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Old 02-01-2012, 04:53   #151
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Re: Neighbor dumping raw AC into water?...what to do?

Let me explain again why galvanic isolators for boats are not fool proof and, IMHO, should be outlawed;

These devices are using a side effect of a diode called the junction voltage. Here is the V-A graph of a diode:

In the top-right quadrant of the graph we can see that the diode only starts conducting at roughly 0.6V. Below that voltage, the diode is not letting any current through.

Now here is the problem; galvanic corrosion from shore power connections is caused by a DC current that travels through the ground wires of at least 2 boats. The shore-ground connects the boats and the circuit is completed by the water touching underwater metals of the boats. This means it takes two to tango and whenever this problem pops up, both are to blame. This alone means the OP has no chance in court.


Now, AC is alternating current, meaning the direction changes 50 or 60 times a second. Diodes are like check valves, only allow current to travel one way. But we can connect two diodes anti-parallel which means they are parallel but in different directions. When AC flows through this, one diode passes the positive parts of the waveform and the other does the negative parts.

So, we pop the anti-parallel diodes into our ground wire circuit. Now, if the voltage over the diodes becomes 0.6V or more, they start conducting providing the safety which is the reason to have this wire. But if it is less than 0.6V, there is no current possible which means a small DC current is blocked and galvanic corrosion prevented (also on the other boat!)

Now here is the catch... if the DC potential is more than 0.6V, then the diodes start conducting and the corrosion happens anyway, like if we don't have this protection just as the problem gets worse and we need it more! Frak! So the manufacturers and dealers and installers who want our money had to solve this and came up with putting two of these diodes in series (each way so total of 4 diodes) which doubles the voltage potential needed to 1.2V. Okay, so now it works for a 1V potential but what if it gets really really bad like 1.3V ? Well, your boat starts bubbling then because the protection is ZERO. Go up to 3 diodes? Remember that the ground wire was supposed to provide safety against electrocution which is already reduced by these diodes and 3 in series for 1.8V potential was simply denied by the local codes. So, protection is only up to a 1.2V potential over the ground loop.

Now all the GI fanboys will start whining but hold on, I will make it worse first before addressing their arguments;

Ever heard of a diode burning through? I do, like in a diode bridge or on an alternator. Diodes tend to burn up now and then. The reason is that same pesky 0.6V potential over the diode... it stays there when the diode is conducting. This means that when 10A of current passes, 0.6 * 10 = 6W of power is dissipated as heat inside the diode. This heat dissipation makes them burn through.
Now, if diodes in a GI burn through, what do we have? Exactly, a life threatening situation!

Okay, the GI fan boys will start talk about modern designs with capacitors and alarms etc. Alarms sound when your AC installation is lethal, very nice. What happens when that alarm circuit fails? Ever seen lightning strikes around boats damage equipment? The whole thing is like a time bomb.... and when the problem of galvanic corrosion gets really big... it completely fails and let your boat or it's metal parts corrode away like crazy.

I understand that many don't exactly know what an isolation transformer does. It's primary use is as a personal safety device. The output of the transformer is floating, not referenced to ground. This means you can take any one lead in your hand and touch the water with your other hand and nothing happens. If you do that with the hot wire from a regular shore power connection and a GI installed you die. A GFCI type of device would protect you in that case (a breaker doesn't) but it's not needed with the transformer. Only when you touch both wires out of the transformer you can get a shock. This is very safe and the reason that electronics workbenches have an isolation transformer to protect the workers that repair electrical appliances etc.

Second thing with the isolation transformer is that because it is so safe, you are not required to use the ground wire on the secondary side of the transformer. On a boat it means that the ground from shore protects your shore power cable, inlet and internal wiring to the primary side of the transformer. That is where that ground wire is stopped, it doesn't get connected to anything else aboard. This means you are protected against any level of galvanic corrosion caused by shore power systems, not just the easy ones where the galvanic isolator helps too.

The GI fan boys will also tell us that these transformers weigh 200-300 pounds and cost $500 - $1,000 etc. In reality, a Victron 3.6kW transformer weighs 23kg which is about 50 pounds and a 7kW version weighs 28kg which is say 60 pounds. The 3.6kW is $780.- and the 7kW is $850.- so at least they get the price right Don't forget that a GI for 50A service will also go up to $300.-

The only question is about the price; how much are you willing to spend on safety for the boat and the personal safety of the people aboard. I find the $500 extra for the transformer money well spent, can't think of many other things where it counts as much.

Okay, I'll make room for the nay sayers now

cheers,
Nick.
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Old 02-01-2012, 07:04   #152
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first thanks for the post, I know you have to filter answers, but lots of good information is exchanged.

