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Old 15-09-2014, 07:25   #46
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Re: Adding a 2nd AC input

Chala, there is no way you can backtrack around what you posted and insulting people for "misunderstanding" your post isn't going to get you anywhere.

You may or you may not know electricity but if you do, you are having serious problems communicating your thoughts. Your bet bet at this point is to just back away from the keyboard and do something else for a while.
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Old 15-09-2014, 07:39   #47
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Re: Adding a 2nd AC input

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Originally Posted by chala View Post
Now if the OP was to use two “different lines”, one line as described in post 40, it is likely that the 12-14A draw of the A/C will not trip a 30A breaker. One benefit. The 14A current in a 30A rated extension cord will create less voltage drop. Another benefit. So will the remaining 16A current in a 30A rated extension cord (original 30A less the 14A of the first line) will also provide the same benefits. Of course there are other benefits but that may be too confusing for some.
Say it any way you like but your post said "A 30 A load", not two smaller loads or some loads or a few loads, but A Load. A load can only mean "one load". In no way can it be interpreted differently. No ambiguity here at all. If you had made it clear you were saying split more than one load between two feeds it would be clear. The way it was stated is incorrect and could be dangerous with US 60 Hz power.


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Originally Posted by chala View Post
If we are talking about a 1 phase versus a 3 phases power that may be supplied to a domestic or a non-domestic installation, a marina or a caravan park, it all depend on a maximum demand calculation.
Sorry but this is not correct in the US. I have never seen or head of 3 phase supply to anything other than for industrial or very large commercial equipment. Homes, marinas RV parks will be fed with 240V 2 phase power.


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Two things. First these are for very high power installations and are exactly what I said before. I said before that you can connect two wires to the same source and run them to a load but in the OP's situation it is much better just to use one wire of the proper size. A simple example, would you want to connect the battery in your car to the starter with three small wires or one wire of the proper size? I think the answer is obvious.



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How can people that are very knowledgeable misinterpret?

Easy when there is ambiguity.
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Old 15-09-2014, 08:25   #48
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Re: Adding a 2nd AC input

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Originally Posted by chala View Post
How can people that are very knowledgeable misinterpret?
Obviously a four year degree is not sufficient if it only make you pretty familiar and leave you confused.
You should have asked your teenage daughter.
One final comment on this issue. Engineering and technology of any kind whether electricity, structural design, mechanics, etc by their nature to be correct, safe and communicated correctly must be exact, precise and use exact and precise language. This applies even between engineers, in fact may be even more so between engineers.

I once lost full credit on an exam question even though I had the correct number I didn't put the units, in that case V or Volts. The instructor pointed out the number could have been in mV or kV or due to the complexity of the problem maybe even Amps. You have to be precise or the information is not correct.

One of the corollaries to Murphy's law, anything that can be misunderstood will be misunderstood.
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Old 15-09-2014, 09:37   #49
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Re: Adding a 2nd AC input

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Say it any way you like but your post said "A 30 A load", not two smaller loads or some loads or a few loads, but A Load.
Yes the boat was tripping a 30A circuit breaker, the boat was A load of 30A but if you do not get it do not worry you are not the only one. This is the internet and more than 80% of readers will not get it either.

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Sorry but this is not correct in the US.
Your question was about in Australia, not the US and the reply was about Australia not the US..


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Originally Posted by skipmac View Post
A simple example, would you want to connect the battery in your car to the starter with three small wires
Yes and not only the tow truck but also the boat for the simple reason that.
Two different lines each rated at 30A each will be more efficient at dissipating heat and for that reason will weight less than an equivalent 60A single line, another benefit and may be cheaper a further benefit.
32A = 6mm2 = 0.54 kg/10m * 2 = 1.08 kg/10m.
63A = 25mm2 = 2.46 kg/10m.

As pointed out by

Quote:
Originally Posted by ranger42c View Post
Can't remember if others have mentioned it, but 50-amp 125/250V shorepower cable is heavy (about a pound/foot) and expensive.
But as an engineer you should know that.
By the way have you been able to evaluate the benefits of supplying to a boat like the OP

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240V on four wires, two hot wires out of phase, one neutral, one ground.
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Old 15-09-2014, 09:55   #50
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Re: Adding a 2nd AC input

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Your bet bet at this point is to just back away from the keyboard and do something else for a while.
Gosh that would be the best advice I have read from you so far, you are improving.
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Old 15-09-2014, 10:07   #51
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Re: Adding a 2nd AC input

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Originally Posted by chala View Post
Yes the boat was tripping a 30A circuit breaker, the boat was A load of 30A but if you do not get it do not worry you are not the only one. This is the internet and more than 80% of readers will not get it either.
Oh I get it that the boat is one load but you still cannot supply one load with two different 120V AC lines.


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Your question was about in Australia, not the US and the reply was about Australia not the US
I might have mentioned Australia to point out the power is different but the OP and the entire discussion is centered on a problem in the US.



