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Three Conductor Shore Power Cord

B

Brian Degulis

Legendary Member
Joined
Apr 25, 2006
Messages
2,886
Hatteras Model
61' MOTOR YACHT (1980 - 1985)
I just replaced another shore power cord using 6/3 instead of the normal 6/4. My boat like most Hats has transformers so the neutral from the shore supply is not carried on to the boat. You wouldn't think deleting one conductor would make that much diffrence but it sure does. The 6/3 is smaller in diameter much more flexible lighter and easier to handle. The only down side is you can't buy the cable already made up you have to put your own ends on. That has some advantages since now it's not moulded and you can replace the ends or make it a little longer or shorter if you like.

Brian
 
How long did you make it and what was the total cost?
 
And what do you have as a voltage difference between the ground on the boat and earth dockside?

The reason you can't buy it is because that kind of hookup violates the code.

Get out the popcorn!

Ted
 
TedZ said:
And what do you have as a voltage difference between the ground on the boat and earth dockside?

The reason you can't buy it is because that kind of hookup violates the code.

Get out the popcorn!

Ted
Click to expand...

Well we've been down this road before the earth ground is carried onto the boat to the transformer shield and on our boats that have transformers the neutral conductor is not carried onto the boat. It goes up to the shore power inlet and stops this is typical for boats with transformers. So if you use a 4 conductor cord your carrying the neutral from the dock to no where so you tell me why would you want to do that?

Brian

Brian
 
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SKYCHENEY said:
How long did you make it and what was the total cost?
Click to expand...

I made it 60' seems like I'm always around 10' short. The cable was $230 and the ends are $50 so around $330 for the set up.

Brian
 
I tried to buy some 3/6 a few years ago. Could not find it anywhere, ended up with 4/6. Where did you get it from?

Randy
 
The reason is the iso's should be of a balanced design and the boat, the dock and mother earth should all be at the same potential, i.e. connected together. I understand some very knowledgeable folk feel differently but no one has advanced a compelling argument why anyone should accept a situation where there is a potential difference between the boat's "earth" and the rest of the world. No matter how difficult the mechanics of getting between earth and earth are, Murphy's law says it can happen and with some iso's you can really light up...or go out!!

Ted
 
So translated into street talk? Should I continue to use the heavy 4 wire cable or switch to the lighter weight 3 wire?

This situation has created a nasty situation for me. I have an isolation transformer, as I'm sure most Hatts with "220" 50 amp service have. The problem I have is that our docks have 208 v. service only and as a result, I do not get the full amount of power that the boat calls for. I have consulted with an ABYC certified electrician and was informed that my transfromer can be re "programed" by switching some wires in it so that I can receive 115 volts (instead of the 104 v which is all I get now). While this sounds fine, the problem is when I travel and stay at a dock that does provide the full power, I will in fact be getting somewhere around 130 volts and that can also be bad. I don't really know what alternatives I have except to replace the isolation transformer at a cost of at least $5 grand.

Any suggestions.....

Walt
 
Walter P said:
So translated into street talk? Should I continue to use the heavy 4 wire cable or switch to the lighter weight 3 wire?

This situation has created a nasty situation for me. I have an isolation transformer, as I'm sure most Hatts with "220" 50 amp service have. The problem I have is that our docks have 208 v. service only and as a result, I do not get the full amount of power that the boat calls for. I have consulted with an ABYC certified electrician and was informed that my transfromer can be re "programed" by switching some wires in it so that I can receive 115 volts (instead of the 104 v which is all I get now). While this sounds fine, the problem is when I travel and stay at a dock that does provide the full power, I will in fact be getting somewhere around 130 volts and that can also be bad. I don't really know what alternatives I have except to replace the isolation transformer at a cost of at least $5 grand.

Any suggestions.....

Walt
Click to expand...


Walt,
You do not need a 4 wire cord as the neutral goes nowhere. The 3 wire is fine. As for the 208 issue, that can be remedied with a switch that will boost 208 when you need it or switch back to normal operation for 240v input. Yachtsmanbill had a nice picture of the rotary switching mechanism for that. It has also been discussed several other times in old threads.
 
C'mon Walt !! Have your electrician put on of these together. Its a tap switch which does voltage and 50/60 Hz too. ws
 
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Just for a few more details, our 48 LRC has a slightly different ground system from the factory. The earth ground from the shore is connected only to the stainless plate that holds the shore power connectors on the boat. The transformer case is connected to the internal boat bonding system at the transformer secondary winding, using a terminal block jumper between the transformer center tap and the bonding system. I have also wired a mid 80's Hatteras to allow switching for 208 versus 240 volt shore service, and it had the same ground system. I actually prefer this system as a transformer case grounded to earth, mounted near anything bonded to the boat ground system, offers the opportunity to get yourself between the two grounds. Not sure it will ever be a problem, but why tempt fate.

