What gauge to feed 4 bank switch/fuse block?

[Jay415]

I have only one good spot to mount a switch/fuse panel and it's about 11'-13' from the battery. 1 bank for FF about 5'-6' (3amp?), 2nd bank for bilge about 15' away but close to battery so a short negative wire (1.5-2amp?), 3rd bank for nav lights eventually, and 4th bank a cigarette lighter accessory plug for cell phone and stuff. All will be connected to a 10 amp breaker at the battery so I am planning to keep it under 10amp total for the 4 bank. 12 awg should be plenty right? At 10amp my voltage loss is .0162v per foot. My max run is the FF which is about 30'-40' including pos and neg. At a full 10amps that's only .486v-.648v loss. I'll only have a 3 amp fuse on it so loss should be much less. At 5 amps I estimate .243v-.324v for 30'-40'. Am I on the right track??? Need some electrician opinions. Thanks!

 

[Bob Landry]

Electrical component manufacturers tend to under rate the load of their parts. I would add a little bit for those. The lighter plug is going to be rated for 10A(most are) and you may want to plug in a spotlight. I came up with an estimate of 17A for the load. No one ever went wrong using bigger load, so I would call it 20A. 13' distance is actually 26, since you have to count both directions. You want to figure for a 3% voltage drop minimum. #10 will give you a little under 4% which would probably be OK for your application, since all of your stuff isn't going to be rumming at the same time, but for a couple of bucks difference in price, #8 will put you a little under 3% which is where I would rather be. That covers the feed to the fuse block. Then you need to fuse the individual circuits for the load that they will be servicing. I personally use #8 for all of my main feeds, except the TM and it gets #6. Also use AWG wire, not SAE, it's a little larger.The idea is to keep the heat down in the wire.

 

[Jay415]

Ok so you recommend running 8awg pos to the fuse/switch panel and then run 8awg to a ground terminal block. From there I'm safe to stick to 12awg for the FF (4'-6') and also back to the bilge about 15' for the pos and prob a 2-3' neg right?

I used 6awg for the bow TM as both batteries are in the stern.

 

[Bob Landry]

Yes. Use #8 for the ground also as it's also a current carrying wire. You could go larger, but there's no need to, just don't go smaller. #6 is plenty good for the TM, just don't forget to put a fuse or C/B within 7" of the battery. Use whatever size the TM manufacturer recommends. You can use smaller wire for the FF if you want to, but no one ever got in trouble using wire that was too big.
As a guide, look around on-line for a voltage drop chart. They are all over the place and West Marine has a good one. You'll see info for wire size/ distance that will give you 3% and 10% voltage drop. You always want the size wire that will give you a 3% drop. There will also probably be info for 110V, but it doesn't mean anything for your purposes.

 

[Jay415]

For the TM I have 2 batteries with a 60 amp breaker at each battery then to a perko switch.

I have been using a voltage drop chart and as per the chart 10awg is plenty for a 12' distance (I measured the exact distance) so for 24' @ 20amp is a .576v drop. I am very rarely if ever, going to go over 3-10 amps of use. FF, Bilge (when it pours), and the socket for a cell phone charger. The whole thing is going to be wired to a 10 amp breaker that's built into the battery box so that's gonna limit the use as well.

Also I'm using Minn Kota TM power centers as my battery boxes which have built in lighter sockets which have 10amp circuit breakers on them. So I'll have them avail too.

Can you recommend a ground block? I was looking online and can't find what I'm looking for. I'm gonna try local when I get a chance.

 

[Bob Landry]

For all of my wiring jobs, I'm partial to the marine specific products, Blue Sea, Marinco, Ancor... You will never go wrong with them and they will probably last longer than you will. The Buss bars made by Blue Sea will work well for a grounding block. Also look at the Power Post.
I may be overkill, but my customers pay me good money and I give them what I thnk is the best and most reliable.

 

[Jay415]

I hear ya. You give good advice though thx!

 

[Jay415]

Hey Bob I went with 8awg. For only $.17 more a foot I figured it would be better in the long run.

Now another question.
Setup: Battery in the stern. Ground block and switch panel in the bow.

For the stern devices (bilge, stern nav light) Should I run a long ground to the bow ground block for one location organization? Or run short grounds directly to the battery (my original plan)

 

[Jay415]

Also this is what I decided to go with:

Blue Sea 2314 MiniBus 100 Ampere Common BusBar 5 x 8-32 Screw Terminal with Cover https://amzn.com/B000OTJ89Q

Seasense Marine 3 Way Switch Panel https://amzn.com/B002VHWLP2