shore power & Reverse polarity

[MrBee]

First off hello all and hope your enjoying these summer temps on the eats coast. We have our boat in Middle river Md. and have been enjoying it, till yesterday.

We bought our 1985 irwin 34 in january. When we inspected it all was fine with shore cords and power. After purchase when we went to hook up the shore cord I noticed the Polarity light came on. Boat was in Annapolis at the time at city Dock. I checked the shore cord and sure enough it showed signs of arching / shorting on the cord at the boat end. Easy check, I plugged in a different cord and bingo, the polarity light goes out, We ran the boat back to our marina and hooked up to shore, all is working fine and we are using one of those West marine Electric heaters, low profile. I don't at this point think the heater has anything to do with the reverse polarity but am not sure. that was Mid January when we brought the boat to our marina and started using the used but in good condition shore cord. When we are away we leave the heater on low, not much draw. We were down on the boat overnight Friday and I notice late Friday evening the Polarity light was on but very dim. I turned of the breaker. In the morning I unhooked it from the boat inlet and found one of the three sockets on the cable and the male prong on the boat connection was a little brown, some shorting going on I guess.
I know there where other shore cords deep in a compartment in the bow and removed them and gave them a good once over. As it turns out, of the 4 shore cords onboard 3 of them had one bad female socket at the boat end of the cord.
So, it would seem this was a problem not found during inspection, the PO was using a cord for a while, when a problem interrupted hi 110v service he just went and got another used cord, never actually finding and fixing the real problem.

I'm sitting at home now so can't check for sure and am also doing some thinking outloud,

*Is the problem at the connection point, I can replace the insert at the outlet on boat were cord connects. The connection prongs there now look very very clean and bright except the one small spot.
*Is it possible that at one time the boat was NOT 30Amp and some of the wiring is not correct for 30 amp service at Annapolis city dock and our marina.
* Is it possible the old style breakers are just worn out.
* Since reverse Polarity goes away when I switch cords is the most likely fix to replace the shore power inlet connection on boat.

Just for further info, the boat breaker panel and swithes are all the old push button type. I don't like these at all and am already planing and pricing replacements, I just was not thinking of doing it this soon on the priority list. (Looking at the Bleasea 8099 or 8412, have to measure for fit next time at boat. )The distance from inlet connection to panel is about 8 feet and I'm thinking since I am going to replace the panel in the future I may just bump this to the top of the list and start from scratch, from the Inlet connection and work my way to a new panel.

I'm guessing that because the problem goes away when I switch to another cord that the problem is at the cord / boat connection.
I didn't have time before we left to pull the connection apart on the boat to check for bad / loose conections before we left. I did leave the power unhooked .

Am I on the right track ?

I have read alot on here about shore power and Polarity , just looking for some clarification if my thinking the cord connection is the probable cause.

Thanks
Brian

 

[Stu Jackson]

The cord could be made up wrong and create the reverse polarity by having swapped the hot and neutral. Buy a tester at the hardware store and confirm.

Additional thought: since you've found so many questions about your electrical wiring, I would be very hesitant to leave ANYTHING plugged when you're not there.

 

[cat38skip]

Over the years I have had 2 instances of reverse polarity on my boat. I have always used quality shore power cords and have not made any changes to the boat's circuits. In both cases the fault was caused by a failure at the dock outlet. In both cases the outlet had corroded and needed replacing. I now use dielectric paste on all connections and have not had a problem in many years. Check both the dock outlet and the boat receiver connections for corrosion. Also check/clean the cord connectors. It doesn't take much corrosion to cause a fault to be registered. We had to discard one shore power cord that appeared OK but was corroded internally at the boat-end connection. I cut the connector off thinking I would replace it but the wire had corroded several inches into the cable. Better safe than to have a fire ...

 

[MrBee]

seems to me if the cord was wrong it would be a problem from the start. It made it a couple months before the problem started.

Dielectric paste is a good idea, have to look into that.
I'm 99% sure it is at the boat end, not the dock post.

Thanks

 

[MLampner]

Marinas

Mr. Bee, where do you tie up in Middle River? We're at Maryland Marina and have found that power on the docks is always right. Somehow when the boat is on the hard we have more problems, but then electrolysis isn't an issue.

