Grounding system on 1993 H375 Legend

[Lander]

I hear there are lot of opinions out there on grounding systems on boats, bonded or un-bonded, and failure to observe a consistent and well thought out protocol can have potentially dire consequences. My boat is a 1993 Hunter 375 and fortunately (or not...) I have the OEM grounding system where the engine block is connected via 0/2 wire to the neg DC battery. NOTE that this is not an “insulated return” found on some more modern boats, and recommended by Nigel Caulder in his excellent book "Boat Owners Mechanical and Electrical Manual". Starter motors, alternators, and so forth are, on this boat, mechanically and electrically connected to the engine block.

My OEM boat is not bonded, that is thru hulls and all underwater metals are electrically isolated, with zincs on the prop, prop shaft and shaft strut, since these are mechanically and electrically connected to the engine block. AC neutral or ground are NOT connected to, and have no continuity with, any DC ground or neutral or any underwater metals (I tested this). There is no voltage read between AC neutral and AC ground. I have neither galvanic isolator nor isolation transformer at this time.

I have some questions which I will get to, but here's what got me thinking... There are 3- 10g black wires connected to the keel bolts in the bilge. Recently, I disconnected these and tested continuity to trace them. With the wire disconnected from the keel bolts:

1. There is no continuity between the 10g black wires and negative 12vdc bus bar on the main distribution panels.
2. There is no connectivity between the mast and anything, (10g black wires, keel bolts, neg 12vdc, engine block)
3. There is electrical continuity between all keel bolts.
4. There is electrical continuity between the engine block and the keel bolts
a. The negative battery cable was connected to the engine block during the test.
5. There is, therefore, continuity between the keel bolts and 12vdc negative buss bar at the main distribution panel.

Nigel Caulder recommends physically separating the current carrying neg dc (ie…at the main distribution panel) from the non-current carrying “common ground” which provides a direct path to water via a ground plate. While the one is still connected to the other, the non-current carrying end is where he connects lightning protection, AC ground, radio ground plates etc., since this end of things is not involved in carrying current. Since the OEM arrangement in the 1993 Hunter 375 does not appear to be an "insulated ground" return system, but the keel bolts are electrically connected with the current carrying 12vdc negative (via the engine block), I wonder... was it Hunter's intention to create a common ground out of the keel bolts, similar to Caulder's recommendations?

If so, this raises a couple of questions...
1. Should I ground the mast to the keel bolts?
2. Are the keel bolts designed to be the “ground plate” to water? Or will they simply blow the keel off the boat if they are wired to absorb a lighting strike?
3. Is there another grounding plate (to water) built into the 1993 H375?
4. What do those black wires service? They do not have continuity to anything I can find...?
5. Would you recommend an Galvanic Isolator, or is this necessary with no inverter?
6. What would make the best place to connect an RF ground?
7. Shall I leave well enough alone and go sailing instead?

Inquiring minds want to know....

 

[Stu Jackson]

The battery negatives are and should be separate. They are the ELECTRICAL system, NOT the bonding system or the grounding system (two separate things also).

Here's what many consider the Bible of this issue:

http://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems

Good luck. Chew on that for a while, please, and I'll go back and reread your post in more detail.

 

[Charles Erwin]

I have the OEM grounding system where the engine block is connected via 0/2 wire to the neg DC battery.

You have a DC negative cable feed to the motor block. This is there to supply DC negative to the starter, alternator, and motor sensors (oil pressure, coolant temperature, etc.) You can call any DC negative connection a 'ground' but I think this is confusing because the term ground better describes connections to the water and the land.
You will see terms like bonded, bonding, ground, grounding, grounded and so forth used carelessly by just about every author so you need to pay attention as you study this stuff.
In any case - you describe a DC current carrying connection.

this is not an “insulated return” found on some more modern boats, and recommended by Nigel Caulder

I do not understand the term insulated return probably because I cannot imagine an uninsulated 'DC negative' returning to a battery. Can you furnish a more descriptive definition of Caulder's term so we can all use the same term to describe the same thing?

