Reply
 
Thread Tools Display Modes
 
Old 10-12-2014, 06:21 AM   #21
Senior Member
 
City: Jacksonville Fla
Country: USA
Vessel Name: The Office
Vessel Model: Marine Trader
Join Date: Oct 2013
Posts: 157
Psneeld is very correct of course. Some others are mudding the water. I suggest if you don't understand electrical AC and/ or DC you hire a marine electrician that is ABYC certified before someone gets hurt. According to BoatUS 11 people drown each year in US most in fresh water around boats with faulty wiring. First of all, all current flow is the same in all branches of the circuit. In AC the black and white wires are equal and the green is 0. You don't lose amps unless there is a path to ground, intentional or otherwise. Amps don't disappear or evaporate they flow back to source. See Kirchhoff's circuit laws - Wikipedia, the free encyclopedia

Second The clamp meter will show any current that is going to the green wire if there is a fault! In AC the green wire should carry 0 current in a perfect world. All grounds should measure zero volts if all is well AC/DC. House electricians some times don't understand this in marine applications. We had/have this condition in our marina and found it was Air conditioning units not properly bonded and the docks terminal ground was not sized properly to carry the load (volt drop) Suggest you read Nigel Calder's boat book before you disagree with anyone. I hope this helps. It is difficult to explain electrical physics via printed word. The Blue sea references and more are easy to understand.
__________________
Advertisement

Autoteacher is offline   Reply With Quote
Old 10-12-2014, 09:23 AM   #22
TF Site Team
 
ksanders's Avatar
 
City: SEWARD ALASKA
Country: USA
Vessel Name: LISAS WAY
Vessel Model: BAYLINER 4788
Join Date: Feb 2011
Posts: 3,952
Guys, some of you are really missing the point from a practical sense. You have the concepts absolutely correct, but in practicality you can miss the problem entirely.

If you put your current clamp on the green wire, unless you have a REALLY big problem its probably going to read zero anyway.

Thats because most current clamps are just not designed to pick up miliamp sized currents all that well.

Your current clamp might be rated for 0-200 amps but that doesen't mean it actually works at near zero amps. I do not care what the label says. I do not care what the specifications from the manufacturer say. I do not care what Wikipedia says, or what a electrical engineer learned in college. I care about the reality of the field.

People that deal with very small currents (like utility guys in the Meter, Relay or SCADA shop(s)) have special very low range current clamps. Little itty bitty things, not the standard electricians clamp. For those that doubt this, try it some time. Set up a test circuit. We did, when I worked as a meter/relay tech at our local utility. Meter techs deal in 0-5 amp circuits every day . We found that it was darn near impossible to actually read sub amp currents accurately using standard electricians current clamps.
__________________

__________________
Kevin Sanders
Bayliner 4788
Seward, Alaska
www.mvlisasway.com
ksanders is offline   Reply With Quote
Old 10-12-2014, 10:05 AM   #23
Enigma
 
RT Firefly's Avatar
 
City: Slicker?
Country: Bumpkin?
Join Date: Oct 2007
Posts: 9,995
Greetings,
Mr. ks. That's exactly what I was alluding to in post #9. I would THINK a meter would have to be VERY sensitive to detect milli amps. I fully realize the problem in that milli amps CAN kill.
__________________
RTF
RT Firefly is offline   Reply With Quote
Old 10-12-2014, 10:24 AM   #24
Veteran Member
 
City: Wherever the boat is
Country: Europe
Vessel Model: 48 foot sailing Yacht
Join Date: Jul 2014
Posts: 92
Quote:
Originally Posted by ksanders View Post
Meter techs deal in 0-5 amp circuits every day . We found that it was darn near impossible to actually read sub amp currents accurately using standard electricians current clamps.
Clamp on ammeters are a great tool to have on a boat. Make sure you get one that will read DC as well as AC. Be careful sometimes the specs imply the unit will give DC current readings, but on some of the cheaper units this can only be done using the meter as a conventional multimeter not via the clamp facility.

The big advantage is that they will read currents without breaking the wire.

