GB42C at a 30 amp dock?

Our new to us GB42C 1986 looks like it is wired for 50amp shore power since both forward and aft outlets are rated at 50amps.

Our dock only has 30amps which is just what it is. There isn’t another 30amp pedestal option so we can’t pigtail two 30amps into a 50amp supply.

When we arrived at this new dock, we noticed there was on board our new to us boat a 50amp (boatside) to 30amp (shoreside) single shore-power cable… no adapters… just 50 on one end and 30 on the other.

Well, not surprisingly in the winter we exceeded 30 amps (actually less would be the ABYC threshold), and I noticed the 30amp plug at the pedestal was burnt on one of the terminals last week.

I would have expected the pedestal breaker to have tripped, but it didn’t.

Possibly the sealed Marino plug was ‘strained’ in a previous life and ‘cooked’ because of a poor internal connection…. So my ire against the pedestal breaker may be misplaced.

We will encounter other cases where only 30amps is available, so has anyone heard of an in-line marine grade 30amp breaker box to trip if the boat draws more than the limit?

What do other Grand Banks owners do when facing this scenario?

Sounds like your 50 amps is 120 volts, not the 240 volts you would normally see with 50 amp service. You rarely, if ever see marinas offering 120/50 service. It is either 120/30 or 240/50.
I used to have a boat that came from the factory wired for 120/50. Apparently, some years ago, back in the eighties, that service could be found.
Like you, the previous owner of our boat had power cords made up with 50 amp female end and 30 amp male end. With energy management, we managed just fine on 30 amp service. We had air conditioning on one cord and everything else on the second cord. With 3 air conditioning units pulling 29 amps, it was close to throwing breakers, but seemed to work ok.

BTW, my boat was a 1988, so both built around the same time with the same electrical service. It’s not a GB issue, but rather an issue with boats built back in the 80’s.

I might add, stick with what you have as most likely you will never see 120 volt 50 amp service anywhere. If your cords are cooked, replace with the same 30/50. You might want to have the pedestal plug replaced as well as the pedestal breaker. Sounds like you had a bad breaker from the get go.

Also if you pull close to 30 amps then you should look at a Smart Plug cordset. They have much more contact area than an L5-30 plu.

First, you should have a master circuit breaker on the boat. What is it’s amp rating?

Second, you can change the master circuit breaker to 30 amps to solve your problem.

Third, your power cord could easily burn up with out ever exceeding 30 amps. A poor connection between your male end and the docks female end could result in extreme heat from as little as 15 amps. It is the heat that does the damage not the amps. Although more amps will generate more heat.

I'm curious how you split the 30A to a 50. Just make two legs off the one hot 30?

Ha - you guys nailed it. Looking at the electrical diagram it shows input is 50amp at 125v. The boat breaker is 50amp.

There is no split other than there is a fore/aft input plug selector. Once selected, power feeds to the central load distribution on the AC panel.

Since there aren’t too many 50amp / 125v docks out there, is it a consideration to look for a 240v to 125v step down transformer?

You can use one of the 50A 120/240 to dual 50A 120 splitters and just plug in 1 leg.

Excellent.. that’s a whole lot cheaper than buying a new gizmo. We have a Y splitter like that on board.

Appreciate all the contributions… learnt something fundamental about our boat today.

Leaves one key question; where the 30 amp dock breaker is flaky, and with the older marinas this is quite possible, has anyone seen a 30amp breaker box unit to be put in-line to save the power cable and reduce the risk of fire?

What I would do is replace the boat socket from 50a 125v to 50a 125/250v. Cut the end off your 50a cord (do not use a 30a cord) and add a 50a 125/250v socket on both ends of your power cord. Your power cord will be black white green wire. The sockets will have hook ups for 4 wire but you won’t use the red.

Now you can plug into a 50a 125/250v socket all will work fine.

Next buy a 30a 125v to 50a 125/250v adapter. You will need to manage power when using the adapter or you will trip the dock breaker.

A two 30a to one 50a 125/25v Y adapter won’t be of any use with this set up.

We are on our 4th Grand Banks. I was told by our long-time GB broker that almost all older GB's were made with 50A 120 volt shore power inlets. One boat still had the 50A inlets but came with a bin full of 30 amp cords and a short 30A male x 50A female pigtail. Other boats had already been converted to 30A inlets. I am only aware of one dock in the PNW that has a 50A 120 volt service although there are no doubt more out there, but definitely uncommon. The current boat came with a newer 30A inlet on the bow and the factory 50A inlet at the stern. I changed them both out for 30A SmartPlug receptacles. We don't have AC and really have no need for 50A service, but YMMV. Good luck!
Regards,
Scott

Thanks Scott, seems like good advice.

Curious to know which Marina around the PNW still runs 50amp at 125v?