My OEM boat is not bonded, that is thru hulls and all underwater metals are electrically isolated, with zincs on the prop, prop shaft and shaft strut, since these are mechanically and electrically connected to the engine block. .

You say the only items with direct zinc protection are the shaft, propeller, and strut. There would be no reason for a wire connecting the strut to the motor block - but a good reason to connect it to the rudder post. Anyway - how is the strut 'mechanically and electrically connected' to the motor block?

AC neutral or ground are NOT connected to, and have no continuity with, any DC ground or neutral or any underwater metals (I tested this). There is no voltage read between AC neutral and AC ground.

AC neutral (White) and AC ground (Green) are never connected to one another on the boat with exceptions if you have generator, inverter, or isolation transformer.
AC neutral is never connected to DC negative and there is no DC neutral.
AC safety green needs to be connected to DC negative and your shaft saver - if any - needs to be jumpered.

There are 3- 10g black wires connected to the keel bolts in the bilge. Recently, I disconnected these and tested continuity to trace them. With the wire disconnected from the keel bolts:
1. There is no continuity between the 10g black wires and negative 12vdc bus bar on the main distribution panels.
2. There is no connectivity between the mast and anything, (10g black wires, keel bolts, neg 12vdc, engine block)
3. There is electrical continuity between all keel bolts.
4. There is electrical continuity between the engine block and the keel bolts.
a. The negative battery cable was connected to the engine block during the test.
5. There is, therefore, continuity between the keel bolts and 12vdc negative buss bar at the main distribution panel.

Are these three wires one to each to each of three bolts? Are the bolts wired one to the next? Do these three wires vanish into the structure such that you cannot find the other ends? How can item 1 and 5 be true simultaneously since DC negative and one of the leads to the keel bolts are both connected to the motor block?

Assuming one or more of these three wires are connected to DC negative - and so necessarily the motor block - your shaft zincs are protecting your keel. This is lousy design because the anodes were never sized for that kind of job. Moreover, with this wiring arrangement you invite stray current trouble - from your own boat as well as the neighbor if you are in a slip. (incidentally if you are in a slip you really need galvanic isolation to protect you from your neighbor's galvanic mischief but it won't help with stray current mischief. )

Ultimately one cannot think of a single reason to have any wire connected to the keel bolts - apart from cases involving a comprehensive lighting suppression system - which you do not have.

By the way if this was OEM then surely there is a diagram (and explanation) available which would answer your questions. But keep in mind many builders had no idea what they were doing nor why they were doing it - in the first place.

Charles

 

[splax]

A possibility comes to mind considering the 10 gauge black wires. They may have been used as lightning protection for the mast and have failed in use. Find the other end and check for wire self-continuity. You may want to replace the wire.
I recall I have some black wires attached to my keel bolts, too. I have too many things needing attention to pursue a single issue like that though as I redo the electrical system I am sure I will find where they go and why they are there.

 

[splax]

Charles,
Perhaps the strut is mechanically and electrically connected to the engine by the prop shaft.
An insulated return may be an insulated wire on the negative side versus a bare wire used in negative ground automobile applications.

 

[Stu Jackson]

I agree with Charles, very good observations.

 

[Bill Roosa]

The strut is not electrically connected to the prop shaft as there is typically a plastic bearing between the two.
I suspect that you will get lots of opinions that will not sute your situation or desires. Read the WM artical and follow that. it works.
On the subject of lightning protection there is new information out by the insurance companies. making the keel the place where the lightning exit the boat is a bad idea. This is due to the way an electrically charged cloud induces a charge on the surface of the water. it does not "charge up" the whole mass of water as it passes overhead. it does charge up the top 0.1 inch of water however. Sooooo the keel is actually below this surface and as the electrical potential causes current to flow it wants to leave the wiring inside the boat as it gets to the waterline level. There is no potetial to drive it to the keel so it leaves and finds a path to the water surface the best way it can. Typically through a large metal object between the lightining grounding wires and the hull and then through the hull.
Better, IMHO, to take the lightning over the side of the boat with dedicated lightining ground coming off each shroud, and the fore and aft stays, going over the gunnel and into the water with the section entering the water not being insulated. FWIW

 

[JamesG161]

if they are wired to absorb a lighting strike?

