125/250-50A or 125-50A?

[Colwyn D]

My 42C schematics show the boat was originally wired with two 30A shorepower sockets, one going to the AC panel and the other to the service panel. At some time the boat was rewired and used a single 125/250 socket and shore cable splitting the two hot legs within the boat, black to one panel and red to the other panel. I added a Glendinning cable reel to the boat and copied the 125/250 wiring. My shore cable is the original 50' length of 6/4 and is rather short.
I have been given a 110' length of new 125-50A 6/3 cable. Can I use this cable with a 125/250 plug and connect it to just one of the hot terminals within the plug?
My concerns are whether one terminal of a 125/250 outlet will provide 50 amps and if 50A is enough power for two AC units, water heater and battery charger. Yes I can work out the amperage draw but not sure of the start up current with the AC units.
I have no 240v items or wiring on the boat.
Thanks in advance for any help.

 

[q240z]

I would advise against wiring the boat in anything other than the standard way. It could be thought of as intentional miswiring...just sounds like a bad idea from the git-go.

There are a few boats in our marina that have 125v 50a service. They seem prone to overheated plugs, especially during winter when loads are consistently high. If you're wired for 250v50a already, I'd advise sticking with that.

Cheers,
Q

 

[rsmith]

I would advise against wiring the boat in anything other than the standard way. It could be thought of as intentional miswiring...just sounds like a bad idea from the git-go.

There are a few boats in our marina that have 125v 50a service. They seem prone to overheated plugs, especially during winter when loads are consistently high. If you're wired for 250v50a already, I'd advise sticking with that.

Cheers,
Q

It's the same plug except the tits on the prongs are different.

 

[Pete]

Does the boat have an isolation transformer? One or two transformers? Do the red and black wires from the shore power inlets currently run directly from the inlet to the two distribution panels?

Pete

 

[Boatnut]

Save yourself the work, and hassle of trying to figure it out. Stay with the system the way it is currently wired. What you currently have is splitting the load very well, and the current draw is lower the it would be by using one 50 amp leg. There is no need to place all the load on one leg, and a/c start up will work much better. That's a pretty long cable I would be more inclined to shorten it if possible.

 

[saltshaker]

Save yourself the work, and hassle of trying to figure it out. Stay with the system the way it is currently wired. What you currently have is splitting the load very well, and the current draw is lower the it would be by using one 50 amp leg. There is no need to place all the load on one leg, and a/c start up will work much better. That's a pretty long cable I would be more inclined to shorten it if possible.

Completely agree, stick with what you have. Why would you want to cut your supply in half? If 50ft of cable isn't enough, buy a proper length of 6/4 cable or a 50/250 cord set to use as an extension.

 

[q240z]

It's the same plug except the tits on the prongs are different.

Same but different...interesting.

Q

 

[Colwyn D]

No isolation transformers and the red and black hots do run directly to the panels. Red to one black to the other.
Have to agree of course that sticking with what I have is the best option. Just the free 100' cable is sitting there asking to be used! I thought maybe that all the original 125-50A boats out there would have been wired with 125/250 plugs and therefore I would be following some proven practice.

 

[Pete]

Without an isolation transformer on a Hatteras, you must use 6/4 wire for dual 50 amp service, as you must bring the neutral from shore onto the boat. With an isolation transformer the neutral is not required or used on the boat so it can be eliminated and 6/3 works fine.

Given the change you described you might want to verify that when the inlet power was increased from 30 amps to 50 amps that the wire between the shore power inlets on the boat and your two distribution panels was changed to number 6. I believe Hatteras used number 8 on the original installation.

Pete

 

[Colwyn D]

OK Pete, thanks for that.Interesting you said about the size of wire, it had been left as 8 but in their wisdom had doubled it up with a green to the main supply panel, nice one. I have now changed them to 6's.
I was thinking I don't need the dual 50A supply as my loads are relatively low. Two AC units, battery charger and water heater, the stove is propane. So a single 50A supply using the 6/3 split and going to both panels.

 

[saltshaker]

OK Pete, thanks for that.Interesting you said about the size of wire, it had been left as 8 but in their wisdom had doubled it up with a green to the main supply panel, nice one. I have now changed them to 6's.
I was thinking I don't need the dual 50A supply as my loads are relatively low. Two AC units, battery charger and water heater, the stove is propane. So a single 50A supply using the 6/3 split and going to both panels.

That's not much available power if you do that. You'd be better off with the original dual 30A set up. Why would you want everything on one circuit?

 

[rsmith]

Same but different...interesting.

