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Author Topic:   AC Boat Wiring for a Battery Charger
jstarzy posted 06-24-2015 05:08 PM ET (US)   Profile for jstarzy   Send Email to jstarzy  
I recently purchased a 205 Conquest and would like to install a battery charger for maintaining the batteries while the boat is docked. The marina offers a 30-Ampere shore power outlet on a pedestal at my slip. The boat is not wired for shore power.

When investigating how to do a safe installation, in one instance in an article from West Marine (pasted below, category 1), the author indicated that if the charger is the only device connected on board to A.C. power, an acceptable practice would be to adapt the 30A protected shore power receptacle to standard parallel blades with ground and run an outdoor rated A.C. power cord to a parallel blade on-board weatherproof receptacle and wire the charger directly to the load side of the receptacle. The "Genius" line of chargers has a receptacle accessory to do exactly this.

This practice would suit my needs but I'm uncertain if it meets industry recommended practices for safety.

Another solution would be to purchase a shore power 30A cable, on board inlet, on board cable, power distribution panel with 30A main and 3 15A branch circuits (smallest available), GFI outlet for the charger to plug into. Essentially adding full shore power to my 20' boat. A very costly project for a single charging device.

Can anyone refer me to the simplest, industry accepted recommended practice for adding AC power for only an on-board 12v charger when the boat will be powered by marina shore power?



West Marine: AC wiring connections

The AC wiring can be as simple as plugging the charger into an extension cord and running that to an outlet in your garage. This would be appropriate for a fishing boat, ski boat or runabout. If a permanent installation is desired it is likely to fall into one of two categories: 1) the charger is the only load on the boat and thus is wired from the shore power inlet to the charger. 2) the boat has a distribution panel (AC breaker panel) and the charger is wired to a breaker in the panel. Let’s consider each.

1) If the charger is the only AC device on the boat you may install a compact shore power inlet that accepts a standard straight blade extension cord (West Marine Model 191991). Locate it in a protected spot within reach of the AC cord on the charger, cut off the charger’s AC plug, and connect it to the AC inlet. Spray the terminals and wire ends with a corrosion preventative as you make it up.

timf posted 06-26-2015 12:07 AM ET (US)     Profile for timf  Send Email to timf     
If you had a 15-Ampere outlet at the dock it would be ideal, but sounds like you do not.

The distribution panel would work, but quite a bit of stuff for what you need.

For me, I would be comfortable using the adaptor you show. A small charger will draw little and it would have to be an unusual failure for it to try to draw 25A for example and cause a possible safety issue.

Probably the biggest risk is that if someone else connected several loads to it through a splitter and drew over 20A. It could overheat the short wire out of the adapter or an extension cord connected to it.

With the short wire it has it is pretty low risk. Electrical codes (I believe) would not generally allow this. Not because what you want to do is especially unsafe, but more because of what people could do with it that are unaware.

If you did do it, I'd consider removing it when you sell the boat because of this.

number9 posted 06-26-2015 12:58 AM ET (US)     Profile for number9  Send Email to number9     
Marinco also has a charger inlet without the pigtail: black 15-Ampere 120-Volt on-board charger inlet par number 150BBI.

jstarzy posted 06-29-2015 10:38 PM ET (US)     Profile for jstarzy  Send Email to jstarzy     
Thank you both....

After some investigation, the marina will permit adapting the 30A twist to parallel blades and running power to a single inlet, connected only to the charger via direct parallel blade outdoor rated cord.

I'm collecting the parts now. The installation should be straight forward.


jimh posted 06-30-2015 09:52 AM ET (US)     Profile for jimh  Send Email to jimh     
On my small boat, for the past decade or longer, I have been carrying a 25-foot 120-VAC extension cord with conductors of just 14-AWG. On the power-source end I have installed a 120-VAC 30-Ampere Twist-lock plug, which mates with the typical marina shore power outlet. On the other end is just a standard 15-Ampere 120-VAC receptacle that you'd find on any extension cord. I use this as means of getting 120-VAC power to the boat when at the dock. The usual use of the 120-VAC power is to operate a battery charger. The charger has a conventional cord, and I just plug the charger into my shore power cord. An alternate load might be something like an AC-powered charger for a laptop or other electronic device that needs its battery charged. We also use that shore power cord every morning to brew some coffee when at the dock.

I doubt that this cord is strictly legal, on several basis. First, it is probably not code-compliant to have a 14-AWG cord connected to an outlet that could supply 30-Amperes. The conductors of the cord could overheat if 30-Amperes were carried on the cord. I believe you will find all the commercially-made and commercially-sold shore power cords will have conductors of 10-AWG. That is the conductor size needed to handle 30-Amperes of current.

