I help maintain a small fleet of sailboats that have 12 V electrical systems. There is a battery charger on each boat that gets plugged into shore power when the boat is not in use. The problem is that whenever we plug the shore power into the receptacle on the boat, the contacts arc. Over time, the receptacle and/or the power cord get damaged and have to be replaced. There is a breaker for the shore power, so we can turn off the power there before plugging in the boat, but people forget to turn the breaker off or back on, and the breaker isn't really supposed to be used as a switch either. I tried contacting the manufacturer of the battery chargers for advice, but they never got back to me. I was wondering about a relay or something that might solve the problem. Any thoughts?

 

Add a switch to the cable. Turn off the power with the switch, connect to battery, flip the switch. Now the sparks will happen in the switch. After time the switch will probably die.

 

Sounds like the normal charging of Power-Supply-Capacitors.

How "Big" is the spark ?
How "bright" is the spark ?, can You only see it at night ?
Does it make a definitely noticeable "crack" sound when it arcs ?
Are You looking too hard, and worrying too much ?
Virtually all Electronic-Appliances will create some sort of arcing when being first plugged-in.
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The spark is clearly visible in daylight and makes a clearly audible "crack". I don't think it is "worrying too much" when we keep having to replace hardware on a regular basis because of damage.

 

Are the Battery-Chargers customer-supplied ?, or supplied by the Marina ?
These may be serious Battery-Chargers, capable of ~20-Amps, or more,
and not merely "Battery-Maintainers" that normally charge at less than one-Amp.

Also, being in a Salt-Environment destroys EVERYTHING that is not
specifically designed to withstand a Salt-Environment.

There are many items that need to be inspected, and/or, replaced, regularly, in a Salt-Environment.
There is no way to get around this required routine-maintenance.

If a ~120-Volt Outlet lasts more than ~3-years in a Salt-Environment,
You have personally witnessed a bonafide miracle.
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I was wondering about a relay or something that might solve the problem.

Seems like an inrush limiter would be more appropriate.

This article is for motors, but it can work in your situation too.
https://www.ametherm.com/blog/inrush-current/ac-motor-inrush/

 

I have observed when visiting in the U.K. that many, possibly most, of the electrical outlets have a switch as part of the assembly, so that the power may be switched off for plugging and unplugging. That approach could work to avoid the problem.
Here is an educated guess, which is that those chargers use a switch-mode system that starts with a full-wave bridge rectifier feeding a fair sized filter capacitor. And an even more good guess is that not a single one of those chargers has an integral power on/off switch. And then i offer a rather nasty guess which is that the land-side if the connection is a quite inexpensive receptacle, rated for 15 amp circuits, not 20 amp, that costs less than a dollar each when bought at the local home improvement store.
In some localities it is required that each dock-side outlet be equipped with a disconnect switch so that the outlet can be switched off for plugging and unplugging. Certainly, adding an on/off switch at the outlet, suitably rated, would allow the outlet to be switched off for plugging and unplugging. And it would remove the shock hazard that is present when using a plug that has fallen into the water prior to insertion.

Another, simpler, option will be to replace the outlets with GFCI outlets. and then manually trip them prior to inserting the plug, and resetting them after the plug is in place. That will be the simplest but not the cheapest solution.

 

I would suggest using the push-button start-stop circuit that is normally found on stationary power tools.
https://www.screwfix.com/p/schneide...tvIA5SOT4FIc2Ua0qehoCqxgQAvD_BwE&gclsrc=aw.ds
The "start" button can only be operated when the circuit already has power and it automatically latches off when power is removed.
They are, of course, designed for a motor load with a high inrush, so should be suitable for a battery charger.

I have observed when visiting in the U.K. that many, possibly most, of the electrical outlets have a switch as part of the assembly, so that the power may be switched off for plugging and unplugging.

That's true for almost all indoor sockets, but the power inlet to a boat will most likely be this sort:
https://www.screwfix.com/p/abb-16a-2p-e-surface-plug-250v/6490f
unswitched.

