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Old 21-10-2016, 10:25   #1
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Have 240 vac shore power, but only 120 vac used

I've always found this strange, and perhaps overkill. I have a standard 240 v 50 amp shore power connection, but on board I have a 120 v 50 amp system. It does use a lot of power with two aircon units, battery charger, hot water heater, more. I have to watch the panel when I first plug in to be sure I'm not drawing over (or close to) 50 amps, but it usually is not a problem. Once the batteries are mostly charged and the charger is pulling little AC current everything else can be on.

So it's pretty clear I'm only using one "leg" of the 240v input. The other leg does nothing, unless someone here teaches me that I'm wrong.

Part of the reason I'm bringing this up is because my AC system is not properly protected near the inlet. There are two ANL fuses in the AC line (I know, strange), no breaker of any type, no galvanic isolator. There is a 50 amp normal breaker in my my main distribution panel in the boat (maybe 20 feet of wire length from the AC shore power inlet). The AC outlets in the boat are properly wired with GFCI protection.

As I've been looking at this I've started to learn more about ELCI breakers, galvanic isolators, etc. It seems that to redo my system by-the-book is a very expensive proposition for a 240 vac system, but somewhat less if it were only a 110 v system.

This is more an academic question than about money. I want to do it right, but I also don't like overkill.

Experts: if this were your boat would you do anything to improve the safety and usage of this setup or just leave it be (after all it ain't broke)? Minimally I'll add a galvanic isolator as I start some world cruising next spring and will be in less reliable marinas at times.

Thanks,

JR
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Old 21-10-2016, 10:45   #2
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Re: Have 240 vac shore power, but only 120 vac used

I am a bit confused about 240V (or 220V) and your mention of "active legs". The european 220V system is based on one of the 3 "legs" or phases of a 380V triphase current distribution system. Taking one of the 3 phases and a ground/neutral wire you get a standard household 220V system. But only one of the wires is "hot", the other wire is "neutral". So there are no 2 "active legs".
For shore power you usually have 16A or 32A connection possibilties, unless you're on a superyacht jetty, then you can find much higher outlets.
Concerning your installation, I would install an isolation transformer and a good connector for the 220V connection on the boat. Those yellow Marinco plugs are dangerous and overheating!
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Old 21-10-2016, 10:57   #3
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Re: Have 240 vac shore power, but only 120 vac used

In the US our standard power setup is two hot legs at 120 volts each, plus a neutral, and a ground. To get 240 v you use both hot legs. To get 120 volt you use one hot leg and the neutral. In an everyday house installation where most things run on 120 v, a wise installer should try to somewhat balance the use of the 120 v legs across the all the loads in the house. Any 240 v load (oven, electric water heater, etc) just gets both hot legs.

So on the boat I have those two hot legs at my inlet, but only one is employed as I have no 240 v loads on the boat.

I agree that shore power inlets can get hot, and I recently read about a fire, which is what has moved this investigation up my priority list.
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Old 21-10-2016, 12:54   #4
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Re: Have 240 vac shore power, but only 120 vac used

I guess you've verified the 50A breaker on your AC mains panel is a single breaker, and the back of your panel only has a buses for L and N? If so, then you'd have to replace the panel with a proper 125/250V panel. You already know you need to replace your shorepower breaker setup.

One would think your two A/C units would have been originally split - on on L1 and one on L2, as well as your battery charger and HW heater. Lot's of boats also split AC outlets port and starboard. But I guess the installer kludged together a 125V/50A configuration with a 125/250V/50A inlet...

sailormed - the US system is properly described as 125/250Vac 50A 3-pole/4-wire system, with the two load wires 180 degrees out of phase, so that as jr-spyder said you can get 250V between L1 & L2 (not using the neutral lead) and two 125V 50A circuits. Neutral and safety ground/earth are not tied together on the vessel - only at the power source (shorepower pedestal and on-board genset or isolation transformer, if equipped).
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Old 21-10-2016, 13:26   #5
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Re: Have 240 vac shore power, but only 120 vac used

Cap'n Jon, it's been a while since I looked at that main breaker but I think you're right. I'll confirm next time I'm on board. Also worth noting is my charger/inverter only takes in 120v, and I believe my genset only puts out 120v. When using the genset I can power everything just like shore power. When using only the inverter off the house batteries it feeds only lighter 120 v loads (all outlets, microwave, previous TV) but will not power the aircon or water heater. Makes sense. So I'm quite sure you're right - I have a system fully built for 120v that happens to have a 240v inlet, probably so I can get 50 amps.
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Old 21-10-2016, 14:01   #6
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Re: Have 240 vac shore power, but only 120 vac used

