Most modern boats contain two electrical systems, 240 volts AC (mains shore power) and 12 volts DC (battery). Few people realise that the low voltage DC system can cause as much danger as the high voltage AC mains. I can only get my head around electricity by thinking of it like water. The wire is a pipe, ‘Voltage’ is the volume passing down the pipe, ‘Amperage’ is the speed of flow, ‘Wattage’ is the energy delivered (or demanded) at the end of the pipe. The + line is the pipe running from a reservoir (mains or battery etc) towards the ‘work’, the – line is the pipe taking the water away. Break any part of the pipe and the flow stops, or diverts to the wrong place! High ‘volume’ at slow ’speed’ will turn a water wheel just as fast as low ‘volume’ at high ‘speed’. So, a 500 watts motor pulling up the anchor may draw over 40 amperes (very fast) at 12 volts (watts ÷ volts = amps) and double that at ‘breakout’ of the anchor, but at 240 volts, the same power motor would only draw 2 amps (very slow). Guess which one will overheat and catch fire first!! Its the slow but sure 240 volts against the fast and frantic 12 volts. How thick are the wires to your windlass motor?
Now 240 volts and 12 volts do not mix well. They should be kept separated from each other. Even wires running next to each other can be dangerous. Run a DC wire alongside a high voltage AC and the current running down the AC will ‘induce’ a current in the DC wire, causing it to overheat. (FIRE!) OK to cross over each other, but keep them several inches apart where they run parallel. And how are you kept safe from faults? At home you have a ‘consumer unit’, probably with trip switches and such like. The 1st photograph shows a system I found on a boat I surveyed. That’s right, it’s the well known breaker plug!! Now I’ve nothing against them in their place, but as the only safety feature on a simple extension lead bringing AC power aboard? The words ‘death trap’ spring to mind!! Take a look at the other photo’s. ‘Crimp’ connecters, always good for a laugh. Very unreliable due to corrosion near salt water. Loose wires to bounce up and down until they break. Corroded wires and thin, loose wire to the battery, just the thing to overheat or break when you least expect it. If in doubt, ask for advice.
One of the best places to visit for advice is www.safeshoremarine.com - look up their advice on galvanic isolators.
A little more thought and a little more care can save you from an expensive repair!!
