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Old 01-08-2014, 03:24 PM   #1
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Ship Shore Switch size question.

My 8 KW generator is set up to supply 60 amps at 120 volts and the feeder has 60 amp overcurrent protection. My shore power is currently set up as 2 x 30 amp 125/250. My Ship shore switch is a Kraus and Naimer 65 amp three pole. Iím going to change my shore cables to a 50 amp 125/250 cable with a smartplug boat side connection and upgrade the feeders and shore power breakers and breaker busses to 50 amps. Anyone see a size problem with the 65 amp ship shore switch?
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Old 01-08-2014, 05:09 PM   #2
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My 8 KW generator is set up to supply 60 amps at 120 volts and the feeder has 60 amp overcurrent protection. My shore power is currently set up as 2 x 30 amp 125/250. My Ship shore switch is a Kraus and Naimer 65 amp three pole. Iím going to change my shore cables to a 50 amp 125/250 cable with a smartplug boat side connection and upgrade the feeders and shore power breakers and breaker busses to 50 amps. Anyone see a size problem with the 65 amp ship shore switch?
I've been wondering the same as the literature I've seen is vague...but you do need enough spaces for the 2 hot legs, plus neutral and I believe the ground to....but PLEASE look up the thing about the ground...I just read something the other day that confused me and led me to believe you have to break the ground to the shore power inlet if your genset/inverter is active.
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Old 01-08-2014, 08:00 PM   #3
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I don't know enough about this question in terms of BOATS to answer it in that regard, but if it helps I do know something about the question in terms of LAND use.

The sizing of your CIRCUIT BREAKERS is important.

Your SWITCH can be over-sized because it's not performing a safety function, it's providing a switching function.

For example...

I have a generator inlet on my house that feeds the panel via a 60amp breaker that is used as a SWITCH.

The circuit is fed by a 50 amp breaker protected generator outlet.

The additional 10 amp overhead for the breaker I am using as a switch also provides transient protection without being too tight. Like when the AC kicks on... The generator can supply a theoretical 78 Amps, but is limited by it's 50 amp breaker.

If that fails, the switch, which is itself a breaker, kicks in at 60 amp.

All my wiring is good for 100amp.

Therefore, nothing should be overloaded.


I would be very interested in finding out if that practice is different in a marine situation; especially because it sounds like it's common to bring two legs of 30amp power in.
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Old 01-09-2014, 07:10 AM   #4
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Bigger question is how will you go to any other dock than your home slip, and still get electric with a plug that fits .00001% of power posts?
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Old 01-09-2014, 07:19 AM   #5
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FF...not sure why you say this (often)...every marina I have been to from Jersey to Florida has 50 amp 125/250..litterally hundreds of marinas. From the cheap ones to the 5 star ones...even Kilkenny, Ga which is basically a rickety fish camp put me on a 50 amp 125/250 outlet.

the 50 amp 125 (only) outlets I have never seen...but the 50 amp 125/250 outlets are very common.

What I like about the 50 amp service more than anything is the outlets are beefier and seem to always be in better shape (not burnt) like the 30 amp outlets.

With some adapters you have flexibility...and yes WAYYYYY more expensive...but for me as a liveaboard.... I want the extra power and electrical fires are what I see as the greatest threat to my boat.
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Old 01-09-2014, 07:58 AM   #6
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I see no issue using the 65A switch. As MC-Escher says, over-sizing a switch is fine, in fact sometimes it can be desirable.
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Old 01-09-2014, 08:56 AM   #7
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Thanks everybody. I too think the 65 amp switch is a good application. I asked the question in this respect: I will be switching the two hots and neutral shore conductors off when changing to the generator hot and neutral. Granted I will not be switching all this power under load but in the case of the shore power the neutral is considered a current carrying conductor and it is conceivably up to 100 amps. Thus the question is the 65 amp switch up to worst case?
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Old 01-09-2014, 09:02 AM   #8
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OH BTW I didn't divulge the rest of my plan so to not complicate the first question.....I am going to leave one of the 30 amp boat side connectors and switch it with the new 50 amp 125/250 shore cable. I already have a separate/ tie switch between the two phases in the load center. This way when I find one of those marinias that doesn't have 50 amps I won't be SOL.
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Old 01-09-2014, 10:49 AM   #9
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The first post,

I’m going to change my shore cables to a 50 amp 125/250 cable with a >>smartplug<< boat side connection and upgrade the feeders and shore power breakers and breaker busses to 50 amps.