First you must define the exact problem, hire a good marine electrician or engineer. Not just some that can hook red wire to red wire.

Next work with him to define and draw a diagram of the issue. Not an electrical diagram but of the boats and a macro view of the power.

Third go talk to the owner of the problem, explain the damage you are seeing and what you are worried about. It could be the marina, it could be the suspect boat. Hopefully the owner of the issue will fix it. If not get your dock contract out and read it. Keeping you boat safe is a reasonable expectation of your contact, make sure they know you expect their help and that you are going to start getting all the dock involved.
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Old 02-01-2012, 07:39   #153
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Re: Neighbor dumping raw AC into water?...what to do?

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Originally Posted by s/v Jedi View Post
120V is available between neutral + L1 or neutral + L2.
240V is available between L1 and L2.

So red is a standard color for the 2nd phase in 240V.
Ok Nick, obviously you are well educated/experienced with this but the idea that the 120/240 that we plug our boat into or our house is wired to is "2 phase" is wrong. The fact that the instantaneous voltages of each leg (equal but opposite polarity) of a center tapped winding with respect to that tap are 180° out of phase with each other does not make it "2 phase". In a multiphase system, the instantaneous voltages are not equal but arrive in sequence. Yes, you can take 2 phases of a 3 phase system and send it to different parts of a dock but the receptacle you plug your boat into is single phase. It is quite common to call our 120/240v power "2 phase" but it is incorrect, another misnomer. That's why we use the term "split phase", a single phase divided into two legs.

In regards to the isolation transformer, I agree it is the best option however there are a couple of scenario's where it can present a safety hazard and is why many advocate wiring them as a polarization system as apposed to an isolation system. Another controversy.

Eric
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Old 02-01-2012, 08:49   #154
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Re: Neighbor dumping raw AC into water?...what to do?

What is in your house and on most dock boxes is Split Phase.
L1 to neutral 120 vac
L2 to neutral 120 vac
L1 to L2 240 Vac 180 deg out.
480 vac 3ph
L to L = 480vac
L to neutral = 277vac
240 vac 3 ph
L to L = 240 vac
L to neutral = 208 vac
In the US red is the color for L2 in marine applications.
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Old 02-01-2012, 10:04   #155
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Re: Neighbor dumping raw AC into water?...what to do?

We have drifted far away from leakage currents, but here goes - - -

Polyphase power systems are typically three phase, and have a direction of phase rotation that determines the direction that 3 phase electric motors will turn. It is not uncommon to hear electricians refer to center tapped circuit as two phase. Since they yield a mirror image plot there is no defined direction of rotation.


One voltage cycle of a three-phase system



A polyphase system must provide a defined direction of phase rotation, so mirror image voltages do not count towards the phase order. A 3-wire system with two phase conductors 180 degrees apart is still only single phase. Such systems are sometimes described as split-phase.

More details are here: Polyphase system - Wikipedia, the free encyclopedia
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Old 02-01-2012, 10:12   #156
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Re: Neighbor dumping raw AC into water?...what to do?

Hum.. I suspect that the differences we're experiencing in terminology is due in part to the methods of power distribution used in different parts of the world.

For example whats standard practice on the US, may be different in such a remote location as oh say Canada, let alone whats done in the EU countries and elsewhere.
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Old 02-01-2012, 10:22   #157
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Quote:
Originally Posted by fairbank56
the idea that the 120/240 that we plug our boat into or our house is wired to is "2 phase" is wrong.

In regards to the isolation transformer, I agree it is the best option however there are a couple of scenario's where it can present a safety hazard and is why many advocate wiring them as a polarization system as apposed to an isolation system. Another controversy.
The reason why I keep calling them the "2 phases" is because they are officially labelled as L1 and L2, which are the same as the L1, L2 & L3 labels in 3-phase. Now that I think about it, a 2-phase feed would be at 180 degree phase shift and thus exactly the same as this split phase.

So whenever I talk about the 2 phases of a 120-0-120 split phase, I mean the 2 legs of the split phase.

For the feed to the dock I really meant two of the three phases. I think we will quickly go to real 3-phase substations on the docks as the standard because power consumption in marinas is still shooting up in the tropics (more people buy and use air conditioners and/or dehumidifiers.

In isolation transformers I do not know of any scenarios that present safety hazards. I mean other than amateuristic clueless installations, but those are unsafe for any configuration.
There is no controversy on isolation transformers, everybody agrees that these are the ultimate safety device.

cheers,
Nick.
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Old 02-01-2012, 10:26   #158
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Quote:
Originally Posted by s/v Jedi
The only question is about the price; how much are you willing to spend on safety for the boat and the personal safety of the people aboard. I find the $500 extra for the transformer money well spent, can't think of many other things where it counts as much.

cheers,
Nick.
Nick, this post pretty much summed up a month's worth of reading I had just done on this topic from quite a few gurus in the field. (I am also not an electrical professional so I turned to books and articles.). I have an aluminum saildrive to protect and I happen to be a safety nazi on my boat which led to my decision of an isolation transformer as the no brainer decision for my boat. Now I'm just trying to decide which one to go with so it can be installed after I finish checking the rest of the electrical system for faults while out of the water.

