Should I have a switched negative ground?

[hzcruiser]

That's correct, only this wasn't a particular concern for the OP and I didn't want to go into too many off-topic details.

[Wotname]

Originally Posted by hzcruiser

That's correct, only this wasn't a particular concern for the OP and I didn't want to go into too many off-topic details.

Good point -

[hlev00]

Stu - Thanks for the pointer to Maine Sail / Rod Collin's post. I had not seen that. I am more or less doing this this year. It will be good to compare my planned digram to his. I hadn't decided what to do with the switched ground. Looks like I can simplify things and work it out of the system.

Harry

[Mike Burch]

Indeed, the RF ground from the antenna tuner should not be a DC ground. The cheapest way to isolate it while still letting the RF through is to use the high-voltage capacitor from a dead microwave oven in series with the lead from the tuner to the earth plate. You need a high-voltage capacitor, but do not be tempted to use an electrolytic capacitor—they generally have measurable impedance at high frequencies.

Another point about wiring a steel boat—be very careful not to drop any bits of copper wire (easy to do when stripping off the insulation) into the bilge. In the presence of salt water, copper will eat steel.

[ErnestV]

Originally Posted by mitiempo

One solution on a metal hull is to switch the negative to the starter/block off when not running the engine, as it can be difficult to isolate an engine and shafting from the hull. This can be accomplished with a solenoid wired to the start switch's run position. This way the connection is only made when the engine is running isolated the rest of the time.

The drawback here seems to be when the ignition that drives the solenoid is switched off before the engine comes to a full stop - this might very well fry the alternator diodes. I believe the Sterling ProProtect should safeguard this.

Originally Posted by mitiempo

Ideally all wiring on a metal boat avoids the hull connection. As noelex points out the ideal is all DC on double pole breakers, disconnecting both positive and negative. Valid only if you don't use an isolation transformer (in isolation mode), and you should have at least a galvanic isolator ("a.k.a. "zinc saver").

All pumps etc should be isolated from the hull as their cases are typically negative grounded.

As far as I know this is only valid for the DC circuit - the shore power PE should very well be connected to "earth" (i.e. hull and/or engine). If you maintain an isolated DC circuit PE should NOT be connected to DC negative, as to my current (limited) knowledge.
(Note - valid only if you don't use an isolation transformer in isolation mode, and you should use a galvanic isolator)

[mitiempo]

Originally Posted by mitiempo

That is most definitely incorrect.

One solution on a metal hull is to switch the negative to the starter/block off when not running the engine, as it can be difficult to isolate an engine and shafting from the hull. This can be accomplished with a solenoid wired to the start switch's run position. This way the connection is only made when the engine is running isolated the rest of the time.

Ideally all wiring on a metal boat avoids the hull connection. As noelex points out the ideal is all DC on double pole breakers, disconnecting both positive and negative.

All pumps etc should be isolated from the hull as their cases are typically negative grounded.

This is what I actually posted. Not sure how my post became modified. I was referring to DC, not AC.

[Stu Jackson]

Originally Posted by hlev00

Stu - Thanks for the pointer to Maine Sail / Rod Collin's post. I had not seen that. I am more or less doing this this year. It will be good to compare my planned digram to his. I hadn't decided what to do with the switched ground. Looks like I can simplify things and work it out of the system.

Harry

You're very welcome, glad to share. That's why I kept the link to it handy!

[Oceanride007]

[QUOTE=seabreez;3384343]The ground should not be switched. It is dangerous. There should be one grounding point and all grounds should go to that point and not through the hull for the return to the ground and to the battery. The engine should be grounded to that point.



I dis agree, According to your electric code in Nth America, which is not known for considering hull corrosion. But I will point out that Amel switch the negative to Engine and shafting on start up only.



I'm prepared to say that no commercial ship, ever has any phase DC, AC, High Voltage AC connected to hull at any time, except maybe when receiving shore power which is a rare event, tugs do it regular, different game, only for reason of shore code, I presume. There is very good reason, why Engineers are diligent to ensure, any phase even if high resistance (Like < 1 Meg) does not stay around for long.

[nofacey]

Sidebar....for metal hulls, it is important that alternators have isolated grounds, otherwise creates stray current corrosion.
- had to do a quick replacement one time, didn’t get that detail right, saw impact PDQ.

Steel hull with all grounds lead to common ground on engine block, no switch. Isolation transformer on shore power.

[Nicholson58]

We have all electronic devices and the windlass provided with + & - interrupt switches. The windlass totally interrupted and isolated from the boat means the galvanized chain lasts longer. The electronics are more protected from lightning induced surge if they can be separated from the ground grid but the air gap two pole switches need to be very close to the protected device. Suggest you also provide a large multi pin connector to disconnect all mast wiring.

Our boat also has solenoid operated main breakers from key switches on the main panel. These isolate both plus and minus when tripped.

[hzcruiser]

Originally Posted by nofacey

Sidebar....for metal hulls, it is important that alternators have isolated grounds, otherwise creates stray current corrosion.
- had to do a quick replacement one time, didn’t get that detail right, saw impact PDQ.

PDQ? Had to look that one up, as it's not really a sailing term -- pretty darn quick. Too hard to spell it out?

Either way, you mean one should have a dedicated ground wire from the alternator to the starter battery? That's always a good thing, however, isolating the alternator from the engine might be difficult and I don't see where stray currents would flow?

[noelex 77]

Originally Posted by hzcruiser

isolating the alternator from the engine might be difficult

Isolated alternators are common and come standard with many marine engines.

Originally Posted by hzcruiser

and I don't see where stray currents would flow?

If the engine is connected to the negative supply then in many installations the negative supply is therefore connected to seawater via the prop shaft or saildrive although alternatively it is possible to electrically isolate the drive train in some cases. If there is second electrical connection to the seawater, for example via the anchor windlass and anchor chain, or the autopilot via the rudder, then current will flow between these two points, as they can never be at exactly the same voltage (even two negative connections). This will cause stray current corrosion on one of the metal parts (drive train, rudder, or ground tackle in this example) or at least more rapid corrosion of anodes designed to protect these metals.

[hzcruiser]

Originally Posted by noelex 77

[...]
If the engine is connected to the negative supply then in many installations the negative supply is therefore connected to seawater via the prop shaft or saildrive although alternatively it is possible to electrically isolate the drive train in some cases. If there is second electrical connection to the seawater, for example via the anchor windlass and anchor chain, [...]This will cause stray current corrosion on one of the metal parts [...]

I agree with you with regards to other parts that are connected to the surrounding water, only the alternator ground should not fall into that category? Its ground (on my Perkins) is through the chassis which is bolted to the engine block.

All that said, I'll check how good that connection really is by using an Ohmmeter tmrw.