50 amp shore power connector but 30 amp breaker at the panel - what do I need to change?

[Alaris]

My boat currently has a 50A shore power connector. The AC panel breaker on the boat, however, is 30A 125V. 30A isn’t going to cut it for me and I am trying to figure out the scope of the upgrades necessary.

There are two ways we can meet my electrical needs: give me a 250V circuit for the new A/C, or get me 50A on the existing 125V AC circuit.

How do I get what I need? A subpanel?

I’m waiting to get answers from my electrician but I want to make sure I’m asking the right questions.

 

[slug zitski]

Not easy to answer

You must post a picture of the wiring diagram with wire gauge specs , transformer specs , breaker specs ……..

perhaps everything is ready to go..but only the wiring diagram can tell you

 

[Alaris]

I have seen the wiring diagram but don’t have it with me. It appears only three wires are coming off the 50A inlet. 110 hot, neutral, and ground. That goes directly to the 30amp master breaker on the AC panel.

Does that mean it’s just a 50A 125V inlet?

I have a new 50A 125/250 smartplug inlet ready to go.

 

[slug zitski]

I have no idea

the wiring diagram tell you everything

 

[vibroman]

Alaris
My new to me Dehler 41 has 2 connectors. One for the general house circuit.... chargers, 110 cabin supply and water heater.The other is dedicated to the AC

 

[longy]

^^^^Correct. You need to establish just what flavor of shore power wiring you have. Common marine shore power for 50 amp is really two separate 'hot' wires, one neutral & one ground. Four wires total.But there are outlets that are 50 amp, with two hot wires & one neutral. Three wires total. Not using the appropriate wiring may result in many bad things & lots of sparks. If you are confident in the use of a multimeter you can figure this out - but much better to get the marina to specify just what you've got supplied. Once you know just what the marina supplies you can determine just what you need to use to connect your shore power cord. Your boat is wired/protected for a 30 amp input, one hot, one neutral, one ground (3 wire) source. Your existing 50 amp cord may only be picking up one hot leg - many times the 50 amp circuit on docks provides better power than the 30 amp circuit.

Alaris' panel is a common method for new boats. One 30 a circuit for most AC users, a separate (and separate cord) circuit for HVAC units. These two cords can be attached to a single 50 amp 4 pole plug by using a 'splitter' that separates the two hot wires out to two 30 amp plugs
Also note that '50 amp' 4 pole circuits actually provide 30 amps per hot leg.

 

[Alaris]

^^^^Correct. You need to establish just what flavor of shore power wiring you have. Common marine shore power for 50 amp is really two separate 'hot' wires, one neutral & one ground. Four wires total.But there are outlets that are 50 amp, with two hot wires & one neutral. Three wires total. Not using the appropriate wiring may result in many bad things & lots of sparks. If you are confident in the use of a multimeter you can figure this out - but much better to get the marina to specify just what you've got supplied. Once you know just what the marina supplies you can determine just what you need to use to connect your shore power cord. Your boat is wired/protected for a 30 amp input, one hot, one neutral, one ground (3 wire) source. Your existing 50 amp cord may only be picking up one hot leg - many times the 50 amp circuit on docks provides better power than the 30 amp circuit.

We are wiring the dock from new. The dock has 100amp 240V service at the meter. What comes into the boat can be whatever we wire it to be.

 

[Alaris]

Excuse the photos, the diagram is 39 years old. The boat does not have a generator so disregard that section.

 

[longy]

Your boat can only handle 30 amp 120 v supply. Wire the dock to provide that. Size the wire to the dock to supply two 30 amp outlets & one 15 amp outlet.

First pic, upper left of blueprint shows your boats AC input wiring. I can't decipher it.

 

[Alaris]

Your boat can only handle 30 amp 120 v supply. Wire the dock to provide that. Size the wire to the dock to supply two 30 amp outlets & one 15 amp outlet.

First pic, upper left of blueprint shows your boats AC input wiring. I can't decipher it.

That’s not enough. My question is what do I need to do to get more power. Either 50A 120v or 50A 120/240.

Here are clearer photos.