This and the West Marine link imply that you can conduct a lightning strike down a path to the sea or you can suppress a direct strike. How big was the bolt/strike? What amps flow can a 4 ga wire conduct?
If a direct strike hits your boat... wave goodbye... keel ground, plate ground or any other grounding system.

Lightning suppression/protection is reducing this...

This is due to the way an electrically charged cloud induces a charge on the surface of the water. it does not "charge up" the whole mass of water as it passes overhead.

and your boat.
As best as you can, you want your boat not to "charge up", and to be at the same electrical potential of the water around you. I like to think of it as making your boat "invisible" to that nasty cloud.
All the 4 ga wire does is make sure you don't have a "charge up"
This is how we keep water towers, buildings, bridges, etc. from major strikes.

DC grounding...
There is no DC ground to my engine. The starter has it own negative return to the starter battery. The engine sensors have their own DC negative to the DC negative buss. By isolating my prop/shaft/engine (or rudder) from a DC ground, there is NO path for marina stray currents to travel. This is one of the ABYC approved methods. The West Marine blog is another.
Jim...

 

[Charles Erwin]

Jim

If your returns are isolated you are lucky indeed. Nevertheless, in your case AC safety green is certainly bonded to the block and since it is also bonded to DC negative there is a path to seawater via this connection.

Certainly manufactures use isolated motor accessories - separate returns as you put it - but every one of those insist on a comprehensive bonding system. And - comprehensive, well maintained bonding is very good at trapping stray current particularly evil current emanating from your own boat.

However, In the vast majority of sail boats the starter, alternator, oil pressure switch, oil pressure sender, temp sensor are all case grounded and so necessarily use the motor block as a conductor - there are no 'separate' returns on these accessories. The DC negative cable runs from the battery to the motor block so you can immediately see the threat. There is a current path on a boat as follows: A battery positive wire leaks to bilge water, then to keel bolts or through hull(s), then to outside seawater, then via the prop shaft to motor, thence to battery negative via the battery negative cable. If the neighbor is the problem the path is the same except the return connection to the neighbor is via safety green.

So everyone would do well to do an occasional hull potential assessment - record the data in their logbook. That way changes are seen and attended to early in the process.

By the way what motor do you have?

Charles

 

[JamesG161]

Nevertheless, in your case AC safety green is certainly bonded to the block and since it is also bonded to DC negative there is a path to seawater via this connection.

Since I have a genset, and a inverter/charger, the AC (green and white) go to the AC ground buss AND to eventually the DC ground buss. This totally surprised me!
I was so used to a battery being grounded to the DC negative of the starter battery and the engine block.
Then @Maine Sail posted a link to ABYC standards. After reading the key ones about 100 times, I started getting it.
I opened the side hatch to my Volvo Penta MD22L and about 5" away there was the big buss with many BIG Black wires bolted to it.
I checked the engine block with my Ag/AgCl galvanic reference cell and was pleased to see the engine was at -982 mVolt (Zinc good) and shocked to find the DC Ground buss (thinking bond system for corrosion control) was at -420 mV.
OMG my boat was corroding away, but not the engine/shaft/prop.
Sprinting forward, I checked my genset engine (thinking it would be dissolved before I could reach it) and found -910 mVolts). WedThurFri was going on? The 16hp Yanmar had is own zinc in the sea water system.

ABSOLUTELY NO conductivity between the engine and the DC buss!

I guess the sea water distance between the engine/shaft/prop and the grounding DC keel wasn't very conductive to my DVM.

There is a current path on a boat as follows: A battery positive wire leaks to bilge water, then to keel bolts or through hull(s), then to outside seawater, then via the prop shaft to motor, thence to battery negative via the battery negative cable.

So True up to the point of the underlined part, which my boat does not have an Engine block to battery Negative!

Look Ma no circuit!

This is the reason I chimed in about DC ground.
Jim...

PS: I still can't find the Hunter 430 wiring schematics.