In most breaker panals the breaker tabs alternate ,leg one, leg two. Two together (double width breaker) is across two tabs so gets 220 ,single width gets 110. By placing the breakers with some thought you can balance the 110 loads into two sort of equal loads on both legs and 220 is available.Still limited to max of 50 amps ,but less v drop as current is on both wires to source .Dosn't address the inverter output to heavy load if it's on the chosen leg .Experts will complete my scattered incomplete thoughts
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Old 21-10-2016, 14:04   #7
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Re: Have 240 vac shore power, but only 120 vac used

Quote:
Originally Posted by Beausoleil View Post
sailormed - the US system is properly described as 125/250Vac 50A 3-pole/4-wire system, with the two load wires 180 degrees out of phase, so that as jr-spyder said you can get 250V between L1 & L2 (not using the neutral lead) and two 125V 50A circuits. Neutral and safety ground/earth are not tied together on the vessel - only at the power source (shorepower pedestal and on-board genset or isolation transformer, if equipped).
Thanks, I learned something new today
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Old 21-10-2016, 14:17   #8
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Re: Have 240 vac shore power, but only 120 vac used

Topmast, what you describe is certainly how a house is wired but it's not how my boat panel is set up. But it's 28 years old so maybe newer ones match household systems. Mine has a vertical stack of horizontal breakers and each breaker has two screw terminals on the back. A single copper (?) bus bar runs down one column of those terminals giving the input to each breaker. Of course the other screw terminal goes to the designated load circuit. The AC column of breakers and the three DC columns are basically wired with the same technique. One thing different on the AC group is that one bus bar doesn't feed them all. It's split, with one feeding the circuits that work off shore power/genset/inverter, and the other a group that won't work off the inverter. It all makes sense to me.

I do wish the 240 v from the dock came to my panel and was properly/smartly split, but like I said before, it all works fine.

JR
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Old 21-10-2016, 14:57   #9
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Re: Have 240 vac shore power, but only 120 vac used

It seems to me that you know too little about electricity to rewire your boat yourself. And while it's possible to learn about electricity, you're not going to do it from what you read on a boating forum.

Electricians spend years learning their trade and there is a reason for this. It's far more than connecting the black wire to the bras screw and the white wire to the silver screw.

I suggest hiring a licensed marine electrician to inspect your boat and correct anything that's seriously wrong with it. Then, get a quote on "improvements".
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Old 21-10-2016, 15:58   #10
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Re: Have 240 vac shore power, but only 120 vac used

Yeah, I get that, but this thread has gotten more complicated than my original post hoped for, but I have learned some things along the way, which is good. I have no intention to change any of the internal wiring setup. My question is just about the inlet situation and the fact that it seems less than ideal, and perhaps unsafe. I think it will be smart to add an ELCI breaker (replacing ANL fuses) and a galvanic isolator. I would like to get expert opinion here so I'm well informed for my chat with the electrical guys in my yard before committing to an expensive mod. No harm in that.

How much I know about electricity is kind of irrelevant if I'm asking the right questions, and I know enough to do that.

But no offense taken...

JR
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Old 22-10-2016, 03:32   #11
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Re: Have 240 vac shore power, but only 120 vac used

I believe ABYC recommends a breaker within 10' of the inlet, hence, as you've concluded, a new breaker close the inlet is warranted. I would suggest the new breaker is an ELCI.

As far as 50a 125/250v entrance, I personally would keep it as that is what most US marina docks have. I have never found 50a 125v on a marina dock. Also, IMO, changing to (2) 30a would be a big pain and essentially going backwards.

I know you don't want to hear this, but IMO, the best solution is to install an isolation transformer that would have a 250v primary and 125v secondary. That way you would have a lower current draw on the long shorepower cable, less voltage drop, and have the capability to have up to 100a of 125v in the boat if ever needed. An isolation transformer provides the very best galvanic isolation (short of never connecting to shorepower).
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Old 22-10-2016, 04:42   #12
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Re: Have 240 vac shore power, but only 120 vac used

Apologies in advance. This got kind of long:

If you have a meter and know how to use it check the voltage across your anl fuses. If it is 240 volts that is fine. If it is 120 then you need some more wires if you care to make it 240. Do the same at your main panel breaker if it is just a two pole. If your main panel is three pole do not waste your time because you have 240 volts at your panel.

The anl fuses may have been added to provide protection at the inlet fitting and only L1 and L2 were protected. That is the way it is done on many vessels over the years but is not currently compliant. Many boats with 120 volt systems bring 240/50 aboard versus 120/30 for reasons that are obvious (more power).

