That was a SHOCK! Has this happened to you?

[CaptBobO]

OK, so this is a first for me, but maybe I'm doing something different.
The other day, I was getting ready to leave the dock and started my engines.
I went to the shore power on my dock, turned off breaker, unplugged cord and started to feed the cord through the hole in the transom. (I take my shore power cord with me)
as I was feeding the cord in towards the very end, I put my palm on the end of the cord where all three plug prongs are and I started to feel a tingling sensation like power. I pulled my hand back and tested it again. To my surprise, I felt the same electrical tingle. Not enough to make me jump, but enough to know that there was a sign of current there. Is this normal? Anyone else ever notice that?
Why would there be current flowing back to the plug end when i am not plugged in to shore power?
Any input from the Electrical pro's on here would be GREAT!!
Should I be flipping the breaker off on the boat at the shore plug?
Thanks!

 

[Shaps]

I was told to shut the shore power breaker on the boat prior to shutting the breaker on the dock.

 

[tony1b2000]

Im thinking your battery charger is possibly back feeding, faulty. Easy test. If you have a meter, unplug the boat and check for voltage the Hot and Neutral (see the attached picture)

. Next check the Hot and Ground. If either has a voltage, shut the 120 volt breaker off the charger and tray the test again. Note the picture is the Socket. So just match up the plug to this diagram when doing your testing!

 

[CaptBobO]

Im thinking your battery charger is possibly back feeding, faulty. Easy test. If you have a meter, unplug the boat and check for voltage the Hot and Neutral (see the attached picture)View attachment 93838 . Next check the Hot and Ground. If either has a voltage, shut the 120 volt breaker off the charger and tray the test again. Note the picture is the Socket. So just match up the plug to this diagram when doing your testing!

Awesome! Thank you!
I will do that test later today.
So if I show power there with it unplugged, then that means that my battery charger is back feeding and needs to be replaced?

 

[ttmott]

Is the generator running?
Do you have an Inverter?
If not then only a capacitor like the starting / running caps on the AC units discharging through your hand.
If your generator was running and you received a bonefied shock at that plug then there is a significant fault in the boat's wiring or something wrong with the switching between shorepower and generator.
Repeat the situation, put a meter on the plug and test between all of the plug's terminals. If you see voltage then short out the plug and hold the short for several seconds then repeat the test with the meter. If the voltage is gone or nearly gone then it's a capacitor and no worries. If the potential is still there as originally measured then there is a fault that needs correction.

 

[CaptBobO]

Is the generator running?
Do you have an Inverter?
If not then only a capacitor like the starting / running caps on the AC units discharging through your hand.
If your generator was running and you received a bonefied shock at that plug then there is a significant fault in the boat's wiring or something wrong with the switching between shorepower and generator.
Repeat the situation, put a meter on the plug and test between all of the plug's terminals. If you see voltage then short out the plug and hold the short for several seconds then repeat the test with the meter. If the voltage is gone or nearly gone then it's a capacitor and no worries. If the potential is still there as originally measured then there is a fault that needs correction.

Generator is NOT running.
I do have an inverter that is set to ON and charges batteries while plugged in to shore power or if the generator is running.
Im about to go down to the boat and do the multimeter test. what I dont know how to do, is short out the plug.
How do I go about doing that test?

 

[ttmott]

Generator is NOT running.
I do have an inverter that is set to ON and charges batteries while plugged in to shore power or if the generator is running.
Im about to go down to the boat and do the multimeter test. what I dont know how to do, is short out the plug.
How do I go about doing that test?

put a screwdriver across the plug prongs and hold it there for several seconds - that is unless you are seeing 120 volts or something really out of whack and you possibly create a real hazard. So you have a battery charger not an inverter? An inverter takes battery voltage and makes AC power.. A battery charger will not back-feed battery power as AC power.
If in fact you have an inverter / charger that is connected to the shore power and it senses you lost shore power and starts making AC power yet does not have an automatic transfer switch you have a very big and hazardous problem in which that thing is back feeding inverted AC power to the shore power cord as well as other things that should not be energized. That can be hazardous in many forms.... For example if the marina looses power and they are working on a circuit, and your boat is energizing that circuit creating an electrocution hazard.

