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Old 15-02-2015, 11:19   #106
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Re: Reverse Polarity

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Originally Posted by thomm225 View Post
I hope you are listening to the right posters then .................good luck.
Sorry If I didn't make myself clear.I agreed with your posts re-N.A. sockets & dangers of reversal.
I've READ all posts & learned that things are done differently around the world.
Some of these posts also confirmed what most of us in N.A. marine electrical field already knew from experience-there are too many different methods being used in boat wiring/grounding here in N.A..

I learned only one thing from all these posts-there is a general lack of knowledge,by all of us,about the different systems in use around the world,& that if we plug our boats into these various systems,none of us are guaranteed safety at present.
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Old 15-02-2015, 12:05   #107
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Re: Reverse Polarity

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Originally Posted by deblen View Post
100% true!!! Well said!
This thread started by a boater in Maylaysia having a rev. pol.lite on.
The thread has enlightened me on the differences in electrical grids & "grounding" methods around the world.
I have now been convinced that if I ever took my boat outside of N.A.,I best not rely on current N.A. NEC/CSA/ABYC codes to keep me safe.
Conversely,non-N.A. recreational vessels should not necessarily count on their homeland standards to protect them elsewhere either.

/ Len
Spot on!

Furthermore, IMHO it is silly to argue about reverse polarity without a clear understanding of the the earthing system being used. I believe that the Wikipedia article someone posted (Earthing system - Wikipedia, the free encyclopedia) can help a lot those who have electrical experience in only one of those settings.

There is no "best" solution; there are pros and cons to each. Letīs compare the US to a place where they use TT earthing such as Argentina, Malaysia or remote parts of some developed countries (or France, I am told).

In (much of) the US they use TN-C-S earthing, which does not require an RCD to trip a breaker when a live wire inside the washing machine touches its chassis (good thing). This explains why Americans (who never got zapped by 220V )are reluctant to use whole-boat or whole-house RCDs. So far so good, but TN-C-S is very vulnerable to broken neutrals that take the potential of the green wire far away from ground potential.

So in the US you do not need an RCD that much, but if there is a broken neutral then the green wire (and the propeller and lots of metal on the boat) can zap you (ask btrayfors) and an RCD in the boat will *not* help on that. Hence in US land it is very important to check that the green safety ground terminal of the pedestal is actually close to ground/water potential using a VOLTMETER between real earth/water and the green wire. Reverse polarity lights and plug-in gizmos that do not actually touch the earth you stand on will not always detect a bad safety ground arising form broken neutral or reverse polarity. People are picky about reverse polarity in the American TN-C-S system mostly because if you get the polarity wrong typically the safety green will zap you, but many smart people do not realize that there are some serious risks that the polarity light or an outlet tester will not detect.

In some remote areas and in countries like OPīs Malaysia, Argentina and (I am told) France they use TT earthing. TT requires you to have a ground rod for the green at your end (ie in the marina), which is one more thing to worry about, but it does not become unsafe if a neutral breaks and it does not really care about polarity. The shortcomings are that the overcurrent breakers will not trip when a live wire inside the washing machine touches its chassis (good thing), hence you NEED an RCD for the whole boat/house/etc. You also need to have a good ground rod at the marina and depend on the marina (not the utility) for that. If there is no good rod installed then you might get zapped when someone elseīs washing machine malfunctions and the greens in the whole marina get hot. Hence you also need to check the green with a multimeter when you are in TT land.

If your US boat in Malaysia shows a reverse polarity light but the green wire is within 1 volt of real earth/water then you only have a reversal of hot and neutral ashore but everything is safe (except for the technicality that you can zap yourself by touching the thread of an AC light bulb, and you need to unplug appliances to work on them instead of just turning them off) . You can ignore the reverse polarity light or install the cool set of switches that Antares 44i boats have to deal with this.

If the green terminal of the pedestal is more than (say) 1 volt away from real earth or water then you can demand that they fix that, because that will be a breach of code almost anywhere. If you cannot wait, then disconnect yourself from the shorepower green and either connect your safety green to a plate in the water or to a ground rod ashore that is not connected to anything else, or make sure you do not touch boat metal while in the water or standing ashore.

