Is it OK to use common earth and neutral for AC wiring routes?

[Bluebeard]

Wow, I'm amazed that some of our contributors do something as dangerous as step on a boat, or do they all have professional skippers and crew?

But to be serious, electricity is fairly simply, but if you are not sure about what you are doing don't cut corners!
You may be able to common earth and neutral but if you do you won't be able to use the best safety device available which is an earth leakage circuit breaker ( ELCB ). An ELCB will trip if any of the current escapes from the live and neutral systems, into your ( or someonelse's ) hands.

In simple everyday terms what you are creating is an outdoor electrical system that is working in the rain.
Would you really ask your wife to work at an electric hob outside in the rain? If you can think that one through.
If it is available use switch gear and breakers etc which has an IP rating, look up what each rating means but IP67 is basically waterproof I think, the higher the number the better.

Don't put electric cables in a conduit that is too small, they may get hot enough to melt the insulation.

There is sound advice about breakers above.

You must put in an ELCB, but remember that everything on the shore side of the ELCB is not safe, so make sure it is as safe as you can make it.

[ramblinrod]

Originally Posted by dinghysailor

I am thinking about adding a shorepower connection, a 240v to 12v battery charger, and a 1600W inverter to a boat that currently has only a 12v system. At the same time considering LiFePo battery. There is an obvious location for the shore power inlet in a cockpit locker. I realise that the battery charger and the inverter are best placed close to the batteries which are well forward near the mast. The 240v supply is mainly needed for galley equipment which is aft and close to the cockpit. So I was assuming that I would have one 240v cable running forwards from the shorepower inlet to the battery area then another running the opposite way back to the galley, following the same route as the first cable most of the way. The thing is that the likely route is through a tubular 'service duct' that at present carries four plastic water pipes but the space left in that duct is small, very tight and maybe even impossible to fit in two 240v cables side by side. I have read that I need something like H07 cable, for 16amp supply with 1.5mm2 per core thats about 10mm diameter, is that the right cable to use? Do I actually need two of these cables, with total of six cores? Obviously I need two live cores but can I have just one earth core and one neutral core in one four core cable? That would fit the limited space better and save a bit of weight - this is supposed to be a performance multihull so I am trying to watch the ounces. Maybe there is some very good reason this would not work or would be potentially lethal?

If you have to ask these questions, the only valid answer is...

"You either need to hire a marine electrician or do enough research, studying, and skills practicing to basically become one."

Way too many ill-equipped people mess with electrical systems on boats, and then bitch when a surveyor claims, "You're lucky to be alive; this has to be fixed."

There is absolutely no shame in not knowing how to do something that one has no specific education, training, or experience in.

But before someone gets electrocuted, hire a marine electrician.

Not someone who says they are an "electrician".

One who can show you "Marine Electrician" certification papers from an organization you can look up on the internet to verify.

I constantly get called in for survey reported electrical remediation by folks whose "electrician" (buddy who doesn't know %$^ from shinola with respect to Marine Electrical Systems, standards and sound industry practice) did some work for them. (They may be a perfectly adequate residential or automotive electrical technician; BUT IT IS NOT THE SAME THING.)

This is akin to asking a cosmetic surgeon to perform your brain surgery. They are both surgeons, BUT IT IS NOT THE SAME THING.

The next thing to do is to ask to see their "Commercial Liability Certificate" so if their incompetence kills someone or burns up a boat, or numerous boats, or perhaps the whole dang marina, you may actually be compensated to some extent for your losses (and still be able to afford your personal boat insurance afterward).

The only reason any "Certified Marine Electrician" does not carry commercial liability insurance, is if:

A) They really aren't a "Certified Marine Electrician".

B) This is not really their business / expertise.

C) They've had a claim and can't afford it any more.

D) They have nothing to lose if they accidentally kill somebody.

In any event of A,B,C, or D above, you don't want them setting foot on your boat.

LiFePO4 battery chemistry is not likely to kill anyone, but the energy released when someone who doesn't know what they are doing does something they shouldn't, most certainly is.

Do not underestimate the power of 1000s of amps at 12 Vdc (let alone 240 Vac).

