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Old 03-21-2018, 12:19 PM   #1
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50 amp electrical service... is mine safe?

Let me start with my priorities are; Safety then corrosion THEN ABYC standards.

In an effort to constantly learn and understand my boat I have been reading Nigel Calder and John Payne books on marine electrical and neither of them suggest a system like mine, Charles Industries isolation transformers has some diagrams that are close.

We all know previous owners of our old boats have been known to do wacky stuff and everything should be suspect. But on my boat, 40 year old steel hull (aluminum house)DeFever, based on what I have seen and the receipts I have found, for the most part he did an excellent job and nothing gives me any reason to doubt his work. The only reason I'm questioning it is because it doesn't match any of the books, the white neutral and green ground are not used.

My boat has 100 amp service, two of the standard marinco 50 amp plugs side by side(they are mounted to an isolating material, i.e. don't make contact to the aluminum house), immediately behind the shore power receptacles the 8 wires are all combined into 4 (red to red, black to black, etc) and the white and green terminate there. The red and black feed into a 100 amp circuit breaker the out put of that CB splits in two directions, one goes to the 240v distribution panel the other goes to a transformer, single phase, 8KW, two wire 240v in three wire 120v out, the standard white black green. The transformer output feeds the 120v distribution panel. In addition, the transformers white neutral is connected to the green bus bar which connects to the DC negative bus bar.

I have searched the web and can't find any information about the brand or make of the transformer I assume it is an isolation transformer, is a transformer an isolation transformer construction? From what I read in ABYC it would mater where the green is attached to the shield. The identification label is difficult to read but I think it says manufacture date of 12-97.

This setup is basically "method 2" of the recommended installation of Charles Industries current 50 amp isolation transformer. The difference is that the 240 supplying the boats distribution panel does not go through an isolation transformer, it is straight shore power 240v red and black.

As for the lack of using shore power green, I don't see that as a problem because all 120v load green wires on the boat are connected to the white natural out of the transformer.

Am I safe using the 240v shore power without the shore power green?

Is the green bus bar only associated with 120V? is there any relation to the 240v circuit?

I understand for 120v loads you should connect the case of the item to the green bus bar, I installed several 240v air conditioners, is there any purpose or value in grounding the case of a 240v load to the boats green bus bar?
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Old 03-21-2018, 12:49 PM   #2
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[QUOTE=Talonewo;647126]
My boat has 100 amp service, two of the standard marinco 50 amp plugs side by side(they are mounted to an isolating material, i.e. don't make contact to the aluminum house), immediately behind the shore power receptacles the 8 wires are all combined into 4 (red to red, black to black, etc) and the white and green terminate there. The red and black feed into a 100 amp circuit breaker the out put of that CB splits in two directions, one goes to the 240v distribution panel the other goes to a transformer, single phase, 8KW, two wire 240v in three wire 120v out, the standard white black green. The transformer output feeds the 120v distribution panel. In addition, the transformers white neutral is connected to the green bus bar which connects to the DC negative bus bar. [QUOTE]

If I'm reading this right, you are combining two 50 amp services into one 100 amp service breaker? That's not safe.

Ted
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Old 03-21-2018, 01:23 PM   #3
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With AC a qualified sparky's really the way to go.

Screen for one who will let you look over their shoulder and ask questions if you like, but don't DIY.
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Old 03-21-2018, 01:40 PM   #4
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You will get a lot of advice on your questions. I am not sure how you separate fact from, well opinion. So with that said, here is mine:

You have an electrical system that can be used with US or European power supply. Your two 50A single phase inputs combine to make one 100A single phase output. This is somewhat unsafe because if you disconnect one 50A cord and the other is still connected to shore powe,r the female terminals in the open receptacle will be hot.

If you never need more than 50A of shore power and most boats your size don't, then you can remove one of the 50A receptacles. Also replace the 100A breaker with a 50A.

There is no neutral because that is what European power does. Your 240V ciruit doesn't need a neutral and the transformer creates the neutral for the 120V circuits.