The one spot that I am aware of is the hadicapped-accesible guest dock (aka guest dock 2) at the Port of Everett marina, near Lombardi's restaraunt. Not the whole marina. That's the only one I can remember!

tiltrider1 said:

What I would do is replace the boat socket from 50a 125v to 50a 125/250v. Cut the end off your 50a cord (do not use a 30a cord) and add a 50a 125/250v socket on both ends of your power cord. Your power cord will be black white green wire. The sockets will have hook ups for 4 wire but you won’t use the red.

Now you can plug into a 50a 125/250v socket all will work fine.

Click to expand...

Seconded, this is the setup I use at my home dock. I use the 240v 50 amp smartplug on the boat end. In the future, this also lets you add a second 120v leg or 240v service to the boat, however that is a much bigger and more complex change. Having 50 amps versus 30 makes a big difference for me and the connectors are much more robust, I would never go back to 30 amp.

In addition, I also have a standard 30 amp cord with the boat end cut off an replaced with the 240v 50 amp smartplug to have a lighter cord to drag around at transient docks with 30 amp service. It isn't ideal relying on the 30 amp dock breaker with the boat's breaker at 50 amps, but is still better than a lot of options.

If you never care about 50 amp service, you could switch out to the 120v 30 amp standard setup and change out the main breaker on the boat to 30 amps, however on my boat that same breaker is used running off the generator which can deliver >50 amps in my case so that is a non-starter.

You certainly could rig up an inline breaker but I'd want it permanently wired into the cord or boat, wouldn't want to add two more plug in connections in the middle. You could also rig up something on the boat using a couple of breakers and a source selector lockout (eg. https://www.bluesea.com/products/8032/Traditional_Metal_Panel_-_120V_AC_30A_Toggle_Source_Selector) but I'd probably consider that overkill.


If this is a long term dock you could consider having an electrician out to swap the breaker and dock side outlet for new ones (120v 30 amp), as both do wear out, especially the 120v 30 amp plugs.

Bongi said:

Ha - you guys nailed it. Looking at the electrical diagram it shows input is 50amp at 125v. The boat breaker is 50amp.

There is no split other than there is a fore/aft input plug selector. Once selected, power feeds to the central load distribution on the AC panel.

Since there aren’t too many 50amp / 125v docks out there, is it a consideration to look for a 240v to 125v step down transformer?

Click to expand...

Why not Change your master breaker to 30 amp and replace fore and aft inlets with Smart plug 30 amp ends, now you are 120V 30amp with great connectivity, totally support changing from Marinco to smart plug we did it 3 years ago, and have not had an issue since.

Cartouche said:

Why not Change your master breaker to 30 amp and replace fore and aft inlets with Smart plug 30 amp ends, now you are 120V 30amp with great connectivity, totally support changing from Marinco to smart plug we did it 3 years ago, and have not had an issue since.

Click to expand...

If his boat is designed for 50A/125V service, a 30A supply may not be enough to power all his systems simultaneously.

-Chris

If OP's GB is a 50A/125V boat...

Given a 50A/125V boat and a 50A/125V shorepower cordset... for the times when a 50A/250V service is available... I'd think this adapter would work easily enough:

https://marinco.com/en/p/P504-503/EEL-Pigtail-Adapter-50A-125-250V-Male

A 4-wire 50A/250V cordset is fairly heavy for schlepping around, heavier than necessary for a 125V boat... so the adapter would get around that issue.

There's also an adapter from 30A/125V to 50A/125V, and I suspect it only allows 30A to pass through... which I think assumes a 50A/125V cordset... but which might speak to OP's question about breakers:

https://marinco.com/en/p/P30-503/EEL-Pigtail-Adapter-30A-125V-Male-to

-Chris

ranger58sb said:

If his boat is designed for 50A/125V service, a 30A supply may not be enough to power all his systems simultaneously.

-Chris

Click to expand...

But his home base is a 30-Amp dock, which means he'll never have enough to support a 50-Amp system and will continue to have burnt ends and the attendant fire hazard. He must change to onboard breaker to 30 Amp or he's gambling every day.

rgano said:

But his home base is a 30-Amp dock, which means he'll never have enough to support a 50-Amp system and will continue to have burnt ends and the attendant fire hazard. He must change to onboard breaker to 30 Amp or he's gambling every day.

Click to expand...

This option was already offered. OP responded with he had access to 50a 125/250v. It was then recommended that he change the ends on his power cord to take advantage of 50a power. This solves his problem.

rgano said:

But his home base is a 30-Amp dock, which means he'll never have enough to support a 50-Amp system and will continue to have burnt ends and the attendant fire hazard. He must change to onboard breaker to 30 Amp or he's gambling every day.

Click to expand...

Absolutely wrong. If the dock pedestal is properly breakered at 30 amps then it's safe to plug in a 50 amp boat with an adapter and you won't be able to overload the 30 amp components.

rgano said:

But his home base is a 30-Amp dock, which means he'll never have enough to support a 50-Amp system and will continue to have burnt ends and the attendant fire hazard. He must change to onboard breaker to 30 Amp or he's gambling every day.