 

[CaptBobO]

put a screwdriver across the plug prongs and hold it there for several seconds - that is unless you are seeing 120 volts or something really out of whack and you possibly create a real hazard. But there is no where else. So you have a battery charger not an inverter? An inverter takes battery voltage and makes AC power.. A battery charger will not back-feed battery power as AC power.
If in fact you have an inverter / charger that is connected to the shore power and it senses you lost shore power yet does not have an automatic transfer switch you have a very big and hazardous problem in which that thing is back feeding inverted AC power to the shore power cord. That can be hazardous in many forms....

Sounds easy enough. Ill go test how much voltage there is at the plug end.
I have both an inverter (running two 6volt batteries to my TRACE system) and I also have the original 30 amp battery charger on the bulkhead in the engine room.
I also have a generator, but that is off and not running.

 

[Creekwood]

A couple comments. Your inverter does not charge the batteries, the charger/converter does that. If your charge is a pure charger, it does not put out voltage to the 110 side. If it is a charger/inverter it would, but then you probably would not have a separate inverter.

But..if your inverter was improperly installed and the 110v output was direct wired to the shore power feed or to the back of the 110v panel feed and not through a transfer switch, you would get power to the cable as you described. And that is not good.

If you have 110v power across the prongs that goes away if you turn off the inverter, then I think that might be your issue.

 

[CaptBobO]

Everyone has great input! Thank you all for that. I just went out to the boat, and took some test. Here is what I got:

Shore power unplugged and Inverter ON:
Shore power unplugged and Inverter in SEARCH mode:


Shore Power unplugged and Inverter OFF: I have ZER reading

So, it seems to me that with the Inverter in the constant ON position, I am feeding a little bit of power to the plug (01.7v)
and with it OFF it props to (00.0v)

All these tests were with both shore power switches on, and the AC Converter switch on and then selecting either (ON, SEARCH, OFF) on the control panel for the TRACE engineering Inverter.

Is this something to really worry about and call a marine electrician ASAP, or can I take my time to figure it out, or just flip off the breakers at the incoming shore power at the transom?

Thank you all!

 

[ttmott]

Everyone has great input! Thank you all for that. I just went out to the boat, and took some test. Here is what I got:

Shore power unplugged and Inverter ON: View attachment 93846
Shore power unplugged and Inverter in SEARCH mode: View attachment 93848


Shore Power unplugged and Inverter OFF: I have ZER reading

So, it seems to me that with the Inverter in the constant ON position, I am feeding a little bit of power to the plug (01.7v)
and with it OFF it props to (00.0v)

All these tests were with both shore power switches on, and the AC Converter switch on and then selecting either (ON, SEARCH, OFF) on the control panel for the TRACE engineering Inverter.

Is this something to really worry about and call a marine electrician ASAP, or can I take my time to figure it out, or just flip off the breakers at the incoming shore power at the transom?

Thank you all!

So, looks like it's related to the inverter. It appears that the neutral conductors on your boat that are within the circuits the inverter powers are not fully isolated and switched with the inverter. The inverter system must switch both the hot and neutral conductors for all circuits the inverter can energize. As it appears the neutral has potential and measurable to the ground. You can verify this by putting more and more load on the inverter and see higher and higher voltage on the neutral.

 

[CaptBobO]

So, looks like it's related to the inverter. It appears that the neutral conductors on your boat that are within the circuits the inverter powers are not fully isolated and switched with the inverter. The inverter system must switch both the hot and neutral conductors for all circuits the inverter can energize. As it appears the neutral has potential and measurable to the ground. You can verify this by putting more and more load on the inverter and see higher and higher voltage on the neutral.

