DC Electrical Distribution

[Wanderer2011]

I have read alot on here and have a DC distribution question. I have worked out a Load/Distribution plan and here is my question.

I understand the CB is to protect the wire (after CB), so here is my setup as an example.
60Amp fused feed from Main Switch to Distribution panel

I'm using 1-15Amp breaker (on Dist. panel) feeding Nav inst./VHF, max load is approx 8Amps.

Should the feed from the CB on the Dist. panel go to a fuse block with the appropriate fuses for the different instrument/VHF loads.

Or feed to a common buss for the instruments/VHF and drop the Amp of the CB, as long as the instruments/VHF have thier own fuse?

Trying to make a nice clean, understandable setup.

Hope this is clear, and Thanks for the advise

Thanks
John

[HPLou]

Most instruments and radios are supplied with their own in line fuse so it would be redundant to to connect the separate instrument leads to a fuse block from the CB.

[mitiempo]

I agree. I would feed from the 15 amp breaker on the panel to a terminal block for neatness and from there to each item.

[PaulfromNWOnt]

I would look at it in this way:

If you eliminate individual fuses, you are essentially protecting each item with a 15 amp fuse. That may be a little high for most components. You could leave the primary circuit at 15 amps, but I'd still have individual fuses at their specified rating.

[mitiempo]

I didn't suggest eliminating the fuses the products come with. I have never seen a vhf that didn't come with its own fuse and many electronics items either come with their own fuse or require an inline of a certain size. These are normally very close to the main unit. But I wouldn't go to a fuse block.

[Wanderer2011]

Hi All,
Thanks for the input, guess what i'm wondering now is, do I drop the value of the CB to a more resonable value for the load. Keeping in mind of the largest wire size i'll be supplying.
And no, i'm not eleminating fuses that are already installed inline with the equipment.

Thanks

P.S. This site is great, and very helpful. Thanks to you all.

[mitiempo]

I would keep the CB at 15 amps. Even if you are using 16 awg - the smallest wire ABYC allows - it has an ampacity of 25 outside and 21 inside engine spaces.
It is the wire you are protecting.

I would use 14 awg minimum for electronics, larger if the run is very long. Aim for 3% voltage drop or less. Here's a wire size calc. http://boatstuff.awardspace.com/awgcalc.html

[fairbank56]

There are exceptions to the minimum 16 gauge rule. The ampacity rating of wire is dependent on size, insulation temperature rating, wet or dry location, and whether the wire is bundled with other wires, sheathed or in conduit as well as if it's in an engine space or not. The 25 amp rating given is for wire in a dry location rated at 105°c and not bundled, sheathed or in conduit. If it's run with other wires in a dry location and rated for 105°c, it's good for 17.5 amps. Votage drop is of equal importance, and if you size it for minimum voltage drop, it will usually be way over-rated for ampacity. (a good thing)

Eric

[mitiempo]

Still well within the loads the op is going to use them for. I would still go a bit oversize at 14 awg. For that 15 amps is fine.

The exceptions noted are for ampacity. It is still the smallest wire that should ever be used on a boat for a wire run.

[fairbank56]

Wanderer2011

Just remember, voltage drop is just as important as the current handling capability of the wire. If your VHF is within 10' (wirerun) of the DC panel, you can use 14 gauge but if longer (up to 20'), you should use 12 gauge. Either size can handle way more than the 5-6 amps required of the VHF but it must be oversized to keep within a 3% voltage drop. The resistance of the wire becomes a big factor in low votage systems. Critical circuits should be kept under 3% voltage drop while non-critical such as cabin lights can be kept under 10%.

Eric