Edit: Sorry if this offends anyone, but I have seen more than my fair share of boat fires and the devastating effects they can have on people's lives. Boating is supposed to be fun. Lets keep it that way. Don't take chances with your precious cargo.

[sainted]

Originally Posted by Bluebeard

You may be able to common earth and neutral but if you do you won't be able to use the best safety device available which is an earth leakage circuit breaker ( ELCB ). An ELCB will trip if any of the current escapes from the live and neutral systems, into your ( or someonelse's ) hands.

The ABYC standard for AC electrical systems explicitly forbids connecting neutral and ground on a boat except at a power source (i.e., an inverter or generator).

The reason is that should you have a short from hot to neutral with ground connected to neutral, all of the under water metals will become hot, which will both quickly destroy them and potentially electrocute anyone in the water near by.

Scott

[blubaju]

Originally Posted by OS2Dude

240 is usually made up of two 120 volt circuits. Unless you NEED 240 forward, you can run just one 120 volt leg forward for the battery charger, etc. If you don't have shore power now, then the assumption is you are adding the galley equipment as well. Why choose 240 volts? I could see an Air Conditioner being 240, but a small galley stove/refrigerator? What amp service are you planning to use? (30/50)


Wires are sized for the load, breaker is sized for the wire.

Sorry, pure laymans nonsense!

Even Philippines switched from 110 to 240, beside North America & Japan (100) I do not know of any others. We do not know where he plans to sail. Outside US almost all public power grids are 3-phase 400V, hence life to neutral/ground gives you 230. Still it is not advisable to plan your boat installation like your house, many countries have no phase control in the plug and an old fashioned generator delivers what you describe, 2x120V

Ground maybe common, above reason prohibits common neutral which is common in house installation in many but not all countries

Fuses/breakers are here to either protect the wire and/or the appliance. For an outlet you protect the wire, I choose 2.5mm. Fixed appliances you go for the maximum load, be aware of high starting loads of motors

I choose breaker/GF combination (integrated) for each circuit and just behind the incoming plug.

Think about galvanic separation, DC-Filter.

Any stray current around your boat could kill people, our body is a much better conductor than seawater, the voltage difference from arm to legs is enough to kill.

Read a lot so you have an idea what that crazy household gingineer is selling you, try to find a good one for marine installation

[ramblinrod]

Originally Posted by sainted

The ABYC standard for AC electrical systems explicitly forbids connecting neutral and ground on a boat except at a power source (i.e., an inverter or generator).

The reason is that should you have a short from hot to neutral with ground connected to neutral, all of the under water metals will become hot, which will both quickly destroy them and potentially electrocute anyone in the water near by.

Scott

First Paragraph:

ABYC doesn't "forbid" anything.

It is an organization that develops standards for boat system design, modification, and repair, and provides training and certification for those working in the industry.

The electrical system is either compliant with ABYC standards, or it is not.

If it is, there is a level of assurance it is relatively safe.

If it is not, "Who Knows"?

In most cases, from my experience, likely not.

Second Paragraph:

This may be a typo, or grammatical error, but regardless, it is technically incorrect.

If one has a short circuit from line to neutral in an ABYC compliant wiring system, it will immediately trip the breaker for that circuit. There will be no loss of metals due to electrolysis as the current (from that source) will be interrupted.

The reason for grounding the grounded conductor (white, neutral), is so that if the ungrounded conductor (live, hot, black) ever becomes short circuited to the grounding conductor (green), that is connected to every metal electrical device enclosure (and some other metal boat parts), the corresponding line voltage breaker will trip.

For example, if the insulation on the black wire becomes chafed and contacts the grounded metal enclosure of the water heater (quite common, especially in DIY installations), the breaker trips and disconnects power from that hot wire.

If the neutral wire was not grounded, and the same scenario took place, the water heater metal enclosure would be hot, and if one touched that with one hand, and any grounded metal (e.g. engine block) with the other, if the corresponding current across their heart exceeds 80 mA, (highly possible in the wet environment of a boat), they could very well be electrocuted and die.

The reason for grounding at the source only, is so that the neutral wire is most definitely grounded over it's entire length, from the source of the electric current.

