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Old 23-08-2009, 00:50   #16
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Originally Posted by btrayfors View Post
If you're talking about a boat out of charter from the U.S. or British Virgin Islands, they're all 110VAC/60 cycle, same as U.S.
Actually, many of the ex-charter boats in the BVI are 220V. Including the one I bought out of Sunsail's fleet.
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Old 23-08-2009, 02:33   #17
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CharlieJ wrote "...there is no dependency on voltage when sizing wiring for A.C. systems ..."

My understanding is that if a boat is wired for 220V that it will be undersized for 110V.

Am I wrong?
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Old 23-08-2009, 03:07   #18
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Quote:
Originally Posted by neelie View Post

My understanding is that if a boat is wired for 220V that it will be undersized for 110V.

Am I wrong?
I think you will find all recent or production boats are wired the same. It wouldnt be worth it for a modern manufacturer to change the wiring of a whole boat one size of one voltage and smidgeon bigger or smaller for the other. The wiring is done by a grid and even includes the wiring for the options you didn't want to buy

Its all economics
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Old 23-08-2009, 05:43   #19
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CharlieJ is right about the standard definition of an "isolation transformer". Normally, one thinks about a transformer with 1:1 voltage ratio in/out. No change to cycles.

However, in the boating world some of the most common high-quality isolation transformers also have step-up or step-down capabilities, i.e., they change the input or output voltage. Let's say you were to take an American 120VAC 60-cycle boat to Europe, where 230VAC is commonly used. By inserting an isolation transformer with step-down capability, you could transform the incoming 230VAC to 120VAC needed onboard. HOWEVER, the transformer doesn't change the cycles--you'd now have 120VAC 50-cycle coming in to the boat rather than 120VAC 60-cycle current.

Here are a couple of the current isolation/step-up/down products which are common:

Victron Energy isolation transformer 3600W 115/230V 32/16A - VICITR040362040

Marine: Isolation and Boosting Transformers

Many appliances would be happy with this, but motor-driven ones likely would not. They could run slower and hotter, reducing their life.

What to do about this? Well, some inverter/chargers have the capability to accommodate a 50-cycle input, and to convert it to a 60-cycle output. The Victron MultiPlus can do this, providing pure sine-wave 120VAC 60-cycle current. It also has a 120A battery charging capabiity.

Bill
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Old 23-08-2009, 05:48   #20
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Quote:
Originally Posted by CharlieJ View Post
... You should also note that, contrary to the previous posts in this thread, there is no dependency on voltage when sizing wiring for A.C. systems in the voltages usually used on boats. What this means is, if the candidate boat's A.C. system was properly sized for 120 VAC/60 Hz, then it is properly sized for the European 230 VAC/50Hz. There is, however, a dependency on bundling; i.e., the more current carrying conductors in a bundle, the lower the allowable current.
Hope this helps.
Charlie
This is a very mis-leading statement, even if partly true, in a fairly common practical sense.

Any specific load (Watts) will draw twice as much current (Amps) at 120 Volt, as it would at 240 Volt.


The smallest wire size, used for AC in North America, is #14 AWG; which is rated for 15 Amps (with 600V insulation rating).
The maximum continuous current rating of a 15 Amp circuit breaker (the largest to which a #14 wire can be connected) is limited to 12.5 Amps (80%), or 1,500 Watts.

15 Amps at 240 Volt = 3,600 Watts ( 4.5 HP)
15 Amps at 120 Volt = 1,800 Watts (> 2 HP)
12.5 A at 240V = 3,000W
12.5 At 120V = 1,500W

Typically, most AC loads, on a smaller boat, will be under 1,500 Watts (a hot water heating element), making #14 wire, and a 15A Breaker, adequate*, in those cases.

* Subject to the various additional derating factors (bundling, high ambient temperatures, etc).

