Why is mine so small?

[family affair]

...the circuit for my main panel that is.
When looking at my battery switch set-up, I was perplexed as to what wire actually fed the main panel. The wires to the batteries and engines are very heavy gauge and understandably so. The wire going to my main panel is only 8 ga on a 50 amp breaker. I thought to myself, that can't be it?! When I add up lights, wipers, pumps, and other electronics, this seems WAY to small for the potential demand, especially if fishing at night. Why would GW not provide more juice? Am I missing something?

 

[seasick]

Yes you may be. Extra capacity means extra cost not just for cable sizing but for all switch gear and distribution components. In general, good manufactures will design a cable plan that meets ABYC specs for the equipment included with a boat model as well as the more common options, That said all may be fine until you install that multi hundred watt music system

First of all, the carrying capacity for conductors depends on the wire gauge and the back and forth run length. So what works well for a 15 ft vessel would not be sufficient for the same load on a 30 foot vessel.
As important is the issue of recommended fuse/breaker size and actual start/run/inrush current loads. Finally, not all loads and max loads are in demand at the same time. For example, your VHF radio draws a lot less current in receive mode than when transmitting. To a degree the length of time a load is used (duty cycle) will affect wire sizing. Circuit breakers typically will be rated lower than the potential max current draw because they take a period of time to heat up under load before they reach the trigger limit.
Another complication is the fact that electronic equipment wiring should not have more than a 3% voltage drop under load ABYC code) whereas non electronic loads such as a windlass or a pump are OK with up to a 10% drop).
My long answer can be summarized by saying that design of DC cabling wire size is not all that simple.

 

[family affair]

Hmm. I guess as long as no one flushes the toilet at night, with the spreader lights on, the live well going, and someone washing the deck or washing hands, I'll be ok. I'm just surprised that GW didn't at least bump it up to 6 ga and give a bigger buffer on the breaker.

 

[Sardinia306Canyon]

The wire going to my main panel is only 8 ga on a 50 amp breaker. I thought to myself, that can't be it?! When I add up lights, wipers, pumps, and other electronics, this seems WAY to small for the potential demand, especially if fishing at night.

50A is a lot of electronic stuff running and if it would be too weak then the 50A breaker would trip.
Should you install more electronics, particular high amp ones you anyway need to add more switches and run the cable properly fused to the bus bar or in extreme cases add a new one. Option would be ta make/have make a new switch panel with more switches, but then you need to beef up the breaker and cable size or make two 8AWG cables, one for each row of switches. Consider also that most switch panels have switches with the flat quick disconnects and power is daisy chained from one switch to the next and that can't take a lot of current too.
Just a hint, replace your old incandescent bulbs with led ones and you will lower your power consumption a lot.

Ex owners added 3 wildly placed fused Blue-Sea bus bars inside my console what makes all the cable routing like a plate of spaghetti, unfortunately and i hate that.
Next winter i will probably rip most out and start over doing it better and with labels on the cables to make future changes or error tracking more simple.

Chris

 

[Hookup1]

On my islander there are two power feeds from batteries to the helm/electronics box/overhead. The breakers/fuses are sized for short circuit protection of the wire runs and the device. The devices don't really draw that much power.

You can use the red/white hardtop power to power all your electronics.



Only time I have found this to be a problem is if you have a monster amp and subwoofer. I installed a 4th battery for the bow thruster/windlass and subwoofer amp located in forward compartment under v-berth.

 

[family affair]

On my islander there are two power feeds from batteries to the helm/electronics box/overhead. The breakers/fuses are sized for short circuit protection of the wire runs and the device. The devices don't really draw that much power.

You can use the red/white hardtop power to power all your electronics.

View attachment 37675

Only time I have found this to be a problem is if you have a monster amp and subwoofer. I installed a 4th battery for the bow thruster/windlass and subwoofer amp located in forward compartment under v-berth.

I'm reasonably sure mine only has one, although there is a separate fuse panel in the hardtop. I can't imagine they would wire that directly to the battery with no manual disconnect. I want to say the only 3 pairs of leads I have wired directly to the battery (other than engine related) are my charging wires, inverter wires, and possibly tabs.

 

[Hookup1]

I'm reasonably sure mine only has one, although there is a separate fuse panel in the hardtop. I can't imagine they would wire that directly to the battery with no manual disconnect. I want to say the only 3 pairs of leads I have wired directly to the battery (other than engine related) are my charging wires, inverter wires, and possibly tabs.

Look at the Owners Manual for the wire list. Look for the high amperage connections possibly with inline fuse. You have a newer model than my boat but it should be similar. These power wires will come out of the rigging tubes and connect to battery terminal or switches. There is a circuit breaker with a red button on it on my switch panel.

 

[family affair]

Looks like the only direct connections I have to the batteries are bilge pumps, tabs, and windlass.

 

[Sardinia306Canyon]

and possibly tabs

I don't think so.
Trim tabs are usually connected to engine ignition key so that they retract when you turn the key to off.
If you don't have auto retract then they will be connected to house battery switch or a connected bus bar to disconnect them when battery switch is in off position.
There is no reason why they should have always on power.

Looks like the only direct connections I have to the batteries are bilge pumps, tabs, and windlass.

Same for windlass control and bilge pump manual switch, auto bilge pump should be connected to the two float switch breakers in your switch panel.
A bilge pump should get +12V thru the float switch and thru the manual switch on your dashboard, but only float switch must be always hot.
There may be a direct short link cable to windlass solenoid so that windlass is pulling the high amps directly from battery but get the up/down signal from the windlass switch on your dash.
Chris