Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 20-10-2013, 07:45   #61
Registered User
 
Capn Morgan's Avatar

Join Date: Jul 2009
Location: South East Asia
Boat: Hans Christian 48T
Posts: 381
Re: Isolating Transformers, The Earth wire connection conundrum

I was checking that there was no continuity between the in and the out earth lines. It is an Isolation Transformer so that is what it is supposed to do. What I found was that with the shore power cord in place, not powered, there is continuity which I believe should not be there.
__________________

__________________
Capn Morgan
'If you can fill the unforgiving minute with sixty seconds' worth of distance run...'
Capn Morgan is offline   Reply With Quote
Old 20-10-2013, 08:05   #62
Do… or do not
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 9,198
Quote:
Originally Posted by Capn Morgan View Post
I was checking that there was no continuity between the in and the out earth lines. It is an Isolation Transformer so that is what it is supposed to do. What I found was that with the shore power cord in place, not powered, there is continuity which I believe should not be there.
From your description, there is something wrong.

1. The Isolation transformer has no continuity between input ground and output ground terminals. If it does, remove the jumper, which is only to be used when the boat is on the hard. If it still does, then the transformer is faulty.

2. At the shore side of the transformer there should be no further connections or jumpers, just the shore power cord, an inlet and a breaker. Nothing that connects to theboat side except thetransformer.

3. I also have a floating setup. It means that on the boat side you have two hot terminals and no neutral. There should be nothing jumpered to ground (not to boat ground either). This requires double pole breakers.
__________________

__________________
s/v Jedi is offline   Reply With Quote
Old 20-10-2013, 08:11   #63
Senior Cruiser

Cruisers Forum Supporter

Join Date: Mar 2007
Location: Santa Cruz
Boat: Boatless Again
Posts: 4,310
Re: Isolating Transformers, The Earth wire connection conundrum

Quote:
Originally Posted by Capn Morgan View Post
Sorry for barging into this thread with a question but I'm a bit baffled.

I installed a Victron 7000w IT. Just out of interest and to check that the connections were correct I checked for continuity between the two earth (yellow/green) wires. I have not jumpered L2 to the boat earth so it is a floating system. I expected to find an open circuit, but found continuity instead, around 400 ohms. I disconnected the shore terminals and tested again, finding an open circuit. I checked the cable from the shore power receptacle to the IT and found not to be compromised. I replaced the shore power connector only to find that the continuity was back.

So, there is no continuity if the cable is out of the receptacle but there is as soon as I replace it. Where is the connection from the boat safety wire to the shore earth?
Could be a reverse polarity light.
__________________
donradcliffe is offline   Reply With Quote
Old 20-10-2013, 13:23   #64
Registered User

Join Date: Jun 2013
Location: canada
Posts: 1,694
Re: Isolating Transformers, The Earth wire connection conundrum

in both these cases, if the transformer was wired correctly. the hot 2 (n) is tied to ground at the transformer. it's a dead short on the ac hot line, and the ac breaker for that appliance would trip.

it's the exactly the same as running your gen. which should also have the N and G tied together at the gen.


Quote:
Originally Posted by goboatingnow View Post
Note, in the drawing below, The earth wire ( protective wire) is always connected to Hot2, or L .

__________________
smac999 is online now   Reply With Quote
Old 20-10-2013, 13:49   #65
Registered User

Join Date: Jun 2013
Location: canada
Posts: 1,694
Re: Isolating Transformers, The Earth wire connection conundrum

Quote:
Originally Posted by pbiJim View Post
On the subject of electro-shock drowning, I assume that would require a swimmer to be a better conductor than the water around him. Does anyone know of a study that has documented the difference in resistance between these two?

It seems strange to me intuitively that a swimmer 10 feet away from a poorly wired boat would have a problem. I can certainly see that a person in the water touching a boat with bad wiring could have a problem though.

