How do you get 30 amps from one 50?

[twistedtree]

I think you are quoting allowable based on certain factors versus pure ampacity of #10 which can be higher.

Sorta like cars can safely go faster than the speed limit, but different places have different speed limits. The car may be limited also by tires (likened to the insulation rating).

So allowed ampacity can be anything some organization allows, but the actual wire with the right insulation and operating conditions could safely handle double that allowed ampacity.

Right. I think it all comes down to how hot you are going to allow the wire to get, which if course is what happens as you run more current through it. The higher the insulation is rated, the hotter you can let it get. Now whether that's a good idea or not is another question. I think any of us would get pretty concerned over a wire operating anywhere near 105C.

 

[sdowney717]

Charlie is correct. The CABLE is rated at 105 deg, therefore the high current rating. Of course, the SYSTEM is only good for 30A, due in large part to the connectors at each end.
FEP insulated 10AWG is rated at 75Amps, btw.

Someone reading what he said might think they can pump 60 amps through their 30 amp shore cable, so that is irresponsible. And maybe 60 amps for unbundled solitary wire in air, while a shore cable is bundled and sheathed in a very thick vinyl or pvc cover. It is going to retain, not shed much heat.

WHO is going to cut the ends off their 30 amp shore cables so as to run 60 amps by connecting somehow to what connection point?? Why no one will, but they might not cut off the ends. And my real old Marinco shore cables, I really doubt the wire is rated at 105*c, unless that standard goes back to the 1970's.

105*c is over the boiling point of water. scalding, sizzling, steaming hot. I can't imagine the ends of the cables or the inlets not melting in that heat. Just imagine pouring water on it and the water exploding into steam. The whole idea of 60 amps for a 30 amp shore power cable is just dumb as can be. Any surveyor who saw that boiling hot cable would condemn the thing on the spot as grossly unsafe.

 

[psneeld]

Unbelievable...

The discussion started more about whether it was safe to run a full 30 amps through a #10, 30A shore power cable.

No one said try and pull a 60A through all day long. It is dumb and others here on TF aren't as dumb as you think we are. At least we didn't post AC wire needs to be bigger for a given amperage. (Post 19)

Plus, it's probably why y adaoter manufacturers are comfy with blaming circuit breaker or system design failures than their y splitting 2 50A legs through 2 30A cords.

I am comfortable with the manufactures norms, recommendations, internet research and practical experience IN THE MARINE TRADES ...

Things aren't grossly unsafe because someone on TF thinks so, industry standards and engineers might have the edge there. And why they rate the cord at 30 amps, even though 60 wouldn't cause the immediate end of the world.

 

[sdowney717]

Unbelievable...

The discussion started more about whether it was safe to run a full 30 amps through a #10, 30A shore power cable.

No one said try and pull a 60A through all day long. It is dumb and others here on TF aren't as dumb as you think we are. At least we didn't post AC wire needs to be bigger for a given amperage. (Post 19)

Plus, it's probably why y adaoter manufacturers are comfy with blaming circuit breaker or system design failures than their y splitting 2 50A legs through 2 30A cords.

I am comfortable with the manufactures norms, recommendations, internet research and practical experience IN THE MARINE TRADES ...

Things aren't grossly unsafe because someone on TF thinks so, industry standards and engineers might have the edge there. And why they rate the cord at 30 amps, even though 60 wouldn't cause the immediate end of the world.

Upgrading my wire from 10 to 8 gauge added in a lot of safety factor! I won't ever have any overheating, failing inlet shore cables, WHICH APPARENTLY some do have wire problems with their 10 gauge shore wires. I thought about using 40 amp breakers instead of 30, but what stopped me was the 30 amp rating on the yellow shore cable and any surveyor would instantly ding it as unsafe. I wont change my mind even if some internet forum poster says 60 is ok. Dumb also because the dock breaker is set to 30 amps. you do realize, it will trip the 30 amp breaker very quickly if for some reason 37 amps were to flow. Closer to slightly over 30, will also eventually trip after some minutes.

It was not dumb. It was cheap for me to do it. The OEM or PO, had used solid copper romex 10 gauge, it had been like that for about over 30 years without any problem, might have been OEM back in 1970. I simplified the runs, used to have inlets mid boat on both sides, now that was dumb, always tripping over wires, dirt tracks along wire runs, real long wires needed. I put just 2 shore inlets at the stern verus 4 mid boat, and wires run straight to the distribution panel on one side with twin 30 disconnects about 5 foot from inlets.

 

[psneeld]

You would not believe what I realize....

 

[sdowney717]

Want some 200*c 8 gauge tinned copper fine multi strand wire with silicone insulation? Get it from Amazon.
https://www.amazon.com/AWG-Gauge-Silicone-Wire-Available/dp/B076PTH72L

Link proves such a high heat wire is available and not too pricey.

With that silicone insulation, people will say you could run 120 amps through it! And boil water too and the wire would survive ok.

 

[diver dave]

Silicone insulation. [emoji15]
Poor cut thru resistance.

 

[psneeld]

I would research wire more but I am comfortable running a few amps through my brand new 50A 125/250V setup and almost completely rewired boat.

