30 vs 50 Amps

[DotDun]

Originally Posted by AllezCat

Surely the question is voltage.
I am thinking, maybe incorrectly, the op is deciding to go for 220v or 110v.
And my advise remains.
Referring to 30amp or 50amp shore power is a misnomer.
The 30amp is usually 110 and the 50amp is usually 220 and that is what your hair dryer cares about...
the gauge of wire is the same as for DC - bigger for more amps...

American 50amp 240volts delivers 120volts also. If the op has a requirement for 240volts, then 50amp 120-240volt is the only choice. If 120volt is the only requirement, then totaling up the power required will determine whether 30amp/120v (3.6kva), 50amp/120v (6kva), or 50amp/120-240v (12kva @ 240v OR (2) 6kva @ 120v) are the choices.

So, for example, even if 120v is the only voltage required, a 50amp 120-240volt shorepower may be needed depending on the total power budget.

[DSDman]

IF you think of your core electrical lines as possible path ways to power equipment the dual 30 amp system is the way to go. Having the ability to connect each power bus also gives you a certain amount of safety backup in case you have a problem with one input source. Powering both 30 amp circuts gives you the ability to run everything you might need. If you are replacing the system anyway then I would go all out. Nothing worse than finding in a year or two that the new gadget you just have to have needs just a little more power than your line can supply.

[AllezCat]

Originally Posted by GordMay

It doesn't appear, to me, that you do understand "perfectly".
ie: 50 Amp (1 phase) can (equally) be either 120 Volt 2 Pole 3 Wire or 120/240 Volt 3 Pole 4 Wire (125/250V).
See the Marinco guide.

I do understand what can be provided.
The question "should I wire 30amp or 50 amp"?

Do you go into the store and buy a 30amp or 50 amp hair-dryer?
or a 220 volt or 110 volt?

if you live and stay in USA - then I would go for wiring the boat 110.
there are too many choices for stuff in the mega stores.

[AllezCat]

Originally Posted by DotDun

American 50amp 240volts delivers 120volts also. If the op has a requirement for 240volts, then 50amp 120-240volt is the only choice. If 120volt is the only requirement, then totaling up the power required will determine whether 30amp/120v (3.6kva), 50amp/120v (6kva), or 50amp/120-240v (12kva @ 240v OR (2) 6kva @ 120v) are the choices.

So, for example, even if 120v is the only voltage required, a 50amp 120-240volt shorepower may be needed depending on the total power budget.

this is the correct question!!!!

[capn_billl]

It really depends on your cruising grounds, but where I cruise there are mostly older marinas that do not have 50 amp connections available. My boat is wired for twin 30 amp circuits, fwd A/C is on one and the aft A/C is on the other, with house loads split between the two.

IN USA houses small plugin appliances run 120vac, and large permanent appliances run two phases giving 240vac. I would not wire a boat for this, as 240vac is not always available, and do you really need a 20KW furnace or combo oven/range on a boat?

The 50 amp is a large round plug usually wired as a single feed, 30 amps are a smaller plug that can be wired as a single or dual feed.

Newer boats are more often coming wired as a 50amp. But the split 30 amp on my boat has several advantages. 1. I have a 50 to 30 amp adapter so I can plug into either one. 2. If needed I can run my boat off of a single 30amp as long as I only run 1 A/C at a time, or even a single 15 amp as long as I'm very carefull with amp load, (lights and coffee maker only).

You can adapt a 50 amp to plug into a 30amp socket, but you risk overloading the 30 amp socket. Second wiring for 50 amps gives only, ...50 amps. Wiring for dual 30 gives, 30 amps or 60 amps if you use dual.
In emergency I have used second 30 amp feed to share power with boat next to me when shortage of working outlets, harder to do with 50 amp. ( At least we both got lights and coffee, and 1 A/C)

Good luck, if you have any questions you should consult with a trained professional.

[capn_billl]

Originally Posted by AllezCat

I do understand what can be provided.
The question "should I wire 30amp or 50 amp"?

Do you go into the store and buy a 30amp or 50 amp hair-dryer?
or a 220 volt or 110 volt?

if you live and stay in USA - then I would go for wiring the boat 110.
there are too many choices for stuff in the mega stores.

In the USA there are only 110 volt hair dryers, but you can buy the small 5 amp, (500watts, at 110vac), or you can buy the bigger 10 amp, (1000watts at 110vac).If you want to plug 5 of the 1000watters in at the same time, your going to need the 50 amp feed, or you'll pop a breaker

The only devices that run at 240VAC in the US are electric clothes dryers, oven/range combos, and central (heating A/C units) in the 10 - 20 KW range. The smaller ones are also 110vac, as are ALL plug in appliances.