 

You might need to have an interlocked socket 16A similar to this, but i think Marians are IP 65, or higher.
https://a1electrics.com/ip44-interlocked-sockets/197/16a-3-pin-230v-interlock-socket-ip44-blue.html

 

@gds42 ,
@Dodgydave and I have two different ideas how this is connected. Is the cable attached to the boat, or is the cable attached to the shore, or is it a flying lead with connectors on both ends?

 

I like Ian0's suggestion of the push-button on/off switch that automatically disconnects when the power is removed.
That way the charger can't be plugged in "hot" even for forgetful/careless boat owners.

 

Consider that this application apparently IS NOT A MARINA where high-price large watercraft berth. That class of operation tends to have much more elaborate "shore power" provisions. In fact, we are aware that the connection is standard AC mains outlets, not even all-weather setups. So the push-button and cotactor scheme is probably far above any budget level.
Somehow my suggestion of using a GFCI and tripping it prior to plug-in has vanished, but that would solve the spark problem totally. It would also reduce the shock hazard created when a boater attempts to insert a plug that has recently been dropped into the water. And certainly that does happen. In fact, that is probably a current requirement for any outlet near water. Certainly it is a requirement in my locality. ALL outdoor outlets must be GFCI protected.

 

Certainly it is a requirement in my locality. ALL outdoor outlets must be GFCI protected.

Same here. It also extends to all sockets where equipment used outdoors may be plugged in (i.e. all ground floor sockets, all outbuilding sockets)

 

This application most definitely is at a marina. I don't know how it was concluded otherwise. The outlets and circuit breakers are provided by the marina, and they have been in place for years. There is no question about whether they are commercial-grade or marine-grade. We use marine-grade extension cords to plug in the boats to the outlets. The blackening on the end of the power cord and receptacle are a clear indication that the problem is arcing and not corrosion. We can't really modify anything on the land side because it is marina property, and if we did install anything, it would have to be commercial and marine grade. I was looking for a solution we could put on the boat. I think the current inrush limiter may be the best option.

 

I think the current inrush limiter may be the best option.

Probably the cheapest and easiest option, but not the best option.
Start-stop pushbutton circuit is the best option. There is no current in the circuit whatsoever until the button is pressed.
I wonder if an NTC inrush limiter has a time constant long enough for connecting an EN60309 connector, which is not quick, especially with a connector that has acquired a bit of corrosion.
Also, NTC inrush limiters have an annoying habit of exploding, like the one in my power tool transformer did.

 

While a lot of the slips do have 30 A service with a locking type plug (I think it's a NEMA L6-30P), our slips have the standard 15 A 3-prong plug. I think the pushbutton will have the same problem we have with using the circuit breakers - people won't remember to turn the power back on. Thanks for the warning about exploding inrush limiters.

 

More to the point, the battery chargers themselves have a standard AC plug.

 

Is this issue regarding "only" your personal Boat ????
If this is the case, simply stop using your un-needed, Heavy-Duty, ~30-Amp+ Charger,
and purchase an inexpensive "Battery-Maintainer", and your troubles will be over,
( and your Battery may last longer, depending upon the sophistication level of your Charger ).
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A simple option would be to add a switch to the battery charger on the boat. Then the burden will be on the boat user, which is where it should be. And one instance of the battery running dead will cure most folks of their forgetfulness. And attach a note to the AC plug-in cord reminding to switch on the battery charger. How are the users convinced to plug in the power cord? What other service is enabled by the shore power connection? Are the sailboat users aware of this problem, even?

Changing to a GFCI outlet for each shore-power conneection point, and then posting a sign requesting users to be safe and test the GFCI every time before connecting power would solve the problem, if folks would use it.

 

Certainly such a switch could avoid starting the charger under load. That might solve the problem.I offer no solution for those who forget to switch on the charging connection.