David Mertz

David Mertz David Mertz, electrical safety engineer, wrote this column. Recently, a PPD employee discovered a 9-volt battery (see picture below) whose terminal polarities were improperly marked. For this type of battery, the smaller of the two posts is the positive terminal. But as you can see in the picture, the larger terminal is marked as the positive one. The employee reported that the battery was obtained from the Fermilab stockroom and had a unique production code marked on the…