Wiring advice

[azazzera]

I'm starting to wire my Pearson 30 and just need to know I'm thinking about this correctly. I have 6 awg that I'm going to wire my shroud with and tie them all to the negative busbar. I'm going to use the same 6 wire to tie my fuel fill and tank together and bring them to the same negative bus bar. A 6 awg wire will be placed on the strut and brought to the neg bus bar. A single ground wire will be taken from the engine block to the bus bar. And lastly all the negative from all my loads will be brought back to the bus bar. Then of course it eventually gets returned to the neg post on the battery.

Does this sound like a usual plan.

Thanks for any thoughts.

[Marian Claire]

Electrical stuff is not my strong suit but I think you want your DC ground and your lightning protection ground separated. http://www.sailmail.com/grounds.htm

Dan S/V Marian Claire

[Al Schober]

Agree with keeping electrical grounds separate from the bonding system. One place this is difficult to do is with the VHF antenna, which connects the radio ground to the mast. I don't know how well the antenna would work if it were insulated from the mast. But the answer should be out there somewhere - I'm sure there are folks using whip antennas with wooden masts.

[hanleyclifford]

Agree with keeping electrical grounds separate from the bonding system. One place this is difficult to do is with the VHF antenna, which connects the radio ground to the mast. I don't know how well the antenna would work if it were insulated from the mast. But the answer should be out there somewhere - I'm sure there are folks using whip antennas with wooden masts.

I have a whip antenna on a wooden mast which is not grounded. The antenna must be grounded thru the radio itself. Reception is excellent (.410 cable).

[azazzera]

Mr. Calder says

So after reading the replies I thought I agreed that one shouldn't mix the bonding/lightning side with the current carrying side. My thoughts were that if lightning strikes or strikes near you don't want give it a path the your panel, radio, or other thing on the boat.

Then I opened up my 4th edition of Nigel Calder Mechanical and electrical manual. On page 279 under Bonding and Cathodic Protection there is a figure 5-17A that showed the current carrying side with its own"DC negative bus" and the "Grounding Bus" that carries normally non current carrying things such as chainplates, electronic ground plate zinc, immersed ground plate or strap, main lightning down conducted, metal objects, they were both connected together. he writes "The bonding circuit is then connected to the boat's ground, with in turn is connected through underwater hardware to the earth's ground, thus holding the entire system at ground potential".

So still confused. can any one clear my thinking. Thanks.

[Marian Claire]

Again I am no expert but why, if you can separate them, would you want to subject/expose your GPS, depth sounder, chart plotter, DC lighting, etc to a surge from lightning?
Dan S/V Marian Claire

[hanleyclifford]

Does Mr. Calder also recommend the bonding and grounding of thru hulls?

[ndutton]

I'm no lightning protection guy but I did install quite a few back in the day following factory specs. Reading the opening post, if the #6 wire to the shrouds is intended for lightning protection, it's awfully small in my experience.

While we are on the subject of wire gauge,

A single ground wire will be taken from the engine block to the bus bar . . . . . Then of course it eventually gets returned to the neg post on the battery.

I saw no mention of wire gauge but please be certain the entire ground path from engine to battery is of sufficient size to carry starting loads ~ 130 amps.

[azazzera]

So. Yes I plan to make the starter wire a 2 wire. From most of the posts I see here and using the blue sea app, a 2awg seems to be a safe, well within limits, size wire. What comes in must go out so I'm going to continue the 2 wire on the negative side of engine.

I gather from the response I got that it would be better to not connect the non current carrying side with the current carrying side. Regardless of what the ABYC suggests. I know that there are many ways to skin this cat and the books point this out as well. I don't plan to connect my one, raw water thru hull to the bonding. Although I have read that saying that I'm keeping it isolated is not true due to the fact that salt water is flowing to the engine. And yes I totally agree with you mr dutton that a 6 wire is small and at the minimum size that the ABYC recommend. I will carry enough insurance to pick it up off the bottom until I get the cash to install a proper system. I'm primarily using the wire installed to the chain plates as a bonding wire because from what I have read about a lightning strike and its power, it will probably plow my strut off the hull. So then the question is sould I even bother with installing any wire up to the stays. It's a deck steeped mast. If I want lightning protection for now hook a heavy wire to one of the top stays and put it over the side?

I'm still interested in understanding why some think it's better not to connect the bonding to the whole system. The idea if I'm correct, from the ABYC is to keep all to a 0 potential. Helping to prevent galvanic and current induced corrosion.

Again all thought are extremely appreciated. Thanks.

[ndutton]

I was recently invited to participate in this discussion on the Catalina 30 forum. It started out well for a few days, received several thanks from members on the content and tone, then came the internet expert throwing in the hundreds of boats he's worked on, supported his position with statistics from a device failure study 'he has on his hard drive' without producing the study for anyone else to read and finally defended the ABYC for looking out for our safety by protecting us from a possible scenario that required an exceedingly rare combined failure cocktail. A little basic math showed the probability of the failure cocktail to be 3/10 of 1 percent. Yeah, 0.3% was causing all the sphincter pucker.

About that study, another participant found (and linked) what he believed to be the same study on the internet which did not support the statistics previously reported (big surprise!). The 'expert' said it was not the same study. Interestingly, it had the same date and exact same sample size, 2527 units. What are the chances?

Point being, it usually turns into a contentious exchange so watch for it as the discussion progresses. Beware of dock experts and self appointed internet experts. You'll have to figure out who's who for yourself but laying out one's resume' to impress or intimidate is often a bad sign.