And a comment on the 3 wire versus 4 wire discussion. Is anyone concerned about their household stove, dryer, oven, air conditioner compressor, electric hot water heater, etc. All are three wire 240 volt hookups, just like the primary on your isolation transformer. I am a three wire shore cable user and have been for many years. Did anyone notice that the Hubble 100 amp, single phase shore power cable is a 3 wire cable. The only reason the 50 amp 120/240 shore power cable is 4 wire is so it works on all 240 volt boats (with and without isolation transformers). It eliminates a lot of help desk calls to the manufacturers.

Pete
 
TedZ said:
The reason is the iso's should be of a balanced design and the boat, the dock and mother earth should all be at the same potential, i.e. connected together. I understand some very knowledgeable folk feel differently but no one has advanced a compelling argument why anyone should accept a situation where there is a potential difference between the boat's "earth" and the rest of the world. No matter how difficult the mechanics of getting between earth and earth are, Murphy's law says it can happen and with some iso's you can really light up...or go out!!

Ted
Click to expand...

What's that got to do with a 3 cond cord and not bringing the neutral up to the shore power inlet on the boat?

What your talking about is weather or not the earth ground coming out of the isolation transformer should be tied into the docks ground and it shouldn't be. The answer is simple it would defeat the purpose of the iso transformer that's why every boat with an iso is wired like that.

Brian
 
Walter P said:
So translated into street talk? Should I continue to use the heavy 4 wire cable or switch to the lighter weight 3 wire?

This situation has created a nasty situation for me. I have an isolation transformer, as I'm sure most Hatts with "220" 50 amp service have. The problem I have is that our docks have 208 v. service only and as a result, I do not get the full amount of power that the boat calls for. I have consulted with an ABYC certified electrician and was informed that my transfromer can be re "programed" by switching some wires in it so that I can receive 115 volts (instead of the 104 v which is all I get now). While this sounds fine, the problem is when I travel and stay at a dock that does provide the full power, I will in fact be getting somewhere around 130 volts and that can also be bad. I don't really know what alternatives I have except to replace the isolation transformer at a cost of at least $5 grand.

Any suggestions.....

Walt
Click to expand...

Walt I had the same problem it's got nothing to do with the cord or # of conductors. My boat has Jefferson transformers and I put the rotary switchs sky's talking about in. You can put them right in the trasformrers case I have the wiring diagram from Hat if you need it.

Brian
 
Thanks guys, I am printing a hard copy of this thread so that my ABYC electrical guy can read it. I'm sure he can figure out what you're advising.

Thanks again, I'll keep you all posted.

Walt
 
Sky, I must have been away end of jun and early july as I missed the thread you refered to. I have printed it as well and will be giving it to my electrician tomorrow.

Thanks to all for the help.

Walt
 
Brian Degulis said:
What's that got to do with a 3 cond cord and not bringing the neutral up to the shore power inlet on the boat?

What your talking about is weather or not the earth ground coming out of the isolation transformer should be tied into the docks ground and it shouldn't be. The answer is simple it would defeat the purpose of the iso transformer that's why every boat with an iso is wired like that.

Brian
Click to expand...


The typical iso xformer is stopping noise and spikes on the supply line from entering the isolated electrical environment (the secondary) and they only do a fair job at that. Ground faults on a boat are much more common than they are on shore. The notion that all on-board faults should be handled on the boat and all dock faults handled on the dock is foolhardy and is an interpretation of "isolation" that was never intended. If i get a fault on the boat i want any GFI that can, even more than one, to trip to protect the people. No continuous neutral, no protection from the biggest and most effective GFI's. That is why you need the fourth wire. Of course you don't need it if you wire it wrong!

Ted
 
BTW there is a boater in the UK that does an extensive job of explaining the pros and cons of each method. Check it out, one can only learn.

http://www.smartgauge.co.uk/iso_wire.html

Also, i would LOVE for someone to show me a manufacturer of isolation xformers whose wiring diagrams show isolating grounds. If the guy who makes the xformer doesn't isolate them, why the heck are we so ready to embrace old and misunderstood technology?

I've heard it a million times. "I've been doing it this way for 30 years". Yes, but you have been doing it wrong for 30 years and you are lucky it hasn't bitten you in the butt! When it bites i would prefer it not be someone on this forum!!

Ted
 
TedZ said:
The typical iso xformer is stopping noise and spikes on the supply line from entering the isolated electrical environment (the secondary) and they only do a fair job at that. Ground faults on a boat are much more common than they are on shore. The notion that all on-board faults should be handled on the boat and all dock faults handled on the dock is foolhardy and is an interpretation of "isolation" that was never intended. If i get a fault on the boat i want any GFI that can, even more than one, to trip to protect the people. No continuous neutral, no protection from the biggest and most effective GFI's. That is why you need the fourth wire. Of course you don't need it if you wire it wrong!

Ted
Click to expand...


Tell Hatteras that! Any boat that they made with a factory installed transformer has no neutral wire. there is no neutral wire on the shore inlet. If the boat has a factory installed cablemaster, it has a 6/3 cable and the Hubbell plug has the neutral pin removed from the plug.
They use L1 L2 and ground.
The 30a 115 inlet has a neutral and ground, but not the 50a 240.
 
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