50 Amp split to 30 amp legs

[zboss]

I need a gut check on something because I think the answer is obvious but I'd rather ask...

We have two 30 amps inlets on our boat. When in many marinas, we need to use a 50 amp splitter. I assume that when we use that splitter one hot goes to one 30 amp and the other hot goes to the other 30 amp.

But how does this actually translate to power delivery? Is the power evenly distributed 25/25 or is it more like a demand where the total of both legs can't be more than 50 amps?

[rslifkin]

If it's using a 50A 125/250V connection and splitting that to 2x 30A 125V, then it's taking each hot and feeding it to one of the output. You can draw 30A on each output with no issues. The 50A 125/250 outlet can supply 50A on each of the 125V legs or 50A at 240V (using both legs and not the neutral).

However, there's a huge safety issue IMO with those adapters. They don't have built in breakers, so you're leaving everything between the adapter and the 30A inlet breakers on the boat unprotected (as the pedestal breakers are 50A and can't protect the 30A shore cords or boat inlets).

So in my mind, the correct thing to do is to DIY an adapter with a waterproof junction box and the appropriate connectors / cord pieces. Take the 50A in, then feed it through a 30A double pole breaker in the box before the 30A outlets. That way everything is properly protected. I'm honestly surprised nobody makes an adapter like this (that I've seen) with overcurrent protection built in.

[Shrew]

Originally Posted by zboss

I need a gut check on something because I think the answer is obvious but I'd rather ask...

We have two 30 amps inlets on our boat. When in many marinas, we need to use a 50 amp splitter. I assume that when we use that splitter one hot goes to one 30 amp and the other hot goes to the other 30 amp.

But how does this actually translate to power delivery? Is the power evenly distributed 25/25 or is it more like a demand where the total of both legs can't be more than 50 amps?

The total of both legs can't be more than 50 amps.

[a64pilot]

Originally Posted by Shrew

The total of both legs can't be more than 50 amps.

I believe if not mistaken that the breaker is a dual breaker that supplies 50 amps at 220V, so that would be twice that amperage at half the voltage, which would mean 50 amps on each 110V leg.

However I don’t think it’s a safety issue, reason is that the boat is protected by its main breakers, so you don’t need breakers at the pedestal.
A house for example doesn’t really have any circuit protection before the main breaker inside of the house.
The breakers on the pedestal are there to protect the Marina’s wiring, not your boat.

[rslifkin]

Originally Posted by a64pilot

However I don’t think it’s a safety issue, reason is that the boat is protected by its main breakers, so you don’t need breakers at the pedestal.
A house for example doesn’t really have any circuit protection before the main breaker inside of the house.
The breakers on the pedestal are there to protect the Marina’s wiring, not your boat.

In my mind, the concern is mostly around the inlets themselves on the boat and whatever wire (however short it may be) between the inlet and the boat breakers. The shore power cords being unprotected is also a concern, but a smaller one (as the risk to the boat is smaller).

[a64pilot]

Originally Posted by rslifkin

In my mind, the concern is mostly around the inlets themselves on the boat and whatever wire (however short it may be) between the inlet and the boat breakers. The shore power cords being unprotected is also a concern, but a smaller one (as the risk to the boat is smaller).

A breaker won’t protect you from a bad plug for example, a breaker will only protect you if you draw in excess of the breakers rating.

As the boat being a 30 amp boat will have a 30 amp main breaker, the only way you can pull more than 30 amps is to have a short or a sneak circuit between the boats breaker and the pedestal breaker.

But unfortunately if you have loose connection in one of those junk plugs, it can still start a fire and never blow any breaker, because your not drawing in excess of the breakers rating.

I still think for example when I go to a Marina that only has 50 amp 220 service and I plug in my splitter and plug my boat into one leg of that splitter, that I am connected to a 50 amp breaker, not a 25 amp one, 50 amp 220V service delivers 50 amps down each leg I believe

[rslifkin]

Originally Posted by a64pilot

A breaker won’t protect you from a bad plug for example, a breaker will only protect you if you draw in excess of the breakers rating.

As the boat being a 30 amp boat will have a 30 amp main breaker, the only way you can pull more than 30 amps is to have a short or a sneak circuit between the boats breaker and the pedestal breaker.

