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Old 04-21-2014, 04:21 PM   #1
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Switch burned out

I have a burned out three position switch for the shore power. Already found an new one online. The shore power pedestal seems to be in good condition with a good ground that opened the breaker before any real bad stuff happened. I power off the 50 amp connection with a marinco splitter to two 30 amp cords to the boat. None of the connectors for shore power show any damage or heat with a temp gun while running all AC service. Two 16000 air units, battery charger, water heater and some lights, computer and etc. Everything powered up on #1 shore power leg shows 14.7 amps on one black wire to panel "A" using a blue sea clamp meter.
The other leg runs off the #2 shore power 30 amp connector for the air units and carries 28 amps with both units operating. Everything works normal with no hot breakers or connections checked with temp gun. I removed the switch and determined that the switch had an internal meltdown that allowed current flow to the black and white wires of the genset from the #2 circuit black wire. This can't be good! I temporary wired the two circuits to bypass the switch so we could still use Air Cond and such . Everything is working but I discovered I could not tie the two 30 amp legs together. Acts like a dead short. My question is why? They both come off the 50 amp splitter? The two black wires are from the two 30 amp inputs from the 50 amp service. All grounds are good and tied together as per Calder's book.

According to the way the switch was wired the Gen set is a 50 amp service and was tied into the two 30amp services as was the shore power, only from a different direction but the same wiring setup. I am not understanding the difference? The switch that went bad Kraus & Naimer Bypass Selector Rotary Switch C42 65A. Any qualified help in understanding would be appreciated.
Thank you,

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Old 04-21-2014, 08:05 PM   #2
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If you ever turn the switch while a load is on the system from either the gen or shore it'll fry the switch. Always throw your main circuit breakers before moving the switch. There is also the possibility that a wire connection in the switch wasn't tight causing resistance and heat, It's a good idea to check this switch with a IR temp gun when you check the shore power inlets on your boat. Good luck

Ron on Northern Lights II
I don't like making plans for the day because the word "premeditated" gets thrown around in the courtroom.
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Old 04-21-2014, 08:15 PM   #3
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If the shore power from the pedestal is a 4 wire configuration( 2 hots, 1 neutral, & 1 ground) then the 2 hots are separate "phases" and measuring voltage between them you should have 240ish volts. If you connect these together it will be bad! Sounds like that may be what happened. Your genset may produce either 120 volt 50 amp 3 wire or 120/240 volt 50 amp 4 wire, either can be made to work.

I think 50 amp shore power can be available in 3 or 4 wire. You'll have to determine which you have.

Hope this helps. PM me if you need any advice, I'm a electrical contractor in real life.

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Old 04-21-2014, 08:27 PM   #4
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The 2 hot legs are "out of phase" from each other.
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Old 04-22-2014, 08:42 AM   #5
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Sounds like your boat is wired same as mine.

Two incoming 30 amp feeds (called split phase) each measures 120 volts to neutral. The incoming feeds are out of phase and measure 220 volts and must not ever connect to each other or you have a direct short. One feed feeds your air conditioners and is at near capacity. The other feed supplies the rest of your boat. Your shore generator switch disconnects the incoming first and then connects the generator in a way that both on board buss's are energized. You probably have about an 8K generator wired to provide 60 amps at 125 volts. Switching ship shore should not be done while energized however most switches have an off position before reversing and therefore not blow the switch. Now you mentioned the tied switch. This switch ties both buss's together when you only have one 30 amp shore coming in. It also should be wired to disconnect one of the incoming 30 amp shore before connecting the 2 panel buss's together. You see, the system should handle most all your dumb moves. More than likely a bad connection finally did you in. Good luck on you repairs. Always turn off the power before working on you system. Get a detector wand and be safe. Boats with inverters are the most dangerous. They can make high voltage from batteries. Again good luck. If you don't understand any of this get an electrician.
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Old 04-22-2014, 09:33 AM   #6
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Thanks to Obthomas for reminding me how stuff works. Thanks to psneeld, Cat Daddy, and River Cruiser for instructions and advisement. You guys are the best!
Sometimes we are to close to the problem to see it and a friend can see more clearly without a pocket book excuse in the way.
You are all exactly right on all advisement and directions.

As far as I can tell the switch got hot and burned internally on a circuit between the genset and the #2 circuit. nothing else seems to be hot or not running properly. I did install a fire alarm inside the locker where the mains are located for peace of mind.

I have found a new switch and it is on order. I am busy this week checking all the ground connections on the boat for integrity.
Thank you All!

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