Electrical Guru's (AC and DC Grounds)

[tommyt]

I have a 2004 C34 that has not been changed Electrically since leaving the factory. The boat was just surveyed, and the surveyor noted that the "120VAC system and all equipment should be grounded to main 12VDC negative bus or engine block. ABYC E-11"

The 120V bus and 12V bus are adjacent to one another, which would make it a pretty simple fix if this were a good idea, but I have no clue. Good idea? Something that should be done? Suggestions? I am fine with a simple fix if it is the right thing to do.

[Stu - modified title for clarity]

[Ron Hill]

Tom : I'm sure that Stu or Mainsail will be on shortly and give you the answer.

[Stu Jackson]

Hi, the ground wires for the AC side come into the terminal strip behind the electrical panel.  Did he open up the electrical panel?

[Stu Jackson]

Tommy, when we first bought our boat in July 1998, I started on doing wiring diagrams, these are dated September 1998, so I got right to it (we'd been on vacation for a month when we first bought the boat!:D).  These are the ones I did for the AC incoming inside the electrical panel.  I was focused on tracing and recording the AC only, and did not check to see whether the DC was connected to the AC ground, which would most likely, as you say, have been done with a simple term strip jumper, although IIRC the terminal strip behind the panel is ONLY AC.  I cannot say for sure whether it has been done on my boat or not.  As you may know, the ground from batteries runs from the panel underneath the saloon sole to the battery box and then back to the engine under the head sole, to the port aft bell housing connection.

This link from the West Advisors shows the AC ground tied to the engine ground per ABYC.  

http://www.westmarine.com/webapp/wcs/stores/servlet/WestAdvisorView?langId=-1&storeId=11151&catalogId=10001&page=Marine-Grounding-Systems#.UnVOCRCQORN

Calder's Boatowners Manual also discusses it in detail.  If you don't have this book, you really should get it.  IMHO, the 2nd edition is clearer than the newer 3rd edition, and you could probably get it on eBay or Amazon used for less than the $50+ for a new one - a VERY good investment.

If the surveyor says do it, nothing wrong with it.  There have been many discussions of this, and you can read them all if you do a simple search on "AC ground" (with the " marks in the search box).  There's LOTS of discussion on this subject.

[sailaway]

the factory guys know best. been electricain for 40 yrs do not mix ac dc grounds two different animals

[mainesail]

Sounds like you may have been a land based electrician not a marine electrician.

AC grounding / green and DC ground ARE tied together on-board, for safety reasons.

AC white/neutral and AC green/grounding are only ever tied together at the source, which for boats means on land, an on-board permanently mounted AC generator, an on-board inverter (but only while operational) or an on-board isolation transformer. Otherwise AC white/neutral and AC ground/green are never tied together on-board.....

Many years ago Catalina used to not bond AC ground to DC ground. Today every boat that leaves the factory has AC ground and DC ground bonded together as do any other US builders who build to US safety standards..

[Ron Hill]

Mainsail : Thanks for your answer, as I couldn't believe that the AC and DC grounds should ever be tied together. 
I've always treated the AC and DC electrics as two separate and distinct systems. 

[mainesail]

ABYC E-11:

"11.5.5.2 Grounded Neutral

A grounded neutral system is required. The neutral for AC power sources shall be grounded only at the following points:

11.5.5.2.1 The shore power neutral is grounded through the shore power cable and shall not be grounded on board the boat.

11.5.5.2.2 The secondary neutral of an isolation transformer or polarization transformer shall be grounded at the secondary of an isolation or polarization transformer. (See DIAGRAM 5, DIAGRAM 6, DIAGRAM 7, DIAGRAM 8 and DIAGRAM 9, DIAGRAM 10 and DIAGRAM 11 See EXCEPTION.)

11.5.5.2.3 The generator neutral shall be grounded at the generator. (See DIAGRAM 2 or DIAGRAM 4.)

11.5.5.2.4 The inverter output neutral shall be grounded at the inverter. The inverter output neutral shall be disconnected from ground when the inverter is operating in the charger or the feed-through mode(s). (See ABYC A-31, Battery Chargers and Inverters.)

EXCEPTION: Exception to E-11.5.5.2.2., E-11.5.5.2.3 and E-11.5.5.2.4: For systems using an isolation transformer or polarization transformer, both the generator or inverter neutral and the transformer secondary neutrals may be grounded at the AC main grounding bus instead of at the generator, inverter, or transformer secondaries. (See DIAGRAM 5.)
11.5.5.3

The main AC system grounding bus shall be connected to

11.5.5.3.1   the engine negative terminal or the DC main negative bus on grounded DC systems, or

11.5.5.3.2   the boat's DC grounding bus in installations using ungrounded DC electrical systems. "

[tommyt]

Thank you gentlemen! Very thorough responses. Appreciated very much.