Toolbox Talk Safety Data Sheets: Fill & Download for Free

It’s the end of December 2019, you are lookin’ out the window and still remember the stressful weeks of November 2019.Your wife died.May she be wherever she wanted to go to. You’ve been working as a farmer in the northern parts of Netherlands and Germany all your life, and there you are, money to burn, no wife to spend it with. You feel emotionally vulnerable.Your kid tells you to invest it, to keep a safety net for the future, you know? People nowadays can turn over a 100 years old..You don’t trust the little git, given he will get your money the moment you perish from this rotten planet but what else are you going to do, put it in a fucking sock?So you grab your best coat and are headed over to your private banker, Joey, who is eagerly awaiting your arrival in his office.He tells you a story his firm has developed new revolutionary trading systems. He tells you he can invest your money in a variety of asset mixes the firm has developed, backed by some of the best “quants in the industry”. And of course, with the full supervision of the regulator.Asset mixes, as in, ‘Invest *’, ‘Invest **’, and ‘Invest ***’ which is nothing more than 50% stocks, 50% bonds (etc).The 1* star package has the lowest risk/return ratio, so very risk averse in case anyone seeks such a safety net.Safety sounds good, you think. But still there is a nagging feeling, that something isn’t right. So you demand more evidence. The banker comes out with a few sheets showing 1 example.In the lowest ‘Invest *’ package we invest solely based on the relative strength index indicator. The banker hands you a pamphlet about RSI. It’s a simple signal processing mechanism. It creates a buy signal when it reaches 30, and a sell signal when it reaches 70.He goes on, your wife died, so let’s see how our strategy looks based on a funeral home, like StoneMor (STON). Just to keep that emotional touch, eh?We pick a so called ‘random’ period which is a full year. If you would have bought the stock from day 1 and sold it at the last day, it would have lost ~175% during that year.Yet, if you bought StoneMor every time when RSI was 30, and sold when it hit 70 (or if it went below 30), and went short (sell the stock) when it dropped below 70 (yet sold it again if would hit 70) you would have made a substantial profit ~35ish %.So it works, you see?You are convinced. And decide to invest.Months later..Aaaaaaaand it’s gone…Whilst the above is a hypothetical scenario ~ I’ve worked in departments of asset management/private banks where this sort of advice was given to clueless, old but wealthy retired people.I was told, face to face, the majority of our clientele are wealthy farmers. They don’t like fancy talk, so we need to keep the talk simple and easy. The pamphlets need to have big pictures, look simple and show large numbers.The above, unfortunately, is very real. Those asset mixes? I’ve developed many of them myself whilst working in a quantitative team. Based on technical analysis? Of course not. Even though the example above is factually correct (STON dropped during the year), a simple RSI buy 30/sell 70 would have made you solid return in that particular bear market circumstances. But what does it tell you? Nothing.It was (1) one example, (2) in a fixed windows (fitting..), (3) with only comparing returns, not risk adjusted returns, draw down, or anything else. Perhaps the RSI had 25 buy and sell signals, 24 of them were shit, one, at the end of the window made it go +30%. Based on what variables do you qualify a technical indicator to be significant in predicting future stock market prices? Well, not when you use (1) one example and (2) a fixed window. That is called waving your dick.. well, data dredging in professional terms.There are a few ways to test this.Either completely statistical and you ignore any kind of fundamental information (from price, volume, volatility to the actual financial state of the company) ~ many hedge funds do this ~ and simply look at the data from a mathematical point of view. All you have is time-series and all you want to do is create a signalling process which generates a buy and/or sell signal on times when the underlying product (a stock, a bond, your dick, who knows) actually increases/decreases.Basically what you want to do is create a distribution out of which you can sample ‘forecasted’ prices of StoneMor and use that data to backtest RSI strategy. Because if you sample that data (new, futuristic data) on your strategy, and it works, you have a golden butt-hole for years to come.To start, you can build a distribution based on past descriptive statistics of a distribution, for example, if you pick a 1-year data set from 2009 to 2010 (don’t do this, it’s stupid), it creates a distribution of StoneMore, you’ll have a mean, variance, skewness, kurtosis.You can build a distribution out of that, and sample it to oblivion. Take out 1000 years of data, and randomly pull bits of data out of this pool, and test your RSI strategy. Then for example compare it with an out of sample data set (actual data, like 