Appears Breaker Trips when AC shuts off

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yellemg

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Joined
Feb 27, 2003
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11203
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I have a dedicated 30 AMP shore power circuit for two AC units on the boat. Both units run for a while, but after a while the 30 AMP shore power breaker will trip.

One AC unit uses 10 amps when running the and the other one uses 12 AMP's. Both will momentarily cause the AMP meter to go over 30 amps when starting, but no breakers trip.

Yesterday, I watched the AMP meter, it sat at 22 amps and everything was fine. Once the boat reached the cooling target temperature, the 30 AMP breaker on the dock pedestal tripped. There was no visible surge on the amp meter, the breaker just tripped. I assume one or both of the units were in the process of switching out of cooling mode.

If I run a single AC unit, the breaker never trips. Only happens when both are running. I plan to do some further tests while running one unit at a time to see if there is a amp surge when one of the units switches out of cooling mode.

Any ideas? Or should I just contact an AC repair person?

Thanks,
Mike
 
You might be surprised that the compressor on the 10 and 12 amp units is the running current not the peak demand current. Either unit may actually draw 2 to 3 times (called peak current) then the rated running amperage when cycling. It happens so fast most boat panel AC meters can't read the actual current. The other thing is the breaker might be overheating causing it to eventually trip? Can you try another 30A outlet on the dock? How about checking the 30A inlet on the boat they often fail or cause excessive heat which means current draw you will never see on a panel meter. Can you watch the voltage does it drop just before the breaker trips? One other potential issue is to try a different 30A shore cord. Sometimes depending on the AC feed from the marina's fuse panel, it's distance and the overall condition of the power wiring to the pedestal you have a low voltage brown out like condition created by a large number of boats on the same circuit effectively causing the AC voltage to sag as other boat's compressors kick on and off when it's hot, muggy and the dock is crowded.
I could never run my 2 16,000BTU Marine Air units reliably of a single 30A cord. I had each on a separate 30A panel feed on the boat.

Eventually I installed soft start kits on both AC units then I could run the 2 AC units off a single 30A circuit if needed.
 
quote:
Originally posted by yellemg

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branch circuit breakers are typically rated for approx. 80% continuous load. at 22 amps you are very close to that. if any of the connections in the breaker are loose or the breaker itself is aged, it will trip. don't forget that any other boats on your circuit that have demands cycling on/off will cause momentary voltage drop and this raises the amperage on all of the loads.

running a pair of a/c units on a single 30 amp is not going to work in the long run because of the start up amperage and line drop. it will run for a while but it is a matter of time before it kicks off. you really need dual 30amp shore power to run a pair of A/C's and the other incidental house loads.

the easy solution is to split the house loads between the two 30 amp circuits and split the A/C's between them.
 
quote:
Originally posted by vic33004

quote:
Originally posted by yellemg

Click to expand...


branch circuit breakers are typically rated for approx. 80% continuous load. at 22 amps you are very close to that. if any of the connections in the breaker are loose or the breaker itself is aged, it will trip. don't forget that any other boats on your circuit that have demands cycling on/off will cause momentary voltage drop and this raises the amperage on all of the loads.

running a pair of a/c units on a single 30 amp is not going to work in the long run because of the start up amperage and line drop. it will run for a while but it is a matter of time before it kicks off. you really need dual 30amp shore power to run a pair of A/C's and the other incidental house loads.

the easy solution is to split the house loads between the two 30 amp circuits and split the A/C's between them.

Click to expand...
great comments I agree. Adding the soft start is an easy task but they are expensive. I never tripped my dual 30A breakers once they were installed even with other boats on the same branch circuits.
 
Forgot to say in initial post that I had tried different power cords and different outlets on Dock. Same result. Note: The two AC's are on a panel that is fed from either the its own shore power cord or as a subpanel off of the other shore power panel. So I can easily feed from either dockside outlet. Same result regardless of the dockside breaker or power cord.

Think I will move the smaller of the AC units to the other panel.

Thanks, for the excellent and quick responses.

