Yes, that´s the logic, an isolator within an electric field prevents a possible flow, and since Enel is literally lightning, he can´t exist as such when in contact with an isolator, hence becomes tangible, which is fine for manga. In real world, there is no perfect isolator, apply enough voltage to it, any material will conduct to a certain amount, and if you look at the numbers of Enel´s attack, well...
Having said that, the gold attack was still consistent since Luffy´s hand made the first contact, making Enel a normal human hit by a golden ball.