I love overkill too.... so I am adding 6 layers of glass to my hull this week.

 

[sdowney717]

Silicone insulation. [emoji15]
Poor cut thru resistance.

Yeah, well then needs to be in conduit if this is worrisome.
You can buy conduit such as liquid tight non metallic in gray from electric supply place. Or use something from H Depot.

 

[CharlieJ]

#25
What is irresponsible is your cherry picking posts to show how smart you are. I will reiterate from my second, explanatory post:

My post was simply pointing out that the conductors that make up the 30A/125V shore power cables are really not the weak links in this system. Rather particular attention has to be paid to the shore power inlet on the vessel and the cable ends.

And as a marine electrician that has replaced dozens of burned/failed shore power cord ends and vessel shore power inlets, I stand by the statement.

I thought about using 40 amp breakers instead of 30, but what stopped me was the 30 amp rating on the yellow shore cable and any surveyor would instantly ding it as unsafe.

As a "Guru" you do realize that the panelboard shore power circuit breaker does not protect your shore power cable as it is downstream of the shore power cable. And, since you have some knowledge of the NEC, you must also realize that the NEC has prohibitions against stressing a system greater than 80% of its rated capacity. With that knowledge, it seems that a 40A DPCB in the panelboard or in an ELCi would be perfectly acceptable if all of the downstream wiring, normally a short run from the load side of the DPCB to the line side of the panelboard's branch circuit breakers, was appropriately sized.

105*c is over the boiling point of water. scalding, sizzling, steaming hot. I can't imagine the ends of the cables or the inlets not melting in that heat

What are you talking about? As a "Guru" I am sure you know that the temperature rating of the insulation is that temperature that the insulation can survive and still be, well, insulating. Further, the insulation temperature rating is functionally related to the amount of current (not power as stated in #19) that is flowing through the conductor.

ABSOLUTELY NOT ON TOPIC, BUT:
And while we are on the subject of insulation; do you know that the conductors inside of a 15kVA 240VAC transformer on both the primary and the secondary side are on the order of AWG 16. How is that possible, you might ask. It is possible because the conductor insulation temperature rating is >200C. And 200C is really, really hot.

 

[twistedtree]

I guess I'm unclear on whether you are advocating use of #10, 105C wire in a shore power cord where it carries more than 30A? So, for example, would you advocate making a 50A shore cord using #10/3 105C cable? It's sounding like the answer is yes?

 

[CharlieJ]

#41
If that is directed to me, then no I am not. I am simply trying to make an apparently overly nuanced point that the conductors that make up the shore power cable are not the weak link in the shore power delivery system. Much more attention should be placed on the cable ends and their construction and installation and to the vessel's shore power inlet, especially the installation of the interior wiring to the inlet assembly.

 

[diver dave]

ABSOLUTELY NOT ON TOPIC, BUT:
And while we are on the subject of insulation; do you know that the conductors inside of a 15kVA 240VAC transformer on both the primary and the secondary side are on the order of AWG 16. How is that possible, you might ask. It is possible because the conductor insulation temperature rating is >200C. And 200C is really, really hot.

Totally on topic[emoji3]

I visited a very large transformer factory this year. They topped out at around 750kV
and about the same MW. Conductors insulated with kraft paper submerged in oil. [emoji847]

 

[sdowney717]

#41
If that is directed to me, then no I am not. I am simply trying to make an apparently overly nuanced point that the conductors that make up the shore power cable are not the weak link in the shore power delivery system. Much more attention should be placed on the cable ends and their construction and installation and to the vessel's shore power inlet, especially the installation of the interior wiring to the inlet assembly.

Of course the wires are well protected.
But they are a still major weak link as they can be easily physically damaged, as in a storm which has happened to me. My ONLY failures with shore power has been the yellow shore cable itself, not any other wires, breakers, inlets, plug ends, etc... Wires well protected inside the boat, at least mine are well protected can not be as easily damaged as a shore cord hanging off boat and docks and inlets flopping around with winds and tides year after year out in the weather.

 

[psneeld]

All the things that I have ever owned that have been damaged in storms work perfectly to spec for the normal duration of their lifespan....

 

[sdowney717]

All the things that I have ever owned that have been damaged in storms work perfectly to spec for the normal duration of their lifespan....

It was a good idea to go to 240 volt and get rid of twin 30 amp. I would like to do that also, but it would not benefit me, half of the marinas I have had boat at have had twin 30 amp or even a single 15 amp plug. Right now, my slip has only twin 30 amp outlets. Too bad all slips are not wired for the 240 vac power.

At my slip, the power is free, no charge, just the $120 per month slip fee, and so is the city water free, so not complaining, they don't want us running the AC if no one is at the boat, but if your there, its fine to run that. The marina is not a haul out place, but it is close to the house and is family run with about 60 slips. they are on the Chisman creek right off Poquoson river which is right at the lower Chesapeake bay. Yorktown is just north of us.
All the slips at end of dock are taken.

Some of the boats, I never see the owner, and it shows. This is a very quiet place except for summer when the ramp is very busy.
Here it is, my boat is off close to end of dock with the blue top.