 

[Bill Roosa]

This is an easy one.
The reverse polarity light is powered by the neutral and ground. So in normal connections the neutral and ground are at the same potential and no light. If you plug in to an outlet that has the hot and neutral reversed then the hot powers the light through the safety ground.
Now if you have some corrosion on the neutral wire at one of the shore power cord connections you get that prong heating up and if you add a salt water environment you get rapid corrosion. I have not figured out exactly how this causes a "back feed" in the safety ground but have noted that if I repair the outlet the problem goes away.
I suspect that resistance on one of the outlet prongs causes a imbalance in the current flowing in the neutral and safety ground which the reverse polarity light sees and lights up dimly.
The fact that you can replace the shore power cable and the light goes off would be sufficient to convince me that the problem is with the shore power cable or the outlets.
99.44% of all electrical problems on boats is corrosion of connections.

 

[MrBee]

MLampner, we are at Stansbury Yacht Basin on Wilsons point. Not far from Carstons Creek cafe. The power on the dock has always been good, even with our other boat. And because this happened at Annapolis city dock also, we feel it is the cord and most likely the connection, as bill said.

I think I had it figured right but really need some conformation that my brain is properly grasping how all this electric stuff works. Seems like I have it mostly figured out.

Bill Roosa,
Thanks for that explanation. i think that is what is happening. If I clean that one male prong or use a cord that has not been affected then everything goes back to normal. For a while.......

Next time at boat I will clean the prong and look into adding some dielectric paste as cat38skip suggest and go from there.

Thanks

 

[Bill Roosa]

hey MrBee
I have a theory that because the shore power neutral and ground are connected at the meter box at the end of the dock that causes the safety ground to have current whenever one of the hot or neutral has a high resistance (corrosion) in one but not both wires.
Current gets in on the good hot wire but can't get out on the neutral, this creates an imbalance in the shore side of the line and feeds back through the ground. That caused the ground to be at something other than 0 volts and causes current to flow in it. That makes the reverse polarity light light dimly.
What I can't explain is how that will not show up on every bodies boat.
Like I said it is a theory.

The bottom line is check your shore power connections regularly and keep them clean.

 

[geehaw]

Also Check the boat for any ground to neutral connections. There should be none of these on the boat. Ground to neutral should be at the shore power or even further back.

 

[Brad Hoff]

I would also suggest you check your entire 110v system in the boat. You need to look at the wire connections to the "inlet" plug as well. I had a situation somewhat related where my polarity light came on out of the blue. Fould corrosion on the wiring connetions on the inlet plug on the boat. Cleaned the connections and still had the problem. After noting the wiring was different at the plug and the panel, I found the PO had spliced household wiring to the boat wiring with electrical tape that was melted into a big wad! I think I came very close to a big boat fire. Now I check all connections every season.

 

[Maine Sail]

Actual reverse polarity can exist either on the dock or on-board your own vessel. It does not matter where the reversing point is, on the dock or on-board, both scenarios will energize the reverse polarity indicator and create a potential for shock hazard.

With a faint RPI light, under high draw loads, you may not have a real reverse polarity situation, but still could, so check with a tester first.

It is likely to be a connection / resistance issue if the dock and polarity test well.. However if an older neon type light is used then it may just be weak and you could still have a reverse polarity situation. Reverse polarity testers are very inexpensive at Home Depot or Lowes.

The ABYC requirement for reverse polarity indicating lights is that they use minimum 25k Ohm Resistor. This is so they "indicate" at below the 5mA that a standard US spec GFCI will trip at. In the old days the indicator lights were neon based and for the last 20 or so years they have been LED but all should have a 25k Ohm resistor in the circuit.. This light sits between the AC white/neutral and AC green/earth ground and responds to a reversal of the ungrounded (black) and the grounded (white) conductors .

Keep in mind that when Muffy and Skippy fire up the brand new Sea Ray, untie the dock lines, and steam away from the dock forgetting about the power cord, it is usually Darrel the dock boy, and his other buddy Darrel, who re-wire the dock post. Don't trust them and start with a test of the dock post for reverse polarity. If you don't have a tester ask the marina to test it for you and be there to watch it..

It is possible for the reverse polarity indicator circuit to faintly illuminate even though the circuit is properly wired. This most often occurs due to resistance and poor connections but some inverters and even some battery chargers have been known to cause this as well. To test this you can simply disconnect your inverter or charger and see if the RPI is still faintly lit.

Thanks to a guy name Ohm, and his law, voltage is always consumed trying to push amperage through a wire. If the voltage differs between the beginning and end of the run or any two points in-between this is called voltage drop. Voltage drop can be caused by undersized wiring, improper or poor connections / terminations or corrosion. Bad or loose friction fits in shore power receptacles can also cause some voltage drop or resistance. This difference is what can dimly illuminate a RP indicator light.

