Hi, folks. I'm not sure how the 240 is handled in the in the non-English speaking countries of the former British Empire [:~|), but in the US, 110-120 and 220-240 VAC are very different.

In the 220 case, the service is composed of 2 110s of opposite (180 degree) polarity, with a ground that is not tied to either side (normal house power). A 110 circuit is made by taking one side of this line and using it for 110 with the other side tied to ground at the entry junction box. Thus, we have a hot line at 110 and a "common" tied to ground. One side of the line is actually a ground (to within the voltage drops induced by the line length to the junction box). Many cheap appliances count on this grounding structure. If the plug goes in backwards, no fuse is blown. The case of the device becomes "hot". A number of rock-and-roll musicians have been killed this way (stand on wet ground and touch your lips to the microphone or grab your guitar).

If one side of the 110 is not tied to ground, the effect is DEFINITELY detected by a polarity detector. The sensing lamp is tied between common and ground on a polarized plug, and should not light (no power differential between the two lines) if the circuit is correct. If common and ground are not tied, the lamp will light. This means that the polarity is reversed (common tied to wrong side) or there is no ground at the source. There can be an "open" (lack of connection) of the proper ground in the boat, or a similar problem at the dock power source. In either case it can be dangerous. Please be careful, Timm and others. For the price of a airline ticket to Portland, and some MGD and steaks (MGD AFTER I'm finished fixing the problem if I'm not dead at that point -- steaks might be self cooked at that point).

Timm, if you're handy with a voltmeter, you can check into this. Is the service at your dock or the 110 variety or is it 220? Typically, if you are running up to 20 amps, the power is 110, above that you can probably have 220 (and a fancier plug and internal electrical system on the boat).

You should only have 3 prong polarized 110 plugs (jacks, actually) in the boat. Use the skinny pin ended leads for the voltmeter, and stick them in the jack holes. You should read 110 AC between the thinner prong hole and the ground (third hole that is kind of round). You should zero between the wider prong hole and ground. If the second measurement is not zero, disconnect shore power and any invertor (bend over, place your head between your legs, etc...), and it's time for continuity checks (ohm measurements to find out if proper grounds are not connected). Having a 12 VDC to 110 invertor should still result in the same wiring arrangement inside the boat, one side grounded. However, it would be harder to check the integrity (ground connection) of the dock circuits if you can't turn the power off.

In Timm's case, the 110 is rectified for battery charging, but I'll bet the 110 goes straight through for appliances. when no 110 is present, the same lines are used to transport the invertor 110 output generated from the batteries. there is conceivably a problem in there depending on how the circuit is built, and the voltages sensed.

In any case, I's have only ground fault interrupt plugs in the boat (the kind you find in bathrooms, especially in hotels where they don't want to get sued too often).

In houses, the power is "balanced" by running one side of the 110 to part of the house and the other side 110 to the rest of the house. High power appliances are connected across the 220 (to reduce current reaqiuired). In this case, the appliance is tied to the ground on its case, and both 110s "float" (i.e., there is not a common line).

Major difference on the European (and other) 240 is the lower current required (half the current at twice the voltage for same power). However, this can lead to skinnier power lines made for the lower current. A friend bought a British boat and ran it on

110. There were problems in the electrics which I would attribute to the skinnier lines used in the boat (intended for 240). Ther would be more power drop at peak loads and draw spikes (e.g., starting electrical appliance).

I'm not sure if the European power has one side grounded, but I'd suggest this is the case since most of the wierd plugs they y=use are polarized. Still, I'm with BC on dangers of 110 on boats. If I'm working on the boat, I use extension cords to shore power, but have no 110 items in the boat. Heck, I have very few operable things that run on 12 volts in the boat.

Hoping this doesn't confuse the situation too much, Cheers Charlie