Wiring dual 240V 50 amp shore power, USA

[skipmac]

Son in law has a new boat with electric everything. Currently wired for a single 50 amp 240V shore power cord which isn't enough when he's running several heavy loads at the same time.

He wants to use two cords plugged into two different outlets on the dock and connect feed from the two cords at his AC panel to get 100 amp service on one circuit.

I am recommending that would not be a safe plan and suggested the best option would be to have separate circuits and breakers for each cord. As I am a little vague on some of the specifics on 240V thought I should as for opinions

US split phase 240 uses four wires: safety ground, Neutral, 120V A and 120V B. A or B to Neutral gives you 120V A to B gives you 240V.

Question: Are all 240V plugs supposed to be wired so 120A and 120B are always on the same connection on the plugs and receptacles or, since it doesn't matter functionally is it random?

However, even if all plugs are supposed to be wired the same for the two hot legs I think it would be dangerous to assume all marina power outlets are wired correctly. If the two 120V legs are wired to opposite terminals on two adjacent outlets on a dock and you combined them with two cords or a Y I do believe you would get lots of sparks.

Suggestions?

[rslifkin]

Definitely don't combine the 2 cords to try for 100 amp service.

Basically, there are a few options: If the boat has any 240V loads, you need 2 panels, each with the ability to run a circuit from either 120 leg A or B, or 240 across both legs.

If there are no 240V loads on the boat, then you just have 4x 120V panels effectively.

Personally, I'd wire it with a selector so that you can use 1 cord and run everything, or select the second panel to its own inlet when more power is needed and then use both cords.

[skipmac]

Originally Posted by rslifkin

Definitely don't combine the 2 cords to try for 100 amp service.

Basically, there are a few options: If the boat has any 240V loads, you need 2 panels, each with the ability to run a circuit from either 120 leg A or B, or 240 across both legs.

If there are no 240V loads on the boat, then you just have 4x 120V panels effectively.

Personally, I'd wire it with a selector so that you can use 1 cord and run everything, or select the second panel to its own inlet when more power is needed and then use both cords.

Thanks. This was my recommendation as well but he insisted that sister ships were wired with a single panel with single circuit fed by two shore power cords. I was skeptical and believe he didn't understand exactly how the panels are wired.

[skipmac]

By the way, there are a few 240V loads including the stove/oven, clothes dryer, air conditioning and hot water.

[stormalong]

It is easy to make a simple tester to see if the wiring is in phase or 180 degrees out of phase with an incandescent light bulb. That test would have to be performed every time he visits a new slip and he would have to make wiring adjustments to correct errors.

When I added a 16.000 BTU air conditioner to a 30 amp service boat I added a completely separate 30 amp inlet for it. Splitting the load would be the simplest way to to go.

That is a lot of power. How big it the boat?

[Quadrille in JB]

Watching
I’m looking at the same problem on a client’s boat

[a64pilot]

Safest / best way to do it is two cords, and two boxes. From an electrical standpoint it would be the same as two boats. I doubt current box can hold 100 amps. I briefly looked into converting my boat from single 30 to single 50, which from an initial blush shouldn’t have been that hard, but ran into the stumbling block that existing panel can’t hold 50 amps, that would have meant a sub panel, and dual 30 amp cords and I didn’t want it that bad, so we just power manage, in the morning I turn off the big AC and heat water, and we turn off the AC to run the toaster, or vacuum too, I pull on average about 20 amps and consider 25 amps to be the max you can safely continuously pull from a 30 amp cord.
Not going to be cheap to do though

[Thumbs Up]

Originally Posted by skipmac

Thanks. This was my recommendation as well but he insisted that sister ships were wired with a single panel with single circuit fed by two shore power cords. I was skeptical and believe he didn't understand exactly how the panels are wired.

Sounds kind of like a reverse y adaptor (1 50 amp 120/240v from two 30amp 120v). Electrically speaking, it will work if you get the L1-L2 polarities correct. There is no way that I can think of to do it legally though. Reverse y adaptors (the legal ones) have special circuitry inside.

[Quadrille in JB]

I hope that this isn't hijacking the thread but I'm facing the same problem.
I so some consulting work for a marina where one of the slips is occupied by a modern 85' aluminum yacht. The pedestal has 2 - 50 amp outlets which are fed by 3- 350 mcm conductors plus a 2/0 ground. No other boat is on that circuit. He is feeding both of these into a 100A cord via a Y-cable.
The owner claims that in the past month, since he's had this new to him boat that he's fried a $3,000 air conditioning control panel, a transformer in his stove , and several other items. He said that his voltage monitor is not working properly as it's reading all over the place.
Last week, when I heard about his problem, I removed the top of the pedestal and read 240VAC on both of the outlets while he was drawing ~15 amps on each circuit. He was in a hurry to leave so I wasn't able to get on the boat.
Now he claims that he had a master "master" (his words) electrician come out and he measured 260 vac on the boat.
I'm going out to check the voltage tomorrow. He probably has an isolation transformer which might be boosting the voltage slightly. Still, 260 vac is within the +- 10% offset that is usually allowed.
I'm asking for any help to diagnose this problem as the guy's starting to get pretty upset.
thanks in advance,
Bill

[a64pilot]

Wow, I had to google 100 amp shore power cord, because I didn’t believe there was such a thing, price was $7,000 for a cord?
At what point do you wire direct?

[s/v Jedi]

It’s okay and I’m pretty sure within code as long as the panel aboard is 100A rated or upgraded to 100A.

Many boats use the 2x50A to 100A Y adapter. There is no need for special electronics because both L1 and L2 are present in each of the two legs.

If 2x 50A inlet is used then each cable is a standard 50A cable. These cables are protected by the 50A breakers in the pedestal. When some idiot reversed L1 and L2 on one of the outlets then the breaker will pop and someone will have to correct the wiring... this is to be expected with bad mistakes like that

On the in-board end of the inlets need to be separate 50A breakers after which conductors can be paralleled. From there on everything needs to be 100A rated.

[Thumbs Up]

2x50A to 100A Y adapters do have special electronics. https://www.imarineusa.com/HubbellMarineYQ100PLUS.aspx
L1 and L2 are randomly assigned so you would have a 50/50 chance of a dead short when you plugged into that second outlet.
If you had two onboard 50 amp inlets, one would have hot male prongs when only using one. If one of the 50 amp shore plugs came loose, it would also have hot male prongs. You can't rely on the pedestal breaker to test the polarity, a 50 amp "spark" can ruin a plug and burn your hands and flashburn your eyes. You would need "special electronics".

[Scott Berg]

Originally Posted by a64pilot

Wow, I had to google 100 amp shore power cord, because I didn’t believe there was such a thing, price was $7,000 for a cord?
At what point do you wire direct?

100amp cords are the norm for boats over 80'. We often have visitors at our docks using two 100a cords (480v three phase); newer big boats use a lot of power.

Hubbell makes a "smart reverse Y" that will combine two (2) 50amp outlets into one 100a outlet. However, they won't work on newer ELCI equipped breakers (required on docks deployed after 2014).

This is the realm of professional marine electricians; I really don't think it's something a boat owner should attempt.

And, yes, I do this for a living, not asking to do yours....

[Quadrille in JB]

Thanks for all of the good information. Do you think a reading of 260 V AC at the boat panel is out of limits.
I measured this using a good fluke meter that I had Factory calibrated recently.
What would cause the voltage on the boat to read 260 vac when the pedestal reads 240 vac?

[Thumbs Up]

What would cause the voltage on the boat to read 240 vac when the pedestal reads 240 vac?????

try the edit feature (you can modify an existing post)