Three Conductor Shore Power Cord

[yachtsmanbill]

C'mon Walt !! Have your electrician put on of these together. Its a tap switch which does voltage and 50/60 Hz too. ws

[Pete]

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

[Brian Degulis]

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

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

[Brian Degulis]

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

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

[Walter P]

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

[SKYCHENEY]

Walt,
You might also want this thread.

http://www.samsmarine.com/forums/sho...voltage&page=3

[Walter P]

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

[TedZ]

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

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

[TedZ]

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

[captddis]

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

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.