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Old 03-09-2014, 09:21   #31
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Re: Adding a 2nd AC input

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In the OP situation it will help. A 30A load shared by two “feeds” each one protected by a 30A CB will most likely produce a 15A current per feed. 15A should not trip a 30A CB secondly the lesser current in the cords will make them more efficient.............
If you are proposing paralleling two 120 volt circuits to increase the capacity that's pretty bad advice and I hope nobody takes it. Suppose someone flips one breaker off to work on the circuit. It's still hot!

Besides, supposedly (although apparently it's never been measured, only assumed) the OP's problem is low voltage at the power pedestal. Connecting two circuits together would not raise the voltage.
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Old 03-09-2014, 12:54   #32
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Re: Adding a 2nd AC input

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If you are proposing paralleling two 120 volt circuits to increase the capacity that's pretty bad advice and I hope nobody takes it. Suppose someone flips one breaker off to work on the circuit. It's still hot!

Besides, supposedly (although apparently it's never been measured, only assumed) the OP's problem is low voltage at the power pedestal. Connecting two circuits together would not raise the voltage.
The title of the thread is "Adding a 2nd AC input".
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Old 03-09-2014, 13:16   #33
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Re: Adding a 2nd AC input

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No in the USA you cannot use two different 30 amp lines together to boost the amps. US power the two 30 amp lines are out of phase and using two, depending on how you try it, will either cause a short or give the load double voltage and probably burn it out.
It is not together it is to share the load. One line supply the aircond, the other supply the water heater or what ever.
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Old 03-09-2014, 16:08   #34
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Re: Adding a 2nd AC input

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Originally Posted by chala View Post
It is not together it is to share the load. One line supply the aircond, the other supply the water heater or what ever.
Sorry but I was going by your original post where you said

"In the OP situation it will help. A 30A load shared by two “feeds” each one protected by a 30A CB will most likely produce a 15A current per feed. 15A should not trip a 30A CB secondly the lesser current in the cords will make them more efficient."

The way this is written saying "a 30A load shared by two feeds" to me when you call it a shared load implies one load fed by two power sources. Further "produce 15A current per feed" again implying two feeds, each supplying half of that load.

If you meant otherwise it was not clear and potentially confusing to a reader.

You do know that US power uses two hot leads 125V each, out of phase with each other vs Australia where power is only one hot lead. You cannot connect the two hot leads together to supply extra power, that will be a short circuit. The two different hot leads can be used to power separate circuits or can feed two connections for equipment designed to used 250V two phase power.
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Old 03-09-2014, 20:29   #35
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Re: Adding a 2nd AC input

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If you meant otherwise it was not clear and potentially confusing to a reader.
If it is so confusing to some readers then you wonder what these readers are doing working on a lethal 125/250V alternating current power supply?
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Old 04-09-2014, 06:45   #36
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Re: Adding a 2nd AC input

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If it is so confusing to some readers then you wonder what these readers are doing working on a lethal 125/250V alternating current power supply?
It was confusing to me also and I am quite familiar with electricity. The problem is not one of understanding what you posted, the problem is what you posted. Insulting people who questioned your post isn't going to fix anything.
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Old 04-09-2014, 07:23   #37
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Re: Adding a 2nd AC input

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Originally Posted by chala View Post
If it is so confusing to some readers then you wonder what these readers are doing working on a lethal 125/250V alternating current power supply?
Right or wrong, people work on their boats and often stretch their limits into areas where they are not expert. That is just part of the learning process in caring for a boat.

However, when the area of interest involves potentially dangerous or deadly risks then I think it the responsibility of anyone offering advice to not assume expertise on the part of the questioner until shown otherwise. In any case one should make sure any advice is very clear and unambiguous.

In similar situations I try to include a warning and/or disclaimer in any replies I post to make sure anyone reading the post understands the risks.

And by the way, I have a degree in electrical engineering and the post wasn't clear to me.
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Old 04-09-2014, 08:03   #38
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Re: Adding a 2nd AC input

Sounds like you are pulling more amps than your marina can supply, or a single 30amp outlet at full power can keep up with. You have two options.
1. Add another 30amp inlet and split your main panel ac loads in two with another smaller ac panel. This is the cheapest option as a new shore power inlet, cord and small panel will be less than $500. But this assumes you have access to a second 30amp supply on the dock or 50amp 110v supply you can use with a splitter.
2. You can buy a Charles Iso- Boost isolation transformer which will solve the low voltage problem due to you being at the end of a long chain of power supply. This is big $$$ but offers a lot of benefits.

I have two 30amp inlets on my 44' boat but I am heavy 110v with a/c units, washer dryer, electric oven, microwave, water heater, and on and on. I designed my system this way during my refit and installed a 8kw generator and inverter for the huge load.
If you do not have experience with electrical on your boat hire some one to source the issue, do the wiring, and test everything so you don't screw up and burn the boat to the water.
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Old 04-09-2014, 08:32   #39
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Re: Adding a 2nd AC input

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Sounds like you are pulling more amps than your marina can supply, or a single 30amp outlet at full power can keep up with. ...........
It might sound like that but as far as we know, nobody has actually tested the voltage at the pedestal to determine the problem.

Spending money on any "solution" without identifying the problem first is just plain stupid.
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Old 07-09-2014, 06:50   #40
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Re: Adding a 2nd AC input

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or splitting up the AC load by putting in a second shore power input. I have access to a 50 amp shore power connection so it seemed like the obvious thing to do would be to put in a 20 amp connection on the boat to run just the AC, then use the existing 30 amp connection for everything else. That seems like the cheaper and easier way to go
The simplest is to get an “extension lead” properly rated for the load. Plug in the AC in one end and plug the other end into a suitable shore supply outlet. This can be improved by the use of a portable Earth Leakage Circuit Breaker.
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Old 07-09-2014, 09:00   #41
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Re: Adding a 2nd AC input

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Originally Posted by skipmac View Post
No in the USA you cannot use two different 30 amp lines together to boost the amps. US power the two 30 amp lines are out of phase and using two, depending on how you try it, will either cause a short or give the load double voltage and probably burn it out.
First: I did not mention “two different 30 amp lines”
Second: I did not mention “together”
Two lines together will not provide two inputs but only one.

