MacBook Pro electricity leak in housing when not grounded

[poiihy]

When I use the small foldable plug (which does not have a ground), there is some electricity leak into the alumimunium casing. It is small but noticeable when rubbing the flat part of fingers on the case. When I use the extension cable for the power adapter (which has a ground) I do not feel this buzz. I also do not feel it when not plugged into the wall. What is it? Is it normal? Should I use the grounded cable?

 

[Intell]

That is normal for nearly every ungrounded portable Mac that has a metal casing. Even the desktop machines will do that on occasion when they are not properly grounded.

 

[poiihy]

That is normal for nearly every ungrounded portable Mac that has a metal casing. Even the desktop machines will do that on occasion when they are not properly grounded.

What causes it?

 

[sjinsjca]

Does the behavior change if you reverse the plug?

 

[poiihy]

Does the behavior change if you reverse the plug?

No

 

[Intell]

It's the 50/60 hertz hum of the AC power. Most electrical devices have it, but Macs display it most because of their bare metal cases and how they are grounded.