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Fitting hull-earth bonding


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There are a number of topics on why there should be a connection between the hull, the negative terminal of the 12V system, and the earth of the 230V system. However, I am struggling to find information on how to connect the systems. The engine is of course connected to the negative of the 12V system but it is mounted on rubber such that there is no connection between hull and earth. Are there any guidelines on how to make the connection?

My plan was to remove the paint on a small portion of the hull and solder a stainless bolt to it which I am planning to connect to battery earth using a crimped cable. But I wanted to check whether that is a stupid idea for any reasons that I haven't thought of.

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The engine mounts used by beta are claimed to provide a good earth.  If not then you can bolt a braided wire between the engine block and the hull earth point.  As to soldering, the wire must be big enough to carry the fault current, so a little bolt soldered on is a bad idea.  I drilled a 10mm hole into the engine bearer and used an m10 bolt to earth my 90mm2 negative cable.  I used 90mm2 for wiring up the inverter and so ordered an extra metre for the earth wire. 

  • Greenie 1
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If you have a landline connection, I'm presuming you have a GI fitted.

My boat is wired as :-

230v earth through GI, outlet side to MCB and to hull.

Earth cable from MCB to hull at same point as other

cable between neg on battery, to hull at same point, surmising that they ,domestic and starter battery are joined at the neg connection 

there is an opinion that the 230v earth and the 12v neg/earth should be on separate earth points, not sure why.

Best to drill and bolt a connection somewhere.

 

Bazza

Edited by Bazza954
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29 minutes ago, Till Hoffmann said:

There are a number of topics on why there should be a connection between the hull, the negative terminal of the 12V system, and the earth of the 230V system. However, I am struggling to find information on how to connect the systems. The engine is of course connected to the negative of the 12V system but it is mounted on rubber such that there is no connection between hull and earth. Are there any guidelines on how to make the connection?

My plan was to remove the paint on a small portion of the hull and solder a stainless bolt to it which I am planning to connect to battery earth using a crimped cable. But I wanted to check whether that is a stupid idea for any reasons that I haven't thought of.

The highlighted sentence does not make sense, without the negative connection your starter would not work. The engine does not need to be directly  connected to the hull, it is already connected through the neg lead which eventually goes to earth.

one of the forum genii will be along to make it more clear than me, probably !!

bazza 

Edited by Bazza954
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27 minutes ago, Bazza954 said:

there is an opinion that the 230v earth and the 12v neg/earth should be on separate earth points, not sure why.

Best to drill and bolt a connection somewhere.

 

Bazza

I think the reasoning is; if that single earth point became detached from the hull, you would not know, as everything would still work, but any subsequent 230v fault to earth would put AC voltage on the neg 12v wiring. Bad!

Two ajacent earth points, while not perfect, possibly safer.

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1 minute ago, Rick-n-Jo said:

I think the reasoning is; if that single earth point became detached from the hull, you would not know, as everything would still work, but any subsequent 230v fault to earth would put AC voltage on the neg 12v wiring. Bad!

Two ajacent earth points, while not perfect, possibly safer.

Ta, now I know something else !!

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2 minutes ago, Rick-n-Jo said:

I think the reasoning is; if that single earth point became detached from the hull, you would not know, as everything would still work, but any subsequent 230v fault to earth would put AC voltage on the neg 12v wiring. Bad!

Two ajacent earth points, while not perfect, possibly safer.

That is indeed the reason. 

The two bonding points (DC -ve and AC Earth) should ideally be in close proximity to each other but be separate bolts. 

Attempting to solder a bolt to the hull is a dreadful idea. Either have a couple of large (say M10) bolts welded to the hull or bolt them through a cross member.  

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There is I believe a safe way to do it using one bolt.

Drill through the steel where you want to attach the bonds put one on one side of the steel and one on the other. This way if they do separate from the hull they don,t remain connected to each other .

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Thanks for all the input.

One more question: If I drill a hole into part of the hull, I will want to remove the paint in the vicinity to ensure a good connection. How do I stop corrosion? Just painting over afterwards doesn't seem very maintainable.

@Chewbacka, the engine bearer is a great idea! I was struggling to find places that I could drill into that weren't external.

@Bazza954, yes, the engine is connected to the negative terminal of the battery as the starter would not work otherwise. However, the engine itself is mounted on non-conductive material such that the hull is not connected to the negative terminal. I initially assumed that the screws that hold the engine in place would create an electrical connection to the hull but that is not the case.

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3 minutes ago, Till Hoffmann said:

Thanks for all the input.

One more question: If I drill a hole into part of the hull, I will want to remove the paint in the vicinity to ensure a good connection. How do I stop corrosion? Just painting over afterwards doesn't seem very maintainable.

@Chewbacka, the engine bearer is a great idea! I was struggling to find places that I could drill into that weren't external.

@Bazza954, yes, the engine is connected to the negative terminal of the battery as the starter would not work otherwise. However, the engine itself is mounted on non-conductive material such that the hull is not connected to the negative terminal. I initially assumed that the screws that hold the engine in place would create an electrical connection to the hull but that is not the case.

Ah, now I see !! correct, no connection as usually anti vibe material on mounting not conductive, hence the lead from neg battery to hull.

 

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2 hours ago, Till Hoffmann said:

One more question: If I drill a hole into part of the hull, I will want to remove the paint in the vicinity to ensure a good connection. How do I stop corrosion? Just painting over afterwards doesn't seem very maintainable

It's as maintainable as any other painted part of the boat, surely?  Drill the hole, clean a small area at the top of the bearer, insert bolt from below with washer above (thereby connecting to the cleaned bit) and a nut to secure. Now prime and paint the washer, bolt head and bearer. 

Welding might be simpler but it still requires priming and painting. 

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Tapping the hole with a thread for the bolt being used will give good metal to metal contact and resist rusting once the bolt is tightened up. If it is a plain hole then the surface around will need to be clear of paint to get good contact. A smear of vaseline over the connection once done should give some corrosion protection. As you should have on the battery terminals.

Jen

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When you do make the bond, please label it so a future owner or maintainer knows why it is there. The DiY sheds sell earth clamps for pipe bonding. They are V cheap and come with a nice metal label which is just right for this job too.

 

N

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On 15/05/2017 at 14:43, Bazza954 said:

The highlighted sentence does not make sense, without the negative connection your starter would not work. The engine does not need to be directly  connected to the hull, it is already connected through the neg lead which eventually goes to earth.

one of the forum genii will be along to make it more clear than me, probably !!

bazza 

It is normal practice to have the negative battery lead bonded directly on the engine or the relevant terminals on the starter and alternator. Rather than relying on a conductive path through/along the hull.

For info, there are starter motors and alternators where the negative terminal is not electrically connected the respective bodies.

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