The 100A service supplies the single phase (ie no neutral) 240V AC buss which is probably only used for air conditioning and maybe the water heater, neither of which need a neutral. It also supplies the transformer which provides two legs of 120V and a neutral. The transformer then supplies typical two phase 120V busses on the 120V panel. European power systems don't produce 120V and the transformer creates it for US appliances just like a travel transformer does.

If you want to hook up to European shore power systems, you just have to change the shorepower inlet receptical. All else should work fine on that single phase 240V power.

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Old 03-21-2018, 01:42 PM   #5
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Why is that not safe?

All wiring to the distribution panel on the boat is rated for 100 amps, each of the two 50 amp supply cords will have 50 breakers at their supply so I can't pull more than 50 amps from each cord and both supply cords will be from the same source so phase won't be a problem.... the only issue is if ONLY one of the two 50 amp plug is connected to the boat... boat side connectors are male, so if only one 50 amp cord is connected the other unused plug has two hot male connectors, definitely not safe and the first thing I will fix.
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Old 03-21-2018, 01:57 PM   #6
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Talonewo

An open forum will get you many replies, tough to discern wheat from chaff. Since you asked, it is safe to assume you need some capable guidance, hands on IMHO.

Your DeFever deserves a qualified marine electrician looking the vessel and its systems over in some detail. A person with demonstrable training and experience on steel hulls and current Code specific dock wiring would be my recommendation.
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Old 03-21-2018, 02:09 PM   #7
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djmarhand, yep... as I started taking a deep look into this system I noticed the issue with the hot male plug. Assuming this system is safe, my plan is to remove one of the shore power plugs and install a new 50 amp CB. But I will leave the 100 amp CB at the distribution panel as the boat has a 20 KW generator.

My though is I will never need more than 50 amps and if and when I ever do I can fire up the generator.

You are correct the only thing on the 240v panel is 5 stand alone air conditioners and single raw water pump(all the cooling water for the A/Cs are run from one through hull and a manifold system. When I bought the boat it had chilled what A/C and 240v electric heaters installed in the ducting. If I ever go to cold places I may install the heaters.

Over the next few years I plan to install a water maker, washer/dryer, compressor to fill dive tanks, I will probably go with 240 as much as I can, as I so hope to travel the world some day. and I don't want to out grow the 8Kw transformer.
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Old 03-21-2018, 02:48 PM   #8
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If I'm reading this right, you are combining two 50 amp services into one 100 amp service breaker? That's not safe.

Ted
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Originally Posted by Talonewo View Post
Why is that not safe?

All wiring to the distribution panel on the boat is rated for 100 amps, each of the two 50 amp supply cords will have 50 breakers at their supply so I can't pull more than 50 amps from each cord and both supply cords will be from the same source so phase won't be a problem.... the only issue is if ONLY one of the two 50 amp plug is connected to the boat... boat side connectors are male, so if only one 50 amp cord is connected the other unused plug has two hot male connectors, definitely not safe and the first thing I will fix.
As far as unsafe:
If you never leave your dock, you can guarantee that both 50 amp shore power outlets are off the same transformer with each leg in the same phase. You can't be guaranteed of that at other docks. Not uncommon for power pedestals to have more than 2 hot legs and have more than 1 transformer feeding them. In essence, you are expecting the outlets to be off the same transformer with matching phases. This isn't a requirement to meet wiring code for the pedestals. When you come across a miss matched pair and turn on the second breaker, it's the equivalent of a dead short. While the breakers are designed to trip, the question becomes, "will there be any arcing throughout the rest of the circuit going from the pedestal to your boat?"

Someone who has more knowledge of breakers may be able to explain what if any damage is caused to the breaker in this scenario, but it certainly can't be good for the breakers in the power pedestal.

