Hi David,
I'm not sure which part is absurd. Nor am I sure how super conductors are involved. Can you please clarify?
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The quiz is a bit wonky in that there are more questions than the results provided at the end take into account. I also got a popup midway through that said thank you for completing the quiz, even though there were many more questions to go. I also thought the question regarding meter category rating was misleading, though that could be because my day job involved "real" transmission circuits (high voltage), which a CAT IV meter is not rated for.
I disagree with the question relating to the effect of halving the throw distance. The illumination will increase as the distance decreases. It is a function of 1/r**2. From a mathematical standpoint, as r gets smaller, illumination increases. From a real world view, it is obvious that shorter throw is higher output.
I agree that the meter category question was misleading, because it lacked reference to use on "service entrance equipment" or "outdoor conductors", or "point of low voltage utility connection", which all describe the typical low voltage (1000V or less) application of a Cat IV meter, not "transmission equipment" (which is inherently high voltage) as the quiz states.
ST
I noted a problem with the quiz section on tap rules which applied NEC section 240.21(B) tap rules to portable feeder cables (with single-pole connectors as shown in the photograph) used at their free-air ampacities. This is incorrect--section 240.21(B) tap rules apply only to permanently installed conductors contained in raceways, switchboards, or other containment. The only tap rules allowed on portable single conductor feeders are those of theatre sections 520.53 (H) (3) and (4), and for motion picture studios section 530.18(B).
ST
Steve,I thought some other questions were confusing and possibly wrong in their answers. Notably, the list of harmonic-producing equipment includes items that are not inherently producers of high harmonic content such as transformers, LED's (not LED fixtures with switch mode power supplies), and motors. While the quiz asks which devices have "high harmonic content", it rejects answers that do not also include those non-harmonic-producing devices, stating "Almost everything we use in live event production produces some harmonics." Perhaps, but that's not what the question asked.
So, while a lot of this quiz might be informative and interesting, I urge caution about using it as an authoritative source of fact until such time as it undergoes appropriate peer review.
ST
I believe we are now debating cause and effect.
Your empirical observation of a neutral current is produced using a meter that provides an average reading.
The observed neutral current is due imperfect phase cancellation.
The harmonics do not cancel so they must be out of phase.
To this point we are in agreement. Where we diverge is on the conclusion. It is based on an association fallacy. It is incorrect to conclude that because some harmonics result in a current on the neutral, all harmonics will. For all practical purposes your conclusion is a reasonable answer but it is not a correct one.
Just as it is possible to combine complex sound waves from 3 different sources and produce silence, so is it possible to combine 3 complex current waveforms and produce no net current.
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