 

[Bill Roosa]

It is not possible to make your boat invisable to lightning clouds. if there is a charged cloud overhead the whole of the water surface underneith it is charged by induction and your boat is sittingin the charged water so it is charged also (by the same induction). Since the water does not have a large metal conductor sticking out of it and you do your boat is the best path between the cloud charge and the ocean surface charge.
The building industry has been doing this for many decades with very little concern. The lightining rod is connected to a large conductor which goes along the OUTSIDE of the building and ends in a good ground. For the record they also find that the area just as the conductor enters the ground (not the burried pipe it ends at) is where the current leaves the cable.
It is possible to direct the lightning over the side and keep it out of the boat. Frankly the guy that thought up running the lightning protection inside the boat was not well versed in common sense IMHO
FWIW

 

[Maine Sail]

Since I have a genset, and a inverter/charger, the AC (green and white) go to the AC ground buss AND to eventually the DC ground buss. This totally surprised me!

It should surprise you because AC Green/grounding and AC White/Neutral are never connected/bonded on-board UNLESS the inverter or generator are in operation.

With your boat unplugged from shore power and with no gen or inverter operating there should be NO CONTINUITY between AC Green and AC Neutral.. You should always have continuity between AC Green and DC Ground.

 

[JamesG161]

It is not possible to make your boat invisable to lightning clouds.

True! That is why I was suggesting an analogy of "invisible" as opposed to a "target". Most people think that "elevation" or height above the water/ground is what is dangerous and that if you are "insulated" from the ground, like a rubber tired vehicle is best. The truth is just the OPPOSITE!

It is possible to direct the lightning

I am not sure anyone as learned to direct lightening but more like avoid it versus the guy next door. However we put it, we are trying to not be and EASY target.

it does charge up the top 0.1 inch of water however.

This is a good analogy to "Static Electricity" shock (same as lightning). I suspect that in a big charged cloud it might be more than 0.1 inch , but you made a good point.
We should not highjack this thread, but electrically ground your mast as best you can.
Jim...

 

[JamesG161]

It should surprise you because AC Green/grounding and AC White/Neutral are never connected/bonded on-board UNLESS the inverter or generator are in operation.

Whew! I feel better now. Thanks for the calcification that makes sense. I did look at few Hunter 2002+ schematics on a boats of similar size and features that shows them connected and ending on the engine starter battery.
@Maine Sail is there a switching/prevention device that makes separation of the white wire in my inverter/charger?

It is makes sense, no AC power, no current flow on White.

Yes, I have verified my AC green is connect to the DC bond ground buss.
Jim...

 

[Lander]

.....You can call any DC negative connection a 'ground' but I think this is confusing because the term ground better describes connections to the water and the land.

Agreed... I have therefore called it the "DC negative" to distinguish it from "ground".

.....You will see terms like bonded, bonding, ground, grounding, grounded and so forth used carelessly by just about every author so you need to pay attention as you study this stuff.
.....In any case - you describe a DC current carrying connection

Agreed.... DC negative, as in return current carrying, which is how Mr. Calder uses it in his book.

....I do not understand the term insulated return probably because I cannot imagine an uninsulated 'DC negative' returning to a battery. Can you furnish a more descriptive definition of Caulder's term so we can all use the same term to describe the same thing?....

An "un-insulated return" is where there is no dedicated negative (current carrying) wire returning from a load inducing device, and instead, the hull, engine block, or other large object is used as the return path. For instance, he describes alternators and starter motors in some newer boats as being electrically isolated from the engine block, so that each of these devices has an individual negative DC return wire and not, as in my 1993 boat, a single shared 0/2 DC negative return wire from the engine block. Since my engine block and my keel bolts are somehow connected internally to each other I was wondering if anybody could shed some light on what Hunter was thinking, since I respect the Hunter engineers and am sure they had something in mind...

You say the only items with direct zinc protection are the shaft, propeller, and strut. There would be no reason for a wire connecting the strut to the motor block -
Agreed, and there isn't anything connecting them at this time...

but a good reason to connect it to the rudder post.

The rudder post is completely encapsulated in rudder and (barring some damage or defect) has no contact with the water... why is this recommended?

Anyway - how is the strut 'mechanically and electrically connected' to the motor block?

