See also:
https://en.m.wikipedia.org/wiki/Mittelstand
I'd be curious if my new gig counts as one of the companies for Italy
810 karma · joined May 19, 2011
I'd be curious if my new gig counts as one of the companies for Italy
Personally, it would inspire more humility about what a certificate means and my ability to consistently apply the knowledge behind it. It gives pause immediately as I consider things I could apply it to.
Healthy (and tasty) fruit infused water was placed front and center. Sodas were hanging out in the fridges in a rather less convenient location.
And LTspice is extremely powerful for a free tool, if challenging to learn.
Many of the "revered" circuits perform very differently due to component variations (e.g hFE or Vgs), and also have substantial drift in performance with temperature. So even different units from same manufacturer will sound different.
Almost all modern class D amplifier ASICS have short circuit protection on their outputs
Solid looking unit from the teardown, I might have to get one...
It was the most humbling thing I remember reading. Moving, despite no personal context for the characters' experiences. Written beautifully without feeling over written.
It made me realize how far I was, and probably would ever be, from proper writing talent.
What I mean is phrasing that makes allusions. You'll find it in writing as a tool to expand meaning, change tone, add connotation, etc. It can lose power and clarity when the reader is unfamiliar with the underlying references.
Here, the writing brings in an aerodynamics concept (coffin corner), a famous bit of psychology about cognitive biases (Dunning Kruger), and a trueism about doubting one's own capacity (imposter syndrome).
Personally, the reference to coffin corner adds richness to the writing. It is from a completely different discipline, less commonly referenced in HN context than the other two, and immediately gives me a sense of greater breadth about the author's experiences.
Edit: kragen has good overview of this below from the generator in a puddle.
Now in practice, most small generators that you buy as a consumer are "floating neutral," which means that the generator chassis, EGC, and generator GSC (i.e. neutral) are NOT bonded together. Floating neutral generators are another, very long post.
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Source: 6 years ago, when the NEC changed substantially for small portable generators, I wrote a multi-part series on all of this for a trade magazine in the pro audio industry, who make prolific use of portable power distribution systems, and generators, in the 3kW to 500kW size range.
In the course of writing that series, I dealt directly with the EE who works for PGMA, the portable generator manufacturer's trade organization.
Stated rhetorically,
"If a GFCI only cares about the current imbalance, and the traditional style breaker opens to due to a big spike in current, why care about what path it takes through the building wiring back to the pole transformer?"
If a sub panel does not have the jumper removed, then the EGC and GSC between that sub panel and the main panel will form a current divider. Let's assume they are the same wire gauge, basically the same resistance, and so essentially split the return current.
This leads to a couple problems:
1. The EGC may no longer able to carry its full rated current load, due to the baseline "normal" current that the EGC is also bearing. You want to bear as much current as possible to quickly trip a conventional breaker in event of a fault to the EGC. This is real, but relatively minor concern.
2. All EGCs "upstream" of the bonding point have been "contaminated" by the normal neutral current that got on to the EGC at the mistaken sub panel bond. This could "put current" on the surfaces of other equipment, exposed ground wires, conductive raceway, etc. This is the more major concern, as these surfaces would have the full voltage potential available to them should there be yet an additional current path.
In the main panel the EGC, GSC, and GEC are all connected at a single point. And from this point there is only one path back to the transformer, via the 0V conductor of the GSC. The transformer side of this 0V potential conductor will match the local Earth voltage, set by the GEC, and wiggle from 0V nominal by the fluctuations caused by current (V=IR) in the GSC conductor between the panel and the pole.
Make sense?
Would refer to NEC 250.21 for discussion of "ground detector" as it relates to the detection accidental first ground connections in ungrounded systems.
I wrote out all the steps for operation of the typical american house electrical system lower in the thread, perhaps that will answer your questions?
The next section is where people go awry, even licensed electricians I have met. But it is also the meat of the safety aspect of the three wire configuration. We will assume a house with a single electrical panel for simplicity.
8. Three wires traverse from the main panel, down a branch circuit to the three prong "edison" outlet on the wall: One of the three prongs connects to either +120V or -120V; another connects to the EGC bar inside the panel; the last connects to the grounded service conductor bar inside the panel.
9. The short blade on the top row of the Edison connector is +120 or -120V; the tall blade on the top row connects to the grounded service conductor (colloquial neutral). The single connector on the bottom row connects to the EGC (colloquial ground).
10. If you plug in an item that has a three wire plug, the lower single plug prong will be longer. This is so that the item is electrically connected (i.e. "bonded") to the EGC before the other two wires. This insures the "fault current" path is connected before the item is energized.
11. Under normal conditions, the current path is through the item plugged in between either +120 or -120V and 0V volt potentials. Crudely think of current coming "out" the short plug prong and "in" the tall plug prong. The EGC (colloquial ground green wire) doesn't do anything under normal operation.
12. The current path is then back down the branch circuit, via the grounded service conductor (colloquial neutral). the metal bar that links all the grounded service conductors together then has a path back to 0V on the transformer by one of the three incoming conductors.
13. Finally, the current can flow from the 0V location on the transformer to the higher potential via the wire of the secondary. Notice that the GEC (earth) connection to the ground rod was NOT a meaningful component of the current path.
14. Returning to #11, and considering abnormal operation. Here current somehow flows outside of the correct circuitry in the powered item. The ECG is bonded (connected) to the item's chassis and provides an alternative current path. The EGC provides this connection back to the panel bar with all the green ECGs tied to it.
15. The EGC bus bar in the panel has a conductive link back to the grounded service conductor bus bar (colloquial neutral) via the removable link that we discussed previously. The link then "brings" the current over to the grounded service conductor (0V potential from the street), and provides the current path back through the transformer secondary.
