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Friday, April 15, 2011

DC Electrical Mains

After finally receiving a couple back ordered parts, I finished assembling the (admittedly overengineered) panel for the main DC terminals and fuses. Always trying to optimize space while keeping things tidy, it *just* fits between two pairs of fuel supply/return hoses for the day tanks.
Panels mounted between fuel hose runs
Mounted in the right hand panel are the pairs of terminal studs for each battery bank. The studs feed through the bulkhead and have a nut/washer on the other side (they are designed for thru bulkhead  applications). The battery cable lugs will be attached on the other side. The battery boxes for the electronics and engine start battery are directly behind the terminals, inside the aft dinette riser. Behind the House Bank terminals is the large PVC conduit that feeds the battery cables for the house banks, located under the floor, center, forward end of the main salon.

Mounted in the left hand panel are the main fuses, shunts and "first stage" distribution terminals. The fuses handle 125 amps. The shunts are used to measure current flow for the battery monitors (coming later),

As you can see, not everything is connected. I have a little flexibility here as to how I can wire things, of which I am undecided. By fashioning jumpers (made of flat copper bar, or short sections of battery cable), I can patch things a couple different ways. I could use all four fuses for the + lead for each of the four battery banks. Or I could fuse each of the + and - leads for each bank with the addition of a few more fuses in the space below. That probably sounds a bit overkill as you do not usually see both sides of a battery bank fused.

Why fuse the '-' lead?
It comes from amateur radio where it is "common practice" to fuse both leads. The reason: lightning does not discriminate the '+' from the '-' wire, it can just as easily strike the non-fused side and fry your battery and/or equipment. In a SSB installation on a fiberglass sailboat, it is common to tie all large metal items together with the ground system in order to get the best radio performance. This includes: life lines, standing rigging, masts, tanks, engine blocks, etc. which turns the boat into one big lightning rod. Anything you want protected from a lightning strike, like batteries, should be behind a (fast acting) fuse. Now lightning strikes are not common around here, but are more likely to happen in tropical areas. Protecting sailboats from lightning strikes, with their big lightning rod sticking up from the middle, is not an exact science. So, it is all down to how paranoid do I wanna be?

Like I said, I am undecided,  and I got time. Which ever way I choose, I could always change it later with little effort.

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