AC-DC ground

[jimford2158]

'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.'

If you ground your 110v to the 12v and there is a short, it will go thru your 12v system. At the minimum, you will get galvanic corrosion caused by the 110v current. At the extreme you could cause a fatality by introducing 110v into the 12v grounded part of your boat and in the water, effecting anyone in the water. If you touch a metal part, say the engine, and it is energized at 110v, you will get shocked. (I had this happen in my boat because of the way it was wired). If you are standing in water when you do that, it will be much worse than the minimal charge that I received. DO NOT ground the 110v wiring to the engine or anything that is also a ground for 12v. What they are saying in the regs is 'ground the wiring in the electrical box'. If you install a battery charger, do not hard wire it, just plug it in to an outlet. It is safe that way and easier to service.

 

[mitiempo]

Jim

I disagree and so do ABYC and Nigel Calder as well as many others. There is usually at least one item on a boat that uses both AC and DC - the charger. There may be an inverter as well. If the charger develops an internal fault there could well be 120 volts in the DC system. The connection to one point of both the green AC ground wire and the 12 volt negative is made so this possible fault has a path to ground that is not through the water but through the green ground wire in the shorepower cord.

Your plan of a charger that is not hard wired doesn't solve the problem of a possible fault in the charger that connects the AC side to the DC side.

This can increase the risk of galvanic corrosion which can and should be solved by installing a galvanic isolator it the shorepower line.

 

[jimford2158]

The green wire from shore power is connected to the metal electrical box along with the green wires that come from the outlets and appliances. The black wires are connected to the circuit breakers. The white wires are connected to each other, including the white wire from the shore power, but are NOT grounded inside the electrical box. The green wires are NOT connected to anything else in the boat, including the engine block, battery ground or a grounding plate. There is NO ground connection between the 110v and the 12v systems.

 

[mitiempo]

"The green wires are not connected to anything else in the boat, including the engine block, battery ground, or a grounding plate."

But they should be.

 

[Ron20324]

The current E-11 is July 2009..

MS, do you have E-8? I'm looking at the Marinco "Boater's Guide to AC Electrical Systems", which says it is based on E-8. The Marinaco is dated 1996 and shows the shore power grouinded to the engine block in a number of differnt voltage arrangements.

 

[tommays]

So if i understand this the reason is to protect from a battery charger fault while on shorepower ?

I am still not completely clear how the AC leak to the battery would flow ? is the thought it would leak to the ground and into the water through the prop or other hardware that may be bonded like the shrouds

 

[Maine Sail]

The green wire from shore power is connected to the metal electrical box along with the green wires that come from the outlets and appliances. The black wires are connected to the circuit breakers. The white wires are connected to each other, including the white wire from the shore power, but are NOT grounded inside the electrical box. The green wires are NOT connected to anything else in the boat, including the engine block, battery ground or a grounding plate. There is NO ground connection between the 110v and the 12v systems.

Jim,

If you don't understand MARINE electrical standards you may want to do a little research from giving advice on the subject. Your suggestions are completely out of line with what the standards call for.

The GREEN GROUNDING wire is ALWAYS connected to the vessel ground. The WHITE/NEUTRAL/GROUNDED wire is NEVER connected to the ships GROUNDING circuit.

ABYC, NFPA, NMMA, Calder, David Rifkin, Casey, Charlie Wing, Ed Sherman and just about every organization and expert on this subject agrees with this. Just pick up any Calder, Casey, Charlie Wing, ABYC training manual, marine electric book or ABYC wiring diagram and you'd quickly see this..

 

[Bill Roosa]

A similar (to charger) issue develops when you have onboard generating capacity. How can you possibly ground the neutral when you run the genset while away from the dock. You can't so you have to ground it "at the source." Course your "source select switch" will disconnect this ground to neutral circuit when you do get back on shore power. This is an often missed point when selecting a source selector switch. You have to have one that makes and breaks all "three wire" sets when you have a genset/inverter. Some inverter/chargers take care of this automagicaly, some do not.
As far as AC leaks to the battery, a marine charger has an isolated neutral return and unless there is some major short (probably blow a CB) it should not be possible to connect the AC hot/neutral to the DC system. Auto chargers are NOT designed this way and have a connected neurtal return which is why you should only buy marine rated chargers for your boat.

 

[Bill Roosa]

On the “what is a source issue”; a source is just that, anything that supplies the AC hot and energized wire. Shore power does that so you ground it at it's source back on shore somewhere, gensets and inverters do that too but the source is on the boat so you have to both ground the neutral to the green ground "at the source (of energized hot wire) and provide a means of switching between sources as you can't have two sources on the same circuit at the same time. I would note nothing prevents you from having two sources on two separate circuits, completely separate except for one ground wire connection
WM has a great article on this and radio, lightning, AC, DC, galvanic corrosion grounding at
http://www.westmarine.com/webapp/wcs/stores/servlet/WestAdvisorView?langId=-1&storeId=11151&catalogId=10001&page=Marine-Grounding-Systems

 

[alexco38]

Discrepancy in AC ground

There is a discrepancy in the Practical Sailor's article.

http://www.westmarine.com/webapp/wc...catalogId=10001&page=Marine-Grounding-Systems

The diagram in Figure 2 shows the AC ground connected to the boat ground.