The strut is probably isolated from the shaft by the cutlass bearing. The shaft, however, is bolted to the transmission which is in metal to metal contact with the block, which, on my boat, has that 0/2 negative return wire.... I just felt a clamshell zinc on the shaft strut would be a good idea, just in case....

AC neutral (White) and AC ground (Green) are never connected to one another on the boat with exceptions if you have generator, inverter, or isolation transformer.
AC neutral is never connected to DC negative and there is no DC neutral.
AC safety green needs to be connected to DC negative and your shaft saver - if any - needs to be jumpered.

Agreed on all points. And, no shaft saver.

....Are these three wires one to each to each of three bolts? ....

All three wire are connected to one keel bolt, via a plate washer under the nut.

....Are the bolts wired one to the next? Do these three wires vanish into the structure such that you cannot find the other ends?...

Bolts are not visibly wired together, the connection is somehow internal... and since this is somehow "built in" am wondering what Hunter's concept was...? My continuity testing was done with the wires disconnected from the keel bolt, and I cannot trace where the other end of these wires go... Hence my other question, what are they for?

....Assuming one or more of these three wires are connected to DC negative - and so necessarily the motor block.....

The wires themselves have NO connection to the DC negative, UNLESS they are connected to the keel bolts, which is somehow internally connected to the engine block. Once at the engine block, then the aforementioned 0/2 wire carries it to the neg battery terminal...

...your shaft zincs are protecting your keel. This is lousy design because the anodes were never sized for that kind of job. Moreover, with this wiring arrangement you invite stray current trouble - from your own boat as well as the neighbor if you are in a slip. (incidentally if you are in a slip you really need galvanic isolation to protect you from your neighbor's galvanic mischief but it won't help with stray current mischief.

I am concerned.... On the bright side, our marina was just rewired and marina AC grounding system new and up to the latest standards with GFI breakers, which I am told, have been causing problems for boats with bad wiring because they trip these breakers frequently...

Ultimately one cannot think of a single reason to have any wire connected to the keel bolts - apart from cases involving a comprehensive lighting suppression system - which you do not have.

Hence my questions... your take-away recommendation would be to simply disconnect them?

By the way if this was OEM then surely there is a diagram (and explanation) available which would answer your questions. But keep in mind many builders had no idea what they were doing nor why they were doing it - in the first place.

Have to OEM schematic, but other than illustrating the situation, no explanation was offered. Does anybody out there know what Hunter was thinking? Again, my point is NOT to criticize, just figure what the original thinking was, before making a departure from what MAY have been a well thought-out, cogent DC and grounding plan by Hunter...

Thanks!

 

[Lander]

True! That is why I was suggesting an analogy of "invisible" as opposed to a "target". Most people think that "elevation" or height above the water/ground is what is dangerous and that if you are "insulated" from the ground, like a rubber tired vehicle is best. The truth is just the OPPOSITE!


I am not sure anyone as learned to direct lightening but more like avoid it versus the guy next door. However we put it, we are trying to not be and EASY target.


This is a good analogy to "Static Electricity" shock (same as lightning). I suspect that in a big charged cloud it might be more than 0.1 inch , but you made a good point.
We should not highjack this thread, but electrically ground your mast as best you can.
Jim...

Nigel Calder has a well written section in his book Boat Owner's Mechanical and Electrical Manual on lightning. I have attached the PDF of that section, and I highly recommend reading this and purchasing the book... It is immensely helpful (and just plain old interesting!) to anyone wrestling with these difficult concepts as I am. When you talk about "avoiding it" Nigel, talks about creating a "zone of protection" and how to do that (see attachment). It was in reference to this concept that I asked about connecting the mast to the keel bolts, and if they would provide grounding the necessary ground to water...if they had a direct path to create the zone of protection. Please, bear in mind that Nigel is NOT talking about carrying lighting voltages THRU the mast to the water....

 

[Lander]

As best as you can, you want your boat not to "charge up", and to be at the same electrical potential of the water around you. I like to think of it as making your boat "invisible" to that nasty cloud.
All the 4 ga wire does is make sure you don't have a "charge up"
This is how we keep water towers, buildings, bridges, etc. from major strikes.

