Electronics > Beginners
What CAT for wall outlets?
Kleinstein:
--- Quote from: jtruc34 on April 17, 2019, 12:24:31 pm ---Yes, I had already read that 10m rule. I find it a little strange. Why would it be less hazardous to work on distant outlet?
EDIT: apparently, it is because of the impedance of the wires, which increases with length, is it?
--- Quote from: Ian.M on April 17, 2019, 12:19:35 pm ---If a mains device doesn't plug in or connect via flex to a fused connection unit, [...]
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What does that mean?
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The distance to the distribution can make a difference in the peak currents in case of a short.
At university I saw the damage from a short at a outlet that was rather close to low impedance source: the normal 16 A fuse (LS switch) did not handle the short circuit current well and 2 more higher current fuses at some 35 and 100 A blew. The cable (should have been 3x 1.5 mm²) to the outlet turned slightly brown - could be seen as it was on the wall and not inside. In this case the outlet was maybe 3 m from a distribution/ fuse panel and that was right next door from the distribution transformer powering the rather large building. So not a good idea to have such short cables ! We had luck that not much more happened.
Neilm:
--- Quote from: Psi on April 17, 2019, 12:01:55 pm ---https://content.fluke.com/promotions/promo-dmm/0518-dmm-campaign/dmm/fluke_dmm-chfr/files/safetyguidelines.pdf
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CAT I was removed from the standard quite some time ago.
If your meter was made recently and claims IEC61010 compliance it should be rated CATIII minimum.
bjbb:
--- Quote from: blueskull on April 17, 2019, 05:07:29 pm ---Despite there's the 10m rule, most of the time a wall socket is considered CAT II regardless.
UL60950-1, which is the standard for ITE device power safety, considers all residential/commercial sockets CAT II, even if they are plugged right away from the panel.
I.E. they are all requested to withstand 2.5kV for household uses, even a CAT III 300V system can see potentially 4kV.
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The basic reference for construction per OV category is the IEC60664-x series. Please note that most national standards based on IEC60950-1 are now essentially deprecated, and the correct reference for ITE and comm and A/V is now IEC62368-1, where most national versions are effective between now and 2020. National standards based on IEC61010-x and IEC60335-x remain the correct references for test equipment and appliances, respectively.
ANSI/UL 60950-1 does, in fact, both consider and allow and define conditions for designs per OV category I. But as overvoltage category I is for equipment having a mains connection where transient over-voltages are limited (that is,'protected' electronic circuits), you are correct that a design for connection to AC mains should consider at least cat II.
Finally, for North America, Australia, Japan, EU, and others, the 'ultimate' and final deciding factor for ratings of construction and materials is the local/national building code (for example, NFPA70 for the U.S).
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