As a starting point, the ABYC requires a bond between the AC system ground and the DC system negative.

[romantic comedy]

From what I have read, even the experts agree that there are different ways and no one can say what should always work for every one.

The "to bond or not to bond" debate is still a debate, as far as I know.


Or maybe I am not current with my reading.

[Ajax]

Maybe I'm wrong on this, but if bonding is linked to DC ground and both are linked to seawater via the engine, then electronics shouldn't be damaged because lightning (current) takes the path of least resistance to ground.

If your cables to ground (seawater) are good, then that's where all of the current will go.

That's also part of the premise behind linking DC and AC grounds- stray current from a short in the 120v system will discharge to the water via the DC ground system, instead of into a human being. This is especially true where the AC and DC system conjoin, such as inverters and battery chargers. If there is a malfunction on the AC side of an inverter, it could send stray AC current through the DC system. Linking the two systems sends that current into the water, protecting you.

This is how stray current gets into the water and eats people's zincs and shocks swimmers.

Based on this, I have opted *not* to link my AC and DC systems.
I do have a battery charger. This introduces a small risk of shock to me, if the charger or my breaker panel malfunctions in just the wrong way. I figure it's better than shocking a swimmer and better than becoming electrically linked to other boats in a marina and burning off my zincs.

I do have an inverter, but it's a "standalone" unit that does not feed my 120v outlets on the boat. It's tied directly to the battery with a fuse. It has its own 120v outlets. This means that even if it malfunctions, I won't be shocked by the boat's main 120v system. Thus, there is no reason to link the AC and DC system.

If I had more complex systems that really risked sending AC current into the DC system, I'd link the two and install galvanic isolators.

Oh- one final risk to protect yourself against, is to not run AC and DC cables together, if it can be avoided. If the cables chafe and AC touches DC, this is another point where you'd be shocked and the AC/DC ground link would save you. Keep them apart, and it's less of a concern.

[Administrator]

From what I have read, even the experts agree that there are different ways and no one can say what should always work for every one.

The "to bond or not to bond" debate is still a debate, as far as I know.


Or maybe I am not current with my reading.

Hopefully, Neil will chip in, but my recollection is that when we bought our last new boat (20+ years ago), the big boys were building bonded and unbonded boats at the very same time, each claiming a superior design.

Bill

[ndutton]

I'll be part of the discussion for sure but it will have to be this evening due to time constraints. I'll do my best not to become what I warned about.

[ndutton]

Here we go

The ground in an AC system is there for one purpose and one purpose only: to conduct enough amperage to earth in the event of a hot leg fault to cause the overcurrent protection to trip resulting in a safe condition automatically. On boats, branch circuit protection opens only the hot leg while the main circuit protection opens both current carrying legs.

GFCI technology compares current on both legs of a circuit and if the difference exceeds 0.005 amps the device trips, opening both current carrying legs of the protected circuit. ELCI's are the same as GFCI's except with a slightly higher trip point. I'll be using the GFCI term generically to refer to both.

First point of contention, with GFCI technology who needs a ground anymore? In a fault event on either leg the GFCI trips at 0.005A or 1/4000th the current required for a conventional 20A breaker (the reason for the ground). It's a provocative question that I'm sure we'll be discussing.

The argument for keeping the ground system anyway is redundant protection if the GFCI fails. This is where the 2001 study with a 2527 unit sample size comes into the discussion which I'll provide when we start digging into it. It's important also to distinguish between different types of GFCI failures: non-operable because of miswiring, non-operable to a tripped (safe) condition, non-operable with no-trip (unsafe). If miswired, you deserve what you get. Other than that, the only practical concern is the no-trip failure. Only in this scenario does the AC ground come into play. To further reduce the risk of failure, GFCI's have a test function and the manufacturer recommends monthly testing. What other electrical system component comes with its own test function?

Notice that we haven't reached the AC ground - DC negative bond yet.

Pre-GFCI era
OK, the ABYC required the bond in the pre-GFCI days in case the shore power ground failed anywhere (boat, cord, plugs, dock system) as a safety redundancy to still cause the overcurrent device to trip. The bond provides connection to the water, an earth ground. Shore power ground failure statistics do not exist as far as I know so all we can do is try to make a reasonable estimate of occurrence.

But there's a new problem, an unintended consequence of connecting the DC negative to the AC ground. Your boat's DC system is now connected to all your neighbors' DC systems via the shore power ground wiring and attracts devastating stray current corrosion in the event of a DC fault anywhere in the vicinity on boats over which you have no control. You've protected your crew with overcurrent protection and ground redundancy, now who protects your boat from the effects of the AC-DC bond?

There are a couple of ways. Installation of an isolator, an additional piece of equipment, is the popular option. To be fair, if we are discussing failure rates of one device, shouldn't we do the same with ALL devices, isolators too? Another way rarely mentioned anywhere is an impressed current cathodic system. It monitors DC fault current and applies an equal but opposite current to the system rendering it net zero. Pretty slick and pretty pricey as I recall. The first I learned of such a system was 45 years ago so it's not new.

Now we have GFCI's
If the GFCI shuts off a circuit in the event of a fault and we retain the shore power ground for redundancy if the GFCI fails, the AC-DC bond is relegated to the back seat, a third level redundancy in case both the GFCI and shore power ground fail simultaneously. This is where probability calculations get microscopic making the ABYC clinging to their bond requirement questionable bordering on absurd.

OK, there's the overview. Where do we go from here? Please note this has nothing to do with lightning protection, an entirely different subject.