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EEVblog #84

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well of the three cheap meter dave tested one actually blew apart and the other bulged and emited flames (for an instant), normally you would not encounter 4 Kv but it does show just what a difference lack of protection in cheap meters can make


--- Quote from: Simon on May 08, 2010, 07:51:48 pm ---
I don't know about Greece but in Italy, statisticly 4.5 people a day are killed at work.

--- End quote ---

We prefer to get killed in holidays and weekends with our cars , its more fun this way  ;D

About the flash unit , what this Australian guy had made , its a flash unit in a large scale,
and nothing more ..

Yes, I think the bottom line in CAT ratings is safety, not survivability of the device.

--- Quote from: alm on May 05, 2010, 07:19:17 pm ---One important parameter that is omitted from the above table is the source impedance, which determines how much current the source will be able to deliver, i.e. the size of the bang if something shorts/arcs. This is the important difference between CAT I and CAT IV. Compare touching the HV electrode of a large CRT (with 30kV acceleration voltage) with touching a 33kV high-voltage transmission line. The former will hurt but probably not kill you (most of the danger is actually from the muscle reaction, not the current), the latter might actually cook or vaporize you. The former is CAT I, the latter is CAT IV. This is why CAT I tests are conducted with a 30ohm source impedance (peak short circuit current for CAT I 600V is 2500V/30ohm = ~83A), and CAT IV with a 2ohm source impedance (peak short circuit current for CAT IV 600V is 8000V/2ohm = 4000A).

I believe IEC 1010 only requires that the equipment should not be dangerous to the user (explode or catch fire), not that it keeps working.

CAT I 300V on your scope means that it's rated for up to 300V on CAT I (i.e. residential/office equipment on the secondary side of the power supply), so 110V (or 230V) mains is outside the specification. So it actually means more than just '300V max'.

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I'd like to see close ups of the damaged areas.

Also, its well known those glass fuses are inadequate for transients, how did they fair in the cheap DMMs?

What happened to any HRC and SIPA fuses, did they blow too?

--- Quote from: EEVblog on May 05, 2010, 02:01:22 am ---Yeah, that was fun. Shame Doug only had the baby 400J unit, we were hoping to see a meter catch on fire. But we did get one to fully explode which was pretty cool.
Next video is a quick explaination from Doug about building a high voltage probe.


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