On DC currents they seem to be OK to about the +/- 0.1 Amp level with a bit of care.
Attached Images
 
Noelex is offline   Reply With Quote
Old 10-12-2014, 10:36 AM   #25
Veteran Member
 
City: Wherever the boat is
Country: Europe
Vessel Model: 48 foot sailing Yacht
Join Date: Jul 2014
Posts: 92
For the OPs problem I would be looking carefully at the Bow thruster. A simple solution that may work is to consider isolateing both the + and - sides of the bow thruster when it is not being used.
Noelex is offline   Reply With Quote
Old 10-12-2014, 12:34 PM   #26
Member
 
Join Date: Oct 2014
Posts: 5
If the "scale" is from galvanic action it may suggest that your boat is providing a connection to the marina's A/C earth grounding system allowing any stray voltage leaking from other boats to dissipate through yours. Isolating the two systems can be simple if the shore power is only used for battery charging, but if it's a live aboard situation it would be more complex ($$). Either way, if this problem is significant/corrosive I would contact a licensed marine electrician for a proper evaluation.
sanjuanjohn is offline   Reply With Quote
Old 10-12-2014, 12:38 PM   #27
Guru
 
Capt.Bill11's Avatar
 
City: Sarasota/Ft. Lauderdale
Country: USA
Join Date: Apr 2014
Posts: 5,422
Do you have anodes of any kind on your boats running gear? If so, it sounds to me like they may be leaching onto your props.
Capt.Bill11 is offline   Reply With Quote
Old 10-12-2014, 05:03 PM   #28
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 15,876
Just to clarify...galvanic corrosion is strictly the action between 2 underwater metals.

Stray current corrosion is just that...either AC or DC....

Stray current on the marina's green wire shore power ground can be blocked with a galvanic isolator for between $100-$400 or isolation transformers that I think start around $600 for a 30A service.

And yes ...again...a clamp ammeter around a shore power cord will show zero unless there is current lost to the water...Kevin Sanders is correct in the fact that depending on how sensitive your clamp meter is....will determine just how little stray current you may be able to detect that you are losing overboard.
psneeld is online now   Reply With Quote
Old 10-12-2014, 05:49 PM   #29
Member
 
Join Date: Oct 2014
Posts: 5
And to clarify, a clamp ammeter will show zero if there is zero draw, meaning no devices are using any electricity, or the draw is too low for a common meter to read.
sanjuanjohn is offline   Reply With Quote
Old 10-12-2014, 06:06 PM   #30
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 15,876
Quote:
Originally Posted by sanjuanjohn View Post
And to clarify, a clamp ammeter will show zero if there is zero draw, meaning no devices are using any electricity, or the draw is too low for a common meter to read.
No...it will show zero if there are no leaks...meaning normal 30 or 50 amp draw will still show zero on the clamp meter around the shore power cord...

Now take it to your panel and put it around just the black or white or red wire going to your panel and it will show what ever you are drawing...but around a normally functioning boat/shore power cord and the clamp meter will show zero even.... with the cords/panels maxed out with draw.

I know I just did it a couple weeks ago when I upgraded to 50 amp shore power and was running all my checks.

That's why if you want to use a clamp meter and determne what an appliance draws...you have to have an adapter where the wires are split so you can just wrap the clamp around ONE wire, not the cord.
psneeld is online now   Reply With Quote
Old 10-12-2014, 06:43 PM   #31
Member
 
Join Date: Oct 2014
Posts: 5
Ah, sorry for the confusion I see what you're saying. I don't have an adapter as there are so many different sockets I always just open the j-box (with the cord plugged in) and test at the breaker.
sanjuanjohn is offline   Reply With Quote
Old 10-12-2014, 06:52 PM   #32
Grand Vizier
 
Delfin's Avatar
 
Join Date: Jan 2010
Posts: 2,487
Quote:
Originally Posted by ksanders View Post
With your shore power disconnected, and your inverters, and generators output isolated, use an ohm meter between your AC neutral and ground.

You should see an infinite reading.

If you do not you need to find and resolve the issue.
This has always seemed the simplest and most accurate way of checking for leakage. Any decent voltmeter measures milliamps, correct?

