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post #1 of 24 Old 04-10-2007 Thread Starter
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Shore power question

Gentlemen

I have come back to this forum after being away for a longish while. If the question I am asking has been dealt with recently, please point me there but I don't relish sifting through years of posts when the boffins can probably provide the answers right away.
I have bought a vessel in the US and will be bringing it home to New Zealand. The shore power in the US as we all know is 110v and the shore power in NZ is 220v.
The question then is obvious . . . in language an idjit can understand, would any one like to venture what issues there are (appliances aside) in using the same system with the higher voltage.
My understanding of electricity is that when the voltage goes up, the amperage for the same draw goes down. IOW, an appliance drawing 1000w on a 110v system would draw 9 amps. A similar appliance drawing 1000w on a 220v system would draw pretty much half of that. That is right, isn't it?
If yes, then the wiring and switches and breakers and whatever else makes up the shorepower system shouldn't have any problem dealing with it right? Right??
Because higher amperage equals heat and the converse is also true, isn't it?
Advice would be gratefully received. I have no problem changing all the plug receptacles and that sort of stuff but rewiring the whole vessel is too daunting to even contemplate.
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post #2 of 24 Old 04-10-2007
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Quote:
Originally Posted by Omatako
My understanding of electricity is that when the voltage goes up, the amperage for the same draw goes down. IOW, an appliance drawing 1000w on a 110v system would draw 9 amps. A similar appliance drawing 1000w on a 220v system would draw pretty much half of that. That is right, isn't it?
Yup, as voltage increases your amp draw would be less.

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Originally Posted by Omatako
If yes, then the wiring and switches and breakers and whatever else makes up the shorepower system shouldn't have any problem dealing with it right? Right??
Because higher amperage equals heat and the converse is also true, isn't it?
The wiring would handle it fine assuming it's good quality wire and properly insulated as marine wire should be.

Breakers are set to trip at a certain amperage reguardless of voltage, so you would still be able to use the same breakers. The downside to this is you might not be as protected if you had a faulty device. If you had breakers for use in 110V they would be rated for a max current for the circuit which might be different from the max current you might want in a 220V system. The would be the same breakers just rated differently.
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post #3 of 24 Old 04-10-2007
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Question 220 vs 110 v SP

I'm a tad confused. Are you going to replace the components with 220 v components? For example, a light bulb has a resistance that is constant and draws X amps at 110v. If you appply 220v, it will draw twice that current and burn out really quickly, If your end use appliance is designed for 220v AND has the same power rating, then the current will be halved, and everything should be good to go. Electric motors are something else, but I don't think applying 220 to something designed for 110 is a great idea. If everything on board is DC operated and the SP only goes to a battery charger, then the charger has to be set up for a 220 input and everything is good. IF you are running anything off the AC directly, then "anything" has to be 220v rated. FWIW. I'd like to see New Zealand someday. Gosd luck and good sailing,
Bill
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post #4 of 24 Old 04-10-2007
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Wearing my EE hat:

Quote:
Originally Posted by Omatako
Gentlemen

I have come back to this forum after being away for a longish while. If the question I am asking has been dealt with recently, please point me there but I don't relish sifting through years of posts when the boffins can probably provide the answers right away.
I have bought a vessel in the US and will be bringing it home to New Zealand. The shore power in the US as we all know is 110v and the shore power in NZ is 220v.
The question then is obvious . . . in language an idjit can understand, would any one like to venture what issues there are (appliances aside) in using the same system with the higher voltage.
My understanding of electricity is that when the voltage goes up, the amperage for the same draw goes down. IOW, an appliance drawing 1000w on a 110v system would draw 9 amps. A similar appliance drawing 1000w on a 220v system would draw pretty much half of that. That is right, isn't it?
If yes, then the wiring and switches and breakers and whatever else makes up the shorepower system shouldn't have any problem dealing with it right? Right??
Because higher amperage equals heat and the converse is also true, isn't it?
Advice would be gratefully received. I have no problem changing all the plug receptacles and that sort of stuff but rewiring the whole vessel is too daunting to even contemplate.
You are correct. Your properly-installed 110v wiring will be just fine for 220v.

