Single pole and 2 pole conflict

I have an aluminum boat, so you will understand that I go to sleep and worry about different kinds of corrosion. What I going to tell you is not abyc, I care for my boat, I avoid other safety issues by not having them. If others disagree, let me know with reasons, I don't mind learning, but I rather keep it kiss and bulletproof.


DC circuits should be isolated, no ground, everywhere and everything. My engines use air for starting and have not electrical to them. Sensors and alternators have isolated grounds. There isolators on shaft to engine. I have no AC to Dc chargers since these go bad and eat your aC/DC isolation. Ac circuits and all appliances are isolated from hull, ground on boat is stand alone, isolation transformer takes care of incoming ground and lines. This way stray currents ac or dc from other boats dont seem to affect my boat.

 

The chassis of Every appliance is grounded to the hull.. earth. Ac and DC...Marine equipment AC and DC is internally electrically isolated from its chassis. If your AC motor floats free of earth on rubber mountings, no grounding strap, develops an internal fault that cannot be dumped to earth, you will be electrocuted when you touch it because your body is the conductor to earth. The question I have I why you need a copper wire to shore earth when the hull, in saltwater, is earth ?

 

OK, I thought the diesel/electric loc was a good example, but I'll explain.

The hull being the 4th best conductor after gold, silver and red copper, it is safe to assume that whatever you are doing inside, the outside will not have any voltage potential vs the surrounding water, so there cannot be any stray currents.

However, if a substantial amount of water would be present inside the hull (rain, leakage, accident etc), there might be a path for electrical current other than the wiring, in which case stray currents would be possible.

Shore power is a different situation that has been discussed at length in several other threads, among which a rather hilarious one where a character called Capt. Littlelegs was my sparring partner.

 

I can understand the locomotive analogy, but....It must be assumed that a boat will always have water inside...tanks, 100 meters of wet plumbing, engine plumbing ......

 

No, not that water Michael, unless someone uses the plumbing as ground, which saves wire but is not a good idea.

I was more thinking of a full bilge, a pump not working but still connected to the 12V supply or extended cables underfloor without waterproof isolation.

 

One of the details that always causes problems for me...and Ive now been sailing aluminium yachts for near 30 years , is this kilometers of plumbing, fittings, pump shafts, heat exchangers, dissimilar metals, in seawater. .....whoa !!!! that can be affected by stray electricity. I never really notice its effect outside, underwater. Its always inside...all the small detailing.
As for the original post...Be diligent about stray dc current...always twin pole breakers for easy isolation of circiuts and always an early warning diode type ground fault indicator system. Today's fix was a DC motor ground to earth...Brush filing dust across the brush chassis. A vacume cleaner and a paint brush fixed it.

 

I'm with CDK on this. An isolating transformer is for shore power protection only. I still don't understand what he means by single pole, etc. Sounds like either nonsense or a bad translation.

 

Single pole is correct. I dont often hear it . All automotive gear is single pole. Single wire on oil pressure sensor for instance.

 

You are totally wrong. The block is the negative, the second pole. There can't be voltage or current withoug at least two poles. Go read a primer on electricity.

 

most all automotive switches are single pole switches, maybe that where it comes from

 

Electrical continuity and Bonding

I am relatively new to the boat building game, but I have many decades of experience with similar problems.
(The 1984 in my name is the date when I started my own R&D company.)

Metal hulls can be a common ground, but in case of a plus minus power supply, the ground must be floated, otherwise the common ground pulls your plus minus voltage level off.

Bonding is OK between dissimilar metals. This way you have reduced the chance for galvanic corrosion. There is a special epoxy that has 0.005" glass balls mixed into the basic material, to guarantee the minimum film thickness of the bonding agent. This way there is no direct contact between the two dissimilar metals. (Steel bonded to aluminum.)

Electrical isolation of different systems is desirable. Vibration isolation is a good practice. This provides you with electrical isolation also.

On large aircraft, at every joint, you must have a ground connection between the connecting parts, (regardless of the bolts and rivets) to ensure electrical continuity. (They measure this resistance in 0.001 milliohm resolution.)
This is one way to prevent galvanic corrosion.
Galvanic corrosion requires three things to be present: Dissimilar metals (anod and cathod) and an electrolyte.. (A liquid to conduct the electrical charge between the two materials.)
Take any one of these three away and no harm will come to your metal boat's hull!

An isolating transformer only isolates you from the AC supply line. However, your boat's hull could still be consumed by the galvanic process on the down side of the isolating transformer by the DC current coming from your electronic gadgets. It is the DC current that will eat your boat in no time if it is uncontrolled.

It is possible to have complete electrical isolation from the hull or the superstructure. You just need to run extra ground wires, and have electrical isolation of all electronic gadgets from the frame.
Regards,

Stephen I. M.

Ps; Single pole means that you are switching only one line, Double pole is switching two lines.. One can be positive the other can be negative or different voltages etc.
Switches are :single pole single throw, single pole double throw, double pole single throw etc...

 

This is simple galvanic corrosion. The details/properties of metals/materials being used inside an ally boat can have a major affect.

Here is what occured on one of our boats.


This is corrosion inside a tank. The cell was set up between the plate 5000 series and the stiffeners 6000 series. The eletrical potential between the 2, whilst low, below what is "normally" considered acceptable, clearly was not. Solution, all stiffeners on the outside of the tank, problem solved.

You need to be very carfeul using copper piping in ally hulls for example, these must be painted, since condensation on the bare copper pipe drips down onto the ally, kills it!

 

...note when installing a galvanic isolator, use the one that have capacitors in them, it increases the ability to conduct current (AC) at low levels and still not bias the diodes.

AC low current basically does not cause electrolitic corrosion, it is the DC that causes it (not let the sparks fly...some will disagree with this statement, but it is still BASICALLY true).

You should also install RCD ( a residual current device) at the power to the boat, first thing in. This will trip is there is high AC leaking through the galvanic isolator.

 

re single pole and two pole, have a look at the senders in the engine, if they have two wires they are two pole if not they are single pole (earth directly to the block/head, as the case may be. True marine equipment is ALWAYS two pole sensors. (The starter also will have two wires to it instead of just one start cable.)

 

Sounds like either nonsense or a bad translation Single or 2 pole is basic, we learnt about as kids building cats whisker transistor radios in match boxes. It only get complex installed in aluminium hulls with multiple power systems.

Yanmar Marine state the 6LY3 380hp engine with electronics control are 2 pole controls but the starter is single pole. The 6LY3 with mechanical controls has a 2 pole starter - Yanmar don't offer the reason why but the conversion of the former to 2 pole has yet to happen.