Earth cable to seacock!

J

Jonathanpaul

Well-Known Member
Joined
8 Mar 2006
Messages
86
Location
Near Woodbridge
Visit site
I am checking over the wiring and adding new switch panels to my 1986 Beneteau First 26 and have come across a cable not attached behind the switch area leading back to the seacock then taped to that as an earth. If its needed what do I connect it too? One other thing can I put one large Buzz bar with all the netural attached then off back to the battery? at the moment they are rammed into acouple of blocks, nasty mess!!
 
Sounds like it was either part of an equipotential bonding system between all the exposed hull fittings originally connected to a hull anode, or, more likely, someone's attempt to install an earth for a radio or a shorepower system. In the latter case a proper earth shoe would be a far more efficient & safer bet.

As to your negative busbar idea: yes it would be the best and it is in fact the way most modern manufacturers go these days.

Steve Cronin
 
As Steve said and then you earth the negative Bus bar. This can be taken to your sacrificial anode, assuming you don't have a dedicated earth to sea.
 
If you're in a marina, get a Galvanic Isolator (GI). This will have the effect of isolating you from the battery which consists of your boat, the pontoon and your neighbour's boat(s).

There is no need to connect the -ve busbar to ground as a one-off action. A bonded anode to protect your seacocks on a GRP boat WILL work but as others have pointed out in the past, is not essential for unless there is a severe leakage or you havn't a GI, the actual rate of corrosion will be slow - but NOT NIL!

I once nearly lost a "P" bracket due to stray galvanic currents in a marina so i did both: the GI AND a bonded anode system.

We need to have fulld etails of where the boat is kept and how the power (if any) is connected before giving accurate advice.

Steve Cronin
 
Not an expert in wiring so will defer if mistaken. However, was guided by an expert to take the -ve to earth to protect the 12v system circuits from faults/degradation. Sea cocks and other non electrical units are not included - i.e. not a bonded system. Steve, are you saying the GI protects the 12v system (as well) - thought it was for AC shore power protection? Thanks.
 
We were advised to earth our differential beacon (one of the first in the UK) to improve the poor coverage at the time, we used the seacock for just that purpose and it worked, it is still there as is the beacon but whether we need it now is debatable.
 
Why ?? Unless as another says they tried to use the SC as a earth to sea point.

I would suggest that if the fitting is bronze ... it is actually a bad thing to do as it will destroy the fitting - why ? because it is not connected to anything until that cable is bonded to it ... now it's in a circuit.

Personally - I would rip the cable of it and leave it isolated.

As to Bus bar - yep good idea .... (i was going to do same - but my local B&Q when in UK last had sold out of the long ones .... so it will have to wait till I can get into electrical wholesalers out here ....)

Of course now I will be shot again .... not only have I connected 12v dangerously ... but now I risk all by disconnecting your seacock !!! And to cap it all mentioned the dreaded B&Q !!!!

/forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/tongue.gif
 
Nigel - I concur with you ...

If you are on a swinging mooring - no shore power, integrated battery chargers etc then there is little reason to "earth" your 12v system to the sea cock ...
Ours isn't bonded to the seacock and we don't have an anode on the hull - just one on the propshaft ...

Either tape the ends to insulate them or remove the cable ... which ever way
 
I don't want to start a controversy here but the old boner about "earthing" is a regular subject with arguments fore and against. My own belief for what it is worth is as follows.
Firstly for electrolytic protection if you are going to protect your seacocks and other skin fittings they should be directly connected to anodes placed as near as possible to the fittings. There is a good argument to connect all such fittings and anodes provided that the anodes are inspected regularly and replaced when necessary. Be aware that if the anodes are depleted one of the skin fittings may well then become the "anode"! So even here there is an argument against bonding everything.
Secondly I have never heard a logical argument for connecting the SERVICE battery negative to the bonded skin fittings that convinces me that it is either necessary or advantageous to do so. There are arguments against in that it will cause earth leakage, etc but I frankly don't know why I should, I never have, so I don't (if you see what I mean) I am also instinctively opposed to connecting all the on board systems to a circuit that carries stray currents from elsewhere and wonder if indeed this is what causes corrosion in onboard systems... dunno.... What I do know is that when I leave my boat and isolate the batteries the onboard circuits are totally isolated, not connected to an anode carrying stray currents...

Thirdly, the ENGINE START battery negative, being earthed to the engine block is probably indirectly earthed through the propshaft anyway..... Don't see a problem with this and see it as a necessary evil, but I would always isolate this battery when not in use anyway so the situation is not permanent. The key point being that it is not connected to the service battery and thus to every circuit on the boat. Of course if you leave a changover switch on "both" or use the service battery bank to start the engine you will probably connect to earth the same way, but this is temporary and should not be necessary unless in emergency.