Click to expand...

Wouldn't the 30A breaker on the dock pedestal be enough protection?

And what if he travels to a transient dock somewhere that might make 50A available (via 250V-125V adapter)? Just live with insufficient power?

-Chris

Folks - this is the crux of the question I was wondering about.

It makes a case for an optional in-line breaker in the shore power cable.

Basically, dial it in as you need it.

Don’t know how you would protect the breaker from damage and waterproofing it. Shore power cords get thrown around and lay in water at times.

Bongi said:

When we arrived at this new dock, we noticed there was on board our new to us boat a 50amp (boatside) to 30amp (shoreside) single shore-power cable… no adapters… just 50 on one end and 30 on the other.

Click to expand...

You probably know this, but...

It finally occurs to me to mention I think that cable could have been made from a 30A/125V cordset (replacing the 30A connector at the boat end), or it could have been made from a 50A/125V cordset (replacing the 30A connector at the pedestal end).

I'd think starting with a standard 50A/125V cordset, in your case, would have been the better approach. Dunno how you'd be able to tell, though, without opening up the ends...

And were it me, I'd probably have just used an adapter; too much other stuff to fix, wouldn't have messed with remaking the cable itself...

-Chris

This is a tangential comment. Our boat is wired like the OP. I run the (two) AC units on a 30 amp cord with an adapter for the boat side 50 amp plug. Two years ago the salon Cruiseair AC control circuit board went into electronic meltdown because of loose wire connections inside the adapter plug. Elusive and expensive problem to troubleshoot and repair, as the adapter appeared to be OK upon visual inspection. The only clue was that it was very warm to the touch. I subsequently disassembled and reconnected the wires inside the pigtail adapter. (A swap to a 50 amp plug for the cord is on the do list). The meltdown on the circuit board was eventually repaired by a company in Philadelphia @ roughly $300...documented in an old thread. (Check for heat buildup around cord connections). Thanks again to the forum members who helped me troubleshoot that puzzle. FWIW.

By the way, I have a 50 amp cord (with appropriate adapter), which I avoid using because it's so dang heavy...

Rufus said:

By the way, I have a 50 amp cord (with appropriate adapter), which I avoid using because it's so dang heavy...

Click to expand...

Is it a 4-wire 50A/250V cord? Yep, heavy. Starting on our previous boat, the first 50A/250V boat we'd owned, we discovered the answer to our earlier "why would anybody want a Cablemaster?" question.

I'd think a 3-wire 50A/125V cord would weigh closer to a 30A...

-Chris

ranger58sb said:

Is it a 4-wire 50A/250V cord? Yep, heavy. Starting on our previous boat, the first 50A/250V boat we'd owned, we discovered the answer to our earlier "why would anybody want a Cablemaster?" question.

I'd think a 3-wire 50A/125V cord would weigh closer to a 30A...

-Chris

Click to expand...

Yes...50A/250V. Thanks for the tip.

ranger58sb said:

Is it a 4-wire 50A/250V cord? Yep, heavy. Starting on our previous boat, the first 50A/250V boat we'd owned, we discovered the answer to our earlier "why would anybody want a Cablemaster?" question.

I'd think a 3-wire 50A/125V cord would weigh closer to a 30A...

-Chris

Click to expand...

The 3 wire 50A cords are still heavy. Mine are about 35 lbs each (50 foot cords). The 4 wire should be about 45 lbs. Neither is great to man-handle, but the 3 wire cords with storage bags are at least tolerable. The 30A cords are absolute featherweights in comparison (under 15 lbs for a 50 footer).

Bongi, you might want to take a closer look at your boat's wiring diagram. First, 240 volt service is simply delivered on two 120 volt legs and a common plus ground. We have 50 amp service with a fuse for each 120 volt leg on our 1993 GB 49 CL. We do not have anything but 120 volt service on the vessel. She is fairly new to us so I haven't verified my observations against a wiring diagram yet, but the 120 volt service panel has two sides with a master breaker at the top of each side. My assumption has been that each leg is serving its own side of the panel. In practice, we can run perfectly well off of a 50 amp outlet or two thirty amp outlets with a combiner. We've been dealing with a weak breaker on the pedestal, so we know that if we lose a leg because of a weak breaker, we lose all the 120 breakers on one side of the panel (the side with the air conditioners and water heater), but I haven't paid attention to whether the other side remains hot or not. So, I am not certain that we could run off of a single 30 amp as you are able to do.

Thanks Chris, the wiring diagrams on our 42c point to what has been suggested. i.e. she is a single 120v line in that can handle up to 50A. This feeds the whole panel and it goes through a single 50A master breaker.

My shore power cable looks like it may be actually be a 30A cable, but with a 50A connector on the boat end with a 30A connector on the pedestal end.

Looking at the other cables supplied, we seem to be operating with mostly a 30A series of cables, which stands to reason if the 50A 120v pedestals are so rare here in Puget Sound.