Reverse Polarity

[deblen]

Originally Posted by svlamorocha

Thanks for the info.


I agree. Of course you are referring to a nice Euro-style 30mA RCDs whole-boat/house RCDs that will only trip if there is something wrong.

[Start rant] If you believe the US story that you need a 5mA because 30mA will kill you then you end up with a bunch of cheap outlet-mounted RCDs that will trip for no reason or don´t trip when they need to. I know of many people that got saved by a 30mA RCD (including me) so I will not believe the US wisdom on RCDs, which is founded on some mysterious studies that go against what people see in Europe and South America every day. [End rant]



Yeap, you could use a ground plate for AC safety ground to protect those inside the boat (as when toaster frame gets hot) and disconnect ourselves from the shore green.

Only drawback could be that a swimmer might get zapped if you have a leak that is under 30mA. That said, I have taken 30mA many times and did not do me any harm, and the swimmer will only get a fraction of the leak. So I am with you on this.



Agree!



Agree again. If btrayfors had sunk a rod next to the boat and tied his green to it he would not have been zapped by the green that was in fact tied to a broken neutral upstream.

The only problem of all this is that it requires people to understand how things work, as opposed to blindly extrapolating rules based on the time when it was deemed good to save one wire to have more copper to fight the War, or relying an a magic "reverse polarity light" or "oulet tester" that does not really test that the green wire is close to real ground that you stand in or water that you swim in.

I believe svlamarocha & K V B have come to an agreement on the problem.
Grounds & neutrals are treated differently worldwide.

Now,I challenge them to come up with a practical system that will allow any boat to plug in to any system in the world and be safe as humanly possible,& have reliable indicators/safety devices to protect that boat from any fault.
Good job! Seriously!

I do have a question:In 240V systems,is there any use of 120V?
Tks / Len

[svlamorocha]

Originally Posted by deblen

I do have a question:In 240V systems,is there any use of 120V?
Tks / Len

I am afraid I do not understand your question? Can you please provide more detail? Thanks

[DotDun]

Originally Posted by deblen

I believe svlamarocha & K V B have come to an agreement on the problem.
Grounds & neutrals are treated differently worldwide.

Now,I challenge them to come up with a practical system that will allow any boat to plug in to any system in the world and be safe as humanly possible,& have reliable indicators/safety devices to protect that boat from any fault.
Good job! Seriously!

I do have a question:In 240V systems,is there any use of 120V?
Tks / Len

Isolation Transformer w/downstream RCD and AC neutral/safety wire bond
(multi-tap primary to handle voltage differences)

Don't need or care about shorepower reversals.

[svlamorocha]

Originally Posted by DotDun

Isolation Transformer w/downstream RCD and AC neutral/safety wire bond
(multi-tap primary to handle voltage differences)

Don't need or care about shorepower reversals.

DotDun

Please help me understand what you are proposing so that we can make the proposal 100% clear:

- Install isolation transformer and RCD downstream of it.
- Just ignore the shore "green"
- Tie the boat´s green to the neutral in between the downstream side of the transformer and the RCD
- No tie between AC system and DC negative/ground plate/engine, etc.

Did I get this right?

[deblen]

Originally Posted by DotDun

Isolation Transformer w/downstream RCD and AC neutral/safety wire bond
(multi-tap primary to handle voltage differences)

Don't need or care about shorepower reversals.

That's what I thought early on.But,apparently,some folks are running the green earth wire from shore to boat.
Also,a txfmr is expensive.
Just wondering if there is a possible alternative.
Not arguing.

[deblen]

Originally Posted by svlamorocha

I am afraid I do not understand your question? Can you please provide more detail? Thanks

Not sure where you're located,or how familiar you are with N.A. system.
It's a simple question.-In N.A.,all small appliances <1500watts are 120V & are connected across L1 & N.(N. is not conn. to housing,but G is)
240V appliances > 1500W are conn. across L1 L2,such as stoves,dryers,etc.
These will have 120V inside them ,to run timers,small stove top elements,etc.,which are conn to L1 or L2 & Neutral.
And then,there are things like 240V home heating elements,which are conn. across L1 & L2 only,& Neutral is not even run thru that system,but the G is.
The above eqpt is all used on boats.
I don't think there would be any problem interfacing the above-but I throw this info out so we're all on same page.

[svlamorocha]

Originally Posted by deblen

Not sure where you're located,or how familiar you are with N.A. system.
It's a simple question.-In N.A.,all small appliances <1500watts are 120V & are connected across L1 & N.(N. is not conn. to housing,but G is)
240V appliances > 1500W are conn. across L1 L2,such as stoves,dryers,etc.
These will have 120V inside them ,to run timers,small stove top elements,etc.,which are conn to L1 or L2 & Neutral.
And then,there are things like 240V home heating elements,which are conn. across L1 & L2 only,& Neutral is not even run thru that system,but the G is.
The above eqpt is all used on boats.
I don't think there would be any problem interfacing the above-but I throw this info out so we're all on same page.

I am familiar with land and boat wiring in various places including the US approach. I have also sailed boats to places with different systems.

Now we are not talking about safety and grounding but it is still a great topic.

I do not like US-style 240V appliances in US boats taken outside the US. It just complicates things too much at the time of getting shorepower or running off a genset.

You can get 120V heater elements and Splendide washer-dryers that work great. Benefit is that you only need two current-carrying wires from shore (L and N) and "one-voltage-at-a-time" genset.

