stray current

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scoflaw

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Re: stray current

Talked to a Searay tech, his explanation was a faulty, loose ground wire which would explain loss of boat power and illumination of RPI. Said it was more annoying than dangerous, and me being so far away from the power source it wouldn't take much to shut power down.
Does this make sense to you?
 
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UncleWillie

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Re: stray current

scoflaw said:
Talked to a Searay tech, his explanation was a faulty, loose ground wire which would explain loss of boat power and illumination of RPI. Said it was more annoying than dangerous, and me being so far away from the power source it wouldn't take much to shut power down.
Does this make sense to you?
Click to expand...

No, that doesn't make much sense! A loose ground wire will not cause a lose of power.
A floating ground would make the RPI go OFF not ON.
You probably have plenty of devises that only have the old school plugs with only two pins and no ground at all.
They all work just fine without a ground. Ground is a safety feature and carries no power in normal service.

Almost any meter you have will be fine as long as it works. If it is accurate with a few volts that is good enough.
We just need to see the difference between 90 and 120 volts . We do not need to measure it to a 10[SUP]th[/SUP] of a volt.
 
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scoflaw

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Re: stray current

Yes I have a meter. The 2 items I leave on all the time are a fridge which is hard wired and a plug in dehumidifier and they both shut down when this event happens. If the ground and the neutral wire are 1 and the same would the loose wire theory make sense?
 
alldodge

alldodge

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Re: stray current

Need a clamp meter to measure not a regular volt meter
 
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UncleWillie

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Re: stray current

scoflaw said:
Yes I have a meter. The 2 items I leave on all the time are a fridge which is hard wired and a plug in dehumidifier and they both shut down when this event happens. If the ground and the neutral wire are 1 and the same would the loose wire theory make sense?
Click to expand...

I suspect that everything shuts down when you loose power.

That is one Big IF!
I assume we are talking about your 28 foot, Twin engine Sea Ray, that was built in 2006! ???
IF (Big IF) the factory Red-Necked the Shore Power Wiring, and deleted all the ground wiring,
then anything is Possible. :rolleyes:

But, let us assume only the Probable at this point, and discount the highly unlikely, until we determine otherwise.

IF the Sea Ray tech told you that faulty ground wiring "...was more annoying than dangerous" and not anything to be concerned about; That statement alone would give me great concern. That is kind of like having your neighbor say, "I don't worry about the kids playing with my loaded guns because that aren't strong enough to pull the triggers."

You are just begging for a disaster to happen.
 
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scoflaw

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Re: stray current

My boat works fine on the shore power cord in my driveway. So to get to the bottom of this can I do some testing on the dock, or do I wait until my boat is there? Would the problem be easier to find when my boat is in the "shut down condition" I speak about?
 
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UncleWillie

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Re: stray current

scoflaw said:
My boat works fine on the shore power cord in my driveway. So to get to the bottom of this can I do some testing on the dock, or do I wait until my boat is there? Would the problem be easier to find when my boat is in the "shut down condition" I speak about?
Click to expand...


You can measure the voltages at the Shore Power Pedestal for a starter.

Hot-Com = ?
Hot-Gnd = ?
Com-Gnd = ?

It will be nearly impossible to find the problem on the boat while it is operating normally.
You can't fix it , if it isn't broken.

We would like to the the same voltage measurements taken from an On-Board Outlet when the system is normal,
and also when it has shut down.

NEMAL5-30.jpgNEMA5-15.jpg
Neutral = Common
 
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scoflaw

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Re: stray current

Can I assume that the boat should be plugged into shore power for the normal and shut down tests? Will probably be a while before I report back. Thanks for your help. Mike
 
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UncleWillie

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Re: stray current

Excellent assumption.
If it were not power up all you would read is a bunch of Zeros. :)

What would be expected is....

Hot-Com = 125
Hot-Gnd = 125
Com-Gnd = 0

Or something similar.
 
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UncleWillie

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Re: stray current

Lets be "Mr. Not so Obvious" for a moment, and try thinking out of the box.....

Going back to my theoretical example in post #17....

Lets assume his Refrigerator and Dehumidifier are operating and drawing 10 amps.
Let's also assume he has a 50 foot power cord to the Shore Power Pedestal and the Pedestal is 250 feet to the breaker panel where the Common and Ground join the Master Ground.
Assuming all wiring is 6awg and a 600 foot round trip; 10 amps is going to drop 2.4 volts across the 0.24 ohms* of the wire, 1.2 volts each way.

So it would not be out of reason to see.

Zero Amp Measurements
Hot-Com = 125
Hot-Gnd = 125
Com-Gnd = 0

and

10 Amp Measurements
Hot-Com = 122.6 (125-2.4)
Hot-Gnd = 123.8 (125-1.2)
Com-Gnd = 1.2 (0+1.2)

The ground is carrying no current whatsoever, So it is still at Zero.
But the Hot has lost the volt+ and the Common has gained the Volt+ due to the Current and the Resistance in the Wiring. (E=IR)
That is why Common and Ground need to be kept separate.
Common is not always at Zero.

*** Ref. 6 AWG = 0.395 Ohms /1000 Feet.
 
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bruceb58

bruceb58

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Re: stray current

The RPI is measuring the voltage difference between the Neutral and the ground. With a load on, as UncleWillie stated, there will be a voltage drop in the neutral leg. The RPI has a voltage threshold between the ground leg and the neutral and the longer the neutral wire and hence more voltage drop, the more likely you will get an RPI indication the further you are away from the panel where ground and neutral are connected. This is why power at the beginning of the dock works fine. I don't think you have a safety issue but a voltage drop issue.

Would be interesting to pull your boat into various slips and try it.
 
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UncleWillie

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Re: stray current

bruceb58 said:
The RPI is measuring the voltage difference between the Neutral and the ground. With a load on, as UncleWillie stated, there will be a voltage drop in the neutral leg. The RPI has a voltage threshold between the ground leg and the neutral and the longer the neutral wire and hence more voltage drop, the more likely you will get an RPI indication the further you are away from the panel where ground and neutral are connected. This is why power at the beginning of the dock works fine. I don't think you have a safety issue but a voltage drop issue. Would be interesting to pull your boat into various slips and try it.
Click to expand...

The RPI is either an LED or a Neon Lamp in series with a 25K resistor.
5 volts on a Neon will not get it to strike over.
5 volts through 25K yields less than 0.2mA. LEDs would like to see more in the 5-15mA+ range to look like they are ON.
Under normal room lighting, most operators would not even notice the glow.

None of this explains the complaint that all power disappears from the boat when the RPI Illuminates.
Dropping 15 volts down to 110 volts would strain the appliances, but not likely stall them out.
The lights would still be ON, slightly dimmed in any event.

Scoflaw, you're killing us in anticipation of the in Marina measurements. ;)
How bright is the RPI when it is ON and what type of lamp is it?
 
bruceb58

bruceb58

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Re: stray current

UW, I was thinking RPIs disconnect power. I guess that is not the case?
 
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UncleWillie

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Re: stray current

bruceb58 said:
UW, I was thinking RPIs disconnect power. I guess that is not the case?
Click to expand...

No! It is Just a Reverse Polarity INDICATOR. A Good Explanation. And Another With Pictures.
A Lamp and a 25k Resistor connected between the Common and the Ground.
It is there to Warn of a Full Reverse connection of the 120 volts; Black swapped with White. The BIG Mistake.
It is just an idiot light.
 
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