According to Mainesail:

The GREEN GROUNDING wire is ALWAYS connected to the vessel ground. The WHITE/NEUTRAL/GROUNDED wire is NEVER connected to the ships GROUNDING circuit.

 

[alexco38]

I think if I read Mainesail's statement correctly:

The GREEN GROUNDING wire is ALWAYS connected to the vessel ground. The WHITE/NEUTRAL/GROUNDED wire is NEVER connected to the ships GROUNDING circuit.

Never connect the neutral to boat ground. The green ground wire does go to the boat ground. I believe that's correct.

 

[Ron20324]

The confusion comes when it is said, "WHITE/NEUTRAL/GROUNDED wire". The White/neutral wired IS grounded , but probably at least way back at the on-shore electric panel where the black-wire circuit breakers are. White might be connected to ground in that box, and on to the power company supply, and NO WHERE ELSE. Once the wire leaves the electric panel on shore toward the consumer, it is NOT ever grounded - as in to the green ground wire.

 

[Maine Sail]

I think if I read Mainesail's statement correctly:

The GREEN GROUNDING wire is ALWAYS connected to the vessel ground. The WHITE/NEUTRAL/GROUNDED wire is NEVER connected to the ships GROUNDING circuit.

Never connect the neutral to boat ground. The green ground wire does go to the boat ground. I believe that's correct.

Yes that is correct.

 

[Maine Sail]

The confusion comes when it is said, "WHITE/NEUTRAL/GROUNDED wire". The White/neutral wired IS grounded , but probably at least way back at the on-shore electric panel where the black-wire circuit breakers are. White might be connected to ground in that box, and on to the power company supply, and NO WHERE ELSE. Once the wire leaves the electric panel on shore toward the consumer, it is NOT ever grounded - as in to the green ground wire.

Sorry for the confusion the ABYC phrasing is different than many boaters would expect. Green is GROUNDING/Earth, white is GROUNDED neutral..

 

[Bill Roosa]

Different grounds for different setups. If you do not have a genset or inverter then the neutral is never grounded on the boat. It gets grounded on the shore side of the circuit probably at the meter box at the end of the dock. If you have a genset or inverter then you have to ground it somewhere when using it away from shore power and code prescribes "at the source". And don't forget the source selector switch which has to connect/disconnect all three wires for each source so you don't have a shore power ground connecting to an inverter ground which is connected to the neutral in the inverter which is connected to all the other neutrals. The source selector switch must isolate each source and give you the proper neutral and ground connection for each source (energized hot) it selects.

 

[heart of gold]

My point exactly

Your attachment says it all.

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.

 

[Bill Roosa]

If you have a "plug in" Honda 2000 genset (or other brand for that matter) that uses the shore power cable to connect then you need to insure that the neutral is connected to the ground in the genset. This is not the norm for most generators that come without a grounding rod. I don't own one so you would have to check your owner’s manual or get out the multimeter. If neutral and ground are not connected (my suspicion) then you are not properly grounded when configured for away from the dock AC. I'm thinking that a jumper wire behind the genset outlet connecting the ground to the neutral (white to green) would work. Course it would then not be suitable for shore side work if you wanted to use it off the boat. Perhaps a "marine - land" toggle switch for such circumstances would be handy.

 

[heart of gold]

Identified conductor

Mainesail, Up here in the cold north we are taught that the white wire or as you call it the grounded conductor is the "identified conductor". This prevents the language form inferring that it is to be grounded. In the circuit is it is the return path to the source, where it is grounded but only at this point and nowhere else. Unless a boat owner is also wiring the main service for the marina, he will never have to deal with it. The Green could be considered the safety ground so that if a short occurs to a device that the green wire is connected to it will trip the breaker, blow the fuse etc. Maybe this angle will help folks to understand the difference.

Sorry for the confusion the ABYC phrasing is different than many boaters would expect. Green is GROUNDING/Earth, white is GROUNDED neutral..

 

[Stu Jackson]

This one has been beaten to death in any number of forums and I'm sure Maine Sail has answered it at least fifty times. There are three wires: black (hot), white (Neutral) and green (ground).

ON SHORE the neutral and ground are tied together. NEVER on a boat. It's pretty simple.

The AC and DC green grounds are connected on a boat.

Reverse polarity is when the HOT and NEUTRAL are reversed, usually at the dockside by, as Maine Sail has written, Darrryl & his other brother Darryl. It is rarely done on a boat unless the PO has snafued his own work.

Reverse polarity is measured between the neutral and ground wire ON THE BOAT with the neon glow lamps with the 25K ohm resistors. However, what they are telling you, regardless of how this is done, is that you have the HOT and NEUTRAL reversed. That's why we recommend that everyone just go down to their ACE hardware store and buy one of those simple plug-in testers. That avoids any confusion about RP. F'rinstance, in our boat we have THREE RP lights, two are indicating NORMAL and means everything is OK. When the third light comes on: PROBLEM!!! Confuses some people. SOME FOLKS ONLY HAVE ONE LIGHT SO WHEN IT COMES ON IT MEANS a PROBLEM.

See the flix here of my panel: http://c34.org/bbs/index.php/topic,2620.msg13781.html#msg13781

Got it?

 

[Bill Roosa]

Never say never. If you have a genset or inverter the neutral and ground are connected "at the source, just like the shore power. The differance is the source (energized hot wire, black in color) is on the boat with a genset or inverter and off the boat in the case of shore power.