Earth for Oscilloscope

I'm a little rusty in this area but I'll try to answer.. You'll have to check... Earth ground exists to prevent shock. Ideally, no current should be flowing through to earth ground unless there's a fault. All metal boxes are at the same potential. For some equipment, removing the ground connection can allow the chassis to be hot either by an internal fault or by an external source.. Could be 100's of volts. Touch this and let's say a earthed pipe and zap! I know that somewhere down the electrical line the neutral and earth ground get connected. About the measurement performance without an earthed scope.... I'd guess none.but don't know for sure.. D from BC

On a sunny day (7 Mar 2007 21:52:54 -0800) it happened "Myauk" wrote in :

It all depends, I had the scope earth removed for a long time. The company moved to a different building one day, and I got my scope back in a box with its leads I thought. Installed it, connected lead. Big boss came in, asked me to measure something for him that had mains power. I connected scope earth to it and all computers on that floor crashed -no power- big bang and spark too. LOL Somebody swapped the mains leads.

Twenty ears before that I did the same thing on something like a 400V 100A thyristor controlled rectifier, came back from holiday, connected scope to thyristor gate, switched on power, BANG. When I was on holiday somebody re-connected scope ground.

So, the official lesson is: Use scope ground, do a differential measurement. (ch1 ch2 substract). It also protects you and others from getting electrocuted.

The not so official lesson is that I do not always follow the official concensus.

A lesson learned as a student lab assistant at University: Connected probe earth lead to mains hot lead in a circuit (was trying to measure mains voltage, or such) and discovered the meaning of "common earth" of scope chassis (input to output). Bang. Smoke. Suddenly an audience. Grins, resetting of breakers. All was well, thankfully.

An important lesson, not too expensive, except maybe for my pride... FBt

Is the clip still usable? Usually when I do that, it practically destroys the clip.

Cheers! Rich

If I recall, black, spot weld on the teeth where the clip touched, but still usable. But it was a long time ago. Scope kept working.

Tek 365, the Volkswagen of scopes. Not pretty, but did everything you needed it to do and well. Many are lasting well into the 21st century. Probably should make a monument to this scope in the Electronics Hall of Fame.

On a sunny day (Thu, 15 Mar 2007 19:58:23 GMT) it happened Rich Grise wrote in :

In that case of the thyristor fluid metal was spraying around... I was not hit. For measuring high voltages a few millivolt can safely be ignored, and I simply use a separate testlead for gound, not the probe crocodile, in fact I remove that, as it may hang against something.