Ted
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Old 03-21-2018, 08:03 PM   #9
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O C Diver/Ted,
You are absolutely correct, thanks. I have never connected two cords and don't ever plan to, if I ever need more than 50 amps I will run the generator. Other than fixing the dangerous issue of the hot male plug I'm really not worried about 100 amps vs 50 amps, plan is to remove one of the plugs and use 50 amps when connected to shore power. I just want to understand the relationship between the 240 circuit and the green grounding wire, it is not covered in any of the books I have.
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Old 03-21-2018, 08:09 PM   #10
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For those saying get a qualified marine electrician, I agree, I'm not going to make major changes on my own, like I said in the original post, my goal is to learn and understand how my boat works.
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Old 03-21-2018, 08:58 PM   #11
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O C Diver/Ted,
You are absolutely correct, thanks. I have never connected two cords and don't ever plan to, if I ever need more than 50 amps I will run the generator. Other than fixing the dangerous issue of the hot male plug I'm really not worried about 100 amps vs 50 amps, plan is to remove one of the plugs and use 50 amps when connected to shore power. I just want to understand the relationship between the 240 circuit and the green grounding wire, it is not covered in any of the books I have.
A typical 240 single phase three wire plug has a safety ground and two live wires. Between the two live wires is 240 volts. Each of these is at 120 v with respect to the ground. The 120s are out of phase to create 240 between them.

I guess the safety issue mentioned above is what happens if the two 240 single phase 50 amp lines are from two different circuits and are out of phase with respect to each other
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Old 03-21-2018, 10:04 PM   #12
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I guess the safety issue mentioned above is what happens if the two 240 single phase 50 amp lines are from two different circuits and are out of phase with respect to each other
Yes, that was the point I was trying to make.

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Old 03-21-2018, 10:34 PM   #13
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I just want to understand the relationship between the 240 circuit and the green grounding wire, it is not covered in any of the books I have.
The green wire is a ground. On some appliances such as an air conditioner, the frame is connected to the ground. If there is a short from the positive wire to the frame, it's designed to trip the breaker. On your boat, with the system as you described it with no neutral (white) or ground (green), there is no capacity for the power pedestal breaker to trip other than drawing too many amps. There is no ground fault interrupt. Maybe all the GFI protection is handled down stream of your Isolation Transformer. That troubles me, but it may just be my paranoia.

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My boat has 100 amp service, two of the standard marinco 50 amp plugs side by side(they are mounted to an isolating material, i.e. don't make contact to the aluminum house), immediately behind the shore power receptacles the 8 wires are all combined into 4 (red to red, black to black, etc) and the white and green terminate there. The red and black feed into a 100 amp circuit breaker the out put of that CB splits in two directions, one goes to the 240v distribution panel the other goes to a transformer, single phase, 8KW, two wire 240v in three wire 120v out, the standard white black green. The transformer output feeds the 120v distribution panel. In addition, the transformers white neutral is connected to the green bus bar which connects to the DC negative bus bar.
If the DC negative bus bar is connected to the ships bonding system, I would be concerned about stray AC current going into the water, especially when the boat is in fresh water. While you may not have a problem, I don't think you want the AC Neutral and Ground tied to the bonding system.

You've reached the limit of my knowledge, hope it points you in the right direction.

Ted
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Old 03-22-2018, 05:36 AM   #14
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Unsafe without shore power green ground

Your words:
Am I safe using the 240v shore power without the shore power green?

Start my words:
I think you are not safe if the green ground from the inlet fitting(s) is not tied into the green ground buss. I think what you are after is the diagram on page 7 of the attached showing the transformer being used for polarization versus isolation. It shows green grounds from the transformer and shore power connected to the grounding buss.

Grounding the neutral at the transformer should not cause a problem since the shore power neutral does not come aboard. Therefore, neutral is only grounded at its power source (the transformer) not creating multiple ground paths to be avoided in regular dock power systems where the neutral is coming aboard via the shore power system.

Not using the shore power ground creates a hazard related to your 240 volt equipment. They should be grounded and the return path to insure that safety is the green ground from the shore power cord. If the equipment is grounded and connected to the onboard buss and not the cord ground then the path of fault current is through the water you are floating in back to the pedestal. If the equipment is not grounded and you come in contact with it and a metal part at the hull interior that is also in the water you could become the path.
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Old 03-22-2018, 11:43 AM   #15
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O C Diver/Ted,
You are absolutely correct, thanks. I have never connected two cords and don't ever plan to, if I ever need more than 50 amps I will run the generator. Other than fixing the dangerous issue of the hot male plug I'm really not worried about 100 amps vs 50 amps, plan is to remove one of the plugs and use 50 amps when connected to shore power. I just want to understand the relationship between the 240 circuit and the green grounding wire, it is not covered in any of the books I have.
I thought that I understood your wiring. Now you say that you never connect both power cords?

