Shorepower -> Standard household outlet

[Sethic]

I'm an engineer - I should know this. School was a long time ago, ok?

How is it that we can use an adapter such as the one sold at this fine site to go from a 30A outlet to a 15A standard, household outlet?

Let's see if I can answer my own question from Ohm's Law: V=IR. Assuming V is constant in this case, then if I is cut in half then we must be doubling R (V1=V2 then I1*R1=I2*R2 then 30*R1 = 15*R2 so R2=2*R1). Ok I think I have my answer. Logic hold up? Somebody let me know if I'm way off here, please.

Guess I'll be buying one of these here or elsewhere. It'd be a huge boon to be able to use corded handtools at the dock, as I don't have a trailer yet. Below is what I'm referring to:

http://shop.hunterowners.com/detail.htm?group=1294&cat=3316

 

[rbijas]

Yeah that will work. made my own single outlet model years ago from parts from home depot.

 

[isaksp00]

Wonder if the yellow box is "just" a current limiting circuit breaker? You obviously need the mechanical connector conversions.

 

[Sethic]

Guess I'm a little spooked by the looks of a shorepower plug. Looks a little too much like a 240V household plug! But that's why I ask questions... Thanks for the confirmation.

I might just go with a cheaper adapter and use a cheaper, standard current limiting circuit breaker on an extension cord.

 

[steve stark]

Sethic...
I think maybe you are over-thinking the ohm's law part.... assuming the voltage is always 120v in this system, the current supplied will be a function of the resistance of the load, not the resistance of the wiring, adapters, etc, which is very low. The thing to worry about in converting to another receptacle is safety - particularly concerning the downstream wiring. If your load (drill, blender, etc.) shorts out or draws to much current, the breaker on the 30 amp source will trip at 30 amps. If you use an adapter to a conventional household receptacle, and then run an extension cord to your load, you run the risk of fire in the extension wiring because it is typically number 14 wire, rated to carry 15 amps, not the 30 amps that the source will supply should the load demand it. The safe wiring for 30 amps of current is 10 gauge, not commonly available in an extension cord. In the adapter above, I assume there is a 15 amp breaker in the unit, so that high loads will trip that breaker and thus protect the wiring downstream.

 

[Sethic]

Excellent. Thanks for the response. So I need to ensure the breaker is matched to the lowest current rating of the cord I'll be using. Probably will get a conventional 15A cord from HD to avoid the "marine screw" effect, with an in-line breaker rated to that cord.

Is 30A typical for twistlock shore power receptacles? I've seen 50A adapters online. I'll be sure to check what's at my dock before I hook up - just want to buy the right adapter.

 

[geehaw]

Just had to add that because a extension cord is not rated to carry 30amps it's not nessacarily a fire hazard. Breakers in house are rated at 20 amps but that light you plug into a outlet it's cord is not rated for 20 amps. Does it pose afire risk when it's on all night? No. Will that cord handle 20 amps if that light shorts out? Yes. Ifyou cut that cord off and put it on something that draws 19 amps then it becomes a fire hazard. Safety? 20 amps will kill you just as fast as 30 amps. But a 15 amp breaker may protect from permanate harm what ever may be conected to it.

 

[C Jones]

I believe the yellow box is a GFI, not a breaker

 

[LarryH]

I have that smae adapter

Mine does tend to trip often..i am not sue if its the adapter or a short on board.