Compromised Electrical system? Help Please

[jamhass]

What type of isolator (if any) do you have between boat and shore power, and is your 12v ground/negative bus isolated from shore power common? If not, and especially if shore power was swapped common for hot, it may have energized your 12v ground to 120 or 240 VAC. That could explain all the symptoms.

[ladyhaggis]

The panel right after the shore power is a 3 pole breaker before it goes to the main breaker panels. I also have a reverse polarity red light on both legs of the main breaker panels. The 3 pole breaker did not trip at any time. When I saw only one leg active in the beginning from shore I clearly did not see the reverse polarity light on as it is red and would be most visible. as to the 12v Ground
bus bar system, I am unable to locate this. I am at present topping up the charge on the 8D house battery, which is the only one I have active, it serves the bilge pump, fresh water and toilets, It used to have the stern thruster on it but I think that was the problem of some sort of short back feeding through the neutral. I am using a mini portable charger connected to a 110v outlet on the dock.

[catman]

I suspect that the phases on the shore power were not aligned. That would give you twice the voltage across your two 30amp plugs. If they use three phase power that voltage could be even higher.
Put a meter across the two hot slots of the 30 amp outlets, if they are aligned you should read 0volts, if not then you will read the voltage that caused the damage.
Cheers, catman

[ladyhaggis]

Thanks again for everyones help in understanding what may have occurred. They worked on the power box after it happened and its now reading 125 on both 30's so we may never know what it was before
I'm unable to do cross check..probes too short on my meter.
12v battery still takes charge...still waiting on Cert electrician to fly in.
Day 2

[Symphony]

Originally Posted by catman

I suspect that the phases on the shore power were not aligned. That would give you twice the voltage across your two 30amp plugs. If they use three phase power that voltage could be even higher.
Put a meter across the two hot slots of the 30 amp outlets, if they are aligned you should read 0volts, if not then you will read the voltage that caused the damage.
Cheers, catman

i am interested in this problem since I use twin 30 amp splitter as often as possible. how would the phases get out of sync on a simple dock set-up?

[Terra Nova]

The phases don't get out of sync.

Most small boat docks around here have two out of phase legs of 110 running down opposite sides of the dock, each serving its own side of the dock. At the end tie these are normally brought together to provide 220 for the larger vessels which commonly occupy the end ties. On bigger boat docks 220 may be provided to each slip.

[catman]

If the 30A outlets on the shore power pedestal had hot lines from two different phases the 240v between the hot slots on the plugs would short the wye connected cable. Additionally if the hot and neutral on the shore power pedestals were connected improperly, (hot on neutral and neutral on hot ) then there would be a temporary 240 volts delivered to the boat. Not for long enough to damage 50 amp cord but long enough to blow charger supply.
I know it's a stretch but as they say " **** happens".
Cheers Catman

[Symphony]

Great information for me to think about, catman.
So when entering a strange marina and using shore power it is well the time to bring out the digital VOM and see what is lurking in the pedastal.

It just now occurred to me that I don't know what the three prongs on the 30 amp or 50 amp cord are actually connected to. I'll have to Google some plug manufacturer site

[donradcliffe]

Whatever you do, don't rely on the advice you are being given on this thread.

Chances are, whoever 'fixed' the dock miswired the pedestals, but its now been changed and you will never get anyone to admit to anything.

Next time, know what voltages to expect from each set of pins on the pedestals, and test each dock before plugging anything in. Get longer probes--its much cheaper than what your repair bill is going to be.

[smac999]

Originally Posted by catman

I suspect that the phases on the shore power were not aligned. That would give you twice the voltage across your two 30amp plugs. If they use three phase power that voltage could be even higher.
Put a meter across the two hot slots of the 30 amp outlets, if they are aligned you should read 0volts, if not then you will read the voltage that caused the damage.
Cheers, catman

you don't want them aligned when trying to get two 30a 120v plugs into a 50a 240 plug you need to find 2 out of phase for the Y to work. in phase you get 0 volts to the boat. out of phase you get 240 which is what the boat wants. (if everything is wired correct)

[catman]

To all that are following this forum, go to Westmarine.com/ and find ' do it yourself; shore power'. They have an excellent write up on this topic, including diagrams of circuits and pictures of cord end types. I would recommend keeping a flash card on board that has a labelled picture of your type of cord end plugs, so you can measure them with a volt meter.
On many marine systems it is possible to have a reverse polarity, because the ground may not tied to the neutral, unlike residential wiring.
Even though you have a 50amp cord you can still only draw 30 amps if you are using a reverse wye.
Cheers, Catman

[catman]

It is also good to get familiar with your boats distribution system.
Lady haggis does your boat use a 125/250Volt system?
Check the 50amp shore power female end, where it connects to your boat.
If it has X,Y and W stamped on it then it is for a 125/250V system.
Cheers, Catman

[ladyhaggis]

Hi Catman...we r so thankful for you help and expertise and I think you have solved what happened...now to get them to understand!!! ...we would love to call you?
Are u open to that?
Tested cross and reading 240v!!!

[ladyhaggis]

yes 125/250
I'm confused now with cross reading ...should it be 0 volts or 240?

[ramblinrod]

Originally Posted by ladyhaggis

Hello all
We have just returned to our 40ft motor boat in the Bahamas and was told power was restored on the dock however when we plugged in our 50 amp splitter to two 30 amp shore it blew the cord. WE then heard the stern thrusters trying to start and noticed the 12v battery had melted the positive side and the Dometic battery charger appears to have been damaged.
We are trying to get an experienced marine electrician to fly in to access boat damage. but would like any input as to what might have gone wrong?

Best guess, based on your original input, is that your boat is wired for 120Vac (characterized by a 3 prong shore power inlet) and the 2 power posts were 180 degrees out of phase, with one having reverse polarity (line swapped for neutral). This would input 240 Vac to your 120Vac shore power connection, creating the symptoms you've described.

Ramblin Rod
www.sheenmarine.com