Originally Posted by Jpernick
How are the 30 amp wires protected when the breaker is 50 amps?
I just can’t figure out the math.
They aren’t. The boat is protected by the 30 amp breakers in it, but the shorepower cable would require a draw of 50 amps in the 30 amp cable to trip the breaker.
But think about this for a minute, if you plug in a thin extension cord in your house and you have 20 amp breakers in your box, how is the thin extension cord protected?
Answer is it’s not unless it has its own breaker which I have never seen.
Your shore power
cord is nothing more than an extension cord, why does it need protecting?
On edit to further clarify, the boats CB prevents more than 30 amps being drawn by the shorepower cord by the boat. The only way the cord itself could draw power on its own is by an internal short and it’s not protected from an internal short, but that’s a very unlikely event.