DC Ground vs. Negative Return

[dougshome]

What''s the difference between 12v "DC GROUNDING SYSTEM" and "DC NEGATIVE RETURN"? Don''t they both go to the negative on the battery?

[fourknots]

The DC grounding system is where all grounds come together. Those grounds are then connected to engine ground. Same thing really.

[GordMay]

GROUNDING vs GROUNDED:

There are four main functions accomplished (on a boat) through GROUNDING:
1. Safety - prevent shock hazzard (AC green gnd wire)
2. Bonding - prevent corrosion (tie all immersed metals together)
3. Lightning Amelioration - provide a preferred path to gnd for lightning.
4. Counterpoise - provide an RF gnd, or zero reference for electronbics.
None of these (4) GroundING wires are current-carrying, under NORMAL circumstances.

There are two main GROUNDED current-carrying conductors:
5. AC Neutral (White)
6. DC Return (Yellow or Black)
Both the AC Neutral and the DC (negative) Return are connected to ground (hence grounded) , but are NOT Grounding wires.

To prevent confusion, it is preferred to refer to groundED (current-carrying) conductors (numbers 5 & 6) by the term(s): AC “Neutral”, or DC “Negative” (return).

See ABYC Section(s):
E-8 Alternating Current (AC) Systems
E-9 Direct Current (DC) Systems (Figures 15, 16 etc)
E-4 Lightning Protection

Hope the helps,
Gord

[joub]

Great reply! I knew some of it, but you certainly cleared up a couple of questons in my mind. Hey! This place is a great resource!

Jim

[WHOOSH]

Further to Gord´s excellent reply, this illustrates why it normally makes sense to keep the ( SSB) rf ground plane separate from the DC ground (#s 5&6). But the confusion in terms usually invites folks to consider these the same thing...leading to all kinds of interesting pathways in the DC system for rf to run down.

Jack

[KenD]

I question the last reply as far as AC grounding on a boat I was under the opinion that AC is grounded through the green wire to the dockside power then to the power source ground.Please correct me if I''m misinterpreting this but I don''t think AC should be grounded on a boat.

[GordMay]

YES - A/C (Green) should be grounded on the boat.
Paraphrasing Shore-Power Grounding per ABYC Section E-8.23.2.6.2
A/C Ground (Green) wire is connected to:
- Optional Galvanic Isolator
then
- All non-current carrying parts of boat’s A/C system, INCLUDING:
- engine negative terminal or it’s bus.

Regards,
Gord