears my bonding system is tied into my grounding buss (did some testing today with a silver chloride reference electrode).

Any thoughts?

Thanks

foggysail · 08-04-2016, 10:59 PM

I believe your electrician is correct. But do not confuse a grounded conductor with a grounding conductor. The grounding conductor is grounded at the electrical load center. It is the green wire found in cables.

Ka_sea_ta · 08-04-2016, 11:33 PM

Ac neutral / ground connections occur at the source. In shore power this happens at the distribution panel not the pedestal by your boat... in this case the ac neutral is separate from the ac ground. The ac ground in this case is tied to the bonding system on the boat typically through a galvanic isolator. In the case of AC sourced on the boat by either the genset or inverter the ground is tied to the neutral. in either case the AC ground is tied to the DC ground which is tied to the bonding system..

Portage_Bay · 08-04-2016, 11:40 PM

To dig in and understand ground, grounding and bonding and get a good working knowledge of boat electrical systems consider studying Boatowners Illustrated Electrical Handbook by Charlie Wing

caltexflanc · 08-05-2016, 05:55 AM

Our 1981 Hatteras, both DC and AC ground and the bonding system went to a single common buss. The boat was also equipped with isolation transformers for AC shore power as well as GFI circuit protection for all outlets.

bglad · 08-05-2016, 06:11 AM

Connecting the AC green ground, DC negative and bonding busses is for safety. Since the AC and DC systems live side by side there is the possibility of shorting between the two. If the DC and bonding systems are not connected to the AC green ground buss then the breaker feeding the circuit cannot see the fault and will not trip. This means the DC negative and bonding systems could be at 120 volts. This can cause some corrosion but MORE IMPORTANTLY KILL YOU (caps for emphasis).

I have attached a couple diagrams from ABYC E-11. The bonding system is not shown but it should also attach to the engine negative terminal (or DC negative buss). The guy who wants to ground your systems is correct. This has nothing to do with connecting the neutral and green ground wires used in your AC system which should not be done for the shore power section on board.

sdowney717 · 08-05-2016, 07:20 AM

Yes, connect AC green ground wires to DC bond wires just for safety to help prevent shock hazards.
Usually, there should be only one common connection point for that.

The AC green ground wire normally carries zero current, all AC power flows back only thru the neutral white wire. IF you have a GFCI, and you got a 5milliamp leak through an alternative path separate from the black and white current carrying conductors, (like a ground or bond wire) then the GFCI will turn off the AC circuit. AlL outlets on the boat should be GFCI protected, (except maybe an AC fridge, for obvious reasons, keep that on separate circuit)

AlaskaDreaming · 08-05-2016, 07:08 PM

Thank you all for your info - BGlad I appreciate the wiring schematic. I am doing my best to get up to speed, but there are lots of systems on this boat! So I am reading Nigel Calder's Boatowners Mechanical and Electrical Manual and trying to understand the boat bonding aspects. It sounds as if you all agree to tie the boat bonding to a common ground bus (the 'DC negative bus connecting to the AC grounding bus, and the generator also connecting to that. When purchased the generator had no 'green' wire connected - they had just run the white/black (neutral/hot) to the distribution panel. I know that in some European boats and some wood boat builder types argue that current leaks in the water at the dock can migrate and be distributed via the bonding system in that boat, and believe that isolating the metals is better versus tying the boats bonding into the grounding bus. My boat does not have a galvanic isolator, so I will be installing one of those as soon as it comes in.

Still reading and sure I am using terms incorrectly - my understanding of wiring has been pretty basic, so still trying to understand it all, but it seems you are all advocating bonding all the systems together (and that is currently how my boat is set up and it looks like this was done from the start), but there are many arguing against this approach. Also, I will need to install more GFI's ... at current they are only in the galley!

Again thanks for replies and hopefully all is well in my boat and no one has inadvertently tied something hot where it shouldn't be!

Bacchus · 08-05-2016, 08:12 PM

Quote:

Originally Posted by AlaskaDreaming

Also, I will need to install more GFI's ... at current they are only in the galley!