If there is a need to split load into two sources then I prefer a) split into two buses and feed each bus separately from a) separate shore cables (which can be at 0, 120, 180 or whatever number of degrees away form each other) ; b) one from shore and one from genset or c) use modern inverter-chargers with "power assist" and "power control".

The Antares boats have a nice implementation of a) and b) but not c).

If you do not mix load voltages then you can easily run that boat in foreign marinas with a single iso transformer that doubles as step-down. If you had a 240V dryer on a boat with 120V minor appliances it would get much more complicated because the dryer could not be fed by the same iso transformer unless the trafo had two simultaneous taps (can yo find such a trafo?) or you connected the dryer ashore and losing the isolation.

We are only left with the frequency problem but that is for another thread!

By the way, you remind me of the strange setup at Crew´s Inn in Trinidad with two 127V hots at 120 degrees form each other. It worked fine for those who understood that 2x127V was 220V (not 254V) in that case, but the rest worried a lot!

[tropicalescape]

Originally Posted by K_V_B

Why does polarity actually matter? This is alternating current after all...


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[Miniyot]

Originally Posted by svlamorocha

... That said, I have taken 30mA many times and did not do me any harm...

Interesting....did ya have an ammeter clamped to yer finger while ya poked that little dangly wire? If not then how do you know you received 30 milliamps?

[rwidman]

Originally Posted by K_V_B

Why does polarity actually matter? This is alternating current after all...

That statement alone pretty well places your credibility on this issue at the very bottom of the scale. You should have quit writing at that point and confined your participation to reading.

[svlamorocha]

Originally Posted by Miniyot

Interesting....did ya have an ammeter clamped to yer finger while ya poked that little dangly wire? If not then how do you know you received 30 milliamps?

Nope; the RCD trips in 1/20th of a second and that is too fast for my clamp.

Jokes aside, the RCDs used where I live are rated at 30mA and 300 miliseconds. To be fair, according to the guys who have the toy to test them (Fluke 1650 series) they typically trip a bit below 30mA (standard requires no trip below 15 and 100% trip at 30, all in 300 miliseconds). In addition, it could be that the current was lower and it took longer given the curve of the device. Still, this is good evidence that 30mA nominal RCDs save people.

The confusion in what they teach in the US (I used to work for a large company in the US and saw visiting European safety guys explain this) is that they quote mA figures without the corresponding duration. Yes, there is a small probability of ventricular fibrilation at 40mA (see curve C1 in attached graph) but only after FIVE SECONDS. Therefore a 30 mA RCD that trips at nominal current within 300 miliseconds is good enough to save you from ventricular fibrilation (or any muscular reaction for that matter). Of course, I am talking about a proper whole-house DIN-rail-mounted RCD made by Schenider or the like, not one of those cheap outlet-mounted things.

[leftbrainstuff]

Originally Posted by btrayfors

Here in the U.S., reverse polarity is dangerous and potentially lethal. Period.

Some examples have been given above. Here's another from personal experience.

A few years ago I hauled my boat for a bottom job. I plugged one of my 30A shore cords into the pedestal in the work area of the boat yard.

When I walked by my propeller and shaft, I happened to touch it and received a 120-volt shock! If the ground had been wet or I'd been barefoot or...any number of other scenarios....I"d likely have been ELECTROCUTED. KILLED. DEAD.

The boatyard's shorepower pedestal was wrongly wired....black hot and white neutral were reversed. This put 120VAC on my boats GROUND system (AC ground and DC ground on the boat were connected to a single-point .... the engine.... in one of the common and "approved" marine wiring practices).

It's pointless to argue whether the European system is better than the American system. The point is, we in North America have several HUNDRED MILLION people using the 120-volt system and it works pretty well for us. The best statistics available show about 50-60 accidental electric shock deaths annually in the U.S......not too bad with over 200,000,000 users!

I'd bet the rate of accidental deaths in 240-volt system countries is much higher, partly because of the increased lethality of 240VAC vs. 120VAC.

No matter. Our system is what it is. And the other systems are what they are.

Bill

I always check polarity of a new connection.

Often land based electricians of varying skill levels are engaged to fiddle with shore power.

You can either use a multi meter or one of the little colored light toolsm

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[rwidman]

Originally Posted by leftbrainstuff

............. Often land based electricians of varying skill levels are engaged to fiddle with shore power.........

More often, they are dock hands or handymen at best. That brings us back to why we have reverse polarity indicators on our boats. Pretty much a complete circle.

[simonpickard]

I get this sometimes. Other who have travelled as far do as well. We've been from the Med over to the Caribbean and yep we get the warning in some Marinas but have never had an issue (just the warning light).

What we have found in common is where we do see the warning light the electric supply is pretty rubbish. Some marinas are just that way.

I think you'll be fine.

[DotDun]

Originally Posted by svlamorocha

.........If you had a 240V dryer on a boat with 120V minor appliances it would get much more complicated because the dryer could not be fed by the same iso transformer unless the trafo had two simultaneous taps (can yo find such a trafo?) or ................

Yep, mine does (ordered it wound to my spec). Split phase Iso transformers are not that hard to find, Charles Ind. makes one. Problem is in the US, 240v shorepower starts at 50a, hence an Iso transformer rated at 12kva isn't small, light, or cheap.