What made sense to me was that your boat derives its 240V from two cords at 120V each with a neutral (grounded conductor). If it were that way and only one cord was connected, you would have only 120 volts on your boat AND the second connector, the one for the other cable WOULD BE SAFE, there would be no voltages on it.

So far so good but along comes your isolation transformer. I am confused at this point because the only way I can think of how the system would work would be the transformer’s primary is connected to and operates from 120V, not 240V.

And yes, it can be wired directly to that 100A breaker which would need to be a 2 pole breaker....ie one that would normally have 120V on each leg or 240V between the legs.

Are you sure that the transformer’s primary is wired to 240 and not 120? Many transformers have windings to support both voltages, different connections of course.

I question that you actually have 240V on your boat with only one power cord attached.

Because my above is technical and involves safety issues, I take no responsibility for anything pertaining to your boat’s power system or anyone’s safety regarding your boats electrical system.

EDIT: IF and only IF your boat’s electrical system gets its power from the isolation transformer or generator your system should be completely safe!
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Old 03-22-2018, 12:32 PM   #16
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I thought that I understood your wiring. Now you say that you never connect both power cords?

What made sense to me was that your boat derives its 240V from two cords at 120V each with a neutral (grounded conductor). If it were that way and only one cord was connected, you would have only 120 volts on your boat AND the second connector, the one for the other cable WOULD BE SAFE, there would be no voltages on it.

So far so good but along comes your isolation transformer. I am confused at this point because the only way I can think of how the system would work would be the transformer’s primary is connected to and operates from 120V, not 240V.

And yes, it can be wired directly to that 100A breaker which would need to be a 2 pole breaker....ie one that would normally have 120V on each leg or 240V between the legs.

Are you sure that the transformer’s primary is wired to 240 and not 120? Many transformers have windings to support both voltages, different connections of course.

I question that you actually have 240V on your boat with only one power cord attached.

Because my above is technical and involves safety issues, I take no responsibility for anything pertaining to your boat’s power system or anyone’s safety regarding your boats electrical system.

EDIT: IF and only IF your boat’s electrical system gets its power from the isolation transformer or generator your system should be completely safe!
His power cords are 4 wire, 50 amp, 240 volt. Using 2 power cords was to double the amperage.

Ted
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Old 03-22-2018, 12:47 PM   #17
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Ted- he could have 240V. I just stopped to think about my wiring which has a 50A power cord and 240 but mine is split to 2 each 30 amp connectors. What makes me think he has only 120 is that I cannot imagine a properly designed boat making his second power connector expose with applied voltage on it.


EDIT: Think of house wiring where one has a 100 ampere system at 240V. The power coming in is 120-0-120V. This is my guess how the boat’s input power is connected. And sure, I could be wrong
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Old 03-22-2018, 01:12 PM   #18
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Ted- he could have 240V. I just stopped to think about my wiring which has a 50A power cord and 240 but mine is split to 2 each 30 amp connectors. What makes me think he has only 120 is that I cannot imagine a properly designed boat making his second power connector expose with applied voltage on it.


EDIT: Think of house wiring where one has a 100 ampere system at 240V. The power coming in is 120-0-120V. This is my guess how the boat’s input power is connected. And sure, I could be wrong
He indicated in subsequent posts that he could run everything (not at the same time ) with one power cord. Since he has a 240 panel parallel to the transformer, the cord would have to be 240 volt.

Ted
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Old 03-22-2018, 01:22 PM   #19
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If his wiring is such that he obtains 100A capability by having power delivered in parallel cable/connector wiring, it was improperly designed. No way should operating with only a single power cable allow hazardous voltages at an exposed paralleled connector.
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