source: EDN article
John Dunn -November 17, 2015
There are all sorts of safety standards you must follow in designing this or that product and of course, you and your company will follow them. At your lab bench however, inadvertent safety hazards may arise with test fixtures that you or an assistant may whip up due to some safety measures either not being taken by dint of careless oversight or, as I once saw, by dint of sheer stupidity with “safety standards” being foolishly tossed out the proverbial window.
As an example, consider the lowly fuseholder which I have now and then seen wired up this way:
The danger with this arrangement is that the AC line voltage can appear at the fuse contact that comes real close to your finger tips when you are inserting or replacing a fuse. This is dangerous. There is a very real shock hazard.
The stupidity aspect of this whole thing came up one time when somebody I was working with insisted that the first sketch above was the only proper way to wire a fuseholder. The fool I was dealing with at the time hasn’t, so far as I know, been killed. At least not yet.
“The surprising thing about young fools is how many survive to become old fools.” – Doug Larson (English middle-distance runner who won gold medals at the 1924 Olympic Games in Paris, 1902-1981. Source: thinkexist.com )
In any case, the proper way to wire the fuseholder is as follows:
With the AC line connection at the tip as shown here, you are not likely to put yourself in accidental contact with that line, especially when inserting a new and good fuse into the fuseholder.