Quote:
Originally Posted by chala View Post
Two different lines each rated at 30A each will be more efficient at dissipating heat and for that reason will weight less than an equivalent 60A single line, another benefit and may be cheaper a further benefit.
32A = 6mm2 = 0.54 kg/10m * 2 = 1.08 kg/10m.
63A = 25mm2 = 2.46 kg/10m.
Again you are stating the obvious but bottom line, for the loads and situation we are discussing one wire is the answer, period. Use the proper, single wire that is rated for the load AND the temp. Wiring in a hot engine room is rated lower capacity than wiring in a cooler location.
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Old 15-09-2014, 10:22   #52
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Re: Adding a 2nd AC input

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Oh I get it
No you do not.
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Old 15-09-2014, 10:45   #53
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Re: Adding a 2nd AC input

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No you do not.
Scroll up and re-read my post #46.

Then step away from the computer.
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Old 15-09-2014, 11:03   #54
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Re: Adding a 2nd AC input

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Example, you have a shower in your house that doesn't put out a good stream of water because your water pump won't make much pressure. It won't make the water come out any faster if you hook the pump up to a bigger well, you still will have low water pressure. Same thing with electricity. Doesn't matter how many amps you have available, if the voltage (which can be thought of as electrical pressure) is low then you will have problems.
Not actually accurate. More amperage would be similar to increasing pump capacity and feed line size: more volume.
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Old 15-09-2014, 12:07   #55
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Re: Adding a 2nd AC input

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A load can only mean "one load".
You guys aren't adding anything to the knowledge base of the OP or any other future readers of this thread. To prove that point I offer that the word "A" in highly technical contexts (example: patent claims) does not limit itself to one and only one. It may mean "at least one" and does not necessarily exclude the possibility of more than one.

But there is no point to this bickering between you folks. It is adding nothing to the subject matter. Please stop!
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Old 15-09-2014, 13:04   #56
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Re: Adding a 2nd AC input

A completely different solution. Not cheap but a good way to deal with these situations in general.

A Victron Multi Plus (or Quattro) inverter/charger has functions that deal with weeak shore power, especially if they are of short duration. Hooked up to a remote control panel it works like this.

1 - On the control panel you tell the inverter/charger how many continuous amps the shore power breaker, cable, or whatever is the weakest link, can deal with. You nvere want to use more than 80% of the rated power or 24A for a 30A supply.
2 - You have no extral load - The charger will use maximum power to charge your batteries, if they are really hungry. Lets say the charger is using 14A@120V (approximately 100A@14V going into the battery)
3 - POWER CONTROL - Now other loads (water heater, AC, lights, etc) on the boat kick in. Once the total reaches 24A the charger will start throtteling down to keep the maximum at 24A AC@120V coming in. Once the loads on the boat (without the charger) equals 24A@120V the charger will stop charging as there s no additional power available for it. Now all 24A times 120V are available to the rest of the boat.
4 -POWER ASSIST - Now the strong inrush current of another AC unit would try to draw much more than 24A - but only for a very short time. The inverter will kick in and take power out of the batteries and add the addtiionally required amps to the incoming power of a maximum of 24A AC @120V. With a Victron 3000 that would be up to an additional 25A for a total of 49A. No tripping of the breaker with a larger buffer.

Once the peak power demand settles down the charger will kick in again and replace what the inverter just used.

It is not cheap, but if you have to update your charging system, or need a new inverter, this is the way to go.

Here is a link to the brochure - Victron Multi Plus
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Old 15-09-2014, 13:41   #57
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Re: Adding a 2nd AC input

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You guys aren't adding anything to the knowledge base of the OP or any other future readers of this thread. To prove that point I offer that the word "A" in highly technical contexts (example: patent claims) does not limit itself to one and only one. It may mean "at least one" and does not necessarily exclude the possibility of more than one.

But there is no point to this bickering between you folks. It is adding nothing to the subject matter. Please stop!
You are correct that this thread has deteriorated into pointlessness but I do find it hard to walk away when someone posts a recommendation that is quite potentially dangerous.

Only because you bring it upm I can't agree that the indefinite articles, at least in common use, indicate plural or more than one. I would never say "a book" when referring to two books or "an apple" when referring to several apples. Even legal use I believe the indefinite articles are assumed to mean only one. Quote from a paper on legal grammar,

"As is well known, the indefinite article developed from the numeral
one

and as such preserves the meaning of ‘one-ness’."

PS
At this point it's pretty obvious that there is nothing more to be said so I'm done with this thread.
If the bickering bothers you that much why not just ignore or unsubscribe? I certainly do not want my disagreement with someone else to be an annoyance to you.
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Old 15-09-2014, 14:21   #58
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Re: Adding a 2nd AC input

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............ But there is no point to this bickering between you folks. It is adding nothing to the subject matter. Please stop!
Yea, it's annoying when you're not in the middle of it, isn't it.
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