Mike
 
IDK something else has to be going on . I run 2 16k units all day long on same 30 amp cord. Something else has to be cycling on . water heater, battery charger. the initial compressor start should not trip the break unless its bad. If u can switch the load thats great but something else is going on

Rob
 
Are you in cooling mode only?
Maybe its trying to cycle to reverse heat.
 
quote:
Originally posted by Robski97

IDK something else has to be going on . I run 2 16k units all day long on same 30 amp cord. Something else has to be cycling on . water heater, battery charger. the initial compressor start should not trip the break unless its bad. If u can switch the load thats great but something else is going on

Rob

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Rob, it depends a lot on the quality of power provided by the marina to the pedestal. If you are the one of the farthest boats from the panel and there are other users cycling their units this will trip the breaker. There are many factors is the marina's AC wiring compromised from age or water, how many other boats are on the same branch circuit, his AC units maybe older and require a higher current to engage the compressor, do the AC units ice up then revert to defrost/ reverse mode, his transom outlet could be deteriorating? When the AC voltage starts to sag anything using Alternating Current in the boat especially the high current AC units will draw more current (even in running mode).
As I previously mentioned I couldn't reliably run my 2 16,000BTU modern units on a single 30A feed without eventually tripping the pedestal breaker until I installed soft start circuits.
I was the last boat on my dock so I could clearly see voltage drop causing excessive current draw especially when others were on their boats with AC units running.
Bill
 
quote:
Originally posted by yellemg

Forgot to say in initial post that I had tried different power cords and different outlets on Dock. Same result. Note: The two AC's are on a panel that is fed from either the its own shore power cord or as a subpanel off of the other shore power panel. So I can easily feed from either dockside outlet. Same result regardless of the dockside breaker or power cord.

Think I will move the smaller of the AC units to the other panel.

Thanks, for the excellent and quick responses.

Mike

Click to expand...


it sounds like we have similar panel configs. when the boat is not occupied I only need one A/C unit and run all loads from a single 30amp shore power cable. when we use both A/C units we are either running the generator or segregated dual 30amp power. remember that if you run two shore power cables simultaneously the panels must be isolated with only a shared neutral and bond as the positives are likely in a different phase.

our generator is configured as a 120v output only and has sufficient ampacity to feed thru one panel, the second panel is bridged in this mode.
 
All very good comments however I am having trouble getting my head around two different breakers tripping on shut down on one AC!!!!
 
I will run some more tests this weekend to try and isolate what is happening.

PDECAT - Only one breaker is tripping at a time. Tried two shore power outlets, one at a time, same result. Breaker trips after running for a while.
 
You said the breaker tripped when the boat reached a comfortable temperature and didn't seem sure a compressor cycled out before the breaker tripped. Personally I think your shore tie breaker is weak or getting hot. It's more likely a thermal design than magnetic. I know you said you tried another breaker with same result. I just don't see why a breaker would trip as load came off. Ordinary breaker, like in a house, right? I can see where maybe if the breaker was an arc or ground fault version, maybe.

What are your cable and connections like? Is any of it getting hot as the A/C runs?
 
As a quick test for you boat's 30A power inlets (where the boat connection is for the shore cords) just put your hand on the fixture see if they are getting hot. If so it's time to remove them and inspect the rear for overheating.
It's the #1 cause for boat fires if left unchecked and they eventually deteriorate.
 
I'm with Rob and Billy.
Check attachment connections (both boat and post) for heat. Shut off water heater etc. Something is causing the trip that doesn't read like a short. There could be a bad spot in one of the compressors, that is causing a surge. Running them one at a time may not surge enough to trip a breaker, but together it is.

Good luck,

Billy K.
 
JD he has tried two different power cords into two different dock outlets????
 
having been in the hvac business for over 45 years, I have never seen a breaker trip when a unit cycles off. my guess is that you have a bad connection either at the boat inlet or on the pedestal. years ago I had a similar issue and found the receptacle on the boat where the power cod plugs in was overheating and starting to melt. I check tho9se connections yearly since then. remember, all the boats power comes in to that connection and is susceptible to overheating. I also agree that you may have a weak circuit breaker. finally, if you have both units on the same side in your panel, I would probably move one of them to the other side of the panel
good luck
 
Did some tests over past few days and problem appears to be with the two 30 amp outlets on my pedestal. A boat next to me was gone, so I plugged into their pedestal and everything worked fine. Since I could not leave it this way, I moved back to my pedestal with one shore power cord plugged into one of the 30 AMP outlets and the other into the 220V 50 AMP outlet (using an adapter I had). Everything works fine now.

Not sure if the one power cord using the adapter is actually on a 50 AMP circuit or not, but inside breaker is 30 AMPS, so circuit is not pulling more than 30 amps.

Thanks for help and suggestions.
Mike
 
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