Q

3 - 50a capacity prongs ground conducted thru the casing. If anything the 250v plug is a bad design. IMHO it should have had 4 dedicated prongs for the 6/4 cable. I don't have a IsoXformer and the ground is tied to the same buss bar as the neutral.

 

[Boatsb]

3 - 50a capacity prongs ground conducted thru the casing. If anything the 250v plug is a bad design. IMHO it should have had 4 dedicated prongs for the 6/4 cable. I don't have a IsoXformer and the ground is tied to the same buss bar as the neutral.

2 50 amp 125v cables have 3 conductors each. Hot, neutral and ground.

A single 50 amp 125/250 volt cable has 4 conductors. that means the people using it for 2 125 v circuits have a single neutral therefore be careful of the length of the cable and the size.

 

[rsmith]

But they both only have one conductor for the neutral.

 

[Pete]

3 - 50a capacity prongs ground conducted thru the casing. If anything the 250v plug is a bad design. IMHO it should have had 4 dedicated prongs for the 6/4 cable. I don't have a IsoXformer and the ground is tied to the same buss bar as the neutral.

I am going to assume you are describing the main electric panel in the boat, and if that is the case Hatteras wired the panel incorrectly. The neutral and the ground wire are ONLY tied together at the source of power. Under no circumstances should the main panel or any panel on a boat tie the white and green together. The proper polarization of AC for shore power is back at the source on land using a grounding rod. On a generator the polarization is at the generator. For an inverter output the polarization is at the inverter, although Canada codes disagree, I believe Canada leaves the neutral and ground separated on an inverter. And on an isolation transformer boat the polarization is at the secondary of the transformer for shore power.

Would take a book to get into all the undesirable circumstances of other wiring, but the main point is never, never, allow any current or voltage potential on the green wire except in a fault situation.

BTW, on late 60's and perhaps early 70's boats, the DC electric panel has a rotary selection switch that allows house DC to be connected to either the port or starboard battery bank. Also, there is a "BOTH" position on this switch that should never be used. This effectively connects a jumper wire across both battery banks and could set the boat on fire under certain circumstances and at least quickly melt insulation off wires in others.

Pete

 

[Boatsb]

But they both only have one conductor for the neutral.

Each 125v has a neutral. The 250 has only one. 2 125v have 2 neutrals.

 

[Pete]

Remember, we are discussing AC power not DC. The line coming down the dock is 240 volts (if you are lucky) center tapped with two 120 volt sides, but 180 degrees out of phase. This is a balanced neutral circuit, and the current that flows on the neutral is the differential of the currents flowing in the two 120 volt legs. Thus the worst case for the neutral in such a 50 amp service is full load on one side and zero load on the other side. This results in a 50 amp flow in the neutral. Load both sides to 50 amps and zero current flows in the neutral. It is the difference between winding sides that flows.

And if your boat is 240 volts, with a 240 volt isolation transformer, it uses both hot sides, by definition presents a balanced load to both legs of the 240 volt supply, thus there will never be an imbalance between hot legs and no need for a neutral to conduct the imbalance. Thus no neutral wire is required in this case.

Pete

 

[Boatsb]

Remember, we are discussing AC power not DC. The line coming down the dock is 240 volts (if you are lucky) center tapped with two 120 volt sides, but 180 degrees out of phase. This is a balanced neutral circuit, and the current that flows on the neutral is the differential of the currents flowing in the two 120 volt legs. Thus the worst case for the neutral in such a 50 amp service is full load on one side and zero load on the other side. This results in a 50 amp flow in the neutral. Load both sides to 50 amps and zero current flows in the neutral. It is the difference between winding sides that flows.

And if your boat is 240 volts, with a 240 volt isolation transformer, it uses both hot sides, by definition presents a balanced load to both legs of the 240 volt supply, thus there will never be an imbalance between hot legs and no need for a neutral to conduct the imbalance. Thus no neutral wire is required in this case.

Pete

I do not believe the neutral zeros out with 2 50 amp loads at 125 volts each. I see too many neutrals burned on the shore cords for that to be true.

 

[q240z]

Marinco cords would be my guess. lol

 

[Pete]

I do not believe the neutral zeros out with 2 50 amp loads at 125 volts each. I see too many neutrals burned on the shore cords for that to be true.

Scott,

We are all entitled to our personal beliefs, so I have no problem with whatever you chose to believe. My posting was intended to provide a fact based view of how center tap 240 volt AC behaves. If you believe that factually what I wrote is incorrect, please provide some FACTS to support your position.

I can not help with why you see many examples of white wire contact problems.

Pete