Second, the outlet should probably be a ground-fault-interrupt (GFI) outlet. I am not an expert on electrical wiring codes, but it seems like any outlet these days that is used outdoors is required to have ground-fault protection. I have given some thought to getting a GFI outlet that is encased in a rubber housing and can be made to be part of the extension cord. The commercially-made shore power cords do not have a GFI outlet, and I believe that is because they are considered just as extension cords running between the shore power receptacle at the marina and the one on the boat. Any protection for ground faults would be provided by the AC power distribution wiring on the boat.

I have also thought about adding a shore power receptacle fitting to the boat. Tthe cost of such a fitting (as JSTARZY mentions), and the rather large opening in the topsides of the boat it requires for mounting, are drawbacks which have discouraged me from installing one.

I rationalize my use of what is probably a non-compliant cord on the basis that I generally do not connect any load to it unless I am on the boat and closely supervising the situation.

It is common to find on marina docks there is, in addition to the 30-Ampere outlet, a conventional 15-Ampere outlet available at the power pedestal. Sometime I carry the coffee pot to that outlet to make coffee, usually in situations were the 30-Ampere outlet is too far away for my short 25-foot cable to reach. I don't know if using a conventional 120-VAC extension cord to extend that 15-Ampere power receptacle to the boat would be code compliant, either.

porthole2 posted 07-01-2015 03:37 AM ET (US)     Profile for porthole2  Send Email to porthole2     
I have used the Marinco Guest one-bank and two-bank chargers with a 15-Ampere shore power adapter on two different Boston Whaler boats, so far. And I will be doing the same upgrade on my newest Boston Whaler boat. There are two versions of the shore power inlet: one with a "you" hard-wire 15-Ampere male plug; and one [with] a unique 15-Ampere cord male plug end on the charger snaps together. The second would be preferred, as the connectors are factory sealed

jimh posted 07-01-2015 12:58 PM ET (US)     Profile for jimh  Send Email to jimh     
The number of banks of battery the charger can charge or the manufacturer of the charger or the amount of current produced by the charger really have no bearing on how one can simply connect a 120-VAC charger to shore power on a boat where it is not desired to install a permanently mounted, approved, 120-VAC 30-Ampere shore power bulkhead-mounted receptacle. Just take the 120-VAC cord from the charger and connect it to a shore power cord with an appropriate receptacle mounted on it.
porthole2 posted 07-01-2015 06:51 PM ET (US)     Profile for porthole2  Send Email to porthole2     
I gave [JSTARZY] some food for thought based on his question;

Can anyone refer me to the simplest, industry accepted recommended practice for adding AC power for only an on-board 12v charger when the boat will be powered by marina shore power?

Did I assume wrong in suggesting something other than bastardized and dangerous extension cords being used in a marine enviroment, potentailly with unsafe standard automotive type chargers? Although not eaxctly related, there is a reason OSHA does not allow "repaired" extension cords on a job site.

Taking a look at the power pedesatals in your marina should answer questions regarding the GFCI--you'll find [a GFCI] on the 20-Ampere duplex.

[A number of sidebar topics introduced in this post have been deleted because they were not on the topic of providing AC power to a boat for a battery charger--jimh]

jimh posted 07-01-2015 11:21 PM ET (US)     Profile for jimh  Send Email to jimh     
Re the sort of 120-VAC receptacle shown in

Although the catalogue listing says "UL Approved for US and Canada," I don't really see much advantage of this device over an ordinary extension cord connecting to the ordinary power cord of an on-board battery charger. If anything, it looks like water could collect in the connector housing that is to be mounted on a bulkhead, which could create a hazard itself.

What is there about this device that will make use of an 120-VAC charger on a boat safer?

jimh posted 07-01-2015 11:21 PM ET (US)     Profile for jimh  Send Email to jimh     
PORTHOLE2: I don't see where there was a recommendation to use "an unsafe standard automotive type charger." You seem to have invented that part of the discussion yourself.

You should more clearly describe the method of connection you are proposing. The link you included to illustrate the method you described did not reveal anything particularly clear. I am confused about your method, which you described as:

quote: with a "you" hard-wire 15-Ampere male plug; and one [with] a unique 15-Ampere cord male plug end on the charger snaps together.

In order to help readers understand what you think is better about this method, you will have to describe it more clearly. If you could do that, it would help readers understand what you are recommending.

jimh posted 07-01-2015 11:30 PM ET (US)     Profile for jimh  Send Email to jimh     

Recall that the original request was for "an industry accepted recommended practice." The best source of that is likely to be found in the ABYC recommendations. Citing some portion of the ABYC recommendations is probably the best way to give a pointer to an industry accepted recommended practice. A portion of the ABYC recommendations can be found at

There is a section of recommendations beginning at that describes the recommended form of the power inlet and shore power cable.

