Grounding Wire Guidance

[Chris87]

Hi all. I was cleaning my bilge, keel bolts, etc. and easily broke the old corroded 6 AWG grounding cable from the FWD most keel bolt. Luckily this happened; once fixed, I noticed the grounding wire running beneath the fiberglass decking, under the base of the compression post, had too much play. I was able to pull it out with no energy; when I did, it was completely corroded. It looks like it wasn't hooked to anything, to begin with.

Question: Under the fiberglass decking, is the grounding wire supposed to be connected to a lightning ground plate; or by bolt/nut via the bottom of compression post? What is your recommendation for the appropriate fix?

See attached pictures. (FYI - I sanded down the copper fitting)

 

[uncledom]

I've never seen a water ground clamp used to secure a lightning ground arrester.

 

[Chris87]

Unclledom - why wouldn’t a water ground clamp serve as a temporary fix? These clamps are bronze, which are highly conductive copper alloy. I would think it serves the same purpose.

Now Im asking two questions: 1) if it is unsafe for a water ground clamp to serve as a lighting ground; 2) how to fix the disconnected fitting.

 

[kloudie1]

Wouldn't see a problem with the water clamp if all the connection points where wire or bolt touch, are clean..AND the end of the wire is somehow waterproofed so bilge water doesn't wick up the wire and corrode it.. Wire probably went through the fiberglass beam, out a limber hole under the plate then attached under the compression post plate with a small screw? The terminal on the end of the wire looks too small to fit the bolt..
Not familiar with that boat, so kinda guessing based on what I see.. Could be fixed by running the wire above the beam and to a drilled/tapped new hole in the plate.. Would require a groove under the floorboard..?
EDIT: Is the plate in the picture electrically connected to the mast?

 

[Will Gilmore]

Below is the electrical conductivity column taken from a neat materials chart I came across (link below).
It looks to me like the most effective solution is, depending on what you mean by effective (electrically conductive and protective from lightning vs somewhat conductive and protective, but easier), is to run a heavy gauge wire (insulated from corrosive elements) up the mast to a lightning rod at the top. That marine grade stainless compression post isn't nearly as conductive as the copper wire the electrical system is using (i.e. the masthead/anchor light, antenna, weather gauges, etc.). I don't know, of course, what you have for any of that, but the whole idea of lightning protection is to protect those systems. An aluminum mast with its enormous radius compared to any wiring inside it, would protect everything internal. So, only connecting to the base of the aluminum mast is just as good, if not better. It is when the mast is no longer there and the electricity tries to disperse thru the available conduits on its way to ground from there. Go with heavy gauge copper as directly to ground as you can. Just a thought to add to the mix.

Electrical ... conductivity, ...

TIBTECH
Electrical conductivity
(10.E6 Siemens/m)
Silver 62,1
copper 58,5
Gold 44,2
Aluminium 36,9
Molybden 18,7
Zinc 16,6
Lithium 10,8
Tungsten 8,9
Brass 15,9
Carbon (ex PAN) 5,9
Nickel 14,3
Iron 10,1
Palladium 9,5
Platinium 9,3
Tin 8,7
Bronze 67Cu33Sn 7,4
Carbon steel 5,9
Lead 4,7
Titanium 2,4
St.Steel316L EN1.4404 1,32 (Marine grade stainless)
St.Steel 304 EN1.4301 1,37
Mercury 1,1
Fe. Cr. Alloy 0,74
http://www.tibtech.com/conductivity.php

-Will (Dragonfly)

 

[uncledom]

Unclledom - why wouldn’t a water ground clamp serve as a temporary fix? These clamps are bronze, which are highly conductive copper alloy. I would think it serves the same purpose.

Now Im asking two questions: 1) if it is unsafe for a water ground clamp to serve as a lighting ground; 2) how to fix the disconnected fitting.

I am a big fan of conductive grease which I would apply to all connections. The wire gauge looks too small to me and there should not be any unnecessary bends in the ground wire run and any curves should be as gentle and minimal as possible.

 

[RoyS]

 

[RoyS]

The image in my post above shows a better lightning protection connection to the bottom of my compression post. A single copper cable probably will not be effective in a lightning strike. Also, beware of mixing metal types in the bilge, particularly copper and aluminum. below is the original aluminum compression post bottom that was connected to a copper shunt strap.

 

[JamesG161]

Mast and boat grounding is not for dissipating a lightning strike. It is to maintain, as close a possible, your boat at a zero volt potential with respect to the "sky" or at Ground potential.
Similar to grounding of a Water Tower, Bridge, Tall buildings, etc.

Normally your mast and standing rigging should be electrically "Connected" to your boat's grounding "plate", normally your metal keel.

As @kloudie1 noted, it is a good clean conduction path with very low electrical resistance that is best. The lower the resistance, the faster a static mast charge dissipates to the water.

Jim...

PS: The house grounding clamp is not for lightning, but for not "stealing" power.

 

[uncledom]

Mast and boat grounding is not for dissipating a lightning strike. It is to maintain, as close a possible, your boat at a zero volt potential with respect to the "sky" or at Ground potential.
Similar to grounding of a Water Tower, Bridge, Tall buildings, etc.

Normally your mast and standing rigging should be electrically "Connected" to your boat's grounding "plate", normally your metal keel.