I have always been taught that the service battery earth should never be attached to anodes directly or indirectly and tend to follow this practice. Of course none of this applies to AC systems which is a seperate subject and should, for safety reasons, be SEPERATELY earthed. Again, not through anodes.

I would be very interested to hear from any marine electrical engineers out there what they think rather than just peeps repeating what they have heard elsewhere. I am a mechanical engineer rather than electrical and would be interested to be corrected if wrong.
 
Curious ...

Do you not have a common earth between engine and service batteries?
If not - how do you independently charge your batteries from the engine - do you have a double pole switch?
 
Good question. Yes I have double pole isolator on service battery bank. I guess if I didn't everything would be permanently connected anyway. Engine battery is just single pole. I have always thought it an excellent thing to do to completely isolate all services from earth when the boat is in the water and not used. Not that I have thought about it extensively, just taught in shipbuilding that it is good practice!
 
The GI is to isolate ANY metal in contact with the sea on your boat from the galvanic effect of dissimilar metals in other people's boats and the pontoon.

Would elaborate but only have a few seconds.

Steve Cronin
 
But why bind a seacock that in normal course of events is not connected anywhere else to ever carry current ? unless your "pee" is electric.

Near all seacocks are connected with electrical neutral plastic pipes ... only conductor is possibly the medium flowing through it ...

Me ? I don't bond anything to anodes etc. except shaft and block - All else is isolated ... but we won't go into my "quirks" again ...
 
I think we began by talking about "stray current" corrosion and protection and have now shifted the debate into cathodic protection/bonding. FWIW, on the former, I use insulated returns from each device back to a common 'grounded negative bus' connected to the battery.

When Steve started talking about galvanic protection it made me think. Since I have no shore power and no AC I've not done anything about GP. Whilst I realize the potential risk of galvanic action between dissimilar metals emmersed in an electrolyte, I've thought the risk not worth the effort. Like sbc says, why create a problem by bonding isolated, non current using units when my boat has been functioning fine in this regard for 20+ years. However, if I had shore power, lived on marina, used an on-board inverter, was AC dependent I would definitely fit a GI; to protect from poorly maintained shore power supplies and other vessels.

So, if you only have DC is it fitting a GI still a wise precaution?
 
I agree the original post was about DC only and has now switched to AC supplies.
As I understand it a galvanic isolator merely protects you from a potential problem when connecting AC to shore supply. It goes in the earth (green) cable and ensures that small stray currents don't flow through it while a big one will still protecting you from stopping a 220v packet if there is a short.
If you are on a swinging mooring and have a DC only supply these devices are totally irrelevant in my opinion. When Steve Cronin has more time I will enjoy reading his explanation of how a GI would help if you have a 12v boat on a swinging mooring.
 
My point exactly ....

Lets add another point ...... when a ship is docked in harbour - it is advised to switch OFF its impressed hull current ..... because of possible inter-action with other vessels and also with shore equipment etc.
Second the more I read - the more I hear about this whole subject - the more I come to opinion that the more bonding and playing around with coupling up various items on a boat - the more trouble and risk ... especially if one link in the "chain" fails or is poor. My reasoning is to leave them isolated .... you can look at my anode and items on my boat .. afloat 12 months a year for last 4 yrs etc. - owned for approx 8 ..... never changed anode, never bonded anything ... no pitting, no galvanic corrosion evident ... anode still about 60% and that is literally same as day I bought her ....

So why create a potential (sorry about the pun !!) for trouble ??

I don't advocate my way for others unless they have similar as me ... but let me say something ... my boat has been marina based with 240V supply to charge batterys. I also use 240V supply when available when visiting other locations ... I have had electricians on the boat ... tut tutting and then checking for faults to point out ... but after checking basically telling me that it's fine .... no problem.
 
It's not a quirk, it's a reasonable plan so long as you inspect your cocks periodically (if you pardon the expression) and are convinced that they are not suffering. Bonding a seacock at one end of the boat to an anode at the other end is NBG anyway. You need anodes near enough to your cock (here I go again) to ensure current will favour the anode. I had a guy recently with a whole bunch of skinfittings near to one another all bonded to one another and an anode that was on the other side of the boat 20 feet away.. All lovely bronze bar one nasty tonval thing. bonding them all together ensured that the tonval one acted as an anode for the rest and after only one season the fitting was on the point of disintegration. Now I hate tonval... it aint bronze and should never be on a boat anyway, but bonding accelerated it's demise.
 
You must log in or register to reply here.

Share this page

Top