Note: It is common to have one GFCI outlet for each AC recepticle circuit...other outlets are fed from and protected by the one (first) GFCI recepticle if wired correctly... not necessary for every recepticle to be GFCI.

bglad · 08-06-2016, 04:56 AM

The attached is straight from a Northern Lights installation manual. Until recently it was commonly missed. Since you have no ground (green wire) you will need to install one and ground the neutral at the generator. Doing this without grounding your entire AC electrical system requires that your AC power source selector breaks both the hot and neutral legs. The green ground circuit should not be broken anywhere.

An explanation I give regarding the whole grounding issue is think of your boat like it is a refrigerator. When you grab a refrigerator handle while standing in your bare feet you count on its grounding to protect you from a shock. The metals in your boat need to be grounded for the same reason. If you are crawling around your engine space leaning on an underwater fitting and touch some other metal part shorted to the AC side of your system you could be shocked or worse (using shore power source).

I suggest going through the entire installation manual for your generator and making sure it is connected properly electrically, doesn't have a scoop on its inlet and is installed with a vented loop if needed. The issues you have pointed out indicate a certain lack of expertise by the installer indicating a complete review is in order.

Quote:

Originally Posted by AlaskaDreaming

Thank you all for your info - BGlad I appreciate the wiring schematic. I am doing my best to get up to speed, but there are lots of systems on this boat! So I am reading Nigel Calder's Boatowners Mechanical and Electrical Manual and trying to understand the boat bonding aspects. It sounds as if you all agree to tie the boat bonding to a common ground bus (the 'DC negative bus connecting to the AC grounding bus, and the generator also connecting to that. When purchased the generator had no 'green' wire connected - they had just run the white/black (neutral/hot) to the distribution panel. I know that in some European boats and some wood boat builder types argue that current leaks in the water at the dock can migrate and be distributed via the bonding system in that boat, and believe that isolating the metals is better versus tying the boats bonding into the grounding bus. My boat does not have a galvanic isolator, so I will be installing one of those as soon as it comes in.

Still reading and sure I am using terms incorrectly - my understanding of wiring has been pretty basic, so still trying to understand it all, but it seems you are all advocating bonding all the systems together (and that is currently how my boat is set up and it looks like this was done from the start), but there are many arguing against this approach. Also, I will need to install more GFI's ... at current they are only in the galley!

Again thanks for replies and hopefully all is well in my boat and no one has inadvertently tied something hot where it shouldn't be!

AlaskaDreaming · 08-06-2016, 05:32 PM

Thanks again BGlad ... yes- it is interesting. My manual is the original and it did not show the green ground (actually tied to the neutral post). I have been working with an electrician who I think is good (and costly!) and he was able to pull up the new manual which showed the green ... so I ran the wire and let the electrician come and hook it up. He also noticed something weird in my breaker panel, where the neutral for several big shorepower draws (water heater, etc...) was coming through the inverter switch neutral. He was quite upset about this and worried as he thought it was original wiring, though as we talked about it - we realized that in 1982 it is unlikely there was an inverter on board, so then he was less concerned about the 'original wiring' being a bit off and figured whoever installed the inverter caused the issue. We got all that cleaned up and I checked thruhulls and other common rail areas and found only one thruhull was not properly tied in. I think I got concerned when the other shipwright working on the boat to install a vacuflush got very concerned about finding 'ground' (accidentally) on a thruhull. He was very very clear that the ship isn't tied into this system, he comes from a wooden boat background and certainly there are some controversies as to whether to tie it in or not that I have found 'online'. That is why I was trying to find out what was done originally on these boats. The current electrician is correct according to what everyone is saying here, though the other shipwright is still saying that I risk running 120 into my thruhulls should someone make a wiring error and 'sinking' the boat.

I will look for the 'plumbing' on the generator ... I don't recall seeing an antisiphon loop on that - clearly there for the Lehman, but I am finding several 'problematic' installations of things (connecting wires with marrats and some very 'strange' connections using telephone wire!).

Anyway, with the help of the electrician I will soon get a galvanic isolator installed as well and bring this boat up with current specs. Learning a lot fast! and appreciate all the info coming my way!