Shore power question - Page 3 - SailNet Community
Old 04-13-2007
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SD, you are right P=EI but I=E/R. P=ExE/R. If R remains constant and E doubles you get 4 times the power.For simplicity in calculation if you have a 1200 watt load at 120 volts the resistance is 12ohms. If you apply 240 volts to this 12 ohm load you get an amperage of 20 amps I=E/R or power of 4800 Watts P=EI. The 1500 Watt drier in NZ is rated at 220 volts.
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Old 04-13-2007
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EBS-

You're missing the whole point of the OP asking about the wiring. We're not talking about useng the same appliances down in NZ... just whether the wiring could be used for 220V since it was originally wired for 120V.

That's also why there's usually a switch on most appliances that can use both, so that the effective resistance changes...and the power used remains the same. If you took a computer power supply, which has a switch on it for 120VAC vs. 240VAC, and left the switch in the 120VAC position and plugged it in... you'd blow it... pretty much as soon as you hit the power switch.

My point is that a 1500W 240VAC hair dryer is going to draw about half the amps as the same 1500W hairdryer designed to work on 120VAC—so the wiring, which was designed for 120VAC is going to be oversized for the 220VAC appliances of the same wattage.

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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.

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Old 04-13-2007
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SD, my point all along has been that any loads connected to 220 volts must be rated at 220 volts. I just get worried when someone says if you connect a 1500 watt hair dryer to 220 volts you get half the amps, because that's only true if the hair dryer's rating is 1500 watts at 220 volts.
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Guys
Just to put a defined point on it - all of the appliances on the vessel now, whatever they may be (TV, inverter, microwave, whatever) will be dumped when the vessel reaches NZ and will be replaced with the equivalent 220v appliances.
So, EBS, there's nothing to worry about on that score. I understand that 220v is going to toast any 110v appliance, for the trip from US to NZ I will continue to use the appliances on the boat now because they're all compatible with the inverter until it is plugged into 220v. That will only happen when I get home.
It was just the wiring, switches, basically the distribution panel, that I was worried about.
It seems that all agree, I have nothing to worry about in that regard.
Thanks again all for the advice.
Oh and SD, "SWMBO" is more about "line of least resistance" than anything else.:-)
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