2010 to 2019) and see if your model performed well during those years. RSI might have fit to perfection during that one year (fiddling with the 14 day, and other parameters), but went tits up the moment you expanded the window. Awww……Or, you can go the way of the Bayesian overlords, and use a prior. Mean, variance, skewness and kurtosis might be w,x,y,z as of 12/7/2019, but a few outliers in the data screw up your data-set. Bayesian statistics allows for taking those samples out and let you build a posterior distribution. A posterior distribution accounts for that relevant information. I personally favor Bayesian, because a lot of behavior in the financial markets, can be modeled (and seemingly makes no sense) yet, you know the people or firms who drive certain processes. The ability to incorporate that, allows for a distribution which ultimately yields in much more realistic (not necessarily more significant) results.You want pertinent consistent success with technical indicators? Validate your model mathematically. There is no broker who offers a good toolbox do this. Of course there isn’t. All they do is give you the ability to draw lines (resistance, MACD, whatever) to give you the feeling you are in control.You are not in control.It’s fake. It’s bullshit. It’s leaving the door open in the night and someone robs your fucking telly. I know it, you should know this too. Brokers don’t give a fuck about you, they just want your money. Start with that. And thereafter validate your fucking model. You can do this in 1001 ways (and an equal amount of programming languages) but be honest. Let someone else investigate your model as well. Human beings have the tendency to oversell their own trading model (as the greatest) and/or confuse trading skills with luck.Those pamphlets from the beginning? I’ve worked on those with marketing divisions. It’s borderline criminal. But who am I? I believe all sales persons are full of shit and would steal your entire savings if they had the chance. Wherever there is someone with money and naive as hell, there is always someone around the corner who will take advantage of this. It’s not capitalism, it’s realism.Btw ~ rich farmers I hear you say? Many countries have a large percentage of farmers who are very wealthy, take for example the Netherlands.The Netherlands has more millionaires, and one in five is a farmer - DutchNews.nlAnd farmers are very easy to exploit.

Why are teachers in American schools give virtually no authority? It seems the students have more privileges than them.I think you need to clarify your question slightly, because I’m not sure what yo mean by “no authority.”I do have authority to govern my classroom. The California Education Code makes clear that my students are expected to follow my instructions at all times, and the Supreme Court has held that the safety and stability of the learning environment supersedes students’ individual rights to freedom of expression.The trouble is enforcing that authority.At the end of the day, the only way teacher authority can be enforced is with parent support.There is nothing an administrator, teacher or other school official can do to force a student to comply.When I was in elementary school, a day of On-Campus Suspension was a terrifying prospect. We were given a sheet of the school rules and required to copy it out by hand three times. If we finished that, we were given a second, more detailed and dense version of the same document and required to copy it out by hand five times.And we did it. Why? Because we were already in deep trouble at home, and we weren’t keen to make the situation worse. And a call home from the OCS teacher to report our lack of cooperation in OCS would certainly do that.At the same time, getting suspended was an abject horror. That day would not be a good day. I was suspended exactly once (and, to be honest, it wasn’t an appropriate consequence for what I did but yaaaay zero tolerance!) and that morning my father gave me a laundry list of chores to complete that day, and made clear that failure to to do so would result in my Playstation (this was 1998) and all my games being sold.I worked at the hardest pace my out-of-shape little 8th grade body could muster and I completed about 80% of the list. My father, of course, knew I could never finish all of it — and I knew that too — so I knew that I had to get enough done to convince my father that I’d given it my best effort. He was convinced but, since I didn’t finish all of it he took my Playstation and hid it from me for a month.I didn’t behave myself in school because of school rules. I didn’t behave myself in school because the Education Code says I had to listen to my teachers. I behaved myself because I knew that my parents would apply strict consequences if the school reported that I wasn’t.Every consequence a school can legally issue is, ultimately, a step toward suspension. If a student refuses to comply with a consequence, the school has no recourse but to step up to the next consequence, until finally the student is suspended. The only way suspension is a consequence is if