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Old 08-07-2018, 21:58   #1
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Mermaid AC is tripping GFI shore power

I have another case of GFI shore power tripping, but my case seems to be a little more unique than what I can search up.

I was over joyed to move into one of the fancy new covered slips in my marina, but then I was slapped in the face with GFI. I can motor over to my old slip and plug in and run all day with zero issue, but the old slip doesn't have a ground fault breaker.

The uniqueness of my situation is that everything works except the compressor motor on my Mermaid Air Conditioning unit which will trip the circuit breaker on the shore about 1 second after powering on. I can have everything else in the cabin running without issue. Even on the Mermaid I can have the water pump and the blower fan running and not have a problem. Could the compressor motor itself have a neutral to ground fault in it? I don't see one in the electrical connections, but seeing as how this same motor works on the old shore power it is sure looking like there is some neutral to ground leakage. I haven't got my hands on a clamp tester yet to prove it, but I will. Though I don't see what else it could be.

My knee jerk reaction was that I'd need to replace the compressor motor, but then I got to thinking that if the motor itself has the fault in it...was it designed like that? Will a new motor even help? Has any one dealt with Mermaids and GFI before?

Apparently there is ONE guy in my area with any experience working on these GFI issues in a marine environment and I haven't been able to even contact him yet. So any help on things to try would be much appreciated.

Thanks


Stuff I've tried:
Plugging into another shore power receptacle that is known to be working.
Used a different cable
Used a different cable with an ELCI breaker built in
Bypassed the compressor motor overload switch
Runs fine on generator and non-GFI shore power...pulls about 12 amps
Isolated the issue to the Mermaid and verified it only happens when the compressor runs
Thanked ABYC for keeping all the people crazy enough to swim in a marina safe (yeah I know...accidents happen, but still...)
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Old 10-07-2018, 05:45   #2
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Re: Mermaid AC is tripping GFI shore power

What is your shore power service; 1 or 2 inlets; 30A/125V or 50A/250V?
How old is the Mermaid unit?
What kind and how old is your boat?
Have you called tech support at Mermaid?
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Old 10-07-2018, 07:38   #3
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Re: Mermaid AC is tripping GFI shore power

Shore power is a single 30amp/125v. I have also tried the 50 amp receptacle with an in line 30 amp adapter and it still trips the 50 amp shore power breaker.

Boat is a 1998 Welcraft 33'. I am pretty sure the mermaid came with the boat when it was new, but I am not the original owner. It doesn't look like a hacked in addition though.

I haven't tried Mermaid support since I am sure it is far out of any warranty coverage.
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Old 10-07-2018, 08:13   #4
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Re: Mermaid AC is tripping GFI shore power

If you had two 30A shore power sources it could be a case of neutral swapping but with a single inlet and the testing that you have done, it certainly appears to me that the compressor windings are failing.

However; before you change the compressor out you need to do a bit more testing.
1. Make a shore power cord adapter so you can put a clamp meter around the L and N conductors.
2. Using this adapter, borrow a clamp on ammeter with mAAC resolution.
3. Clamp L and N and turn on everything AC one at at time (leave them on) except your A/C equipment. Record the total mAAC leakage as each device is energized.
4. Turn on the A/C water pump">raw water pump. Record.
5. Turn on the compressor. Record with capture.

The reason to do all of this is you may be leaking 28mAAC with everything AC on the boat running except the A/C compressor which leaks a paltry 2mAAC. You turn it on and the pedestal GFP trips because you have exceeded the 30mAAC trip point.
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Old 10-07-2018, 09:14   #5
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Re: Mermaid AC is tripping GFI shore power

One thing to consider that you haven't mentioned is the start-up draw of the AC. Although it runs at 13amps, the start-up load which kick-starts the compressor can be many times that. Maybe this is what is tripping the breaker. For example, my 30amp shore power handles the start-load on my AC but my 30amp generator trips. I fixed the problem by purchasing a (rather expensive) soft start which gradually lets the load increase without the big spike.
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Old 10-07-2018, 09:19   #6
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Re: Mermaid AC is tripping GFI shore power

There was one thing I realized I omitted. Once I isolated the fault to the compressor motor I've left every other circuit breaker off on the boat, but the mermaid's (including all the 12v though if that mattered I'd have some much larger issues, it's just off for safety sake).

So the only thing that might leaking neutral to ground is the Mermaid's pump, fan, and compressor motor. I need to try and see if the pump and fan aren't leaking though.
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Old 10-07-2018, 09:56   #7
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Re: Mermaid AC is tripping GFI shore power

Quote:
Originally Posted by Privilege View Post
One thing to consider that you haven't mentioned is the start-up draw of the AC. Although it runs at 13amps, the start-up load which kick-starts the compressor can be many times that. Maybe this is what is tripping the breaker. For example, my 30amp shore power handles the start-load on my AC but my 30amp generator trips. I fixed the problem by purchasing a (rather expensive) soft start which gradually lets the load increase without the big spike.
I will look into that. I doubt a soft start capacitor would be more expensive than a compressor motor. Plus even if it doesn't fix my issue it would be a good thing to have anyway. I have an Onan 6.5Kw generator so it might be able to handle the start up surge. Though the non-gfi shore power should probably trip as well if this was the issue, but the key word is "should". Electricity has a mind of it's own sometimes.


Thanks for all the replies.
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Old 10-07-2018, 13:23   #8
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Re: Mermaid AC is tripping GFI shore power

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Originally Posted by Gustuv Wynd View Post
I haven't tried Mermaid support since I am sure it is far out of any warranty coverage.
Talk to Tom down at Mermaid. Yes it's probably far out of warranty, but they are really nice and are happy to help with any issues, based on personal experience. Enough so that I purchased a new 12K BTU unit off of them recently. That's all I've got to say about that...
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Old 10-07-2018, 18:05   #9
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Re: Mermaid AC is tripping GFI shore power

I have the same problem with my cruiseair system, ac runs fine for 30 to 90 minutes then trips gfi.
Things I’ve done tested shorepower cord, had run and start capacitors checked, cleaned raw water circuit. Domestic suggest it’s tbe fan motor windings or control board electronics but both cost a $1000 each and no guarantee!
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Old 11-07-2018, 15:37   #10
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Re: Mermaid AC is tripping GFI shore power

I have/had the same issue with my AC units and marina GFIs. My units were installed by the prior owner who wired them like house wiring neutral and ground together in the same contact block. I just took the ground wires together to a lug in the box and is fine now. The marina mgr, who is an electronics guy, thought it might be the varnish on the motor windings failing and causing the fault. My system faulted as soon as I connected shore power so it was a neutral - ground issue, but you have power to the pumps and etc, so it may be the compressor motor windings.
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Old 14-07-2018, 16:51   #11
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Re: Mermaid AC is tripping GFI shore power

I think I am going to go ahead and try switching the compressor. Any one ever done that? I think I can pry the specs of what refrigerant to use and how much out of Mermaid, but it would be nice to not go into the job blind. To be honest I don't have much clue as to what I need to do with the water lines. I am not too concerned about anything else. It is probably simple, but I've just never messed with them before.

Worst part will be to silver soldering the lines I am going to have remove the unit from the boat. I am going to look into hiring some one to do it, but from what I've seen so far it is hard to find any one will to do much on a boat in my area...I miss blue water.
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