Loads are rated in Watts (power); and Wire Sizes are rated in Amperes (current), which varies as the inverse of the applied Voltage, by the Ohm’s Law formulae:

Watts = Volts x Amps

Amps = Watts Volts

Thus, any given load (Watts) will require twice as much current (Amps) at 120 Volt, thus theoretically larger wire sizes, as it would at 240 Volt.

Eg:
Assume a 2,500 Watt Load (nominal 3.33 HP) at 240 Volt.
2,500 240 = 10.4 Amps (minimum #14 AWG wire size, rated 15A), which would require a 15 Amp Breaker (10.4 0.8 = 13A).

HOWEVER, the same 2,500W load would draw 20.8 Amps at 120V, requiring a #10 wire rated at 30A (the next size up from #14 is #12AWG, which is only rated 20 Amp). Since a breaker’s continuous load is limited to 80% of nameplate current rating, even a 25A breaker would be too small (in many cases) requiring a 30A breaker.

As should be obvious, a boat that’s adequately wired for 240 Volt, may have wiring too small to properly supply similar loads at 120V.
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Old 23-08-2009, 06:43   #21
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My statement was misleading...I should have said that:
"...if the candidate boat's A.C. system was properly sized for 120 VAC/60 Hz, then it is could well be sized for the European 230 VAC/50Hz. An analysis of the A.C. circuits should be performed to ensure adequately sized conductors and over current protection devices are installed."

Your math is correct, of course. Your wire sizing is not and I suspect that you used the NEC for wire sizing. Using your example:

Quote:
Assume a 2,500 Watt Load (nominal 3.33 HP) at 240 Volt.
2,500 240 = 10.4 Amps (minimum #14 AWG wire size, rated 15A), which would require a 15 Amp Breaker (10.4 0.8 = 13A).

HOWEVER, the same 2,500W load would draw 20.8 Amps at 120V, requiring a #10 wire rated at 30A (the next size up from #14 is #12AWG, which is only rated 20 Amp). Since a breaker’s continuous load is limited to 80% of nameplate current rating, even a 25A breaker would be too small (in many cases) requiring a 30A breaker.
2,500 watts at 240 VAC requires 10.4 amps:
Entering the appropriate ABYC E-11 table for bundling ( I chose Table VI for 4 to 6 current carrying conductors) with load, insulation rating (105C is standard boat cable) and for a conductor outside of the engine spaces, I find that 10.4 amps can be carried by AWG 18 wire which is rated at 12.0 amps outside of engine spaces. This would require a 12.0/0.8 = 15 amp over current protection device.

2,500 watts at 120 VAC requires 20.8 amps:
Entering the appropriate ABYC E-11 table for bundling ( I chose Table VI for 4 to 6 current carrying conductors) with load, insulation rating (105C is standard boat cable) and for a conductor outside of the engine spaces, I find that 20.8 amps can be carried by AWG 14 wire which is rated at 21.0 amps outside of engine spaces. This would require a 21.0/0.8 = 26 amp over current protection device which is not available so a 30 amp aocpd would be required.

As a designer, I never specify AWG 18 wire and rarely use AWG 16 except in appropriately size lighting circuits. For any fixed loads > 1,500 watts, I generally specify > AWG 14. If the designer for the candidate boat was conservative and understood the standards, there is a very good chance that he specified enough copper to handle the doubling of current when voltage is halved. Again, the circuit breaker ratings would have to checked carefully.

So, my statement as originally written was, in fact, misleading. My reworded statement above is accurate. I apolologize for any misunderstanding or confusion that I may have created.

Best regards,
Charlie
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Old 23-08-2009, 10:13   #22
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After reading all these responses, I'm positive I'll hire a marine electrician for the survey and employ a marine electrician to upgrade the electrical system once we own the boat.

I have no desire to burn the boat to the water line. Jeepers, I'm afraid of electricity.

my new year's resolution is to read about 5 books on marine electrical systems.

Thanks very much for all the advice, folks.
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