Wow! Thank you!
So, I think I should leave this one to a certified marine electrician.
How do you think I should go about working with this until I have someone correct the problem?
Should I flip the breakers at the plug in on the boat when I am using the inverter, and then turn them back on when I plug back in?
Would you say I have a very dangerous situation here? Im sure its been this way for YEARS and for previous owners of my boat. two to be exact.

 

[ttmott]

As a follow up maybe this will help. This is the inverter configuration on my last boat. Note the AC hot and common configurations and how the common is also switched.

 

[boatman37]

When we had our Crownline surveyed he tested the shore power cord with an ohm meter. The cord was fairly new but he tested it at the dock end to see if there was any continuity between any of the terminals. Can't remember the specifics of it but it passed and he said the concern was backfeeding to the pedestal on the dock. I don't have an inverter or generator. Pretty sure he said this was a test of the cord and not of the boats electrical system

 

[Stee6043]

This is very interesting. My generator is always running when I roll up my shore power cord in my transom locker and I've ALWAYS had a phobia about touching the male end of the cords as I push them through the opening. You've just rationalized my 6 seasons of irrational fear of those prongs.

 

[pyro]

1.7VAC is not enough to feel. This is equivalent to a AA battery. Double check the DVM in DC mode just to make sure there is no DC offset.

Then if it's still reading < 2VAC between ANY pin, I would touch it again, because I don't believe you felt anything I will admit I once thought I got shocked but it was some weird muscle spasm I was getting when moving in a weird position.

 

[Creekwood]

As a follow up maybe this will help. This is the inverter configuration on my last boat. Note the AC hot and common configurations and how the common is also switched.
View attachment 93850

@ttmot , this is a great diagram to have. If I am reading this right, the inverter is wired on the house side of the transfer switch so as long as the transfer switch is set to inverter/generator, there should be no way for 120v to back feed to the power cord. Have I got that right?

On a separate note, is there anything in that wiring that would prevent having both the generator and the inverter both on and feeding 120v into the system? How is that addressed?

 

[CaptBobO]

@ttmot , this is a great diagram to have. If I am reading this right, the inverter is wired on the house side of the transfer switch so as long as the transfer switch is set to inverter/generator, there should be no way for 120v to back feed to the power cord. Have I got that right?

On a separate note, is there anything in that wiring that would prevent having both the generator and the inverter both on and feeding 120v into the system? How is that addressed?

THIS IS A GREAT QUESTION!!
When running the generator should we have our inverter in "CHARGE" mode, or should we put the inverter to "SEARCH" mode? Isnt the generator supposed to be supplying the 120v? If that is the case, then I would think the inverter should be taking advantage of the AC current and use it to charge the house bank.

 

[ttmott]

@ttmot , this is a great diagram to have. If I am reading this right, the inverter is wired on the house side of the transfer switch so as long as the transfer switch is set to inverter/generator, there should be no way for 120v to back feed to the power cord. Have I got that right?

On a separate note, is there anything in that wiring that would prevent having both the generator and the inverter both on and feeding 120v into the system? How is that addressed?

You are correct it is a flexible arrangement in that if the inverter is not seeing line voltage either from the shorepower connection or the generator it switches (if it's turned on) it's transfer switch to invert and energizes the circuits it is feeding. As it has a transfer switch it will not back-feed current to any circuit before it like the generator or shorepower. If, for example, you start the generator the inverter senses line voltage and transfers back to generator power and terminates inverting; similarly with the shorepower also. So, as you can see and to my point to the OP the common conductors (white) must be switched with the hot conductors (black) by the inverter transfer switch so current does not feed back to those generator or shorepower line circuits.

 

[ttmott]

Now this is the configuration we are working on for the boat I have now. This is a Lithium batter powered Inverter/Charger arrangement with automatic generator start that provides 220VAC to power some of the 220VAC equipment on the boat. The salient difference here is there is a large isolation transformer consequently the common for the entire boat is derived from the boat's ground and a secondary tap on the transformer and no need to switch the common. And, this model inverter/chargers manage two independent power sources.