KS, when you say that the inverters and gensets are "isolated" please clarify precisely what you mean... thanks!!
__________________
Delfin
"Dad always thought laughter was the best medicine, which I guess is why several of us died of tuberculosis." - Jack Handy
Delfin is offline   Reply With Quote
Old 10-12-2014, 07:33 PM   #33
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 15,876
If you had a hot wire rubbed through the insulation that contacted any of the bonded or DC grounded systems and it was going to ground...would that show up on the Neutral to Ground test???
psneeld is online now   Reply With Quote
Old 10-12-2014, 08:00 PM   #34
TF Site Team
 
ksanders's Avatar
 
City: SEWARD ALASKA
Country: USA
Vessel Name: LISAS WAY
Vessel Model: BAYLINER 4788
Join Date: Feb 2011
Posts: 3,952
Quote:
Originally Posted by Delfin View Post
This has always seemed the simplest and most accurate way of checking for leakage. Any decent voltmeter measures milliamps, correct?

KS, when you say that the inverters and gensets are "isolated" please clarify precisely what you mean... thanks!!
What you are checking for is a neutral to ground short. This would create two parallel paths for what should be neutral current. One path is as it should be, from your loads to the boats panel, then out to shore power, over the neutral conductor. The other path, the one you do not want is from your loads, through ground, and sea water, back to shore power. (your shore power feed from the dock has its neutral shorted to ground and the ground conductor connected to earth ground)

Using the ohm meter is a very quick easy way to check for this. On the AC panel with no power to it you should see infinite resistance between ground and neutral.

You need to isolate the generator and inverter to do this. Thats because at the generator its neutral is connected to its frame, which is grounded. This is the only way, when running on generator power your ground actually does any good. Thats why your generator selector switch needs to disconnect both the hot and the neutral from the generator.

Your inverter/charger works kinda the same way. When AC is present at its input the neutral to ground is not shorted by the inverter. When the inverter is in invert mode (no AC present at its input), it automatically shorts neutral to ground, so that your ground actually is effective.

This all makes sense if we remember the job of the ground conductor. Its whole function is safety. The metal parts of your applicances are connected to the ground conductor. If there is a short in your appliance from hot to any metal part, the ground conductor provides a path for the current so we do not get electrocuted when we touch it.


Quote:
Originally Posted by psneeld View Post
If you had a hot wire rubbed through the insulation that contacted any of the bonded or DC grounded systems and it was going to ground...would that show up on the Neutral to Ground test???
If you had a hot to ground short, it would most likely operate the circuit breaker or start a fire. To test for a hot to ground, you could also take an ohm meter reading. Hot to ground should be open. Hot to neutral will of course show your loads. I've honestly never seen a hot to ground short in a properly grounded system that did not operate the circuit breaker.
__________________
Kevin Sanders
Bayliner 4788
Seward, Alaska
www.mvlisasway.com
ksanders is offline   Reply With Quote
Old 10-12-2014, 08:21 PM   #35
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 15,876
Quote:
Originally Posted by ksanders View Post
cut for space.....

If you had a hot to ground short, it would most likely operate the circuit breaker or start a fire. To test for a hot to ground, you could also take an ohm meter reading. Hot to ground should be open. Hot to neutral will of course show your loads. I've honestly never seen a hot to ground short in a properly grounded system that did not operate the circuit breaker.
Thanks...

I have read and seen examples that I thought were this....maybe not...I'll have to do a little looking but boat breakers are notorious for being squirrely about tripping.
psneeld is online now   Reply With Quote
Old 10-12-2014, 09:57 PM   #36
Grand Vizier
 
Delfin's Avatar
 
Join Date: Jan 2010
Posts: 2,487
Quote:
Originally Posted by ksanders View Post
What you are checking for is a neutral to ground short. This would create two parallel paths for what should be neutral current. One path is as it should be, from your loads to the boats panel, then out to shore power, over the neutral conductor. The other path, the one you do not want is from your loads, through ground, and sea water, back to shore power. (your shore power feed from the dock has its neutral shorted to ground and the ground conductor connected to earth ground)

Using the ohm meter is a very quick easy way to check for this. On the AC panel with no power to it you should see infinite resistance between ground and neutral.

You need to isolate the generator and inverter to do this. Thats because at the generator its neutral is connected to its frame, which is grounded. This is the only way, when running on generator power your ground actually does any good. Thats why your generator selector switch needs to disconnect both the hot and the neutral from the generator.

Your inverter/charger works kinda the same way. When AC is present at its input the neutral to ground is not shorted by the inverter. When the inverter is in invert mode (no AC present at its input), it automatically shorts neutral to ground, so that your ground actually is effective.

