12v breaker panel wiring question

[domer94]

in doing an install of aux 12v panels in my 1982 sabre 30 which has a very limited 12v capacity. the paneltronics unit i have has a neg buss that goes to "DC neg" and another buss right next to it that goes to "DC ground" . i will be jumping the two panels neg buss with an 8ga wire and the two pos buss with an 8ga wire. i understand the "dc neg" buss should go to the boats neg buss bar which is connected to ground / engine. so what is the additional buss that says "DC grounding" ?

steve
s/v kanaloa
north jersey

 

[JoeWhite]

DC ground or negative in your case is the same thing. A ground may be connected to AC ground aswell. From your image it appears that the DC ground labeled bar is not connected to anything. So you can use that as DC negative. You can also measure the DC voltage diffetence between the busses to see if there is any difference in voltage compared to a positive point. Use digital volt meter to be accurate.

 

[domer94]

thanks... the papers that came with the panel says all the buss bars are isolated... so your point may be the answer. the neg should be same as ground if its going to the boats neg buss. i just got confused by the other bar

 

[dlochner]

Those are not original DC panels, they were added on by a prior owner. The original panel is just inside the companion way on the starboard side.

DC ground is an archaic term for the DC- connection. The DC- is very different from an AC ground which is a safety feature and not part of the circuit. To avoid confusion, it is best to not use "ground" when talking about DC-.

On this panel there are 2 DC- buses to accommodate the panel lights, those are the small yellow wires. The other bus is for the DC- on the circuit. It is not necessary to bring all the DC- wire back to the panel if there is an appropriately sized DC- bus elsewhere and closer to the battery. A shorter DC- reduces the overall length of the circuit which reduces line loss and improves efficiency.

The wire from the DC- bus on the panel should be sized to carry all of the load from the panel, thus if the current draw on the panel with all circuits on is 50a, the return from the DC- Bus should be sized to carry 50a, which may need to be as large as 6 ga depending on the distance to the battery to maintain a 3% loss.

 

[domer94]

dave, yes i just did the modification due to i will be adding electronics and lights etc etc.... the original panel allowed no room for accessories. so far my plan is to run an 8 ga to jump the panel busses and as you suggest a 6 ga to main neg buss with the engine ground. the panels are not far from the neg buss on this boat, so i might as well use the good access of the panel bar. thanks for the clarifications!

 

[jssailem]

i have has a neg buss that goes to "DC neg" and another buss right next to it that goes to "DC ground" . i will be jumping the two panels neg buss with an 8ga wire and the two pos buss with an 8ga wire. i understand the "dc neg" buss should go to the boats neg buss bar which is connected to ground / engine. so what is the additional buss that says "DC grounding" ?

Clarity in wiring is important.
DC Ground and DC NEG are not identical.
BlueSea engineers provide clarity to the subject when installing a traditional metal breaker panel.

DC Ground Optional - install grounding system wire​

The grounding wire (bare, green or green with yellow stripe and normally non-current carrying) should not be confused with the negative ground wire (black or yellow and normally current carrying).​

In Boatowner’s Illustrated Handbook of Wiring, Charlie Wing identifies three purposes of DC Grounding:​

1. Holding conductive housings of low voltage (under 50 volts) DC devices at ground potential by providing a low resistance return path for currents accidentally coming into contact with the device cases.​
2. Providing a low resistance return path for electrical current, preventing stray currents that may cause corrosion.​
3. Grounding metal electrical cases to prevent emission from inside or absorption from outside of radio frequency noise (RFI).​

ABYC requires that grounding wires be sized no smaller than one wire size under that required for current carrying conductors supplying the device to which the grounding wire is connected.​

A full treatment of this subject is not possible within the scope of these instructions and there is controversy surrounding the general subject of DC bonding, of which DC grounding is a component. It is suggested that installers not familiar with this subject consult one of the reference books listed elsewhere in these instructions.​

​

Your Statement:

"i understand the "dc neg" buss should go to the boats neg buss bar which is connected to ground / engine."​

​

If by this you mean that the "DC Neg Buss" (on the panel labeled "DC - Buss") is connected to the battery NEG post.... then yes as most engines have a wire from the Batttery Neg post to the engine.​

​

The statement "Isolated" on the Paneltronic documentation refers to the choice that the metal frame of the panel is not connected to the boat ground wiring.​

​

Stay Safe.

 

[domer94]

john , since the "dc neg" and "grounding buss" as labeled on the panel bars are isolated, i will just use one bar to connect all the neg load wires and connect those to the ships ground (neg buss bar) which is grounded to the engine

 

[dlochner]

The grounding wire (bare, green or green with yellow stripe and normally non-current carrying) should not be confused with the negative ground wire (black or yellow and normally current carrying).

The wires identified here are typically used in AC wiring not DC wiring. Most of us are familiar with household Romex wire, which used the bare copper wire. When stranded wire is used the ground is green in North America and green/yellow in Europe.

Current ABYC convention is for DC- wires to be yellow to avoid confusion with the AC hot wire which is black. In older boats this is an issue, black DC- can be easily confused with black AC hot.

The DC ground is simply a suitably sized cable that goes from the DC bus to a common point, point typically on the engine block where is it joined with the AC ground (green wire). Practically, this the is the DC- wire necessary to complete the circuit for the starter, which is typically case grounded, meaning there is no dedicated DC- connection, the metal in the engine serves as the DC- cable. Some alternators may be case grounded, again meaning there is no dedicated DC- post or connecting a dedicated DC- wire to the alternator is not needed.

In devices which have both AC and DC circuits in them, such as chargers and inverters, it is important to have a case ground, which will complete the AC circuit in the event of a short to the metal case. This is primarily to prevent shocking should some one touch the metal case while also touching something grounded, doing so would complete the circuit across the person's heart, a practice generally frowned upon by cardiologists.

 

[BAD ORCA]

john , since the "dc neg" and "grounding buss" as labeled on the panel bars are isolated, i will just use one bar to connect all the neg load wires and connect those to the ships ground (neg buss bar) which is grounded to the engine

I have the same panels. Thats what i did as well. I believe the other ground busbar would come into play if a boat has a bonding system.