Reverse Polarity

[Mike Smith]

Odd... We came in today from sailing - I plugged in the shore power cord. When I turned the AC power breaker on I got a Reverse Polarity indication.  I switched it off and unplugged the shore power cord.  I'll call my electrician Monday.  Nothing had changed since we left this morning.  Does anyone have any idea about how this could happen?

Mike

[Stu Jackson]

Someone worked on the dockside power while you were away.

[amoreau]

Hi,  I was also told that if you don't twist and lock your shore power plug in you can get flickering on your reverse polarity indicator light.

[Mike Smith]

Stu-

That is far and away too simple and straight forward an answer for anything going wrong on Breezer!  Amoreau - the connections were tight and the indicator was ON, not flickering.  Breezer is at our private dock, but there was some re-wiring done on the dock next door (the house was destroyed) the previous day.  Also, while we were out sailing, there was a lot of heavy equipment and dump trucks hauling away the house across the street, so maybe something happened to the main supply. Marinco makes a $33 circuit tester, which I should have aboard anyway, so I'll pick one up and check the dockside receptical today. Our electrician is coming in Tuesday to finish wiring the kitchen, so I'll have him check the dock as well. He did the original wiring.  Hopefully Stu is right.

Mike

[Mike Smith]

I picked up the Marinco circuit tester this morning and plugged it into the dock receptical.  Circuit is OK.  Plugged in the shore power cable and checked the power cable connector - circuit is OK.  Connected Breezer to shore power and turned on the main AC breaker.  Circuit is OK.  Neighbors on both sides haven't had a problem.  So, it is either intermittant, or it may have been a loose connection to the shore power receptical as Amoreau suggested.

Mike

[Mike Smith]

I really reccomend that anyone cruising or routinely using dockside power pick up a Marinco Circuit Tester ($35) to check for some common wiring problems before you plug in your shore power cord.  It is very compact and plugs directly into any locking-type 125V 30A dockside power receptical or the female end of your power cord.  It's yellow (of course) and has three lights on the end (Red, Yellow, and White). The pattern in which they light up diagnoses several potential problems.  The legend for the different patterns is printed on the side of the plug.  The unit will test for and instantly display the following light patterns:

No Problem - properly connected wiring (White & Yellow)
Reverse Polarity - Black/White wires reversed (White & Red)
Shock Hazard - Black/Green reversed (Red & Yellow)
No Neutral - White wire not connected (Yellow Only)
No Electrical Fault Protection - Green wire not connected (White Only)
No Power - Black wire not connected (All Off)

For safety purposes alone, I think this is money well spent.

Mike

[John Langford]

Good idea. However, you can do this even more cheaply. Most hardware stores sell a small 3 prong polarity checker.  I leave mine permanently plugged in to one of the receptacles above the nav station. Very helpful if you are travelling to new marinas during a long cruise.

[Mike Vaccaro]

It's also a good idea to install a quality AC multi-meter.  They are expensive, but like a polarity tester, well worth it.  A good meter will show system voltage, Hz and draw in amps and watts.  This boils down to a "what you're getting" display and a "what your using" display.  

The "what your getting" display shows not only frequency, but also system voltage.  On many shore power systems, it's interesting to watch the system voltage drop on warm weekends (plenty of folks plugged in and plenty of air conditioners running).  Lower voltage means less capacity to deliver required amperage.  Overall, the whole system "sags" as it is stressed and you may not be able to run all of the appliances you desire.

The "what you're using" display scientifically displays why your main breaker trips if you return to the dock, plug in and turn on the 30 amp battery charger, the air conditioner and try and vacuum the boat with the stereo cranked up!  Just like a good battery monitor, it will show you amperage draw of specific circuits and/or appliances.  This is not only handy for power management, but can help with trouble shooting as well.  

The number one benefit to having proper monitoring systems/displays is to avoid fixing a boat that isn't broke!  Mike's recommendation is right on the money:  Always test a new shore power circuit at the dock before you plug in.  

Cheers,

Mike

[Ron Hill]

Mike  S : Interesting.  On my 1988 I have a single throw double pole 30 amp breaker that trips when there's reverse polarity.  The red (reverse polarity) light comes on and the breaker immediately trips.  Has happened only a few times, but reverse polarity was infact there!

If someone was helping you plug in that day, might they have gotten the hooked connector into a wrong slot?  

[Mike Smith]

Ron -

I think Al is right and the cord was loose - nothing else makes sense.  As Sherlock Holmes said, "When you eliminate the impossible, the implausible becomes truth".

Mike