Change all the receptacles so you can use all 220v appliances.

It is not necessary to change the breakers--they are there to protect the WIRE, not the appliance.

Gil
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post #5 of 24 Old 04-10-2007
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The wiring and switches should be fine. Most AC breakers are designed to handle up to 220v... so those should be okay, but you might want to double check them. So you shouldn't need to re-wire the vessel at all to retrofit the boat to suit the 240VAC shore power system you'll need in NZ.

AFAIK, the wiring in the NZ electrical system uses three wires to provide 240VAC, unlike the US, where four wires are required to the box, as the 240V is provided by two 120V circuits.

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Last edited by sailingdog; 04-13-2007 at 10:10 AM.
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post #6 of 24 Old 04-12-2007 Thread Starter
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Hi Bill,
Thanks for your input. At this time I'm not sure what runs on 110v and what runs on 12v. The boat has a 2.5 kw inverter installed so I guess that it may be so that the only use for the SP is a charger to keep the batteries up. If that is so then one could assume that all the lights etc are 12v and the inverter is there to power appliances like microwaves, hairdryers, computers etc.

In that case it's a doddle and only the charger needs changing to a 220v one. The thing that flies in the face of the above is that the boat is littered with 110v receptacles but once again, I'm assuming they are all wired to the inverter.

Gil, thanks also for you input. I just wasn't too sure of the switches etc but as said, lower amps has to be good news.

SD ditto your advice. I'm not sure of the 3 vs 4 wires. AFAIK the 3 wires in NZ are a live, a neutral and an earth. I must confess to never having heard of twin 120v circuits and I grew up in South Africa with 220 - 240v which has the same setup as NZ.

Each circuit in domestic applications here in NZ only has one breaker or fuse holder so twin wiring is not evident. Interesting. What would the 4 wires in the US carry with 110v? Is the extra one to spread the amperage, perhaps?

Hey thanks again guys, I feel a whole lot more comfortable about the thing now. And Bill, if you want to see NZ, take a trip, you won't be sorry. God's own country, this.
Andre
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post #7 of 24 Old 04-12-2007
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Andre-

In the US, household current is 120VAC... so to get a 240V circuit, the AC come into the circuit breaker box on two 120VAC feeds. The outlets are generally wired with three wires. I've probably botched the explanation a bit.. but that's the gist of it, and it's been a long time since I've had to install any 240V equipment, so I'm a bit rusty.

Most of the rest of the world went with 240VAC so they could use smaller transmission lines and such, and as I understand it, that was what Nikola Tesla had advocated... but Edison was set on using 110VDC and then switched over to 110VAC.

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post #8 of 24 Old 04-12-2007
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SD - Are you talking about single phase or 3-phase AC? I think the power generation companies all make three phase power, which factories and large stink-pots use direct - so three wires, one for each phase, a neutral wire and an earth wire makes five. Most households receive just one phase, so the phase wire, the neutral and the earth. But there are odd countries, like Germany, that use the neutral wire as the earth. I don't think they are supposed to, but remove any socket off the wall there, and you can bet the earth pins are wired to neutral and there's no earth wire in sight. (This is to drive the Brits nuts, who are earth wire addicts, it's very effective too.)

Omatako - you could keep your boat on 110 VAC by installing an isolation transformer. The one I have transforms between 220 VAC and two 110 VAC (or in reverse). Then when you plug into 220V shore power, all your applicances will see 110 V.
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post #9 of 24 Old 04-12-2007
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Omatako...I know a lot of European 220 systems are 50 hz whereas the US runs on 60 Hz and this can cause significant issues with motorized equipment like firdges and air conditioners. Don't know what Hz you use down under but thought it was worth a mention.
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post #10 of 24 Old 04-12-2007
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Australian electrical gear (should be same as Kiwiville) is usually marked 220-240v AC. 50-60hz.

Omataka, said not to worry about appliances but as far as the wiring is concerned, provded the existing wiring is decent three core, properly shielded then it should be OK. While 110v wiring is usually suitable for 240v in my travels to the US the standard of some of the wiring I've seen gives me the heebie jeebies.

Andrew B

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