the parent makes the suspension unpleasant.Thus, every consequence a school can legally issue to a student ultimately hinges on parent support.Today, however, for a variety of reasons, parents are generally less supportive than they used to be.A few rare parents genuinely don’t care, either because they’re selfish assholes or because they believe that school is a complete waste of time. One parent in my first year supported her daughter’s extreme disrespect toward her teachers, arguing that “All [name] needs to do is go to school until she’s an adult. Then she can pursue her acting career.” Wow.A great many parents are mired in poverty, working multiple jobs to make ends meet. That means they aren’t home during the day and they aren’t home in the evening. Older siblings are tasked with caring for younger siblings. Elderly and infirm grandparents must often shoulder this burden, as well. The more urban the environment, the easier it is for the unruly child to escape the home and seek the “safety” of an equally unruly peer group.A large number of parents insist on exclusively employing alternative — and sometimes ineffective — methods of discipline, refusing to face the reality that, ultimately, the real threat of physically enforced obedience must exist or many children will not see any point in obeying their parents. The erosion of corporal punishment is rendering parents powerless when faced with defiant children. It should not be the first, second or even third tool in a parent’s discipline toolbox, but sometimes there is no other choice but to spank the child or to let the child run amok. And a surprising number of parents, either misguided about spanking or emotionally incapable of it, choose to give up on discipline before resorting to it.Finally, the vast majority of parents are simply inconsistent. This is the single greatest danger of parenting. The expectations must be clear, and the consequences for not meeting them equally clear and consistently enforced. I see many parents in my social sphere that change their expectations based on their mood, that change their reaction to disobedience based on their mood and that fail to follow through on promised consequences. In the teaching world, we have one golden rule: Never make a threat you cannot follow through on. That’s a one-way ticket to loss of authority in your classroom. Parents should heed it as well.Some of my students have no great concern about getting suspended. It means they can “play video games all day.” That happens because their parents are either too busy or too disengaged to take an active role in supporting their child’s character development. I teach in a rural district now with a fairly involved group of parents, so in general behavior problems are minimal in my classroom.When I taught in an inner city school to deeply impoverished students, this effect was massive. The school administration was pressured by the district to reduce suspensions (because suspension rates are a factor in a school’s performance rating) and prohibited from suspending students for mere defiance. My students could cuss me out, talk over me, refuse to follow instructions, disrupt the learning environment and, as long as they didn’t get physically violent, steal anything or have drugs on them, we just had to try to teach through it. Calls home to parents typically involved “he does that to me, too, I just don’t know what to do!”In my head: “Why don’t you take away his Galaxy S4? Why don’t you stop buying him new Nike's every month? Why don’t you take away his X-Box? His brand name clothes?”What I had to say: “That’s unfortunate.”Of course, I go to the student information system and I can see that the student qualifies for free lunches and a host of other services based on his parents’ sub-poverty-level income. I ask questions, and I find out that these cash-strapped parents basically prioritize spending what little extra money they have on buying luxuries for their kids so that they won’t “feel poor.”Maybe your kid needs to “feel poor” for a while and learn some humility rather than being enabled to strut around campus like a peacock, wallowing in the approval of their peers while they completely flush their free education down the toilet and try to ruin the same for as many other students as possible.So, at the end of the day, I blame a system and a society that pressures parents to pamper their children and then expects an education system with no real ability to discipline those children to magically transform them into upstanding citizens.I blame a system and a society that has become more concerned with achieving utopian ideals in a single generation than accepting hard realities and the slow, steady evolution of society.I blame a system and a society of emotionally driven wimps that willingly obfuscate and cherry-pick data and studies in order to push their agenda that our children need to be protected from all discomfort.We’re creating an entire generation of entitled brats. And when the social safety net that keeps them afloat fails, those brats are going to bring society down with them.