As @kloudie1 noted, it is a good clean conduction path with very low electrical resistance that is best. The lower the resistance, the faster a static mast charge dissipates to the water.

Jim...

PS: The house grounding clamp is not for lightning, but for not "stealing" power.

It does create a zero volt potential with respect to the water and helps bleed static from the surrounding air which allegedly lowers the risk of lightning in your immediate area. Lightning will go where ever it wants, Period. It does not have to follow any defined law that we make up.
That clamp is used to create a zero volt potential between your incoming copper water connections and the ground rod(s) that are part of your service entrance from the local utility. This stops the possibility of a ground loop where two items being of unequal potential could cause an electrocution.

 

[JamesG161]

Lightning does follow known laws of science, period.
The "random" nature of strikes is from the yet unmeasured local weather effects, which appear to be "random".
To a much larger extent, the unpredictability is the Voltage potential between Sky and earth/water.

The key avoidance is still to make your boat appear electrically like the water around you, thus minimize your chance of a hit.
This is the good link on lightning discussions.
https://forums.sailboatowners.com//index.php?threads/newbie-lightning-protection.179404/
______

Now Im asking two questions: 1) if it is unsafe for a water ground clamp to serve as a lighting ground; 2) how to fix the disconnected fitting.

My attempt to answer...
Answer to #1...
Safety for your boat and crews is always a key. It is hard to comment on that in a forum. It is perhaps as safe as another type connection, if maintained as to conductivity.
Answer to #2...
If you read the Nigel Calder PDF file on my post #5 in the above SBO link, you will get more info on how to fix it.

Good Avoidance for you and your boat!
Jim...

 

[Chris87]

Every response in this forum is very informative and helpful - thank you! The links especially.

I'm going to look at a bigger gauge grounding wire, or possibly grounding strip as Roy mentioned (grease bolt/terminal, straight shot, groove floorboard, running above the beam and to a drilled/tapped new hole, etc.). As some of you pointed out, I was kind of baffled at how the current wire and fitting looks too small for whatever it was originally connected to under the floorboard... Will G's response made me conduct some more research: https://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems. Heres a pic of what I found.

I'm going to take all information and come up with a solution. Thanks, everyone!

 

[JamesG161]

From the West advisor you linked...

The lightning ground needs to be a direct DC connection to the keel or to a ground plate to handle currents due to lightning strikes.

No way to do this, sorry if WM thinks a 4 AWG or your keel will handle lightning strike current.

BTW a direct strike , not a side branch, will blow a hole in your Fiberglass hull and sink the boat. The concussion caused by that strike, ionized air sudden expansion, will most likely kill anyone anyone near the bolt.

So lessen your chances of a direct strike, by WM advice, which is really a ABYC standard.
Jim...

 

[walt]

No way to do this, sorry if WM thinks a 4 AWG or your keel will handle lightning strike current.

BTW a direct strike , not a side branch, will blow a hole in your Fiberglass hull and sink the boat. The concussion caused by that strike, ionized air sudden expansion, will most likely kill anyone anyone near the bolt.

You must have a link for the backup on that???

If you want, I will go through the effort to find Dr Ewen Thomsons paper from a while ago where they looked at the total energy deposited in a wire carrying the lightning current for the duration of a strike, found the temperature rise from that energy and compared that to the wire melting point. In that study, 8 gauge was the minimum. 4 gauge is a better choice. I think WM is correct. I will dig up my reference if you dig up yours..

However, for a given weight, a metal strap has lower inductance than a round wire and therefore is somewhat better for a lighting ground.

 

[Brian D]

Interesting you posted that image. I was going to ask if by chance, the original owner may have had SSB/Ham radio aboard. That is usually where most hams/SSB users ground their radio(s).

 

[JamesG161]

You must have a link for the backup on that???

What size wire will pass 20,000-30,000 Amp?

https://www.quora.com/What-is-the-voltage-and-amperage-of-an-average-lightning-bolt

Science based on Ionization of Air.
Jim...

PS: Closer sky to ground distance than 7km, will of course be less amps

 

[walt]

What size wire will pass 20,000-30,000 Amp?

I suppose if you are looking at the issue in terms of how your DC battery runs a light bulb that would mean something.

The lightning event is a little more complicated than DC as its a short duration time wise. If you are interested in the the real science behind that, below is the paper from Dr Thomson (down load the pdf)

www.mikeholt.com/download.php?file=PDF/Thomson1991.pdf

Look under section D "down conductor damage". Figure 3 shows the temperature rise for the action integral for a few wire gauge sizes.

 

[CarlN]

This wire is almost certainly a bonding wire for galvanic corrosion not lightning protection. It's too long and not straight enough for lightening. Lightening will not follow sharp bends (although this wire could reduce the electrical potential pre-strike). The ABYC standard E2 on bonding specifies an 8 gauge wire connecting all underwater metal - they look like the wire in the picture. The idea is that with everything tied together electrically, the zinc will go first - assuming you replace your zincs. Bonding is not done as much today, maybe because the "hot marina" problem is such a big issue now. 30 years ago, more boats were on moorings and many boats in a marina were not plugged in all the time. My boat still has the bonding wires. I occasionally check the bonding screws to makes sure they are tight and not corroded. I find that people who know more than me about this are split about 50/50 about whether to bond or not. Although most agree that you should bond everything or nothing.