If you flip on a high amp draw load there can often be enough resistance along the neutral path to overcome the resistance in the 25,000 Ohm resistor thus lighting it faintly. Resistance issues are not as dangerous as sucking on live wires, but should be attended to if discovered as they can create heat to the point of a fire..

Check all connections, use a tester, and make sure your AC input wiring from the dock to the panel are sufficiently sized for your loads. In some cases just trying a different dock pole and shore power cord can eliminate issues on-board and isolate them to the cord or dock post. If the neutral wire & connections are not sufficient to return all the current to shore, the green earthing wire try's to take up the slack and thus the RPI light can indicate.


ABYC E11 - SHORE POWER POLARITY DEVICES

E-8.10.1 Reverse polarity indicating devices providing a continuous visible or audible signal shall be installed in 120 V AC shore power systems and must respond to the reversal of the ungrounded (black) and the grounded (white) conductors (See E-8.23.1, Diagram 3,)

E-8.10.1.1 the polarity of the system must be maintained for the proper operation of the electrical devices in the system,

E-8.10.1.2 a branch circuit is provided with overcurrent protection in only the ungrounded (black) current-carrying conductors per ABYC E-8.11.6.1

E-8.10.2 Reverse polarity indicating devices are not required in systems employing polarization or isolation transformers that establish the polarity on the boat.

E-8.10.3 The total impedance of polarity indicating and protection devices connected between normal current carrying conductors (grounded [white] conductor and ungrounded [black] conductor) and the grounding conductor shall not be less than 25,000 ohms at 120 volts, 60 hertz at all times.

 

[Stu Jackson]

And some boats, like mine, have two reverse polarity indicator lights: one for good and one for not good!

Some of our skippers didn't understand the difference

http://c34.org/bbs/index.php/topic,2620.msg13781.html#msg13781

 

[Captphil24]

A couple of testing tips.

Brian,
When you are dealing with 120/240 VAC,l you are dealing with a life threatening level and just changing cords or lubricating contacts is not a good way to try and correct a condition. You must understand the condition and your correction must be well understood.

Some basic conditions: 1) There should never be any a.c. current in the ground wire.

2) With the shore power cord disconnected,either at the shore or boat end, there should be no continuity between ac neutral and gnd. Measured with an ohn meter, this should show infinity. If any resistance reading is found here, you should start opening a.c. breakers until you locate the piece of equipment at fault. When you do this test, turn on every on board a.c. device.

The fact that you get a fault detection light does indicate a voltage between neutral and gnd.

Good luck tracking this problem down, but I don't think that I would leave and a.c. power applied to boat while you're not there until you really solve it.

Phil in FL





We bought our 1985 irwin 34 in january.

*Is the problem at the connection point, I can replace the insert at the outlet on boat were cord connects. The connection prongs there now look very very clean and bright except the one small spot.
*Is it possible that at one time the boat was NOT 30Amp and some of the wiring is not correct for 30 amp service at Annapolis city dock and our marina.
* Is it possible the old style breakers are just worn out.
* Since reverse Polarity goes away when I switch cords is the most likely fix to replace the shore power inlet connection on boat.

Just for further info, the boat breaker panel and swithes are all the old push button type. I don't like these at all and am already planing and pricing replacements, I just was not thinking of doing it this soon on the priority list. (Looking at the Bleasea 8099 or 8412, have to measure for fit next time at boat. )The distance from inlet connection to panel is about 8 feet and I'm thinking since I am going to replace the panel in the future I may just bump this to the top of the list and start from scratch, from the Inlet connection and work my way to a new panel.

I'm guessing that because the problem goes away when I switch to another cord that the problem is at the cord / boat connection.
I didn't have time before we left to pull the connection apart on the boat to check for bad / loose conections before we left. I did leave the power unhooked .

Am I on the right track ?

I have read alot on here about shore power and Polarity , just looking for some clarification if my thinking the cord connection is the probable cause.

Thanks
Brian[/quote]

 

[SailingHarry]

For some help in understanding what is going you can use a voltmeter. There are three prongs on a 110V plug (household type, inside the boat). Using the volt meter, you should have:

Wide to Narrow -- 110V
Wide to Ground -- 110V
Narrow to Ground -- 0V

I may have Wide and Narrow reversed -- I can never remember.

The polarity lights are good, but they are kind of go-nogo. The volt meter can give you a bit more detail. The key part is "Narrow to Ground -- 0V" because that is what is driving your reverse polarity light. The light comes on because the "neutral" wire isn't neutral any more -- and that is because of a high resistance path SOMEPLACE between the reverse polarity lights and the point where the ground and neutral are tied together -- probably back at the main panel on shore.

