Shore Power - 50/30 amp Question

Bacchus said:

I think you will find the BoatUS Seaworthy article supports exactly what Ski states... it's the hi resistance - no overloading - that causes heat and heat is the culprit in boat fires.

I would bet there are many instances of 30 A cords plugged into 30A pedestals that have overheated and burned inlet connections or worse caused boat fires - I don't believe this is limited to using "Y" adapters - while I don't have the data I don't believe adapters alone have contributed significantly to boat fires - anyone have real data to prove me wrong??

Still not convinced... take a look at RC's/ Compass marine article on boat shore power cords... RC is an independent "ABYC Certified Marine Electrical Systems Specialist". If you are really concerned about overheating shore power cords I think you would be installing one of the new SMART PLUGS - No I have no interest in Smart Plugs but I believe what he has done a great job explaining the +/- in an unbiased fashion.

Just my opinion!

Click to expand...

Has not Smartplug been debunked? A very active thread on this about two years ago.

Also, breakers at dock trip on time and voltage. A good test is to intentionally load the dock breaker above 30 amp and monitor voltage and time.

As often is the case, there is a fair amount of confusing several issues into one. Kevin summed it up best. There is a reason there is a breaker at the dock pedestal, and that it is sized a certain way. And why there should be an appropriately sized fuse or breaker right after any connection point leading to a smaller sized cable or lower ampacity circuit.

There are a variety of ways fires happen. The RC (who I am generally a big fan of) article discusses an all too common one, nicely and in depth. Though he is discussing why he loves Smart Plugs, and hates the old standard, his cautions about proper use of traditional cords and connectors is essential reading for any boater.

I just got a call from the marina owner (it isn't your typical shiny new big marina, it's just one long old wooden floating dock) and he said he would change the breaker so that it will trip at 30 amps. So I'll be all set with a plug adapter.

No real need .

Most boats with a 30A power cord are wired so if the total on board load goes over 30A a breaker on the boat will pop.

Your power cord is protected because your boat is limited in its load.

FF said:

Most boats with a 30A power cord are wired so if the total on board load goes over 30A a breaker on the boat will pop.

Your power cord is protected because your boat is limited in its load.

Click to expand...

This thread has kind of gone full circle. What FF is saying is true. Most boats have an onboard breaker and those that do not should because it is an electrical requirement.

NFPA 302
9.9.2* Overcurrent Protection Location. Conductors other
than cranking motor conductors shall be provided with overcurrent
protection at the source of power unless permitted by
9.9.2.1, 9.9.2.2, or 9.9.2.3.
9.9.2.1 Where not practical to locate overcurrent protection at
the source of power, conductors other than cranking motor conductors
shall be provided with overcurrent protection no more
than 7 in. (18 cm) from the point at which the conductor is connected
to the source of power measured along the conductor.
9.9.2.2 If the conductor is contained in a sheath or enclosure,
such as a junction box, control box, or enclosed panel,
throughout the required distance, and where not practical to
locate overcurrent protection at the source of power, conductors
other than cranking motor conductors shall be provided
with overcurrent protection no more than 40 in. (102 cm)
from the point at which the conductor is connected to the
source of power.

With an onboard breaker, the argument that the 50 amp shore breaker does not protect the 30 amp shore cable is almost mute. To make it more insignificant,.... look at the electrical standard. All 30 amp shore power cords using #10 wire with 140 degree F insulation is good for 40 amps. With 176 degree F insulation and #10 wires it is good for 50 amps. Outdoors in open air anybody that questions the ability of a 10 gauge 30 amp shore cable carrying up to 50 amps is blowing air in a paper bag.

NFPA 302
Table 10.13.6(a) Ampacities of Insulated Conductors
Temperature rating of insulation
AWG 140F 167F 176F 194F 221F
10 ...40A .. 40A.. 50A . 55A . 60A

Most popular 50A pedestal receptacle

I have a smallish boat (Rosborough 246) w/30A service (protected with a 30A breaker just after the input receptacle).

I had my first experience a month ago being assigned a transient slip that offed only a 50A receptacle. Fortunately that marina had a 50A>30A adapter that we could borrow with a deposit--I didn't notice the format of the 50A receptacle at the time.

Anticipating the time when a future marina either doesn't offer an adapter or has their stock already checked out, I'm looking to add one to our power cord collection. Which version of the 50A to 30A adapter should I be looking for to be most compatible with 50A pedestals (at moderate-to-short slips) these days--

50A 125/250V > 30A 125V or

50A 125V > 30A 125V?

Before I read this thread, I would have assumed the 50A 125V would be the most "popular", but a previous post mentioned that the 50A 125/250V receptacle is much more common. Is that true across the board regardless of slip length or could that maybe be skewed toward the longer slips?

--Mike

We usually see 50A/250V receptacles.

I've only ever noticed one 50A/125V receptacle in the general area, and it seemed to have been a special install for that particular boat's home slip in his marina.

-Chris

Yep, our boat is 50Amp/125V, and so are our shore cords. PO had his pedestal at his home dock set for 50A 125. First thing I purchased was a nice Adapter for 50A 125 to 50A 250. PO had an adapter for 50A 125 to 30A, that he left on the boat, so I think I should be in good shape for traveling the rivers, and then the loop.

It likely depends on what area you are in and age. Our State Park Marina in the NE was built w 50A 120V and that's what we needed and I have both 50A 120V to 30A 120V adapter and a 50A Y 2X 30A 120V splitter.
My guess is 240V more common in South where multi ACs more common.
Our marina is in the process of being rebuilt and will have 30A 120V and 50A 240V outlets.
I will likely sell st least one of the 120V adapters and replace it w a 240V one. Let me know if you decide on a 120V and interested in one of these.

Right re the air conditioners. So far I've been in four different marinas on MS and AL coasts and all have been 50A/250.

There are also a lot of 50amp and somewhere between 200V and 220V pedestals. Helps to have a step up transformer to preserve voltage sensitive equipment as well.

My boat is an odd ball with a 50A/120V connection. Fortunately, my slip is also a rare one with the same. I hardly ever see 50A/120v pedestals away from my home dock. It is always either 30A/120 or 50/240. I have a 50A/240 -> 2 x 30V/120 splitter that I use when I run into a situation where I only have a 50A/240 available, the rest of the time I use my 50A/120 to 30A/120 adapter.

I am 50a 125/250v. And I carry adapters to go to 50a 125v, 30a 125v and 15a 125v. Why get caught empty handed.

thanks for the replies!

Kudos to the folks that replied to my 50A pedestal "popularity" question. We're mostly cruising Florida and the Canadian portion of the Great Loop this season (65 mph in between, nice to have a boat with wheels!) so it looks like the 50A 125/250V > 30A 125V adapter is the way to go at least for now.