Does anyone have more info on this sort of thing?

when a boat is leaking ac in fresh water you can actually measure the rings of voltages around the boat (carefully with a wooden pole and a voltmeter probe)

if a 6' person is is lying in the water perpendicular to the leak, he's going to have a decent voltage potential between his toes and head, and will get shocked. if he swims by parallel the voltage gap is much smaller and would get a nice tingle.

same idea as shuffling away from a downed power line vs walking.

electro-shock drowning is covered in the abyc corrosion course, and there is numbers and values in that course book.

in our course we actually stuck live wires into a tub of water. (not the safest training but good )
__________________
smac999 is online now   Reply With Quote
Old 20-10-2013, 13:56   #66
Registered User

Join Date: Jun 2013
Location: canada
Posts: 1,694
Re: Isolating Transformers, The Earth wire connection conundrum

in my above picture comment I made the asummtion it was 120v. I see the point if 230v. (won't let me edit the other post)
__________________
smac999 is online now   Reply With Quote
Old 20-10-2013, 14:11   #67
Registered User

Join Date: Jun 2013
Location: canada
Posts: 1,694
Re: Isolating Transformers, The Earth wire connection conundrum

Quote:
Originally Posted by Capn Morgan View Post
Sorry for barging into this thread with a question but I'm a bit baffled.

I installed a Victron 7000w IT. Just out of interest and to check that the connections were correct I checked for continuity between the two earth (yellow/green) wires. I have not jumpered L2 to the boat earth so it is a floating system. I expected to find an open circuit, but found continuity instead, around 400 ohms. I disconnected the shore terminals and tested again, finding an open circuit. I checked the cable from the shore power receptacle to the IT and found not to be compromised. I replaced the shore power connector only to find that the continuity was back.

So, there is no continuity if the cable is out of the receptacle but there is as soon as I replace it. Where is the connection from the boat safety wire to the shore earth?
do you have a tv cable or phone cable pluged into boat? they can share boats ground back to shore bypassing IT,s and galvanic isos
__________________
smac999 is online now   Reply With Quote
Old 20-10-2013, 17:15   #68
Registered User
 
Capn Morgan's Avatar

Join Date: Jul 2009
Location: South East Asia
Boat: Hans Christian 48T
Posts: 381
Re: Isolating Transformers, The Earth wire connection conundrum

Quote:
Originally Posted by donradcliffe View Post
Could be a reverse polarity light.
How so? The shore earth comes straight into the Isolation Transformer. I found no other connections on the receptacle either, no tv or telephone connectors.
__________________
Capn Morgan
'If you can fill the unforgiving minute with sixty seconds' worth of distance run...'
Capn Morgan is offline   Reply With Quote
Old 20-10-2013, 17:35   #69
Registered User
 
Capn Morgan's Avatar

Join Date: Jul 2009
Location: South East Asia
Boat: Hans Christian 48T
Posts: 381
Re: Isolating Transformers, The Earth wire connection conundrum

Quote:
Originally Posted by s/v Jedi View Post
From your description, there is something wrong.

1. The Isolation transformer has no continuity between input ground and output ground terminals. If it does, remove the jumper, which is only to be used when the boat is on the hard. If it still does, then the transformer is faulty.



2. At the shore side of the transformer there should be no further connections or jumpers, just the shore power cord, an inlet and a breaker. Nothing that connects to theboat side except the transformer.




3. I also have a floating setup. It means that on the boat side you have two hot terminals and no neutral. There should be nothing jumpered to ground (not to boat ground either). This requires double pole breakers.
1. This is what I was trying to confirm. If I remove the shore cable, the IT shows no continuity between the earth terminals. The jumper is removed.
There is an 30ma RCD just after the Isolation transformer, but I am not sure if this is correct, don't know if it will work with the floating ground.

2. Exactly as you describe. Double pole breaker to switch off from the boat.

3. There is a RCD after the output from the transformer but I'm not sure if this is going to work with the floating setup, ideas?
__________________
Capn Morgan
'If you can fill the unforgiving minute with sixty seconds' worth of distance run...'
Capn Morgan is offline   Reply With Quote
Old 20-10-2013, 23:35   #70
Do… or do not
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 9,198
Okay, so I understand that only after you connect the shore power cord, you get ground continuity? What is your boat ground? You may be measuring the ground path through ground instead of through the transformer. It must be, because there is no continuity through the transformer.