16. Let's assume the outlet is a GFCI / RCD. It notices the current coming back on the grounded service conductor doesn't match the current going "out" into the device, and opens the circuit. That is because the fault current is "lost" to the EGC, and goes around the GFCI outlet. The outlet trips, assuming a human body is the fault current path.
17. People commonly assume that the GEC (earth) conductor somehow matters for current path in event of a fault, but this is rarely the case. Usually the water pipe or grounding rod(s) are high impedance relative to the wire in the transformer secondary, and so the current divider formed is essentially all through the grounded service conductor.
18. The GEC (earth) connector holds the pole transformer secondary center tap near the same relative 0V potential as the house. The GEC may also provide the lower impedance path at very high frequencies encountered during a lightning strike.
If you made it this far, I'm happy to field further questions :-)
0. Before the transformer secondary on the pole outside the house, the wiring is dictated by the NESC, which is like the NEC for utilities. We'll leave that there.
1. Most US homes have a single phase, "center tapped" transformer secondary. This gives three voltage potentials to feed the home: (Nominal) 0V - from the center tap; +120Vrms - from one "end" of the transformer; -120Vrms from the other end of the transformer. And, yes, I am glossing over the phase relationship here. All three potentials are connected through the chunky copper of the transformer, which provides a current path to complete the circuit.
2. The three potentials feed the house meter and disconnect. The 0V potential may, or may not, be insulated on the path back to the transformer secondary, and often doubles as the mechanical support for the incoming lines (the "service"). The other two potentials will be insulated wiring.
3. Inside the main service panel the +120V and -120V inputs are split between the breakers. Every other breaker is connected to +120V or -120V. Typically a breaker that spans multiple slots is connected from -120V to +120V. That is the "240Vrms" for ovens, hot water heaters, dryers, air conditioners, etc.
4. Adjacent to the metal bits that fan out the +120V and -120V is a strip of metal that allows multiple connections to 0V potential. Colloquially this the "neutral bus," but in the NEC this is termed a "grounded service conductor." All of the white wires from the circuits in the house ("branch circuits") are tied to the spaces in this metal bus bar. This metal bar is also electrically connected to the 0V potential entering the house from the transformer center tap.
5. Also inside the main service panel there is strip of metal that allows connection for a number of "grounds." It looks just like the "neutral" connection bar, but instead has a number of green wires attached to it. Colloquially these wires a called "ground," but the NEC calls them "Equiment Grounding Conductor" or EGC.
6. Between the grounded conductor ("neutral") bar, and the EGC ("ground") bar there is a removable conductive link. In the main panel this link remains installed, but in secondary panels it is removed. The link is removed in "subpanels" to insure correct operation in the event of a fault. Fault conditions are discussed below.
7. Also connected to the EGC and grounded conductor is a third wire. The NEC terms this the "grounding electrode conductor" or GEC. The GEC then goes to a water pipe or "grounding" rod(s). Thus the GEC is the connection between physical Earth voltage potential and the power panel. It is unfortunate that the EGC and GEC are such similar abbreviations.
In the event I'm out of characters, I'll pause and reply to myself now.
Another surreal Keys moment for me was seeing the MTV cribs episode with Aaron Carter. I'm virtually sure that compound previously belonged to another of my grandfather's friends. His business was helicoptering around financial documents in sort of the pre-networking version of HFT. I used to bike in that compound as a tween.
If you like working with your hands, that upkeep can be therapeutic. But otherwise it can be drudgery. The ongoing cost, and effort, of upkeep has taken many enthusiastic boaters as eventual casualties of the pursuit.
After my grandfather sold his business and retired to Big Pine Key, Florida, he befriended a fellow who lived on No Name Key. No Name Key is connected to Big Pine by the "Old Wooden Bridge" (made of concrete).
No Name Key is known for a rock quarry, being the practice grounds for the Bay of Pigs invasion, and for complete lack of public utilities.
Now this is the early 90s, as my grandparents left the Keys after hurricane Andrew. In those days solar power was properly challenging. And yet the fellow in question had a fully solar powered house.
He was a physicist by education, rescued from deliquency by an insightful first mate on a Navy ship. Per my grandmother he worked "not one day longer than required to retire to a life of poverty."
In my grandfather he found a (mostly) willing source of free labor. And labor who was trained as an electronics technician during WW2. So the two worked on his solar house in the bad old days of solar on very little budget. His backup generator was the front third of an 80s something Honda Civic with a hotrodded alternator.
In addition to the solar house, he also had a 9 meter(ish) sailing catamaran of his own design and construction. The catamaran, like anything he cared about, was meticulous. I never did understand how one could be both so haphazard and so careful, depending on the task at hand.
He was a lazy sailor, but had traveled all over the East Coast and Carribean looking for his "soul mate." Indeed, he left the Keys to stay with a lady friend when hurricane Andrew hit. The problem with that plan? Said companion lived in Homestead. Oops. My grandmother suggested that perhaps he would have better romantic luck with a "smaller beer belly and fewer 'banana hammock' swim suits."
When he sailed on the open water, he used a small commercial autopilot that used a servo to move the tiller. It was based on a compass heading set on a dial. It only "worked" if you weren't that particular about where you saw the sun rise above the horizon. That was perfect for his adventures.
Grandpa died January 1, 2017, and I doubt his friend is in any condition to sail so many years later. But, if he is somehow still out there chasing soul mates, I guarantee the boat has solar power, and it's probably navigating with pypilot.
They took only their winnings and used it to buy entertainment in the casinos where they gambled, which went a long way with the military discounts.
I want to say their original X was $500 or so, and it funded several years of local entertainment.