[DotDun]

Originally Posted by capn_billl

Second wiring for 50 amps gives only, ...50 amps. Wiring for dual 30 gives, 30 amps or 60 amps if you use dual.

Not quite true, a 50amp 120/240v shorepower delivers (2) 50amp 120v services for a total of 100amps @ 120v.

Yes there is a 50amp 120v shorepower configuration available, but I have not found this offered at marinas I have visited (which isn't very many).

[AllezCat]

The real question - the OP has to clarify is whether he is deciding on greater capacity, or different voltage(perhaps for international cruising).
it is a common question/decision as to whether an international 220v system is preferable to a 110v American system.
My original statement about confusion still stands. And it is not about the reality and physics - it is about people banding about the 30/50 amp question in either scenario.
One is capacity for an american 110 volt boat - which is a valid question regarding amperage. the other refers to voltage which is not valid, and confusing when talking about 30/50amps when it really refers to 110volts versus 220volts. Only one is correct - the other could get you killed. - or at least burn-out equipment.
My boat has 2 shore power connections - which are labeled 110volts and 220 volts - and are connected to battery chargers accepting 110volts and 220 volts respectively. there are a plethora of connections - anyone can wire them anyway. Luckily I know exactly how to do it.
When I brought my boat into America(and intend to stay) I chose to install a 110volt inverter and wired in some more 110volt outlets. Sure, I could have found some 220v "things" - but 110v stuff is more readily available - good and cheap...

[AllezCat]

Originally Posted by capn_billl

In the USA there are only 110 volt hair dryers, but you can buy the small 5 amp, (500watts, at 110vac), or you can buy the bigger 10 amp, (1000watts at 110vac).If you want to plug 5 of the 1000watters in at the same time, your going to need the 50 amp feed, or you'll pop a breaker

The only devices that run at 240VAC in the US are electric clothes dryers, oven/range combos, and central (heating A/C units) in the 10 - 20 KW range. The smaller ones are also 110vac, as are ALL plug in appliances.

you are missing the point

[skipmac]

Originally Posted by capn_billl

The only devices that run at 240VAC in the US are electric clothes dryers, oven/range combos, and central (heating A/C units) in the 10 - 20 KW range. The smaller ones are also 110vac, as are ALL plug in appliances.

Correct, BUT a US 240 VAC can also provide two, separate 120 VAC circuits which will allow you to run more of the smaller 110 VAC plug in gadgets.

[S/V Illusion]

I never realized people can so easily complicate two paper bags.

[Bash]

Back to the original question...

You might want to run down to the local chandlery and price a 30 amp vrs 50 amp shore power cord. Then ask yourself, "Do I really want to pay so much more for something I don't actually need?"

[AllezCat]

Originally Posted by capn_billl

In the USA there are only 110 volt hair dryers, but you can buy the small 5 amp, (500watts, at 110vac), or you can buy the bigger 10 amp, (1000watts at 110vac).If you want to plug 5 of the 1000watters in at the same time, your going to need the 50 amp feed, or you'll pop a breaker

The only devices that run at 240VAC in the US are electric clothes dryers, oven/range combos, and central (heating A/C units) in the 10 - 20 KW range. The smaller ones are also 110vac, as are ALL plug in appliances.

I do think there are some 208/220 volt appliances and there is a standard US domestic outlet for them...
the analogy about the hairdryer is any appliance that can be bought anywhere that accepts EITHER only 110 or only 220...

[skipmac]

Originally Posted by Bash

Back to the original question...

You might want to run down to the local chandlery and price a 30 amp vrs 50 amp shore power cord. Then ask yourself, "Do I really want to pay so much more for something I don't actually need?"

Another question to ask, what type connection is most common at the marinas in my cruising area.

I have to admit that it has been a long, long time since I have spent much time at marinas but in the past a 30 amp, 120 V connection was most common. I think most marinas now offer 30 A - 120 V and 50 A 120/240 V connections as standard but would be interested in hearing from cruisers with recent experience.

I plan to standardize on 30 A, 120 V. It's not difficult to monitor the few, high power systems on AC to keep your total power draw within the supply limits.

[St. Elsewhere]

We may be well past the OP's desire for information, but here goes . . . .

North American power companies provide 120/240 volt electricity to residential users. They typically supply 480/277 volt three phase power to industrial users including large marinas. Such marinas often have "Y" connected three phase transformers on the docks that reduce the voltage to 208/120 volts because they are cheaper than 240/120 volt "Delta" connected transformers to convert to single phase. Three phase circuits have three hot wires and a neutral. The 120 volts would come from a hot to neutral connecton, and 208 volts comes from connecting to two hot wires.

North American single phase appliances are almost all designed for 120 or 240 volts. 110 and 220 volt rated appliances are not found here. Wiring devices (outlets, plugs, wire, etc) may show ratings above such voltages that they are intended to supply.