Its the Smart Plug I wonder about not the 30 year old 120/240 common dock sockets..

If only on the boat end , no problem , but looking for one on a dock might be a never ending task.
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Old 01-09-2014, 11:02 AM   #10
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Smartplug only markets boat ends. IMO they are a good upgrade.
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Old 01-09-2014, 01:30 PM   #11
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I have basically the same question..is the selector swuitch rated at 65 amps....65 amps per leg? Or 65 amps per total load as each hot leg on 125/250 is capable of carrying 50 amps?
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Old 01-09-2014, 01:45 PM   #12
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Where are the switch folks? Will a switch rated at 65 amps actually handle the arcing if the switch is operated under load of 65 amps? Or is the rating just a current carrying capability once switched. How about a 220 volt neutral where it is carrying twice the current of one hot leg. If the hot legs are 50 amps does the switch then need to be rated for 100 amps?
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Old 01-09-2014, 01:56 PM   #13
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Kraus & Naimer is an industrial switch manufacturer. If you get the specific switch model number, you can likely get catalog to verify the information you require.

Edit. A quick google and a look at some of their switches indicate that they are horsepower rated switches. This would be a good thing as inductive loads have high inrush amps.

You still need to get the model number to get real rating of your specific switch.
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Old 01-09-2014, 02:49 PM   #14
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How about a 220 volt neutral where it is carrying twice the current of one hot leg.
The neutral conductor only carries the difference between the two phases. A perfectly balanced load between the two "hot" sides would produce zero current on the neutral.
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Old 01-09-2014, 02:52 PM   #15
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Kraus & Naimer is an industrial switch manufacturer. If you get the specific switch model number, you can likely get catalog to verify the information you require.

Edit. A quick google and a look at some of their switches indicate that they are horsepower rated switches. This would be a good thing as inductive loads have high inrush amps.

You still need to get the model number to get real rating of your specific switch.
I was in their catalogs awhile back and it never was clear to me whether they were designed to carry 2 hot legs and what was each leg rated for...I would think that would be all over the literature for us "electrical for dummies types"...

When my time comes I'll just have to call or use a panel where the CBs have guards and do the switching
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Old 01-09-2014, 02:54 PM   #16
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The neutral conductor only carries the difference between the two phases. A perfectly balanced load between the two "hot" sides would produce zero current on the neutral.

Years back when I first got started I thought "how can they just have one, same sized neutral conductor" till I read a lot more...then more made sense...

But I'm still puzzled why the literature about a lot of these source switches don't clearly state total amperage or "per leg".
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Old 01-09-2014, 03:06 PM   #17
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The neutral conductor only carries the difference between the two phases. A perfectly balanced load between the two "hot" sides would produce zero current on the neutral.
Me and my boat ain't never been balanced. Looking this $h!t up in a catalog leaves me to interpret the data and that is bad. I'm going to use the switch and after I'm done I will crank everything up and and use my buddies infrared imager to see if I got a problem.
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Old 01-09-2014, 03:10 PM   #18
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They do state the total amperage because the current on the neutral cannot exceed the current flowing in a single leg. If there is zero current on one side, the neutral will carry the same load as the loaded side, as the load on the other side increases, the load carried by the neutral decreases until the point where if each side is carrying (for example 60A) then the neutral carries 0A.

The neutral only carries the difference between the legs. If you had 60A on one side and 50 on the other, the neutral would carry around 10A or so. Get three clamp ammeters and see.
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