Hope this helps,

Harry

 

[mitiempo]

You do have it backwards.

 

[Orion253]

Electrical Polarity Problem

It seems you have a few problems going on here.

First the burnt plug: You did not specify which prong on the plug is burnt. You also did not say if this is a twist-lock plug..... I assume it is though.
If a prong on the plug is burnt in only one spot you most likely have a bad connection on that prong of the plug which is burnt. It's not a short. A short would cause a breaker to pop on land..... Let's hope anyway.
Solution: Replace the power cord and the male plug on the boat. Put some Teflon Grease on the plug to keep the corrosion down. Also, check the wire from the plug to your breaker panel to make sure the wire is 10 gauge or larger. 10 gauge is capable of 30amps. 8 gauge is the next size capable of 40amps. Then comes 6 gauge, 4 gauge and then your boat will sink from the weight.
If the whole Prong is burnt and it is the hot prong, you may be drawing to much currant through that plug and or it has a bad connection.
Your polarity problem can be caused by several issues and you would have to run a series of tests to determine which is at fault. If your AC ground is connected to your AC Neutral and both are bonded to a through hull connection or the keel, your boat may look a better ground connection than the shore neutral and power could be going through there which could light your polarity light. It would also burn up the through hull, keel, prop or shaft on your boat. If the bad connection at your cord is on the neutral prong and the ground and neutral are connected, this could also cause the polarity light to illuminate.
I would Replace the boats male connector and power cord first, checking the cable size to your power panel. Put Teflon Grease on ALL connections.

Good luck,
Tom

 

[steve stark]

Mainsail....
If, as you said: "..the neutral wire & connections are not sufficient to return all the current to shore, the green earthing wire try's to take up the slack and thus the RPI light can indicate", then how exactly would the green earthing wire ' take up the slack'? This would imply to me that the green safety and the neutral wires would have some kind of low impedance between them that could pass that return current. I am at a loss to understand where that low impedance would be. Am I correct in understanding that neutral and ground are never connected together on board? If that is true, then a low impedance between neutral and ground would be in a piece of equipment somewhere and that seems to indicate a fault in the equipment, no?

 

[Maine Sail]

Mainsail....
If, as you said: "..the neutral wire & connections are not sufficient to return all the current to shore, the green earthing wire try's to take up the slack and thus the RPI light can indicate", then how exactly would the green earthing wire ' take up the slack'? This would imply to me that the green safety and the neutral wires would have some kind of low impedance between them that could pass that return current. I am at a loss to understand where that low impedance would be. Am I correct in understanding that neutral and ground are never connected together on board? If that is true, then a low impedance between neutral and ground would be in a piece of equipment somewhere and that seems to indicate a fault in the equipment, no?

When a high current or amperage load is dumped into the circuit, like a heater, there may be enough voltage drop in the white/neutral to exceed the resistance in the 25K resistor required by ABYC for the RPI light. When this happens, likely due to under sized wire or a high resistance connection, enough current can be driven through to light the RPI to cause it to faintly illuminate as the OP described..

Also one of the worst offenders of neutral to ground connections on boats are water heaters. Water heater empty, someone turns it on, element cracks now we have a leak to ground. You'd be amazed at how often this happens...

 

[Bill Roosa]

The same can be said of the shore side situation MS
Current to the boat has to equal current returned from the boat.
So if there is a high resistance in one of the wires would that not just lower the total current in both the hot and neutral? The hot and neutral are connected through any load that is turned on so the current in that circuit "sees" the total resistance and can't really tell which wire it is in. right?
If you buy that then by turning off all loads you should be able to eliminate all but a true reverse polarity situation. Alternately you can turn on each appliance in turn and find the trouble spot.
Does that sound correct?

 

[Maine Sail]

The same can be said of the shore side situation MS
Current to the boat has to equal current returned from the boat.
So if there is a high resistance in one of the wires would that not just lower the total current in both the hot and neutral? The hot and neutral are connected through any load that is turned on so the current in that circuit "sees" the total resistance and can't really tell which wire it is in. right?
If you buy that then by turning off all loads you should be able to eliminate all but a true reverse polarity situation. Alternately you can turn on each appliance in turn and find the trouble spot.
Does that sound correct?

Yes when you have a "resistance" issue the RPI will not usually remain lit with little to no load. As you increase the load the current pushes its way past the RPI resistor and faintly illuminates it.