BTW nice write up on your blog. I tripped over that during one of many google searches. SC
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Old 02-01-2012, 10:47   #159
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Re: Neighbor dumping raw AC into water?...what to do?

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Originally Posted by sailorchic34 View Post
Hum.. I suspect that the differences we're experiencing in terminology is due in part to the methods of power distribution used in different parts of the world.

For example whats standard practice on the US, may be different in such a remote location as oh say Canada, let alone whats done in the EU countries and elsewhere.
Right again. I am in a marina at the present that is considered rural in Canada. Three phase is not available here so the dock distribution is derived from single phase 440 to transformers on each dock run ( only 3 main docks 86 slips). From the transformers the common service panels, each containing 40 circuits provide power to the power posts at the end of the slips. The receptacles are all 125v 30 amp type. Each post will have at least two being fed from the opposite side of the split. This means that the hot reference between your boat and the neighbors is 220v. This can be a problem but is also handy if you need to run a small wire feed 220v welder on the dock. Unfortunately many things in life are a compromise. I would prefer 125v 50 amp. but I like the marina. New docks and new wiring. One has to protect their own interests, so I have an isolation transformer and a galvanic isolator. In the end we are responsible to protect our own stuff.
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Old 02-01-2012, 10:56   #160
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Re: Neighbor dumping raw AC into water?...what to do?

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Thanks Skipmac. There aren't too many Victron dealers in the US that I have found besides Jamestown Distributors. I agree Victron is a good product. Their instruction manuals are lousy at least with the at the battery charger I installed last year. It appears their equivalent unit is ~$250 more and 10# lighter. Some older threads reported noise from these nits too. SC
I have gotten good deals on Victron equipment from Peter Kennedy Yacht Services Peter Kennedy Yacht Services - Marine Electrical Systems and also the Fischer Panda dealer in Miami. For a complete list of distributors go to Where to buy - Victron Energy
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Old 02-01-2012, 11:07   #161
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Re: Neighbor dumping raw AC into water?...what to do?

Only problem I see the OP has is one of control. He obviously came here not for advise but for support that he was right and the fellow next to him was wrong. Some great advise was given and all he did was snub his nose at it. Ease up cowboy, life is a long rodeo. Here is my advise and I believe it will cure 99% of your problems:
Be more of a learner and less of a know-er!
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Old 02-01-2012, 11:42   #162
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Re: Neighbor dumping raw AC into water?...what to do?

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Let me explain again why galvanic isolators for boats are not fool proof and, IMHO, should be outlawed;
cheers, Nick.
Nick, thanks for taking the time to explain this, a tricky subject for most and when our US cousins start talking about joining the negative and the earth together well that just about tips me over the edge

Pete
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Old 02-01-2012, 12:16   #163
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Re: Neighbor dumping raw AC into water?...what to do?

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Now that I think about it, a 2-phase feed would be at 180 degree phase shift and thus exactly the same as this split phase.
In a true balanced 2 phase system, the phase shift is 90°, not 180°. 2 phase distribution was used in the early 1900's in the US but I doubt you would find it anywhere today except for a historical display. You can create a true 2 phase supply from 3 phase with a special transformer and connection.

Quote:
In isolation transformers I do not know of any scenarios that present safety hazards.
The scenarios are a fault from xformer primary to xformer case or secondary to shield.

The professional electricians that I know cringe when they hear 120/240 being called 2 phase or L1/L2 being refered to as different phases.

Eric
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Old 02-01-2012, 12:51   #164
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Re: Neighbor dumping raw AC into water?...what to do?

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hang anodes over the side,connected to the boat ground,common practise on alloy yachts
this sounds like a good practice whenever you plan to stay at a dock for a while. I think I'm going to look into it. Maybe I can save my zincs without bothering anyone else. Prevention is cheaper than a fix.
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Old 02-01-2012, 13:06   #165
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Re: Neighbor dumping raw AC into water?...what to do?

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Should he return, maybe next time he can begin by specifying the exact advice he is willing to listen to prior to asking a question. This will no doubt save him a great deal of the type of frustration he's articulated in this thread.

This could be a whole new type of discourse for Cruisers' Forum. You begin a thread by stating, "Here's the answer I want to hear...." and then ask a pertinent question afterwards.
i will keep me muth shut in future
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