 

[slug zitski]

Yah

hard to read ..looks like 6 gauge wire…30 amp breaker

 

[Alaris]

Yah

hard to read ..looks like 6 gauge wire…30 amp breaker

That’s how I read it

 

[longy]

What do you need more input power for? Easiest & most common will be adding a complete duplicate system - new boat side input plug, new wiring (as per ABYC) to a new AC distribution panel

 

[Alaris]

What do you need more input power for? Easiest & most common will be adding a complete duplicate system - new boat side input plug, new wiring (as per ABYC) to a new AC distribution panel

Two zone air con, 110V refrigeration, water heater.

I plan to install a SmartPlug inlet so I figured I might as well put the right thing on there and upgrade the wiring as necessary.

 

[Alaris]

Why can’t I just take the two hots off a 50A 125/250 and use one to run the old AC panel and the other to run a new subpanel just for the air conditioning? I’m simplifying but do you understand what I mean?

 

[longy]

Yes, you can do that. I cannot tell you if it conforms to ABYC standards. Your insurance provider will care about this! Or a marine sparky with a current copy of ABYC standards

If you do this, the only difference will be one input socket on the boat - everything after that will be the same regardless of number of sockets. Also note current regs require a galvanic isolator and a double pole breaker immediately adjacent to input sockets.(existing wiring per diagrams does not have this)

 

[Alaris]

Yes, you can do that. I cannot tell you if it conforms to ABYC standards. Your insurance provider will care about this! Or a marine sparky with a current copy of ABYC standards

If you do this, the only difference will be one input socket on the boat - everything after that will be the same regardless of number of sockets. Also note current regs require a galvanic isolator and a double pole breaker immediately adjacent to input sockets.(existing wiring per diagrams does not have this)

Not arguing—if this doesn’t conform to standards, how else do you get a second AC panel without bringing in a second power cord (which is not feasible)?

Not looking to break any rules. No more than 50 amps would ever be needed. But 30 isn’t enough given HVAC start up draw even with slow start.

 

[Slick470]

#6 AWG wire per NEC (which would govern wiring on that side of things) is good for 55A using the 60 degree C rating. That would make sense as the upstream overcurrent protection (shore side) would be rated for 50A. Your 30A circuit breaker only protects the distribution downstream. I'm not sure on ABYC standards are for AC circuits but you should be able to intercept that feed and put in a new "panel" after the shore power inlet that has two 30A branch circuit breakers. One to serve your existing system, and the other to serve your new HVAC loads.

Edit to add, you'd probably still want a 50A, 3-pole main on that panel to switch the three conductors, after that you could probably go 1-pole for 30A branch breakers, but I'd need to think about it for a bit. When it comes to AC my brain is on the shore side of things and my boat's AC system is so simple it's basically a big power strip...

 

[longy]

I believe you can bring 4 wire 50 amp service onboard & split the hot legs at the plug. But I don't have the standards book to verify

 

[mckenzie.keith]

Here is an ABYC ampacity table that tells you what kind of wire you can use for 50 A. The gauge depends on the insulation temperature rating and whether the wire passes through engine spaces.

Ancor 4 conductor shore power cable is 6 AWG, and that will definitely do the job. You may be able to use smaller gauge wire (per the ampacity table) but I don't know that much about ABYC wiring codes. Like do you need conduit or something?

Here is an AC main panel which supports 50 Amp 120/240 VAC 60 Hz (north american split phase). It is blue sea systems part number 7372 (in case the link doesn't work).

From the main panel, you can wire to two separate 120 V sub panels. Use 50 A wire from main panel to sub panel. From the sub panel everything is exactly the same as before.

Maybe you can route one hot wire from the new AC main panel to your existing 120 V panel. Install a small 120 V sub-panel for loads that only run on shore power. Maybe this will allow you to keep your existing 120 V sub-panel as-is.

There is a lot more to all this if you have inverters and whatnot. This is just a sketch of a suggestion, really.

Like isolation transformers, dielectric barriers on ground wire, inverter chargers. Also do you think you might visit places that only have 30 A shore power and do you want to be able to plug in there? Etc.