Wire size?

[chbarnha]

Question? I’m going to be running electrical off my cranking battery to a panel. This panel is going to have 6 switches as well as a USB port. I’m going to be putting a battery disconnect switch inbetween. What gauge marine wire should I run from the battery to the disconnect and from the disconnect to the panel? I was thinking marine 10ga. Would that be enough or do I need to go to 8? Thanks


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[MN Fisher]

10 gauge should be fine for that application.

I would personally run 10-Gauge to the disconnect, then 10 Gauge to a fuse box, then you can drop to 14 or 16 from the fuse box to the switches.

 

[chbarnha]

10 gauge should be fine for that application.

I would personally run 10-Gauge to the disconnect, then 10 Gauge to a fuse box, then you can drop to 14 or 16 from the fuse box to the switches.

I forgot to add the fuse box, I already have a fuse box. That is the plan.


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[DaleH]

Ditto what MN Fisher said …

 

[maintenanceguy]

Depends on how much current (amps) everything on your fuse box draws.

You can use any size wire you want, as long as the fuse at the battery is sized properly to protect the wire. But...if that wire and fuse from the battery isn't big enough to power everything on the fuse panel, you'll constantly blow that fuse.

Add up your loads to figure out the total amp draw of the fuse box and look up a wire ampacity table to size your wire. Size your battery fuse to the ampacity of that wire.

 

[DaleH]

As Ryan posted, an 'ampacity calculation' is certainly the by the book method to do so, where you make sure your ampacity can handle the maximum worst case amp load. That 'worst case' is where every circuit is energized or ON. Most items list their amp draw, but if you have something like a light rated in watts, simply divide the wattage by 12.6 to get the amps.

Also remember that the total ‘ampacity’ for your circuits will be the total length FROM the battery TO the load and BACK again, so if 10’ away, that’s at least a 20’ run for factoring the correct wire size. Too many miss this key detail ... of doubling the circuit length!

If critical circuits, like Nav lights, VHF radio or bilge pump, use the 3% loss value coulmn. NOTE on my bigger boats, I run two main circuits, for critical items and then house items (deck or cockpit lights, am/fm radio, or livewell pump etc.), otherwise considered as non-essential to the boat's running and primary safe operation.

But FWIW I've equipped many a small boat to 14' of typical wired accessories with main runs of 10 AWG without issue.

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