Boat rewire: Am I going to die

[deblen]

Originally Posted by mikedefieslife

The electrical system on my boat is a mess. Overloaded bus bars, unfused positives, chaffed battery cables, missing grounds, uninsulated terminals in the bilge, cheap self combusting Chinese LED strips, to name just a few of the issues I've spotted.

I plan to address it this winter with a bit of a rewire, and would like something of a sense check on my diagram below. How badly am I going burn and die?

Just knocked up in Illustrator so not a really schematic, but should give an idea of what I'm proposing.



Appreciate any feedback on further simplifying it, or any additional safety features I've missed.

You'll notice that my boat does not have a grounding plate. I plan to use the engine block as a common ground. I should have drawn that a bit clearer, but that's what it is supposed to be.

Nice plan!!
Some people put a 2-300 amp fuse @ the Start bat. feeding the starter motor circuit.
An Emergency start bridging switch could be wired between the positives of the House & Start bats.

Len

[thunderhoof]

Regardless of the topology there are general wiring rules you should follow:
1. Determine the maximum current in each wire and the wire length then size the wire accordingly allowing for a 0.25 to 0.5 volt drop in normal use.
2. Use a "multi-star" configuration rather than "daisy chain" for connecting multiple equipments to a single breaker. That means - from a breaker or ground bus run individual wires to each piece of equipment.
3. It is very important to avoid common currents in the ground path. That means - assuming the alternator neutral (engine block) is your ground reference, each item should be brought to a ground block near that point. If you must have a second ground block, say near the instrument panel, use a heavy wire (say 2-4 AWG) to the main ground block. This avoids voltage spikes that can cause unwanted noise in electronics.
4. In my monohull the rig is lightning grounded by 6 AWG wire in a separate configuration that is tied to the keel. I believe a single wire should connect the main ground block to the keel connection. There is debate on how to do this but there must be a stable way to dissipate static electricity accumulation on electrical equipment.
5. Use wire markers and keep a list.

[foggysail]

Originally Posted by CarinaPDX

As long as you are operating in salt water it may not be too important, but in fresh water you should have all thru-hulls and metal underwater fittings bonded together, and usually to an anode such as a large zinc. ABYC calls for this for a very good reason: protection against Electroshock Drowning (ESD). Our local ABYC rep lost his son to ESD because he was swimming near a boat with a leakage path between Line (hot) AC and an underwater fitting. The propeller/shaft isn't a good ground, and any anode would be small and needing constant replacement. Step up and put in a proper ground plate.

Greg

I thought it was only fresh waters that is dangerous to swim in/near marinas

[foggysail]

Originally Posted by billknny

A couple of things...

An engine in general makes a poor negative bus bar and a poorer yet lightening ground, and those two systems should NOT be the same anyway. You can not count on an engine actually being grounded to the water, if that is what you are hoping for. And if you DO send a lightening strike through the engine and transmission, count on all the bearings and gears to be welded together.

Yes, an engine is not intended to be a bus bar. The DC grounded conductor should be tied to the engine's negative terminal which in most cases is the engine's frame along with the bonding wire/bus as noted by ABYC. The bonding system should only see currents during fault conditions.

I doubt there would be any damage to an engine/transmission in case of lightening. Do you have evidence to support such claims?

[CarinaPDX]

Originally Posted by foggysail

I thought it was only fresh waters that is dangerous to swim in/near marinas

Fresh water is extremely dangerous because it is a poor conductor of electricity vis-a-vis our bodies, so in an electrical field we provide the path of least resistance. Our bodies are approximately the composition of salt water so while we are not a preferred path in sea water we still conduct; it is much less likely that we would experience ESD as a result, but I wouldn't say it couldn't happen - particularly with higher voltages present (240VAC, 480VAC). People have been killed by reaching into sea water to recover dropped tools that are still live, whereas a bonded boat might trip the breaker. OTOH we all should be using GFCI sockets for power equipment.

Greg

[mitiempo]

Originally Posted by CarinaPDX

No disagreement. Still, there are folks that resist bonding and the resulting need for a zinc and regular replacement in salt water, and given that ESD is much less of a problem in salt water that may not be too crazy of a position (not acceptable to ABYC for sure). But the great safety hazard of ESD in fresh water, and the liability associated with it, argue strongly for bonding. I think that once installed it is more effort to keep changing it for conditions than just replace the zinc on a regular basis. I just note that I have known many cruisers who are against bonding, whether sensible or not, and I have seen boats where the bonding systems were undone. I want them to know of the greater danger in fresh water.

Greg

Bonding of the through hulls in itself has nothing to do with ESD, which is caused by AC faults, not DC faults. Bonding of the through hulls ensures that they are at the same potential. This relates to corrosion of underwater metals.

Bonded or not there is no danger due to this in either fresh or salt water.

ABYC requires the AC ground (green wire) be connected to the DC negative bus. This gives an alternative path to a AC fault at the dock if the shore side ground is faulty or non-existent as well as a path for a fault away from the dock when using a generator or an inverter.

ABYC now requires an ELCI on new construction. This is in effect a whole boat GFCI which further increases safety. ABYC still requires the AC ground to DC negative bus connection with an ELCI.

[CarinaPDX]

Intent is one thing, possibilities another. By connecting the AC ground to DC ground and hence the bonding system, a return path is available through the water between a "hot" Line in the water and bonded below water parts, and the potential for ESD thus exists. Of course not likely as a dropped cord or device would more likely short to its own Neutral or Ground, and hopefully kick out a breaker but better a GFCI.

As an alternative, or better in addition to an ELCI, I am a firm believer in an isolation transformer. With the secondary Neutral and Ground lines connected to the sea water interface there exists a common local ground, independent of the Neutral and Ground shore power. And of course any stray DC is blocked, although that could be taken care of with a galvanic isolator. Most older cruising boats don't have any of this equipment, or a functioning bonding system for that matter. A few have added some GFCI outlets. But I think the situation is pretty bleak in this regard.

Greg

[rwidman]

Originally Posted by CarinaPDX

No disagreement. Still, there are folks that resist bonding and the resulting need for a zinc and regular replacement in salt water, and given that ESD is much less of a problem in salt water that may not be too crazy of a position (not acceptable to ABYC for sure). But the great safety hazard of ESD in fresh water, and the liability associated with it, argue strongly for bonding. I think that once installed it is more effort to keep changing it for conditions than just replace the zinc on a regular basis. I just note that I have known many cruisers who are against bonding, whether sensible or not, and I have seen boats where the bonding systems were undone. I want them to know of the greater danger in fresh water.

Greg

Most of us already have anodes on our boats for other metal components like the prop shaft, prop, skeg, etc. These are installed to protect the parts they are attached to and are replaced as needed. This goes for fresh, salt or brackish water.

Any other underwater metal should be connected to the bonding system that connects these parts.

[rwidman]

Originally Posted by thunderhoof

............. 2. Use a "multi-star" configuration rather than "daisy chain" for connecting multiple equipments to a single breaker. That means - from a breaker or ground bus run individual wires to each piece of equipment............ .

"Multi tapping" of circuit breakers is not good electrical practice. Either a buss bar or daisy chaining is acceptable. You wouldn't run wires from ten cockpit light fixtures back to the breaker, common practice would be to run pairs of wires from one fixture to the next or possibly branch out at one fixture to multiple groups of fixtures.