Newbie Electrical Question

[KeelsonGraham]

Apologies for asking such a dumb newbie question. I've searched the technical wiki and can't find the answer, probably because it's too basic.

Looking behind the electrical panel I see two rows of connections attached to the hull which I assume form a common (negative) busbar?

So, is there also somewhere a common positive busbar?? In aviation parlance a 'DC busbar'. Presumably not every CB on the panel is connected directly to a battery terminal??

[Stu Jackson]

The terminal strips behind the electrical panel that are glued to the hull form the DC negatives points of connection simply for convenience sake.  It is one of many methods to do so, and simply the one Catalina chose to use.  If you look closely, you'll see that the terminal strips, which have barriers between the screws and lugs, have bridging connectors or jumpers, between many of them.  These, in turn, are connected to the various fuses or switches on the inside of the panel.

There is no positive set of terminal strips because the positive power comes from the batteries, through the switch, with the single positive feed from the C post of the switch to main positive bar on the panel itself.

When I bought our boat, I drew a wiring diagram of that entire set of term strips.  IIRC, the left (aft) section of it also included the incoming A.C. wires.  You might consider doing the same.  Sorry, I never did scan that drawing.

[KeelsonGraham]

Thank you Stu. So, effectively, the DC busbar is on the circuit board. That explains it!

[KWKloeber]

This explains the strips behind the distribution panel:
https://c34.org/bbs/index.php/topic,10640.msg82739.html#msg82739

As always no one knows for sure what "your boat" has or what a PO has done so it's always best to provide a pic when asking about something specific to YOUR boat.
The manual shows the strips (although as noted in the explanation the manual isn't 100% accurate/complete (and refers to a terminal strip as a bus.)

[KeelsonGraham]

Thank you KWK. That post was a really useful read. So, the strips I was referring to are not simply a common ground - apparently. And yet on my boat I see no red wires emanating from either strip. Unless the PO used green/white for positive.

[Dave Spencer]

Green and white wires in the picture are 120V AC Ground (green) and neutral (white).  The black wires are DC ground.  The DC positive comes from the battery via a fairly large cable to the 1 / 2 / Both / oOff switch and then the power is distributed to the circuit breakers from the common post on the switch.  There is no terminal strip or bus bar for the positive DC.  Instead, you will see jumper wires running first from the common post on the switch to a breaker and then from breaker to breaker to provide power for each circuit.

Hopefully this is clear.  May I suggest that you be extremely careful working in that area if you aren't able to distinguish AC from DC wiring and make sure the AC power is off.

Good luck with your project.

[KeelsonGraham]

Thank you Dave. Now I understand!

[KWKloeber]

Thank you KWK. That post was a really useful read. So, the strips I was referring to are not simply a common ground - apparently. And yet on my boat I see no red wires emanating from either strip. Unless the PO used green/white for positive.

Consider a corollary.
You appear somewhat familiar with wiring and bus bars.  If you look at the inside of a house breaker panel (a distribution panel-breaker panel-load center,) just like the distribution panel on your boat there are bus bars.
The negative (neutral) bar and a positive bar that runs down the middle and the breakers clip into.
A boat panel is the same, a separate negative bus and as Stu explained the positive bus that is on the breaker part of the panel that breakers don't clip into, but get screwed down onto on that bus.

I have switches and fuses and there is no positive bus per se, but the series of switches are ganged together with wires jumping from one to the next.
Of course each circuit is then fed from each hot wire > switch > fuse > circuit, or in your case hot bus > breaker > circuit. If a circuit consists of two loops (say to different cabin lights) there's two feeds from a breaker, rather than a feed from a breaker to a bus (or terminal strip) then to the two circuits.

More newbie questions just hollar.

[KWKloeber]

PS:

yellow is the new black (alternative to black for -12v conductors to avoid confusing -12v (black) with +120v (black) when they run together.)  So you may see both black and yellow connected to a negative 12v bus.)

It **appears** that your -12v bus may not be bonded to your 120v ground (green) portion of the terminal strip, which is non compliant w/ the ABYC standard.  The bond is for safety to prevent an electrocution.  So you might want to have a qualified marine electrician inspect the boat.

[KeelsonGraham]

Thank you KW. More very useful insights.

I'm not planning to go near the 240v system. But now I at least know what I'm looking at and how to look for a suitable DC CB to tag my AIS transceiver onto!