This all makes sense if we remember the job of the ground conductor. Its whole function is safety. The metal parts of your applicances are connected to the ground conductor. If there is a short in your appliance from hot to any metal part, the ground conductor provides a path for the current so we do not get electrocuted when we touch it.




If you had a hot to ground short, it would most likely operate the circuit breaker or start a fire. To test for a hot to ground, you could also take an ohm meter reading. Hot to ground should be open. Hot to neutral will of course show your loads. I've honestly never seen a hot to ground short in a properly grounded system that did not operate the circuit breaker.
Much appreciated.
__________________
Delfin
"Dad always thought laughter was the best medicine, which I guess is why several of us died of tuberculosis." - Jack Handy
Delfin is offline   Reply With Quote
Old 10-13-2014, 08:07 AM   #37
Guru
 
LaBomba's Avatar
 
City: Beaverton, Ontario
Country: Canada
Vessel Name: Airswift
Vessel Model: Ontario Yachts Great Lakes 33
Join Date: Nov 2012
Posts: 818
Wow, great information. I have just moved houses so been busy a few weeks. The boat is on the hard now for the winter. This problem started before the bow thruster was installed and I don't have either an inverter or a generator, everything is 12v. Do have an anode on the shaft and metal extension of the keel for the rudder support. If I hook my generator up to the boat would I be able to test this on the hard or do I need to be in the water? Or could the problem be with the marina shore power plug? My dock neighbours do not have the same issue. I really want to solve this issue for both the sake of safety and potential harm to the boat. BTW, there does not seem to be any corrosion just a thick extremely hard calcium magnesium like hardness buildup, like over an eighth of an inch thick. You can't even scrape it off, it takes acid which quickly dissolves it. Thanks all for your help!!
__________________
Allan & Ann
Airswift
LaBomba is offline   Reply With Quote
Old 05-30-2016, 07:29 PM   #38
Guru
 
LaBomba's Avatar
 
City: Beaverton, Ontario
Country: Canada
Vessel Name: Airswift
Vessel Model: Ontario Yachts Great Lakes 33
Join Date: Nov 2012
Posts: 818
Well just an update on this old post as I have recently just resolved the electrical problem after many attempts. Actually the marine electrician found a couple issues after an exhaustive search. The PO the year before I bought the boat had a new battery charger installed and did not direct wire it but had a plug installed in the ER. Well turns out the plug was wired by some moron with the wires reversed, reverse polarity, problem one. This somehow screwed the new battery charger and the electrician found while going through each circuit and using the silver silver chloride probe in the water, that when the battery charger would kick in, 6 to 7 volts were reading from the DC boat ground to the water. This was not causing any corrosion but was actually attracting minerals in the water to attach to the metal parts of the running gear. Waiting on a new charger and hope this all goes away and I can do the happy dance.
__________________
Allan & Ann
Airswift
LaBomba is offline   Reply With Quote
Old 05-30-2016, 08:15 PM   #39
Guru
 
boatpoker's Avatar
 
City: Port Credit
Country: Ontario
Vessel Name: DIRT FREE
Vessel Model: Benford Fantail 38
Join Date: Sep 2012
Posts: 2,011
Quote:
Originally Posted by djmarchand View Post
Let me give it a try:

AC current from the shore power outlet goes down the black wire (I am using DC terms but bear with me) to the various appliances on the boat and then back up on the white (neutral wire). If you have any kind of fault- a short to ground in an appliance or wire then the current comes back on the green- the ground wire.

If you put an AC clamp on ammeter around all three wires you should see zero amps. The incoming black cancels out the outgoing white (or green).

But if you have a leak to the water (typically in the bilge) then some of the current will leave the boat through the water and there will be less current in the white or green wire and your clamp on ammeter will show some current.

It is a crude but effective test for AC leaks to the bilge.

But having said all of the above, AC leaks to the bilge don't cause what you are seeing. And I am not sure it is an electrolysis issue at all.

David
If you have current in the green you have an even more serious issue and one that is potentially lethal. You shouldnot see current in the green.
__________________

__________________
If you can live with the consequences, go for it - wg
Y'am what I y'am an' thats' all that y'am - Popeye
As God is my witness, I thought turkey's could fly. Mr.C
boatpoker is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 05:03 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012