Handy safety tip

Thread Starter


Joined Nov 4, 2008
How to Determine Correct Polarity of Non-polarized Electrical Plugs

Many older electronic devices lacked a polarized AC power plug, presenting a potential safety issue. The following procedure should be followed whenever installing an undocumented unit of test equipment, particularly of older vintage.

Step 1: Locate a folding metal chair

Step 2: Obtain an automotive jumper cable (color is unimportant). Connect one end of jumper cable to leg of folding chair, being sure that the teeth of the clamp penetrate the paint on the chair. Connect the other end of the jumper cable to a reliable ground connection, such as an electrical conduit or cold water pipe.

Step 3: Plug unit in question into nearest electrical outlet

Step 4: Remove all clothing

Step 5: Sit in folding metal chair

Step 6: Place hand on chassis of device in question.

Step 7: Evaluate if you feel uncomfortable tingling sensation or pain.

Step 8: If you feel a strong tingling sensation, remove yourself from chair. Unplug device, and reverse plug. Repeat steps 5 through 7.

Step 9: Compare results of steps 7 and 8. The correct orientation of the plug is the one which produces the least unpleasant sensation.