So... bottom line, to keep from sharing the same potential as the surrounding water, one would want to provide lightning ground from the top of the mast to below the top layer of charged water?

 

[Lander]

Jim

If your returns are isolated you are lucky indeed. Nevertheless, in your case AC safety green is certainly bonded to the block and since it is also bonded to DC negative there is a path to seawater via this connection.

There is no connectivity between AC green ground and the block or the DC negative. The AC green ground returns exclusively to the newly wired shore power system. Don't know if this is correct, but it is the way it is. I would be concerned about stray currents between them if it was otherwise.... Am I correct about this?

By the way what motor do you have?

Yanmar 3JH2E.. original engine.

Charles

 

[Charles Erwin]

The conventional use of the term DC grounding implies connecting metallic cases of DC equipment - like windless cases, battery charger cases, metallic pump housings, and the like - to the motor block. If there is a DC fault to the case a DC breaker or fuse will trip and so the wiring is protected from meltdown or fire. DC grounding is not intended to carry current except in the case of a fault and so kept separate from DC (battery) negative current carrying feeds.

Rudder post to strut bonding is precautionary. The precaution assumes the post is exposed to seawater because nothing encapsulated remains so for ever. Bonding the post to the strut means the strut zinc protects the rudder post as well as the strut - just in case. If you want to know for sure whether your rudder is completely isolated from seawater measure the potential at the post.

As to the apparently invisible connection of the keel bolts to motor block when the three mystery wires are disconnected - the keel bolts are immersed in seawater and thus connected to the motor block through seawater via the shaft. So what one might think is an internal connection is really an external connection.

Based on your having verified these mystery wires do not lead to DC negative - disconnecting them at the keel bolt does not matter since they don't go anyplace anyway.

And also - no need for zinc concerns. Since the other ends of these mystery wires go nowhere the shaft zincs are not protecting the keel and that is as it should be.

In any case - there is simply no reason for connecting a keel bolt to the motor block or DC negative with #10 wire. - let alone three separate ones. Are you sure this is a factory install. If so, then these would be shown on the diagrams you have seen. Even if it is not explained - the diagram would show both ends of each of these three wires?

A comment on shore power pedestal GFIs. There are going to be nuisance trips even on boats well wired. If these new units are ECLI units (which is not likely) you are very lucky and nuisance trips will be all but eliminated. However, in either case these devices do not provide protection from a neighbor who has neglected his anodes. Hence consider a galvanic isolator at the least.

Charles

 

[Charles Erwin]

There is no connectivity between AC green ground and the block or the DC negative. The AC green ground returns exclusively to the newly wired shore power system. Don't know if this is correct, but it is the way it is. I would be concerned about stray currents between them if it was otherwise.... Am I correct about this?

Concerning this shore power case - AC safety green (AC grounding) needs to be connected to DC negative (DC grounded) and so necessarily to the motor block. Two reasons are:

If AC safety green became broken on the shore side for some reason there is no AC safety green path back to the transformer in the parking lot - but you don't know anything about this. As a result an AC fault on the boat has no way to return to that source. However, if AC safety green is connected to the motor block then there is a second path back to the source via seawater. That means when you have an AC fault and if AC safety green were broken there is still a second backup path which would not exist unless you fasten AC safety green to the motor block. Breaker trips - all is safe.

If AC got shorted to DC - for example you had a wire meltdown or you made an AC/ DC wiring goof - you now have AC in the DC wiring but there is no path back to the parking lot transformer. However, if safety green is connected to DC negative then there is a path from the AC/DC short back to the source because DC negative has been connected to AC safety green. Breaker trips threat eliminated.

This rule - connect AC safety green to DC negative - is to keep people safe from an AC shock hazard on the boat. This has nothing to do with galvanic or stray current corrosion issues.

The philosophy is - people get protected first. Corrosion problems are a very distant second priority and can be fixed.

If you are unsure about this stuff get an ABYC certified electrical guy on your boat to take you through an on-site assessment. You will learn plenty more with hands on than any other way.

Charles