Summing up, the only two universal truths I find in this are:
  1. You should always check the green at the pedestal not with a "outlet tester gizmo" with a multimeter in volts mode between green terminal of the outlet and real earth or water or both. Always use your multimeter to check the pedestalīs ground against real earth or water. "Easy solutions" like the reverse polarity lights and outlet-testers that are common in the US are not enough!
  2. Make sure you have a whole-boat RCD, particularly if you use AC in any place that is not a 1st class marina in a 1st world country with TN or TN-C-S earthing (in which case you could rely on overcurrent breakers to deal with hot-to-ground faults because you are 100% sure that the green wire is connected all the way to the neutral of the supply transformer.)
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Old 15-02-2015, 15:38   #108
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Re: Reverse Polarity

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So in the US you do not need an RCD that much, but if there is a broken neutral then the green wire (and the propeller and lots of metal on the boat) can zap you (ask btrayfors) and an RCD in the boat will *not* help on that.
I don't follow this logic. If current is flowing through an RCD then into a person's body to earth the RCD must trip. If it doesn't then it's not doing its job.
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Old 15-02-2015, 16:27   #109
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Re: Reverse Polarity

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I don't follow this logic. If current is flowing through an RCD then into a person's body to earth the RCD must trip. If it doesn't then it's not doing its job.
This thread long ago passed the point of any usefulness. It should come with a disclaimer stating that cruisersforum.com is not responsible for any information or misinformation presented here.
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Old 15-02-2015, 17:19   #110
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Re: Reverse Polarity

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I don't follow this logic. If current is flowing through an RCD then into a person's body to earth the RCD must trip. If it doesn't then it's not doing its job.
You said it; for the RCD to trip the fault current has to go through one and only one (neither zero nor two) of the the RCDīs coils (hot and neutral) . Short of it, in this case the current that zapped the fellow did not go through the boatīs RCD at all, if it had one.

If a boat is sitting on a dry storage yard in a place with TN-C-S earthing (normal in the US) where the green wire that goes all the way into the boat is not tied to a single-purpose ground rod (as would be the case in TT land) that carries no current when there is no earth fault, but to the neutral wire at some point X half-way between supply transformer and boat, and the neutral is broken (or has higher than normal impedance) between X and the supply transformer, then the neutralīs potential will move "closer" to the hot and further away from earth. That high potential in the neutral will "carry" the green wire (hence the boatīs propeller, which is tied to the green wire without any breakers in between) away from earth. Then the propeller will zap the first guy who touches it while standing on "real ground" with shoes that are not well insulated.

That current went from the utilityīs supply transformer hot terminal, then followed hot wire to to some load somewhere outside the boat, then it went back a bit on the neutral wire, to the point where neutral and protective green neutral are tied together, then on the green wire to the propeller, then through Billīs body, then through earth to a ground rod somewhere, then to the neutral wire tied to it and followed that wire back to the transformer.

That is why I do not trust TN-C-S earthing in a place that is not really "1st world".

That is why in 3rd world places where engineers come up with codes that are consistent with the 3rd world class of service from the utility company (I happen to be a licensed PE in one of those places), they make you use TT earthing where you install your own safety ground rod in your own property at least 10 feet away from any other ground rod or buried metal. Then you know your green wire is at ground potential!

By the way, in the UK they require (BS 7671 709.531.2) RCDs for each shorepower outlet in a pedestal and they mandate TT earthing with dedicated ground rods. The TT requirement effectively avoid the eproblem described by Bill. Then the only way to electrocute yourself in a UK marina is to grab both hot and neutral one with each hand and have rubber shoes, but that is called suicide!
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Old 15-02-2015, 19:17   #111
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Re: Reverse Polarity

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Originally Posted by svlamorocha View Post
You said it; for the RCD to trip the fault current has to go through one and only one (neither zero nor two) of the the RCDīs coils (hot and neutral) . Short of it, in this case the current that zapped the fellow did not go through the boatīs RCD at all, if it had one.