But unfortunately if you have loose connection in one of those junk plugs, it can still start a fire and never blow any breaker, because your not drawing in excess of the breakers rating.

Correct, a poor connection at the inlet doesn't require high current to cause a meltdown. But a short from a damaged shore power cord, or in the inlet or wiring right after it could draw more than 30 amps and cause an issue. And that's the case a breaker protects against.

[zboss]

Originally Posted by a64pilot

I believe if not mistaken that the breaker is a dual breaker that supplies 50 amps at 220V, so that would be twice that amperage at half the voltage, which would mean 50 amps on each 110V leg.

This is the correct answer. I had a qualified marine electrician come by today and he explained to me that a pedestal delivers 50A @ 240 volts so when split you get two 50 A legs @ 120 volts, so a 50A to 30A splitter will each get 30 Amps per leg.

[boat driver]

Originally Posted by zboss

This is the correct answer. I had a qualified marine electrician come by today and he explained to me that a pedestal delivers 50A @ 240 volts so when split you get two 50 A legs @ 120 volts, so a 50A to 30A splitter will each get 30 Amps per leg.

I think you have a typo- 50 amps will come down each leg, thereby giving the potential of a 50 amp draw on the 30 amp cord.

[boat driver]

Originally Posted by zboss

I need a gut check on something because I think the answer is obvious but I'd rather ask...

We have two 30 amps inlets on our boat. When in many marinas, we need to use a 50 amp splitter. I assume that when we use that splitter one hot goes to one 30 amp and the other hot goes to the other 30 amp.

But how does this actually translate to power delivery? Is the power evenly distributed 25/25 or is it more like a demand where the total of both legs can't be more than 50 amps?

Besides the previous explanation of the splitter-technically you are supplying 100 amps @110 and 50@220v. I want to also bring to attention what may be bothering your gut-
how is your incoming breaker set up?
If you are simply using two separate 110v lines- and breaker panels- then you are fine. But if your 30 amp breakers are being combined internally for a 220 service, be sure the panels are balanced. The issue is often the second line is simply for a stove or 220 service and carries less current, and when loaded up one line becomes overheated. This leads to burning plugs and cords

[Frankly]

There are several different configurations of splitter /adaptors. The reason a single 50A to 2- 30A is considered safe is that the two 30 amp sides are protected by the main breakers on the yacht (by definition/ design the loads are all downstream of the mains). A rare short circuit in the adaptor (think thousands of amps) will be cleared just as fast by a 50 amp pedestal breaker as a 30 amp.

Less hazardous than stepping from the dock to the yacht.


Frankly

[waterman46]

Don't be confused by the name of the adapter "50A to 30A". That's only the name of the connectors it uses, not the current capability of the pedestal circuit you connect to.

A separate breaker box with 30A breaker on each 30A cord, as suggested by rslifkin in post #2, would protect against a high leakage or short right at the boat's inlet socket, but only in the range of current between 30A and 50A. Above 50A the pedestal breaker would trip.



Leakage at the boat's inlet has caused fires in the past, but I don't think there is much difference whether the circuit is protected at 30A vs 50A, for that kind of fault. Say you have only 10A leakage across the boat's connector pins, then at 120V thats more than enough power to heat the surrounding area to flammable temperature.

[BruceS]

I often wonder why it's so hard to include "USA" in some of these electrical posts?
Nothing like "2 legs" in my marina............... or even 120V ....

[S/V Adeline]

Originally Posted by BruceS

I often wonder why it's so hard to include "USA" in some of these electrical posts?
Nothing like "2 legs" in my marina............... or even 120V ....

Ok you had me on the net searching for 230v 50amp sized plugs, can only find 220/240. Does a 50amp plug down under pull all the amperage off a single 230v leg?

[BruceS]

Only place there are "2 legs" down under is mostly in factories or other bigger users.
Work it backwards in watts?
110V X 50A = 5500w
240v X 25A = 6000w
Our marina only has 15A receptacles but in reality they have 32A breakers. Many big houseboats have normal house sized kitchens plus a couple of reverse cycle air conditioners.
I'm not an electrician so I'm not going to be going into more detail other than what I see...