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Old 10-18-2017, 12:05 PM   #1
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Going from 1 50 amp to 2 30 amp plugs

I am thinking of moving to a more desirable slip at my marina but it has two thirty amp plugs instead of the one 50 amp plug that I am used to. I have a smart Y but don't know if I would want to use it on a full time basis. Plus, I am not sure if the 30 amp plugs are on different legs, but assuming they are am I going to have a problem?

I have three 16,000 btu A/C's that sometimes run a the same time.
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Old 10-18-2017, 12:53 PM   #2
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Why not use the smart y to connect your 50 amp inlet to the two 30A outlets, assuming they are on opposite legs?

If not then ypu will have to replace the 50A inlet with two 30A inlets, two breakers and two new wiring circuits from the inlets to each of the two AC busses. It won't be cheap to do and unless you know exactly what you are doing I would hire a marine electrician.

Finally the two 30A circuits may not be enough to run three 16,000 btu units simultaneously. I would suspect that one is on one buss and two are on the other. But with only a 30A supply it will be difficult to run two 16,000 btu units simultaneously particularly with any other loads on the circuit.

So, I would first check to see if the new slip has 30A outlets on opposite legs and use the Y-adapter, but be prepared to only use two A/C units simultaneously. If not opposite legs or you have to have three A/Cs running simultaneously, I would stay at my current slip.

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Old 10-18-2017, 01:17 PM   #3
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I am thinking of moving to a more desirable slip at my marina but it has two thirty amp plugs instead of the one 50 amp plug that I am used to. I have a smart Y but don't know if I would want to use it on a full time basis. Plus, I am not sure if the 30 amp plugs are on different legs, but assuming they are am I going to have a problem?

I have three 16,000 btu A/C's that sometimes run a the same time.

Take your Smart Y down to that slip and try it, see if the diode lights.

Or... when I moved to our current marina/slip, the pedestal had twin 30s... but they reconfigured it to a single 50 for me. Didn't even have to ask...

-Chris
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Old 10-18-2017, 02:37 PM   #4
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If the 2 30 amp breakers are on the same leg won't that just matter if you need 220 volts?
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Old 10-18-2017, 02:48 PM   #5
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If the 2 30 amp breakers are on the same leg won't that just matter if you need 220 volts?

A Smart Y won't light up unless the two 30s are out of phase with each other.

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Old 10-18-2017, 03:28 PM   #6
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I would suspect that one is on one buss and two are on the other. But with only a 30A supply it will be difficult to run two 16,000 btu units simultaneously particularly with any other loads on the circuit.

David
Nope. All three A/C's are on one 120v leg. The other leg is only for things that can be run through the inverter so it has very little draw on it while at the dock. The refer, the microwave, the icemaker and some outlets.

Unless they rewire the slip for 50 amp I probably will not move there.
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Old 10-18-2017, 04:44 PM   #7
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If all three A/Cs are wired to one leg of the 50A supply, then those three will certainly not run at the same time on a 30A leg and maybe not even two at the same time.

16,000 btu A/Cs typically draw about 15A each.

I agree, stick with your current slip unless your marina will rewire the pedestal for 50A 240/120.

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Old 10-18-2017, 04:49 PM   #8
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David's got the key issue; you just end up with a 30 amp capacity circuit on each leg.
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Old 10-18-2017, 05:15 PM   #9
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If all three A/Cs are wired to one leg of the 50A supply, then those three will certainly not run at the same time on a 30A leg and maybe not even two at the same time.

16,000 btu A/Cs typically draw about 15A each.

I agree, stick with your current slip unless your marina will rewire the pedestal for 50A 240/120.

David
Agree.
If you go to two 30A, one of the AC units will have to move to the other cord.
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Old 10-19-2017, 06:21 AM   #10
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"Unless they rewire the slip for 50 amp I probably will not move there."

Its not just the 50A socket , the dock wiring needs to support the 30A wiring load.

IF there are other 240/50 power poles past the slip location , you might be in luck.

The RV folks have devices that prevent 2 air cond from starting at the same time , which might be a help if the heavy wiring is not there..

OR you could feed one (the most used) air cond from the inverter fed wiring , and switch it back when cruising . 2 sockets and a plug would be cheap/simple to install.
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Old 10-19-2017, 09:43 AM   #11
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Going from 1 50 amp to 2 30 amp plugs

I have a Y adapter that takes a 50a and splits it to two 30a. How do I know if mine is "smart"? It seems to run both AC units OK. It came with the boat, so I have no paperwork for it.

My boat has two 30a cords so when there is only a 50a plug at the dock I use this adaptor. Is this a good practice? I can't seem to wrap my head around AC electricity and how it works for some reason. Need a book.
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Old 10-19-2017, 10:45 AM   #12
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I have a Y adapter that takes a 50a and splits it to two 30a. How do I know if mine is "smart"? It seems to run both AC units OK. It came with the boat, so I have no paperwork for it.

My boat has two 30a cords so when there is only a 50a plug at the dock I use this adaptor. Is this a good practice? I can't seem to wrap my head around AC electricity and how it works for some reason. Need a book.
A smart y does the opposite of what yours does and it is dangerous if not done correctly.

