Electrical wiring yet one more time

[ffaubert]

I'm attaching my proposed wiring diagram for my boat (hopefully, it's readable).

The boat is a 25' MacGregor so there's not a lot in the line of electric toys (windless, fridge, hot water, etc).

With the exception of the battery wires, the rest will be tinned 12ga AWG. I haven't figured out the fuses yet since I don't know what fixtures I'm going to use or what the draw from them would be.

I'm hoping a few of our resident experts will have a look and tell me if I'm on the right track or not.

Of course this is only the 12v part. I haven't figured out the recharging process yet though I am thinking of a combination of shore power, solar and a Honda EU2000iA.

Thanks,

Frank

 

[Johnb]

Frank,

So far so good. For #12 wire the voltage drop for 100 paired feet carrying 1 amp is 0.32 volts. A paired foot is from source to load and is therfore 200 feet of actual individual wire. If you double (or halve) the distance the voltage drop will double (or halve). If you double the current the voltage drop will double. From this you can figure out how much voltage you will lose for each circuit once you know the current draw and distance. I personally don't believe it should be more than 3%, which in a 12 volt system is 0.36 volts. (10% is for house wiring!).

Some other things,

Use marine grade everything.
Follow the ABYC standards, you won't have hassles later if you have to get your boat surveyed for insurance or whatever.
110 volt breakers are not suitable for 12 volt service. It may well be worth springing the bucks and buying a ready made panel.
The breakers only protect the size of wire leaving the panel. Example - if you run #12 down to a bilge pump and then connect up the wires the pump came with they may be 4 or even 6 sizes smaller. When a bilge pump jammed I smoked the bundled up pump wires and added in line fuses after that.

Do you have electric start?
Why do you not have a "off-1-2-all" selector switch?
Do you want to consider bypassing the battery isolation switch for a bilge pump?
Will you get some charging from the engine, how is it connected?

 

[Ed Schenck]

John gives good advice. I like a #10 from the battery to the panel, both positive and negative. Actually I have two #10s but I run a HAM radio. Your diagram shows, I think, battery to battery switch and then to 12v common. That is the wire that is a #10 on my boat.

 

[Johnb]

Formula's are

Vd=0.2*current load*1.26^(AWG-10) -- where Vd=voltage drop per 100 paired feet, current load is amps, AWG=american wire gauge

AWG=10*LOG(Vd/current)+17 -- defined similar to above, except Vd is desired voltage drop per 100 feet

Paired feet is the distance to the load and is thus half of the total amount of wire in the circuit​

 

[Maine Sail]

Formula's are

Vd=0.2*current load*1.26^(AWG-10) -- where Vd=voltage drop per 100 paired feet, current load is amps, AWG=american wire gauge

AWG=10*LOG(Vd/current)+17 -- defined similar to above, except Vd is desired voltage drop per 100 feet

Paired feet is the distance to the load and is thus half of the total amount of wire in the circuit​

There are also many good on-line wire sizing calculators like this one:

http://boatstuff.awardspace.com/awgcalc.html

 

[ffaubert]

Thanks for the quick responses.

My boat has an outboard with no generator so nothing need to go or come from there. I put in part of a 1-2-Both-Off just above the battery. I figured that since there was no electric start needed, I could get away with just an On-Off.

I've put the main fuse on the + side of the battery. Is that correct? I was reading the Ample Power Primer pdf that Stu Jackson recommended in other discussions and it says the negative side.

Thanks again and Merry Christmas,

Frank

 

[Maine Sail]

I've put the main fuse on the + side of the battery. Is that correct? I was reading the Ample Power Primer pdf that Stu Jackson recommended in other discussions and it says the negative side.

Thanks again and Merry Christmas,

Frank

In theory either side can work but the industry, ABYC, insurance companies etc. prefer to see fuses on the positive wire not the negative wire.

 

[ebsail]

Regarding the bilge pump switch.

In theory either side can work but the industry, ABYC, insurance companies etc. prefer to see fuses on the positive wire not the negative wire.

It's acceptable to wire the bilge pump, by passing the on off switch. It still needs a fuse. Now for my own controversial view which is that the bilge pump switch should be at the floor board level or higher for the following reasons.

1. If you have a leak and the bilge pump always empties the bilge you'll never notice you have a leak
2. When the leak worsens, you'lll still not notice
3. When it gets bad enough, the pump will draw down the batteries while you're not around
4 Bilge pump quits
5. Boat sinks
Alternately. If you show up to use the boat and the floor boards are afloat, you'll certainly notice the leak and do something about it. The bilge pump will still go on but late enough for you to notice the leak and do something. If the leak is really bad, (like a hose broke) you can start with #3 in the sequence above.

I've been boating for over 55 years and seen several boats go down while the owners thought all was well. The last one a forty footer at my club last year. Owner has now installed a high water switch which calls him on his cell phone when it goes off. Just my 2 cents

 

[Johnb]

I figure if you have two batteries it is logical to be able to separate them so if one gets used up with interior lighting, entertainment etc you have another in reserve for needs like running lights, VHF bilge pumps etc.

Agree about bilge pumps. I am about to upgrade my system to the smallest pump I can find, manually switched in the absolute lowest part of the bilge and an automatic pump set higher up. I have sailed up the coast on a freinds boat and he required when motorong that the watchkeeper do a bilge check every 1/2 hour, at least through the night.

 

[Johnb]

Also agree about putting fuses in the positive side - you might as well have them where people expect to find them.

 

[mklein@iowatelecom.net]

I hate to ask, but where is a good place to purchase good tinned wire and fuse panels?
Thanks, Mark

 

[Johnb]

http://shop.genuinedealz.com/

Seems to be a good source. You get stuff like heat shrink with adhesive on the inside and heavy duty lugs. I have picked a wire size, #12 actually, and laid in a stash of wire, terminals etc that I bought in bulk. Sometimes it is over size but it remains cheaper than buying it in bits and pieces and it sure is nice to always have it on hand.

There has been considerable discussion on the forum about workmanship, especially in the area of crimping, sealing and support and I suggest it is worth going back and looking for that.