If a boat is sitting on a dry storage yard in a place with TN-C-S earthing (normal in the US) where the green wire that goes all the way into the boat is not tied to a single-purpose ground rod (as would be the case in TT land) that carries no current when there is no earth fault, but to the neutral wire at some point X half-way between supply transformer and boat, and the neutral is broken (or has higher than normal impedance) between X and the supply transformer, then the neutralīs potential will move "closer" to the hot and further away from earth. That high potential in the neutral will "carry" the green wire (hence the boatīs propeller, which is tied to the green wire without any breakers in between) away from earth. Then the propeller will zap the first guy who touches it while standing on "real ground" with shoes that are not well insulated.
I can't see how that's possible. If the green wire is connected to the neutral back at the source there is no way current can flow balanced through the RCD on the boat but unbalanced through the green circuit inside the boat through a person to earth then back to the source. That is unless the boat has green and neutral connected but that would be a major violation of the standard. On a US boat green (earth) and white (neutral) may only be connected together when on internal power. They should never be connected together when on shore power. I don't know how it works in Europe. Maybe they never connect those two wires which would be ok I think. But ABYC says you have to connect green and neutral when on shore power.
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Old 15-02-2015, 19:42   #112
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Re: Reverse Polarity

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Originally Posted by transmitterdan View Post
I can't see how that's possible. If the green wire is connected to the neutral back at the source there is no way current can flow balanced through the RCD on the boat but unbalanced through the green circuit inside the boat through a person.
I did not say inside the boat. This could not happen inside the boat with whole boat RCD, as you know.
The guy that got zapped was standing on the ground outside the boat when he touched the propeller that was connected to the green wire that was a bit hot because of a broken neutral somewhere upstream Same thing could have happened to a diver that touched the prop.

The RCD inside the boat has nothing to do with all this. Boat RCD and breakers could be switched off, pedestal could be switched off and nothing would change. It is a protective earth problem and the PE wire is not affected by the RCD or breakers.



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Old 15-02-2015, 19:42   #113
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Re: Reverse Polarity

As an electrician, I am seeing a lot of misinformation. From both sides of the pond,
In the USA we do have plastic screwshells. Usually found on candelabra bases, we also have metal screwshells found on any size light fixure.

Polarity is very important. You will not find the wires of the neutral prong and ground prong attached inside an appliance, however you will find the neutral prong wire will (in most instances) be attached to any exposed metal frame on appliances UNLESS that appliance is double insulated.

The neutral wire (white for 120, natural gray for 277) will be bonded at the service entrance, AND TWO ground rods not less than 8 feet long and not less than 6 feet apart are to be installed.....that is the electric meter not anywhere else. There is now a 4 wire service entrance from the meter to the panel, and the ground wires and neutrals are separated in the panel.

Years ago the neutral was bonded from the panel to the water pipes in the house. Grounds and neutrals shared a common buss bar. Not that way now.

European standards ARE DIFFERENT, NOT BETTER....
European plugs are not polarized because things over there are double insulated....EXCEPT items that are considered antique. Plug one of those in and hang on for the ride!

IF the European standard were to be so much better and safer there would not have been 2.5 million people who received an accidental shock (350,000 severely injured, 22 killed) (2010 data for Great Britain, not all of europe).

As for wiring of boats? I don't know, I am not a marine electrician....
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Old 15-02-2015, 19:51   #114
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Re: Reverse Polarity

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You said it; for the RCD to trip the fault current has to go through one and only one (neither zero nor two) of the the RCDīs coils (hot and neutral)
Actually the fault current fails to return through the rcd which creates an unbalanced condition that trips the device.
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Old 15-02-2015, 20:27   #115
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Re: Reverse Polarity

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Originally Posted by Miniyot View Post
As an ..you will find the neutral prong wire will (in most instances) be attached to any exposed metal frame on appliances UNLESS that appliance is double insulated.
Thanks for all the good stuff.
Do I guess correctly that you meant to say "not attached"?



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Old 15-02-2015, 20:35   #116
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Re: Reverse Polarity

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Thanks for all the good stuff.
Do I guess correctly that you meant to say "not attached"?
In the US, the wire from the polarized neutral WILL (might be) be attached to the metal frame and housing EXCEPT when the appliance is double insulated.
Double insulated means the neutral wire is NOT attached to the frame/housing AND any electrical parts (motors, printed circuit boards, etc.) are isolated from the frame and housing by plastic.
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Old 15-02-2015, 20:47   #117
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Re: Reverse Polarity

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Actually the fault current fails to return through the rcd which creates an unbalanced condition that trips the device.
We are not talking about the same situation. I bet you did not get the (strange) facts right. See post 112. The guy is outside the boat that is stored ashore, gets zapped between green wire (ie the propeller that is tied to it) and actual earth. Nothing goes through the boat's RCD, which could be tripped and the guy would still get zapped by the boat's propeller.

