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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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Old 09-25-2012
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What size AC breaker?

My new to me boat has 30amp shorepower which is wired to 2 15amp breakers. These are household breakers that are located on the cabin deck inside of a standard home metal box! I have a Blue Sea 120v ac panel with burned out 30amp dual breakers. I would like to hook up the Blue Sea and get rid of the household setup. My question is should I go with the original 30amp dual breakers or go with a 15 or 20amp dual breaker to power the onboard electrics. Heater, lights etc when docked? Thank you.
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Old 09-25-2012
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Mine has dual 15 on a 30 amp sp

Not being a electrical expert but, I would want to know how or why dual 30 ( 60amp house main ) burned out first
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Old 09-26-2012
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Re: What size AC breaker?

A breaker only protects the circuits beyond the breaker. Thus, if the first breaker in line from the shore power inlet is at the panel any short in the wire from the "house entrance" (where the shore power is plugged into the boat) and the panel will not be protected and could result in a fire. You should have a 30 amp breaker right inside the boat at the house entrance. It should be in a waterproof box.

To see what bad shore power can do at the "house entrance" see Sailing - Reboot (USA 60493): I never saw a thing

If you do not need to leave the boat plugged in to charge the batteries it is a good idea to turn off the power at the marina pedestal and unplug the wire when you leave the boat. Many marinas have stray electrical currents that will eat your zincs alive. By unplugging the boat you reduce these stray currents and your zincs will last a whole lot longer.
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Old 09-26-2012
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The maximum breaker size is bound by the type and size of the conductor going to the load.
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Re: What size AC breaker?

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Originally Posted by svzephyr44 View Post
any short in the wire from the "house entrance" (where the shore power is plugged into the boat) and the panel will not be protected and could result in a fire.
It is protected by the breaker in the shore based distribution panel that feeds the shore power receptacle.

Eric
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Old 09-26-2012
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Re: What size AC breaker?

Hello there, I don't understand why you have a dual breaker on 120 V. AC 30 amp. This circuit requires only one single 30 amp breaker.you should have a black wire that delivers current, a white wire which is neutral, and a green wire which is ground. The circuit breaker only protects the black wire which is commonly called a hot lead. Normally when you have a double breaker you're dealing with 220 ac which in that case there are four wires. You really need to have someone who is familiar with marine wiring help you with this. You don't know what someone else has done. Attempting to do this yourself without experience, could cause damage to your boat or you. Or someone might be swimming close to your boat..... this is something I really believe you should get help with.....captg
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Re: What size AC breaker?

A dual simultaneous trip circuit breaker is an ABYC requirement for 120vac single phase shore power feed.

Eric
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Old 09-26-2012
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Re: What size AC breaker?

Quote:
Originally Posted by Capt. Gary Randall View Post
Hello there, I don't understand why you have a dual breaker on 120 V. AC 30 amp. This circuit requires only one single 30 amp breaker.you should have a black wire that delivers current, a white wire which is neutral, and a green wire which is ground. The circuit breaker only protects the black wire which is commonly called a hot lead. Normally when you have a double breaker you're dealing with 220 ac which in that case there are four wires. You really need to have someone who is familiar with marine wiring help you with this. You don't know what someone else has done. Attempting to do this yourself without experience, could cause damage to your boat or you. Or someone might be swimming close to your boat..... this is something I really believe you should get help with.....captg
On boats it is an ABYC requirement to break both white/neutral and black/hot even on a single phase 120V circuit. This is why main breakers for AC on boats are doubles. On branch circuits after the main AC breaker only the black/hot needs to be broken....

Also if the wire run between the AC inlet and the main AC panel breaker is longer than 10' (wire length not as the crow flies) there should be an additional main breaker at the entrance point or close to it.
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Last edited by Maine Sail; 09-26-2012 at 11:05 AM.
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Re: What size AC breaker?

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Originally Posted by Maine Sail View Post
On branch circuits after the main AC breaker only the black/hot needs to be broken....
Only if the boat is equipped with a reverse polarity indicator or isolation transformer. If not, the branch circuit breakers must be douple pole.

Eric

Last edited by fairbank56; 09-26-2012 at 11:29 AM.
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Re: What size AC breaker?

I'm used to dealing with systems that have polarity protection, however it sounds like this gentleman needs some help. Especially if he has household wiring or distribution. That in itself tells me that it would be very difficult for him to have ground protection in a household distribution panel. I think he needs professional help, maybe you can help him. Eric
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