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post #2 of Old 11-25-2007
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Originally Posted by Perithead View Post
I am currently working on my '83 Mac 25's wiring system. I have never really understood what I was looking at till I purchased The 12 Volt Bible for Boats by Miner Brotherton revised by Ed Sherman (second edition), which really helped me understand the electrics on my small boat.

The running lights have never worked since I have had the boat and currently dont still after fiddling with them today. My FM/CD player was hooked up straight to the battery so I rewired it to my control panel(this was the first thing that I have done correctly in my vast trials with electricity).
That's a start.
My wiring system (I think) is not normal. The + and - coming off of the battery run directly to an approximatly 4x12 peice of thick plexiglass with 2 narrow copper sheets running parrell down it lengthwise (one is for + and one for -). This has about 4 seperate + and - studs on it for various items. From one of them is wire leading to my control panel. Also off of it are wires leading to my bilge switch and bilge, and my VHF radio. I dont think this is a good thing but I am not sure. Do my bilge and radio need to be ran to my control panel? If anyhting what is so bad about my switch and fusesless plexiglass control panel?
The two copper sheets really should be replaced with proper marine buss bars, that are made of tinned copper. Untinned copper just corrodes to damn easily, leading to increased resistance, and then eventually fires.. IMHO, you probably should have a big fuse between the battery and the positive bus bar if the run is of any significant length.

As for the bilge pump, having that hard wired isn't necessarily a bad thing... but I don't see why you'd have the VHF wired directly to the battery.

As for the switch, are you talking about the big rotary battery switch? Also, can you post a photo of the plexiglass control panel, since that could describe a lot of different things. BTW, the photo posting on sailnet basically blows chunks. Get yourself a photobucket account and post the photos to that, and then link to them using the icon.
The main panel works and I wired my FM/CD to it today and it works well. I have a total of four ummmm... switches? to wire different applications too. BUT there is only a place for ONE ground????? I dont get it, shouldnt it have 4 different places to ground things?????? A freind and home electrician told me to splice wires together and ground all the applications on the one ground. Is this correct?

On my control panel, the ground is a copper strip with a ground wire attached that runs to the - point on my battery. I guess that being so then everything that I ground (on the panel and the plexiglass panel) is then grounded to my battery. Is this alright? Should I make a ground that is on my swing keel winch or something?
Are these switches or circuit breakers?? If they're just switches, you really need to replace them with either a fused panel or circuit breakers IMHO. The grounds should connect to that copper strip.. but again, if it is plain copper, you need to replace it with a marine-grade panel. One other question—is the wire your working with stranded and tinned, stranded but plain copper or solid? Marine grade wiring should be stranded and tinned. Solid wiring has no place on a boat, and neither does untinned wire. Both are serious hazards—the solid wire can fatigue with the vibration of the boat movement and then work harden and break... the untinned wire corrodes and then can cause a fire... also the strands in marine-grade wire a bit finer, so they're less prone to work hardening and fatiguing.
Do I need a master battery switch for only one battery? My assumption is that the master switch is only there to eliminate anything that may use the battery even when it is not turned on. For example, a VCR still draws a little power when switched off for the clock. Is this needed?
Yes, you really should have a master battery switch, and it should be mounted in an easily accessible location.
I have a good freind who is an home electrician by trade and good at what he does but I am not sure what he knows about boats. (he is the one that wired up my FM/CD to the battery) I knew that wasnt good but it worked at the time.
The main difference between wiring a home and wiring a boat are:

1) You have to use marine-grade tinned stranded wire
2) All connections should be made using marine-grade tinned crimp connectors
3) Any terminal connections should be captive type terminals—preferably ring terminals
4) Solid wire and wire nuts have no place on a boat
5) All circuits, with the possible exception of a bilge pump must be on a breaker, and the breaker should be of smaller current rating that the wiring attached to it
6) The wiring should be supported every 18" at a minimum, if it is not running inside a conduit to prevent work hardening of the wiring
7) Most of the marine 12 VDC wiring is much heavier in gauge than the 110 VAC home wiring due to higher amperage requirements

If you don't have two batteries aboard, it might be wise to get a Blue Sea Dual Circuit Plus Battery Switch with ACR and a second battery to use as a dedicated starting bank.

If you need a circuit breaker panel, you could get this, or get a fused switch panel, like this.

Hope this helps.


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Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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