The ground rod at the meter helps a lot in reducing the voltage of the green wire but is not good enough to avoid the zap. This is because the rod is also being used to take lots of neutral current as a result of a broken neutral upstream, as when a storm cuts a neutral wire and significant current flow between two ground rods that would normally do not carry (much) current, effectively creating an alternative current path.

When I say rod read "pair of rods" in the US of course.

Are we on the same page now?

This is an example of the importance of having a green wire at the right absolute potential (= ground potential) , which is not assured when the safety ground rod is used as a service ground rod and there is a broken (or high impedance) neutral upstream. Fancy "testers" that only measure relative potential between 3 wires will not detect this problem. You know this but many boat owners (and house inspectors! ) will not.

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Old 15-02-2015, 22:08   #118
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Re: Reverse Polarity

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In the US, the wire from the polarized neutral WILL (might be) be attached to the metal frame and housing EXCEPT when the appliance is double insulated.
Are you sure that is is current info? I understand that attaching the neutral wire to the exposed metal frame of a normal appliance (range, dryer, etc) is not only a bad idea but also a breach of 1996 (and later) NEC.

I think you are referring to the old Amendment 53 rule from 1942 when the US was trying to save copper for the war. As far as I remember that rule went out with the 1996 version of NEC. Both 1996 NEC 250.60 and 2005 NEC 250.140 do require separate neutral and ground on new installations. The appliances themselves will not have a connection between frame and neutral unless you use the "strap" that can be used to ground the frame to neutral if it is a pre-1996 NEC house without a ground wire.

Please correct me if I am wrong. Thanks in advance!

I believe it is great for foreigners to know all the historical reasons why polarization is important in old American AC wiring, but as Dave has pointed out, there is quite a bit of myth around that and most of it is not valid or necessary anymore.

A good protective earth will always be important (and this is not always understood), but that is another story.

Charlie
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Old 16-02-2015, 05:01   #119
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Re: Reverse Polarity

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Are you sure that is is current info? I understand that attaching the neutral wire to the exposed metal frame of a normal appliance (range, dryer, etc) is not only a bad idea but also a breach of 1996 (and later) NEC.

I think you are referring to the old Amendment 53 rule from 1942 when the US was trying to save copper for the war. As far as I remember that rule went out with the 1996 version of NEC. Both 1996 NEC 250.60 and 2005 NEC 250.140 do require separate neutral and ground on new installations. The appliances themselves will not have a connection between frame and neutral unless you use the "strap" that can be used to ground the frame to neutral if it is a pre-1996 NEC house without a ground wire.

Please correct me if I am wrong. Thanks in advance!

I believe it is great for foreigners to know all the historical reasons why polarization is important in old American AC wiring, but as Dave has pointed out, there is quite a bit of myth around that and most of it is not valid or necessary anymore.

A good protective earth will always be important (and this is not always understood), but that is another story.

Charlie
Please quote the text of 1996 NEC 250.60 In The 2008 version that has to do with air terminals and the code hasn't changed THAT much!

As for NEC 250.140? Read ALL of it AND you also need to understand that on a 3 wire 120/240 volt system, there is no neutral only a ground. The ground was being used as a return path for any unbalanced current (120V timers).
There are several exceptions listed for existing circuits. For example, if your home was wired before the adoption of the 4 wire system, and you get a new dryer, range, etc. then the "neutral" is bonded to the frame.
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Old 16-02-2015, 06:00   #120
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Re: Reverse Polarity

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There are several exceptions listed for existing circuits. For example, if your home was wired before the adoption of the 4 wire system, and you get a new dryer, range, etc. then the "neutral" is bonded to the frame.
You may want to read again.

You have said it. Bonding frames of ranges/dryes to neutrals is not a rule, it is an exception applicable to houses with old (ie pre-1996 NEC) wiring. Don't we agree on that?

Forgive Dave and other guys in Europe ( I am not there these days) who know quite a bit of engineering and boats and know that a code exception for old houses (or an old code for boats) is not a good reason to wire your boat in a way that will make it vulnerable to factors outside your control.




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