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Old 03-19-2019, 03:05 PM   #1
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No Power to Air Conditioners

Hello -
Hours ago, we plugged up to 50 amp shore power, visiting a marina, and our voltage gauge shows 120, as normal. All of our AC plugs and devices work, except our air conditioners. I assume that the on/off switches have circuit breakers, and none of them have thrown. We started the generator, and it also shows 120 volts, and the air conditioners work fine.

So I'm wondering if its the power pedestal but the marina is clueless.
In background, we travel extensively, and often change marinas, but have never encountered this. Our boat also has an amp meter (other then the engine amp and volt meters), and the meter has never shown the draw from the air conditioners.

My assumption all along have been that the air conditioners are wired so as to not show up on the amp meter.

Seems like someone once said that a "side" the service out of the pedestal could be an issue. In other words, the voltage supply is typically split.
If that's the case, then perhaps we're simply not getting the air conditioning side of the service.

But since I'm way over my head here, I'm hoping that someone can straighten me out.

Thanks -
Wizard
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Old 03-19-2019, 03:39 PM   #2
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The marina pedestal may be missing one leg of 120 volts and maybe that is where your A/Cs get their power. Did you test the pedestal before you plugged in? Maybe pull our a voltmeter and check the pedestal. Do you have voltmeters on your power panel in the boat?
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Old 03-19-2019, 04:13 PM   #3
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Are you sure your on shore power and not running off the inverter?
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Old 03-19-2019, 04:52 PM   #4
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A sister boat of ours could not run his A/C units when he was docked at the far T-Head, the current dropped just enough due to the distance from the shore transformer. My boat worked fine - the difference was I have a Charles Iso-Boost (Buck transformer) that helped my A/C units see enough current.

By chance are you connected with a 30a/30a Y?
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Old 03-19-2019, 06:30 PM   #5
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Thanks all -
When its said that we could be missing a "leg" of 120, are you confirming my vague understanding that a 50 amp set up is split into two 120 circuits?
Indeed I'm on shore power, not inverter.
We're in the Bahamas and its been raining to the point that the notion of putting a volt meter on the pedestal has little appeal at present. But if I did, should I see 120, or 240?
I am not using a 30/30 Y.
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Old 03-19-2019, 07:38 PM   #6
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Yes, you will have 2 120 volt 50 amp legs of “hot” power. Maybe you are only getting one of the legs and your A/Cs are powered off the dead leg? The easiest way to check is to get a voltmeter and check each of the 2 hot legs to ground one at a time. The 120 legs are 180 degrees out of phase so when you go across the two legs you get 240 volts. If some of your shore power is working and some not this is the first thing I would check and make sure power is getting to the boat properly. If you are indeed getting both 120 legs into the boat then it is time to start digging deeper to find the problem. Good luck and if you do not feel comfortable doing electrical work then get someone who is experienced to check it for you.
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Old 03-19-2019, 09:25 PM   #7
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You're sure that the A/C's are 120V? If they're 240V and you're missing one of the 120V legs from the pedestal, they won't run. Can you move the plug to a different receptacle temporarily? Like on a different pedestal... Cycle the pedestal breaker a couple times, twist the cord back & forth in the receptacle, spray some WD40 into the slots & re-plug the cord.


For the most definitive DX, get a meter on the receptacle. Yours should match the bottom one on the diagram. You should read 240V between X-Y, 120V X-W/G or Y-W/G. -0-V between W and G (the metal indentation in the circumference of the receptacle. That's the ground, it mates with the plug where there's a spring loaded tab in the same position. The (X-Y) power carrying prongs have an "L" shape, the neutral does not. Checking for correct voltage is not difficult, it should not be intimidating once you understand what you're looking for, and is safe if you use a DVM with the correct probes. Sometimes it's easier to check the boat end of the cord, you can position it better and not get whacked on the head by the pedestal cover. That's if you're sure the cord is OK!



If you find a receptacle that reads 240V but you can't get it to read 120V to the W, that's a miswired or missing neutral, and it's a potentially dangerous connection, don't use it & report it to the marina.



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Old 03-20-2019, 02:12 AM   #8
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I’m guessing your AC panel does NOT have a switch to read voltage on the “1” and “2” legs separately? That would have possible saved you a possible trip to the pedestal.
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Old 03-20-2019, 02:21 AM   #9
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I did mention that in a previous post. Didn’t get an answer.
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