Note that the requirement for a locking plug in the shore power cord is only for the shore-power-end of the cable, not the boat end.

jimh posted 07-02-2015 12:02 AM ET (US)     Profile for jimh  Send Email to jimh     
While this discussion seems to have initially focused on the receptacle and cordage used to bring 120-VAC to a boat for connection to a battery charger, there is a further question of use of a ground-fault interrupter (GFI). Again, the ABYC recommendations deal with that topic.

A reasonable device for use with a small boat may be an in-line GFI to be inserted at the marina shore power outlet. For an example of a commercially made device, see

TRC 30A Portable w/GFI
Model 67040
Rated 120V, 30A - 10/3 AWG Cord

jimh posted 07-02-2015 09:16 AM ET (US)     Profile for jimh  Send Email to jimh     
PORTHOLE2 refers to my homemade shore power cord as being "bastardized and dangerous." On the other hand, WEST MARINE suggests in their do-it-yourself shore power article:

quote: can buy shore power cable by the foot, purchased the male plug and female connector separately, and custom-build a cordset...

The cordage for "shore power cable" is given in the ABYC recommendations I cited earlier. They suggest:

quote: The shore power cable shall be flexible cord with the minimum properties of Type SOW, STW, STOW, SEOW, or STOOW, and shall be suitable for outdoor use.

The connector at the shore power end of the cable is specified:

The shore connection end of this cable shall be fitted with a locking and grounding type plug with the required number of poles and shall comply with Article 555 of the National Electrical Code.

Now we turn to Article 555. Here is a secondary source:

LINK to PDF secondary source of Article 555 of NEC

Regarding receptacles that provide power to boats, Article 555 of the National Electrical Code says:

Receptacles that provide shore power for boats must be rated not less than 30A....Receptacles rated 30A and 50A must be of the locking and grounding type.

Back to the WEST MARINE DIY article. It cautions:

It’s tempting to use a shore power pedestal as a handy way to power drills, sanders, and other power tools. This is a particularly dangerous activity for two reasons.

They cite two problems. The first, as I already mentioned, is the problem of the wire gauge:

You’re connecting a light gauge extension cord into a 30A circuit, so the cord is not sufficiently protected against short-circuits and fires. The only circuit protection is the 30-amp breaker on the shore power center, which will undoubtedly exceed the power rating of the cord that’s plugged into it.

Next, as I already mention, the problem of GFI protection:

There’s no operator protection from a GFCI, since that would normally be found onboard the boat, and there’s no boat involved. Therefore, the operator of the power tool, while using it in a wet environment, is in danger of electrocution. In fact, shore power centers are only intended to supply power to a boat, using an approved shore power cord, and not as general-purpose AC outlets. More importantly, if you’re working around water, you must have a Ground Fault Circuit Interrupter (GFCI) in place to prevent potentially fatal shocks.

The problems of my "bastardized and dangerous" shore power cord can be overcome by:

--adding over-current protection appropriate for the wire gauge, and

--and ground-fault interruption

I mentioned earlier a device that will add ground-fault protection:

TRC 30A Portable w/GFI
Model 67040
Rated 120V, 30A - 10/3 AWG Cord

As for the problem of connecting a cord whose conductors are not the same gauge as the conductors feeding the power outlet, I haven't found a definitive rule about this. However, this situation occurs all the time. For example, in your house you have an outlet rated for 20-Amperes and protected by a circuit breaker rated 20-Amperes. Into this outlet it is very common to plug a load like a small lamp. The lamp cord is wired with what is known, curiously, as lamp cord , and the conductors are often no larger than 18-AWG. If there were provisions in the electrical code that said any device connected to an electrical outlet must use a cord of the same wire gauge as the outlet is being supplied power with, you'd have to change every lamp in your home to have a cord with 12-AWG conductors.

When I plug in my coffee pot to my "bastardized and dangerous" shore power cord, a lot of the time the coffee pot is actually sitting on the dock, not on the boat. I am not powering my entire boat with this cord. I am just powering a coffee pot. A battery charger probably draws even less current than my coffee pot. Am I really in danger? I consider my use of this cord to power my coffee part or the charger for my laptop or the charger for my boat battery to be the equivalent to operating a "power tool."

I also carry a convention extension cord, and I would be most pleased to plug that cord into a 20-Ampere or 15-Ampere outlet with GFI protection at the marina power pedestal, if only there was one. I do a lot of boating in rather rustic locations in Canada, and the power provided at the dock is not always compliant with the latest codes of the USA. Sometimes, if you want to make coffee in the morning, you might just have to improvise.

jimh posted 07-02-2015 10:02 AM ET (US)     Profile for jimh  Send Email to jimh     
By the way, I am still curious how use of the power receptacle shown in

is going to provide a remedy for inappropriate wire gauge and GFI protection. If someone can explain how the above receptacle does that, I would be most interested. Thanks.

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