If the neutral wire was instead grounded part way down it's length, and it was opened before that connection (common in DIY wiring) the length to the source would be unrounded, and the electric shock hazard described above exists over that length.

If the neutral wire is connected to ground at more than one location (e.g. at the source and somewhere else), (common in DIY wiring) if someone measures for the grounding connection somewhere down the wire, they have no idea if it is grounded over its entire length.

Therefore, the neutral wire is to be grounded at the source only.

In addition, the AC distribution system can be powered by only one source at any given time, and all other sources have to have both the grounded and ungrounded conductors disconnected from the AC distribution system.

This assures that the entire grounded conductor, is in fact grounded, over it's entire length from the active source, and not just over a portion to/from an inactive source.

Just imagine when it gets complicated.

My recommendation?

Electricity and water don't mix.

Instruction manuals, YouTube, and internet forums do not make one "properly qualified" to work on marine electrical systems.

In an emergency, away from skilled services, anyone must perform whatever repair they can effect to get home safely.

If you are not qualified to perform electrical system installations (as recommended in every electrical device instruction manual), either hire it out or at least have it inspected by a "properly qualified" person at your earliest convenience.

[sainted]

Originally Posted by ramblinrod

First Paragraph:

ABYC doesn't "forbid" anything.

It is an organization that develops standards for boat system design, modification, and repair, and provides training and certification for those working in the industry.

The electrical system is either compliant with ABYC standards, or it is not.

If it is, there is a level of assurance it is relatively safe.

If it is not, "Who Knows"?

In most cases, from my experience, likely not.

Second Paragraph:

This may be a typo, or grammatical error, but regardless, it is technically incorrect.

If one has a short circuit from line to neutral in an ABYC compliant wiring system, it will immediately trip the breaker for that circuit. There will be no loss of metals due to electrolysis as the current (from that source) will be interrupted.

The reason for grounding the grounded conductor (white, neutral), is so that if the ungrounded conductor (live, hot, black) ever becomes short circuited to the grounding conductor (green), that is connected to every metal electrical device enclosure (and some other metal boat parts), the corresponding line voltage breaker will trip.

For example, if the insulation on the black wire becomes chafed and contacts the grounded metal enclosure of the water heater (quite common, especially in DIY installations), the breaker trips and disconnects power from that hot wire.

If the neutral wire was not grounded, and the same scenario took place, the water heater metal enclosure would be hot, and if one touched that with one hand, and any grounded metal (e.g. engine block) with the other, if the corresponding current across their heart exceeds 80 mA, (highly possible in the wet environment of a boat), they could very well be electrocuted and die.

The reason for grounding at the source only, is so that the neutral wire is most definitely grounded over it's entire length, from the source of the electric current.

If the neutral wire was instead grounded part way down it's length, and it was opened before that connection (common in DIY wiring) the length to the source would be unrounded, and the electric shock hazard described above exists over that length.

If the neutral wire is connected to ground at more than one location (e.g. at the source and somewhere else), (common in DIY wiring) if someone measures for the grounding connection somewhere down the wire, they have no idea if it is grounded over its entire length.

Therefore, the neutral wire is to be grounded at the source only.

In addition, the AC distribution system can be powered by only one source at any given time, and all other sources have to have both the grounded and ungrounded conductors disconnected from the AC distribution system.

This assures that the entire grounded conductor, is in fact grounded, over it's entire length from the active source, and not just over a portion to/from an inactive source.

Just imagine when it gets complicated.

My recommendation?

Electricity and water don't mix.

Instruction manuals, YouTube, and internet forums do not make one "properly qualified" to work on marine electrical systems.

In an emergency, away from skilled services, anyone must perform whatever repair they can effect to get home safely.

If you are not qualified to perform electrical system installations (as recommended in every electrical device instruction manual), either hire it out or at least have it inspected by a "properly qualified" person at your earliest convenience.

Thanks, Ramblin, for your clear explanation. I stand corrected and bow to your superior knowledge.

Scott

[blubaju]

Originally Posted by sainted

Thanks, Ramblin, for your clear explanation. I stand corrected and bow to your superior knowledge.



Scott

[emoji106]