If I were in your shoes I would keep the 240/50 in any case. The age of your boat it may very well have been fitted with a 120/50 originally but that is not found anywhere I have been up and down the east coast. Some lake marinas may have it still but that does not apply.

To keep this simple to explain to the guys who know how to do it you want to bring 240/50 to your panel using current standards some you have already mentioned. You would like to split your busses to balance all your 120 volt loads so you can have 100 amps 120 volts available when using shore power. You want to keep your generator 120 volts. The generator 120 volts is compatible with the shore 240 by how your selector switch is wired. You do not have to change the generator to 240 and should not.

Relatively speaking none of this is immensely costly or difficult if you know how. In a nut shell unless your AC generator is 12.5kw or larger you should be able to run more stuff using shore power if it is 240 volts. Visit Blue Sea Systems web site. They have lots of diagrams and boat candy to look at that will help you wrap your head around it all.

Quote:
Originally Posted by jr_spyder View Post
Yeah, I get that, but this thread has gotten more complicated than my original post hoped for, but I have learned some things along the way, which is good. I have no intention to change any of the internal wiring setup. My question is just about the inlet situation and the fact that it seems less than ideal, and perhaps unsafe. I think it will be smart to add an ELCI breaker (replacing ANL fuses) and a galvanic isolator. I would like to get expert opinion here so I'm well informed for my chat with the electrical guys in my yard before committing to an expensive mod. No harm in that.

How much I know about electricity is kind of irrelevant if I'm asking the right questions, and I know enough to do that.

But no offense taken...

JR
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Old 22-10-2016, 04:48   #13
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Re: Have 240 vac shore power, but only 120 vac used

Quote:
Originally Posted by DotDun View Post
I believe ABYC recommends a breaker within 10' of the inlet, hence, as you've concluded, a new breaker close the inlet is warranted. I would suggest the new breaker is an ELCI.

As far as 50a 125/250v entrance, I personally would keep it as that is what most US marina docks have. I have never found 50a 125v on a marina dock. Also, IMO, changing to (2) 30a would be a big pain and essentially going backwards.

I know you don't want to hear this, but IMO, the best solution is to install an isolation transformer that would have a 250v primary and 125v secondary. That way you would have a lower current draw on the long shorepower cable, less voltage drop, and have the capability to have up to 100a of 125v in the boat if ever needed. An isolation transformer provides the very best galvanic isolation (short of never connecting to shorepower).
Jr-

Exactly as Dot says here...

And curious minds want to know... Where does the other leg go??? Sounds like you have an empty terminal on the backside of your 250V/50A inlet...

Another option is to power your heavy hitters (aircon) with the unused leg, install a second small AC panel...
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Old 22-10-2016, 04:52   #14
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Re: Have 240 vac shore power, but only 120 vac used

I checked Blue Sea Systems for AC electrical diagrams and did not find one. I printed this from ABYC E-11 so you could have a look:
Attached Files
File Type: pdf 240-120 volt AC electrical system.pdf (221.4 KB, 49 views)
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Old 22-10-2016, 05:28   #15
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Re: Have 240 vac shore power, but only 120 vac used

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Originally Posted by jr_spyder View Post
I've always found this strange, and perhaps overkill. I have a standard 240 v 50 amp shore power connection, but on board I have a 120 v 50 amp system. It does use a lot of power with two aircon units, battery charger, hot water heater, more. I have to watch the panel when I first plug in to be sure I'm not drawing over (or close to) 50 amps, but it usually is not a problem. Once the batteries are mostly charged and the charger is pulling little AC current everything else can be on.

So it's pretty clear I'm only using one "leg" of the 240v input. The other leg does nothing, unless someone here teaches me that I'm wrong.

From that, I can't tell that "it's pretty clear" yet.

Our system is similar to yours, 50A/250V input, feeding two 120V legs, only 110-115V systems/appliances, no 220-240V systems or appliances on board... Main double-pole breaker on shore power to the boat, individual double-pole breakers on the panel to select either shore power or genset power.

The only other hint we have -- that maybe you don't -- is that our panel also includes an AC voltage meter and ammeter, and a "leg" switch so I can read each leg separately.

Otherwise, there's not much about the basics of our panel that would tell me one leg isn't connected or working. (That'd need some checking at the inlet terminals, and connections behind the panel.) Our individual circuits are indeed spread roughly evenly across the two legs...

One of our legs runs one AC (aircon), the water heater, the electric cooktop, one charger... so start-up loads with all that on at the same time can be significant, might approach 50-amps momentarily. (Haven't ever had cause to check that closely.) Perhaps you could still have two active legs, but the overall load -- especially start-up loads -- on one or the other is approaching max? In which case, maybe better load balancing across the two legs would be simple and useful?

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