AC-DC ground
- Thread starter Tom23352
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The ac ground should not be connected to anything except the green screw on the ac outlet or ac switch and the metal of the circuit breaker box. If there is a short, the current will go back to the dock and hopefully pop the circuit breaker. There should be a protection device on each set of outlets. If an appliance shorts to ground you do not want 110v current going into the water.
The 12v is fine connected to the engine block since the battery also grounds there.
Lightning protection should also be grounded to the block or the hull plates(which is what they are for, not ac).
Whomever hooked the ac ground to the hull plate was thinking in terms of house wiring whereas they hook a ground cable the plumbing or a iron rod driven in the ground. As long as you could drive a rod into the seabed and attach the ground there, it would be ok. But it might limit your sailing distance.
The 12v is fine connected to the engine block since the battery also grounds there.
Lightning protection should also be grounded to the block or the hull plates(which is what they are for, not ac).
Whomever hooked the ac ground to the hull plate was thinking in terms of house wiring whereas they hook a ground cable the plumbing or a iron rod driven in the ground. As long as you could drive a rod into the seabed and attach the ground there, it would be ok. But it might limit your sailing distance.
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By current standards it is required that the AC grounding wire (green) is grounded on-board the vessel and it has been this way for a long time. AC white and AC green are never connected on-board unless at a "source" such as an inverter, generator or back at the shore power source..
Multiple grounding points on boats can create issues so it is good to pick a grounding point and stick with it.
I just installed a galvanic isolator and actually found one AC panel with no in boat grnd. The main AC panel had the green to the grnd plate where the lightening grnd and fuel tank filler pipe grnd wire are also connected. The AC panels are both 30 amp and the isolator is rated 100amps. Now, the green wires comes from the shore inlets to the islolator then the AC panels then run to the grnd plate which is about three feet from the DC grnd connection on the block. Having them physically separated causes issues? I can easily connect the AC and DC ground wires to the same point.
By our code, Canada , you must connect all metal parts to ground(AC safety ground) which means you can have a galvanic problem with shore power. The way around this is to install a galvanic isolator in the shore power ground that will only connect the grounding system when the voltage on it rises above 1.4volts.( in the event of a short to ground or metal parts of the boat.) The white or neutral wire or identified conductor must not be tied to the safety ground on the boat. It is only bonded at the shore power service. With regard to lightening protection, there is an excellent article at the West Marine site that makes total sense to me and I am going to ensure my boat is set up this way.
http://www.westmarine.com/webapp/wc...catalogId=10001&page=Marine-Grounding-Systems
http://www.westmarine.com/webapp/wc...catalogId=10001&page=Marine-Grounding-Systems
The AC ground (green) should be connected to the same point as the DC ground. This is to prevent current going into the water in the event of a short in the charger (or inverter). Without this connection between the AC and DC systems a fault such as this can energize the DC system with 120 volts. The connection gives a path the ground on shore for any stray AC current in the DC system.
ABYC E-11 excerpt below.
ABYC E-11 excerpt below.
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This is true but only for house (i.e., land-based) wiring. Electricians used to working on houses who are not marine electricians often make this mistake.
As Jim said in the second post:
"The ac ground should not be connected to anything except the green screw on the ac outlet or ac switch and the metal of the circuit breaker box. If there is a short, the current will go back to the dock and hopefully pop the circuit breaker. There should be a protection device on each set of outlets. If an appliance shorts to ground you do not want 110v current going into the water.
The 12v is fine connected to the engine block since the battery also grounds there."
Don,
What you and Jim have said is incorrect as it applies to marine AC electrical standards. ABYC E-11 requires the AC green/grounding wire to be tied into the ships DC ground on-board the vessel and white/neutral and green/grounding should never be connected on-board accept at a "source". This has been the marine standard for many.
Info below from ABYC E-11:
"11.5.3. FOR AC SYSTEMS
11.5.3.1. The system shall be polarized as
defined in E- 11.4
11.5.3.2. A grounded neutral system is required.
The neutral for AC power sources shall be grounded
only at the following points:
11.5.3.2.1. The shore power neutral is
grounded through the shore power cable and shall not
be grounded on board the boat.
11.5.3.3. The main AC system grounding bus
shall be connected to
11.5.3.3.1. the engine negative terminal or the
DC main negative bus on grounded DC systems, or
11.5.3.3.2. the boat’s DC grounding bus in
installations using ungrounded DC electrical systems.
11.5.3.4. In AC circuit, all current carrying
conductors and the grounding conductor shall be run
together in the same cable, bundle or raceway.
11.5.3.5. There shall be no switch or overcurrent
protection device in the AC grounding (green)
conductor.
11.7.2.2. APPLICATION OF TYPES OF
SHORE POWER CIRCUITS
11.7.2.2.1. Single Phase 120-Volt Systems
with Shore-Grounded (White) Neutral Conductor and
Grounding (Green) Conductor.
11.7.2.2.1.1. The shore grounded (white) and
ungrounded shore current carrying conductors are
connected from the shore power inlet to the boat's AC
electrical system through an overcurrent protection
device that simultaneously opens both current carrying
conductors. Fuses shall not be used instead of
simultaneous trip devices. (See E-11.12.2.9.2.)
11.7.2.2.1.2. Neither the shore grounded
(white) neutral conductor nor the ungrounded current
carrying conductors shall be grounded on the boat.
(See E-11.5.3.2.1.)
11.7.2.2.1.3. When more than one shore power
inlet is used, the shore power neutrals shall not be
connected together on the boat. (See E-11.5.3.6.)
11.7.2.2.1.4. The shore-grounding (green)
conductor is connected, without interposing switches
or overcurrent protection devices (See E-11.5.3.5.),
from the shore power inlet to11.7.2.2.1.4.1. an optional galvanic isolator, and then to
11.7.2.2.1.4.2. all non-current carrying parts of
the boat’s AC electrical system, including
11.7.2.2.1.4.3. the engine negative terminal or its
bus.
This kind of well-intentioned, but ultimately dangerous DIY confusion about wiring is why I always include a an ABYC / CE certified marine electrician to round out a survey. In every case the money was well spent and DIY problems were identified. Know your limits and pay a pro to do it right.
Mainsail.. you gotta picture cause you lost me.What would be a "source" to connect your AC ground to the DC ground, assuming you have no inverter or generator. If your only source of AC is when connected to shore then the ground would be to the shore outlet...right?
This is a good idea and it is one service I offer to my customers. Many surveyors know little about marine wiring or how to properly spot a potential safety issue. Some are very good but some tend to just hit the "high spots".. That being said even a marine electrical inspection can't catch everything unless you really want to tear the boat apart.
OK Mainsail that last post was more clear. I think I got it now. Not sure I can pay a Pro Gunni, can barely pay my slip fee. But I understand where you're coming from.
AC green & DC ground are not the "source" issue. AC ground is always connected to DC ground on-board the vessel, AND back through the shore power cord.
AC white and AC green are only ever connected together at an power generating SOURCE such as the shore, a generator or inverter..
No, you would still ground AC green wire to the ships DC ground and you'd also have the AC green running back to shore as well through the shore power cord. The AC white and green "source" issue is not the same.
Downloaded E-11. I'm not changing my AC system, Just wanting to learn more. right now it's as it came from the factory. I would hope they knew what they were doing. I just want to compare it to what I see in E-11.
Keep in mind that any E-11 you found on-line, unless you paid for it, will be an older standard, most likely from 1998 or so as that is the one I remember floating around. There have been changes since then but none that would affect AC/DC grounding to a large degree. The current E-11 is July 2009..
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