I can't bring up the incentive to discuss this silly repeat of having to ground a leg from a transformer or genset and live with a neutral. I will only say that this is the result of ignorance; this has been discussed to death too often now and many boats are 100% safe without a neutral and thus a floating system with two hot's.
__________________
s/v Jedi is offline   Reply With Quote
Old 21-10-2013, 02:43   #71
Registered User

Join Date: Feb 2009
Posts: 1,321
Re: Isolating Transformers, The Earth wire connection conundrum

Quote:
Originally Posted by s/v Jedi View Post
many boats are 100% safe without a neutral and thus a floating system with two hot's.
In some case, not in all. It is normally the supply authority that decides of the wiring system to be used.
So with your system without earth, let say that the insulation of one of yours “hots” as chafed and the conductors is touching something conductive, like the plumbing installation. So, this plumbing will become “hot” or live. Now because it can happen someone decide to fill a metallic electric kettle, that is electrically faulty and under voltage (live) from the other “hot”, using a conductive tap connected to the plumbing. In one hand the kettle in the other hand the tap. That person may survive electrocution if an RCD is present in the wiring and if the RCD open in time.

Quote:
Originally Posted by CarinaPDX View Post
In the US the neutral and safety ground are "earthed" at the transformer near your house or apartment (or marina) and should not be earthed again as you suggest.
Greg
Curious.
__________________
chala is offline   Reply With Quote
Old 21-10-2013, 03:33   #72
Registered User
 
Capn Morgan's Avatar

Join Date: Jul 2009
Location: South East Asia
Boat: Hans Christian 48T
Posts: 381
Re: Isolating Transformers, The Earth wire connection conundrum

Quote:
Originally Posted by s/v Jedi View Post
Okay, so I understand that only after you connect the shore power cord, you get ground continuity? What is your boat ground? You may be measuring the ground path through ground instead of through the transformer. It must be, because there is no continuity through the transformer.

I can't bring up the incentive to discuss this silly repeat of having to ground a leg from a transformer or genset and live with a neutral. I will only say that this is the result of ignorance; this has been discussed to death too often now and many boats are 100% safe without a neutral and thus a floating system with two hot's.
Thanks for your post Nick.

Agree. I think that is what I must be measuring. Just don't understand why just yet. Will keep at it. I see what you mean, lots of posts on this subject. I'm with you. Do you think RCDs don't work in the floating system?
__________________
Capn Morgan
'If you can fill the unforgiving minute with sixty seconds' worth of distance run...'
Capn Morgan is offline   Reply With Quote
Old 21-10-2013, 07:08   #73
Registered User
 
transmitterdan's Avatar

Join Date: Oct 2011
Boat: Valiant 42
Posts: 4,018
Quote:
Originally Posted by Capn Morgan View Post
Thanks for your post Nick. Agree. I think that is what I must be measuring. Just don't understand why just yet. Will keep at it. I see what you mean, lots of posts on this subject. I'm with you. Do you think RCDs don't work in the floating system?
I agree with Nick, you are measuring the resistance of the water back to earth of the dock power system. Something in your AC ground or neutral is connected to a submerged metal object.

RCDs in my opinion are mandatory when using a floating system. They will protect you from electric shocks. They trip when the current in the hot and neutral are out of equilibrium which is not dependent on the "earth" wire actually connecting to earth.
__________________
transmitterdan is offline   Reply With Quote
Old 21-10-2013, 07:49   #74
Do… or do not
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 9,198
Quote:
Originally Posted by chala View Post
In some case, not in all. It is normally the supply authority that decides of the wiring system to be used. So with your system without earth, let say that the insulation of one of yours “hots” as chafed and the conductors is touching something conductive, like the plumbing installation. So, this plumbing will become “hot” or live. Now because it can happen someone decide to fill a metallic electric kettle, that is electrically faulty and under voltage (live) from the other “hot”, using a conductive tap connected to the plumbing. In one hand the kettle in the other hand the tap. That person may survive electrocution if an RCD is present in the wiring and if the RCD open in time. Curious.
Hold on, there MUST be an isolation transformer installed to do this. The only way to get shocked is when your body completes the circuit between the two hots from the transformer. You are adding two failures, one for each hot. With that much wrong you would die because a moonrock woukd fall from the sky on top of you long before you get this fault.
__________________
s/v Jedi is offline   Reply With Quote
Old 21-10-2013, 07:52   #75
Do… or do not
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 9,198
Quote:
Originally Posted by s/v Jedi View Post
Hold on, there MUST be an isolation transformer installed to do this. The only way to get shocked is when your body completes the circuit between the two hots from the transformer. You are adding two failures, one for each hot. With that much wrong you would die because a moonrock woukd fall from the sky on top of you long before you get this fault.
May be somebody can explain how the RCD protects and how ground protects? I'm a but short on time today...
__________________

__________________
s/v Jedi is offline   Reply With Quote
Reply

Tags
rum

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 16:55.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.