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Originally Posted by skipmac View Post
You do know that US power uses two hot leads 125V each, out of phase with each other vs Australia where power is only one hot lead. You cannot connect the two hot leads together to supply extra power, that will be a short circuit. The two different hot leads can be used to power separate circuits or can feed two connections for equipment designed to used 250V two phase power.
Australia power is a serious 240/415V 3 phases (red, white, blue) system (3 hots if you like) and other countries may use a 220/380V 3 phases system.
You can parallel (together} a red with a red, a white with a white, and a blue with a blue and this is done routinely for maintenance purpose and can also be done in special situation to supply extra power.
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Old 07-09-2014, 09:23   #42
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Re: Adding a 2nd AC input

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Originally Posted by rwidman View Post
If you are proposing paralleling
I am not, you are.

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Insulting people who questioned your post isn't going to fix anything.
I am not, you are.
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Old 07-09-2014, 11:33   #43
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Re: Adding a 2nd AC input

Quote:
Originally Posted by chala View Post
First: I did not mention “two different 30 amp lines”
Second: I did not mention “together”
Two lines together will not provide two inputs but only one.


No you didn't say two lines you said two feeds. Your original post

"In the OP situation it will help. A 30A load shared by two “feeds” each one protected by a 30A CB will most likely produce a 15A current per feed. 15A should not trip a 30A CB secondly the lesser current in the cords will make them more efficient."

The only way I can interpret this is to mean two different lines unless you have a way to supply two "feeds" on one line. And in the US "A 30A load" when "A load" can only mean one load, if it is a standard 120V circuit (like the OP mentioned) cannot be shared by two "feeds" unless you just run two wires to the same 120V source hot line. That will not add any benefit unless the wiring to the boat is undersized which should be corrected by increasing the wire size instead of running more wires in parallel.




Australia power is a serious 240/415V 3 phases (red, white, blue) system (3 hots if you like) and other countries may use a 220/380V 3 phases system.
You can parallel (together} a red with a red, a white with a white, and a blue with a blue and this is done routinely for maintenance purpose and can also be done in special situation to supply extra power.

But we are not talking about industrial power which is where you will find high voltage, multi phase power. We are talking about power that one might find in a home or small boat. In that case in Australia, unless I'm very confused is one hot wire of 230V, one neutral wire and one safety ground. In the US it can be 120V on three wires, one hot, one neutral, one ground or 240V on four wires, two hot wires out of phase, one neutral, one ground. Homes in the US are fed by the four wire, 240V system. Typically half the house is fed by one 120V hot, the other half by the other 120V hot and a few large loads like hot water or electric stoves fed by both hot wires but they are not connected together or in parallel since they are out of phase and would make big sparks.

In the US you cannot parallel hot supply wires to add additional power except as I noted if you are just connecting two wires to the exact same supply line which will not give any benefits.
Bottom line whatever you are trying to say may be right or wrong but the way you are saying is not clear and could very easily misinterpreted, even by people that are very knowledgeable. Like I said I have a BSEE which is a four year degree, in electrical engineering and am pretty familiar with basic AC wiring and I was confused.
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Old 07-09-2014, 18:12   #44
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Re: Adding a 2nd AC input

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I am not, you are.



I am not, you are.
Pretty touchy aren't we?
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Old 15-09-2014, 07:04   #45
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Re: Adding a 2nd AC input

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No you didn't say two lines you said two feeds. Your original post.
Feed is the word used at post 12 and quoted in my reply to post 12. I may not agree with the term so it was written in “…”. The poster is also an engineer and at no time did he give me the impression that he was meaning that the two feeds where joined together at the ends nor did the OP give me that impression.

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The only way I can interpret this is to mean two different lines……… That will not add any benefit
According to colemj the electrical load of the OP boat may be made of:

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Originally Posted by colemj View Post
A 16kbtu A/C will draw 12-14A (much more on startup), the water heater will draw 12-14A, a 100A battery charger will draw 14-16A in bulk mode. I will assume the reefer/freezer is DC powered and isn't in play, but if not, it will draw 8-12A.
and also

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So is it possible that the breaker trips only when a certain combination of the above exceeds 30A? Just your A/C starting up with the water heater on is close to the breaker rating, and will trip if your breaker is a bit weak.
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.

As an engineer you may also evaluate the benefits of supplying to a boat like the OP
Quote:
Originally Posted by skipmac View Post
240V on four wires, two hot wires out of phase, one neutral, one ground.

We are talking about power that one might find in a home or small boat. In that case in Australia, unless I'm very confused is one hot wire of 230V, one neutral wire and one safety ground.
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.

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Originally Posted by skipmac View Post
In the US you cannot parallel hot supply wires
I doubt this is correct. See picture at Electric power transmission - Wikipedia, the free encyclopedia and
Conductors Connected in Parallel | EC Mag
Quote:
Originally Posted by skipmac View Post
Bottom line whatever you are trying to say may be right or wrong but the way you are saying is not clear and could very easily misinterpreted, even by people that are very knowledgeable. Like I said I have a BSEE which is a four year degree, in electrical engineering and am pretty familiar with basic AC wiring and I was confused.
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.

Bottom line is

Quote:
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If it is so confusing to some readers then you wonder what these readers are doing working on a lethal 125/250V alternating current power supply?
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