This should explain it. Scroll down the page to Smart Y.

Marine: Cable Adapters & Smart Y Adapters
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Old 10-19-2017, 10:54 AM   #13
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I have a Y adapter that takes a 50a and splits it to two 30a. How do I know if mine is "smart"? It seems to run both AC units OK. It came with the boat, so I have no paperwork for it.

My boat has two 30a cords so when there is only a 50a plug at the dock I use this adaptor. Is this a good practice?

I think quite acceptable approach.

As SS7 said... while yours is splitting a single 50 into twin 30s, a Smart Y is conceptually combining twin 30s into a single 50.

(Whole bunch of details omitted.)

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Old 10-19-2017, 11:24 AM   #14
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So The smart Y converts two 30a 120v plugs on the dock to one 50a 240V. My Y combines two 30a cords to one 50a plug.

Still trying to figure out why one Y needs to be "smart". Is it because if one of the 30a plugs fell out of the dock power pedestal it could still be energized?

Brain cloud!
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Old 10-19-2017, 11:38 AM   #15
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No it changes it to a 30a 240V. Smart Y really comes into play if you are powering 240v equipment, as you need both legs for that. And yes the "smart" feature is a safety issue.
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Old 10-19-2017, 01:23 PM   #16
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I have a practically new 50/250 to 2x 30/125 pigtail for sale in the classifieds and 2x 50ft 30amp chords if you are interested, just sayin'

I just converted from dual 50/125 (obsolete) inlets to a single 50/250 Smartplug inlet.

My free 2 cents, since you asked:

Keep the 50 amp inlet and wiring. Add 2 additional 30 amp inlets. I'd then wire the 30 amp and 50 amp inlets to a big barrel switch that then feeds your Ship/Shore switch. This way you can always switch back and forth depending on where you are at
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Old 10-19-2017, 01:29 PM   #17
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Still trying to figure out why one Y needs to be "smart". Is it because if one of the 30a plugs fell out of the dock power pedestal it could still be energized?

Brain cloud!
Someone correct me if I'm wrong, but I thought it would knock one hot line 180* out of phase if it wasn't already out phase from the pedestal.
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Old 10-19-2017, 02:20 PM   #18
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"I have a Y adapter that takes a 50a and splits it to two 30a."
"My Y combines two 30a cords to one 50a plug."

Hi Dude, you made both of the above statements. They are not the same thing.

I'm guessing that your boat has two 30Amp 120 Volt inlets. Your Y connector allows you to attach your two 30 amp shore cords to one 50 amp outlet. You don't need a Smart Y to do that.

The OP has one 50 amp 240 volt inlet and his Smart Y allows him to plug his 50 amp shore cord into two 30 amp 120 volt outlets.

It's pretty confusing and when these guys start talking phasing, I'm completely lost.
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Old 10-19-2017, 04:21 PM   #19
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I have a Y adapter that takes a 50a and splits it to two 30a.
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My Y combines two 30a cords to one 50a plug.


No. The way you described it the first time is more likely correct: your Y probably takes a 50A input and changes the output to two 30As. (Unless it's got a big honking box in the middle of it, and probably an LED to let you know when it's correctly working.)

IOW, it's not turning two 30s into one 50; it's turning one 50 (supply from pedestal) into two 30s (connect to a boat with twin 30s).

You could think in terms of flow direction, perhaps like water hoses for an analogy. Your Y takes input flow from the pedestal (50) and changes it to what the boat will accept (twin 30s). A Smart Y takes input flow from the pedestal (two 30s) and converts that into what the boat will accept (a single 50).

(The water hose analogy breaks down a bit, because you could likely use a simple Y water valve thingy in either direction. With electricity, not so much, given safety concerns.)

And actually what caltex said is even more correct. I really mostly addressed the plugs on each end. But what you really get with a Smart Y is two 30/120s (with 30A connectors) from the pedestal combined into a single 30/240 (with a 50A connector at the boat).

-Chris
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Old 10-19-2017, 05:26 PM   #20
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Still trying to figure out why one Y needs to be "smart". Is it because if one of the 30a plugs fell out of the dock power pedestal it could still be energized? Brain cloud!
You can make a homemade reverse Y adapter that will work but it would not be safe if one of the male 30 amp plugs fell out of the dock pedestal. That plug would still be hot. The Smart Y has a box that shuts down the entire train if that happens,

This is from West Marine:

You canít pull 50A out of a 30A circuit, or at least you canít for very long! Therefore, you have to restrict your use onboard to less than 30A, or youíll spend your time resetting the pedestal breaker. There is a way for this vessel to find the power it needs in this situation, and thatís by using a Reverse Y Adapter. This converter connects to both of the 30A outlets on the shore power pedestal and determines if the hot and neutral are correctly polarized, and if the hots are opposite phase, and if both male plugs are connected properly. If not, a special circuit in the Reverse Y does not allow current to flow. If the wiring is OK, the Reverse Y provides 50A of 125/250V power to your boat.
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