ConchyJoe

[Trawler Scott]

My boat came with a 30 amp inlet and a upgraded AC panel that is rated for 50 amp service. I bought a 50 amp 125 volt inlet and wired it with the correct gauge wires the same way the 30 amp was installed.I bought a 50 amp 125 amp shorepower cord.The pedastal says 50 amp 125/250 so I plug it in and uh oh (all breakers were off) the voltage gauge was off the chart (250v)
I checked it out and I have two 125 volt wires and a ground.The electrician was there wiring new pedastals so I asked him and he looked everthing over and told me to use one 125v leg, the ground and then connect my ground and nuetral together on the boat.I did and everything has worked as it should for some time but I have read that on a boat the nuetral and ground should not be connected.
Whats going on ? How do I fix it ? Does it need fixing ? I will be installing a inverter soon so I need this part to be correct.

Thanks
Scott

[CharlieJ]

Holy #@"+*&&(= Batman!!!!

Scott-
I will try and unravel this for you but you really, really need an ABYC Certified Electrician to check this system out.

First of all, some explanations of common shore power set-ups:

The most common shore power in the USA is 125 VAC/30 amp normally referred to as "30 amp". There are two current carrying conductors and a safety ground that normally carries no current. These current carrying conductors are hot (Line, L, black in color) and neutral (N, white in color). The hot wire goes to the AC hot bus in your panel, the neutral wire goes to the neutral bus and the green safety ground goes to the safety ground bus.

The second most common shore power arrangement is two 30 amp shore power services. Typically one services all the house loads and the other services air conditioning and any other very heavy loads. The house hot (L1) and the house neutral (N1) are connected to their respective hot and neutral busses. The air conditioning shore power inlet L2 and N2 are connected to the independent hot and neutral busses. The two safety green wires are connected to a common safety ground bus. It is important to keep the two neutrals separated.

The third most common shore power where I boat is 50 amp/250 VAC; commonly referred to as "50/250". With this arrangement you have three current carrying conductors; L1, L2 and N. There is, of course, a safety ground green wire. This safety ground makes its electrical connection to the dock ground via the case of the plug. With this arrangement, two 50 amp legs of 125 VAC are brought aboard. L1 is connected to that isolated portion of the panel board it is to feed (house loads) and L2 is connected to the isolated portion of the panel board it is to feed (air conditioners?). Load balancing between the two legs is important. Since there is only one neutral in this arrangement, it is connected to a common neutral bus. The safety ground is handled as above. Of note is that L1-N will give you 125 VAC; L2-N will give you 125 VAC and L1-L2 will give you 250 VAC if needed. Of course, in the latter case, the panel board needs significant modification (double pole breakers, for instance.).

The least common arrangement is 50 amp/125 VAC that you now have on your boat. This is much like the single 30 amp service above but with heavier conductors and a different plug arrangement. As before, hot goes to the hot bus on your panel, neutral to the neutral bus and safety ground to the ground bus.

You are very lucky that all of your breakers were off when you plugged in as you were applying 250 volts to the panel bus. Any equipment that had experienced that voltage would have had the magic smoke leave the box. I suspect that the magic smoke did leave your panel voltmeter and that will have to be replaced.

[Trawler Scott]

Charlie,

If I use adapter 123A, remove the nuetral to ground connection inside the boat I would then be able to hook the 3 wires from the inlet correctly 1 hot, 1 ground and a nuetral...right ?
The volt meter still works as does everything else.I am in this spot from misinformation from not 1 but 3 people 2 of which work on boats to earn their living. I didnt trust what they told me.I posted here to hear from you specificaly...correct information is what I need and I hope you are willing to help me.Thanks for the response.
Let me know if the above is correct and I can correct it.

Thanks
Scott

[CharlieJ]

Scott-
You've got it. Once you have correctly wired your boat, check to ensure that the voltage coming thru the 123A adapter to your panel shore power breaker is correct before turning the breaker on. This is just to check that the electrician that was wiring the pedestals hasn't done something incorrectly. If you are reading a nominal 120 VAC L-N and L-G and reading <2 VAC N-G then you should be ok.

By the way, check to ensure that the safety ground bus and your DC negative bus are connected with at least AWG #8 wire.

Again, I encourage you to get an ABYC certified electrician to check this out. As you have found out, a guy with a tool bag that "works on boats" sometimes isn't the best source of info.

If you want to learn more; Nigel Calder's excellent book "Boatowner's Mechanical and Electrical Manual" is a must have. You can find it at Amazon.com: http://www.amazon.com/Boatowners-Mechanical-Electrical-Manual-Calder/dp/0071432388/ref=pd_bxgy_b_text_b/002-9132628-5808809

Good luck!
Charlie
_________________
Charlie Johnson
JTB Marine Corporation
St. Petersburg, FL 33701
www.jtbmarine.com

[Trawler Scott]

Thanks Charlie !

[ConchyJoe]

Scott,

Let me be real clear here.

125 volts can kill you!!!!!


Of course, so will single and dual phase 220V. Not to mention burn your boat down.

Make sure you heed Charlie's advice and have everything checked out by a certified marine electrician.

Be safe! And thanks for checking with us.

ConchyJoe
_________________
ConchyJoe Administrator