Grounding Wire on the Hard

[lehighsail]

I saw a reference in this forum to grounding your boat while on the hard if your were plugging it in. Can't seem to find the thread. It involved connecting a wire from the prop shaft to a ground rod?

Can someone comment on whether this is necessary while using outlets on the boat when the dock power line is plugged in and exactly how to do it?

Thank you.

 

[shemandr]

I think it was in regard to lightening strikes if I remember correctly.

 

[CCrane2299]

I'm no electrician, but, I am a generator guy. When you ground something that is connected to an existing electrical service, you create a "difference in potential" between the house ground and the new sailboat ground. When lightning hits the ground the electrical current travels through the ground in ripples like a stone thrown in the water. A single point ground will protect your electronics, while in this case you would have two grounds. As the wave passes the house with higher current in the earth than the earth near the boat, some distance away, the energy that is directed to ground is now transferred in part through the grounding conductor in the power cable and now instead of a "ground" you have a hot wire as the current tries to travel to your boat ground. we discovered this because we had a lot of control boards damaged during lightning storms. The factory figured it out (somebody told them) and now they will not allow us to ground them except through to the single ground rod near the service entrance. It has been a long road with the electrical inspectors, but they are finally seeing the light.

 

[Sailvayu]

Its for safety in case there is a AC fault on your boat or the equipment you have plugged in to your boat. In most cases assuming the boatyard outlets are properly grounded and everything on your boat is ok there should not be a problem. That said I have been knock backwards when grabbing a prop while standing on wet ground more than once. Good practice is to connect a #8 wire from your prop shaft to an earth ground like a metal water pipe. You do not "have" to do it but it adds a level of safety to working on your boat when out of the water.
See my article on boatyard safety http://www.projectboatzen.com/boat-yard-safety/
Not sure how important the lightning thing is as I ahve never encounter a boat on land that was hit but I am sure it happens.

 

[Charles Erwin]

In the case of shore power - AC (safety) green is not connected to AC white (ground) anywhere on the boat. Instead AC (safety) green leads to earth separately (usually by way of the motor block/shaft/prop assembly) and then necessarily via seawater back to the shore power source.

When the boat is out of the water this alternate AC safety green path back to earth (via seawater) no longer exists.

So when on the hard - this alternate AC (safety) green to earth path needs to be re established - so a conductor from propeller/shaft to a ground rod does the job.

Charles

 

[Maine Sail]

Not sure how important the lightning thing is as I ahve never encounter a boat on land that was hit but I am sure it happens.

If you know Jeff H. from Sailnet, his boat was hit really hard, while it was on the hard. His boat was not even plugged in..... Strike came down teh spar through the keel/spar bond jumped a near 2' foot gap between the bottom of the keel and the parking lot and burned the asphalt..

 

[Maine Sail]

In the case of shore power - AC (safety) green is not connected to AC white (ground) anywhere on the boat. Instead AC (safety) green is goes to earth separately (usually by way of the motor block/shaft/prop assembly) and then necessarily via seawater back to the shore power source.

When the boat is out of the water this alternate AC safety green path back to earth (via seawater) no longer exists.

So when on the hard - this alternate AC (safety) green to earth path needs to be re established via a conductor from propeller/shaft to a ground rod.

Charles

Charles,

The reason we create this secondary path for the green safety wire, in marine electrical standards, is because marina wiring is and has been historically horribly unreliable.

In water you still always have two potential paths, back through the shore power cord, or if that safety green drops, as it does, then you still have the water path. Two safety paths intended to create redundancy based on the historical unreliability of marina wiring. the water path is an emergency last ditch safety back up. The shore cord green wire is primary.

On land the electrical pedestals are not being torn out by Buffy & Skippy in the new Sea Ray ripping the dock pedestal out by forgetting to unplug... Yards are usually wired by a licensed pro, not Darrell & Darrell the dock boys who mix up green & white or white & black after Buffy & Skippy tear out the pedestal....

The systems in boat yards can be sketchy but are usually MUCH more reliable than a marina.. You don't need to bond the prop shaft IF the yard has a well wired system, which legally they should, and it should include green safety ground... If the marina has only a two wire system, no safety ground, then grounding the boat can be wise..

 

[Charles Erwin]

If the primary safety green conductors throughout the yard wiring are completely solid (and so also is your cord/and the socket connections from boat to yard service) then this secondary path to ground is nothing more than an unnecessary alternative.

However, on the hard situations may present an example why an alternate path is important. For example, Hubble type socket/plug combination are typically poorly engaged - including safety green contacts - and so the primary safety green may be compromised.

Many folks simply plug in on the hard - use a circuit tester to verify safety green is intact - and that is an end to it.

Seems to me the point to be considered is that degraded yard wiring and/or a failing Hubble type connector can conspire to create a safety issue.

Charles

 

[lehighsail]

Thanks for all the information. I was referring, not to a lightning strike, but to working on the boat with a power line plugged in. If I read the posts correctly, it seems that there is no downside to grounding the boat via the prop shaft so it seems prudent to do it. I will probably be using a #8 stranded copper wire from the shaft to a 3 foot copper post that I will pound into the ground before working on the boat. Any objections? Thanks again.

 

[tommays]

In the work world we HAVE to use a GFI cord-set on anything remotely risky

Even at home down this way anything outside your house has to be GFI and all my boat repairs are done with GFI protection

 

[uncledom]

In an electrical circuit, the ground (which is green in America), is a non current carrying conductor used to allow a fault current to trip the circuit breaker or blow the fuse. It is a safety. But every time you pass through a transformer in order to step voltage up or down or simply to isolate the original source as we do on boats, you have the POTENTIAL to induce current on the new ground as opposed to the original ground. In order to equalize them and eliminate any current differences, you bond them together. The difference in electrical potential between any two wires, including two grounds, can easily be enough to kill you. Funnily enough GFCIs don't work on ground. They sense an imbalance between the "hot" wire and the return or "neutral" wire and open the circuit if an imbalance is detected. They do not require a ground to the device to work.

Nothing stops lightning.