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Old 27-02-2019, 18:45   #1
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Adding power distribution block

Looking for some sound advice about 12V DC systems. Iím planning to add some 12volt accessories to my boat. For now, a forward facing LED light bar and 3 underwater lights to the stern with other accessories later on. I need to add a 6 circuit Blue Sea System power distribution block with negative bus to the helm. The distance from house battery to the helm is approx. 27 feet. My question is what size copper cable to run from the house battery to the PDB and what size switchable breaker would I need in-line between the battery and PDB? I believe the light bar draws 11+ amps and the underwater leds draw 650mA each. Thanks
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Old 27-02-2019, 20:22   #2
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Re: Adding power distribution block

you would run it from the house swtich. not the battery.

get the blue sea app. for just the lights it says 6awg. but then you can't add anything else to the fuse block. 4awg would be better.

the helm would already have a power feed. if that is too small for the new stuff. consider replacing it with one bigger one, instead of running a 2nd small one.
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Old 28-02-2019, 04:46   #3
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Re: Adding power distribution block

Sizing app is called Circuit Wizard, use RT distance, ask if any of the variables aren't clear.

Best to use a rope or hose to get the actual distance rather than guesstimating.
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Old 28-02-2019, 14:56   #4
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Re: Adding power distribution block

Thanks for the replies. Smac999, why do you suggest running to the house switch and not the battery. It appears the cables feeding the house battery switch are smaller in size. The largest wire feeding the helm that I can see is feeding the power accessory plug which is probably 10 ga or smaller. I have plugged the variables in the App and with 13.02 amps it suggests 6AWG for voltage drop. It calls for a capacity with derating factors---81.6 amps. With that being said, would I install a breaker with a rating less than 81.6 amps?
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Old 28-02-2019, 18:23   #5
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Re: Adding power distribution block

Quote:
Originally Posted by Jetboater View Post
Thanks for the replies. Smac999, why do you suggest running to the house switch and not the battery. It appears the cables feeding the house battery switch are smaller in size. The largest wire feeding the helm that I can see is feeding the power accessory plug which is probably 10 ga or smaller. I have plugged the variables in the App and with 13.02 amps it suggests 6AWG for voltage drop. It calls for a capacity with derating factors---81.6 amps. With that being said, would I install a breaker with a rating less than 81.6 amps?
I dont know what your future plans are, but if it was me I'd size the fuse to be about 10amps over the total amp draw.

For wiring I would likely go 2 or 3 sizes up from the recommendations as this gives you ample grow for electronics.

I would run from battery post to bus bar to switch to DC panel to individual items.

You will fuse wires:
- battery to bus bar
- bus bar to switch
- switch to DC panel
- DC panel breakers will be sized to be just over max amp draw of each unit.

IF any wires in the circuit have a LOWER capacity than the fuse/breaker, you will need to fuse that section accordingly.
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Old 28-02-2019, 21:28   #6
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Re: Adding power distribution block

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Originally Posted by Jetboater View Post
Thanks for the replies. Smac999, why do you suggest running to the house switch and not the battery.
because everything needs to run off the main switch except for bilge pumps and co2 monitor, propane monitor etc. only safety things go direct to battery.
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