Q: If the neutral wire is grounded, why is it still necessary to connect a third cable being the ground in a standard electrical wiring?A: In simple terms, without a ground connection if the hot conductor makes contact with an electrically conductive surface and you contact that surface, depending on the condition of your body’s resistance and its grounding you may feel a shock or be electrocuted.The purpose of the ground wire is to provide a path of sufficiently low impedance such that if a hot wire comes in contact with a grounded metal surface the circuit overcurrent protective device (circuit breaker or fuse) will operate quickly to remove the hazard.Q: Or better still what's the difference between the neutral and the earth cables?A: The most basic difference is that the neutral conductor conducts electrical current in its normal function, whereas the ground wire conducts electrical current (as a general rule) only under ground fault conditions.The neutral wire, being the grounded conductor, is at or near ground potential even when current is flowing to the load.Safe Electrical InstallationsA grounded neutral conductor and the grounding/earthing system are but two parts of a system designed to insure electrical safety. We will discuss those in a lot more detail below.We will also discuss the roles of the following in the safety of residential electrical wiring systems in the US:Circuit overcurrent protective devices (fuses and circuit breakers)GFCI’s (ground fault circuit interrupters)AFCI’s (arc fault circuit interrupters)Tamper-resistant receptaclesPut together as a system these components work to provide an electrical system that is essentially free from the hazards of electricity.If you have an interest in the details of this read on …Overview - In Basic WordsThe purpose of circuit overcurrent protective devices (fuses and circuit breakers) are to protect equipment and wiring from short circuits and ground faults that are greater than the fuse or circuit breaker’s rated capacity.(For our purposes here a short circuit is an “short” or an unintentional connection between hot and neutral. A ground fault is an unintended electrical connection between hot and ground.)The purpose of an effective ground fault current path (grounding system) is to trip the overcurrent protective device when a ground fault condition exists.The purpose of a GFCI is to protect when a ground fault occurs that is too low in current magnitude for the overcurrent protective device to trip.The purpose of a AFCI is to protect when arcing faults occur. Those faults generally will not trip a GFCI and often are of too small a current level to trip the circuit overcurrent protective device.The purpose of tamper-resistant receptacles are to protect (largely children) from the hazard presented from inserting a metallic object into a receptacle.CaveatsI can’t possibly write an electrical power engineering level answer to this here, but I will try to discuss it in some detail. I realize this is a lot more information than what the typical Quora reader might be interested in - so feel free to stop reading at any point.This discussion is for residential applications - not for commercial or industrial applications.To understand the answer to your question requires an understanding of how a grounded electrical system operates, both under normal and under fault conditions. (Almost all residential electrical systems throughout the world are grounded systems.)Since I live in the US and am most familiar with US-based electrical systems, I will answer from that perspective. Many of the concepts discussed here are similar to concepts in other world areas, however there are significant differences too. If others would like, feel free to write your own answer for the system used in your world area.Any calculations I may present are to be considered “back of the envelope” “order of magnitude” calculations and not engineering-level calculations.This is a “work in progress.” There are areas that I want to expand and expound on, and I am sure I will think of other things to add over time. I am sure I have typos, spelling errors, and various technical errors - all of which I will attempt to fix over time.Background - Ohm’s LawIt helps, but is not essential, if you have a basic understanding of Ohm’s (DC) Law and of the concepts of voltage, current (amps), resistance and power (watts).I won’t go into these concepts in any more detail here as there are many excellent resources available on the Internet on these subjects.Grounded Electrical SystemsIn a grounded electrical system, electrical power is supplied from the secondary of a transformer, with the secondary of the transformer being connected to ground (via various methods).An overly simplified diagram of this is shown below.In this diagram above the conductor labeled X1 is called the “Hot” conductor, because it is at line voltage (in the case of the diagram it is 120 volts - but can be different voltages in other world areas). In the US the hot conductors in residential applications typically have insulation that is black in color, or sometimes red.The wire labeled X0 in the diagram is called the neutral conductor, variously also called the “grounded conductor” because it is connected to earth ground. In the US the neutral conductor typically has insulation that is white in color, or marked in white.Following the arrows as shown in the diagram - current flows from the transformer, through the load (generally first through circuit breakers, switches etc. not shown here for clarity), through the neutral conductor and then back to the source of the current - the transformer.This is an important concept to understand - that electrical current seeks to return to its source, in this case the transformer. Electrical current coming from a transformer does not and can not “drain off to earth” - as the earth is not a sink for electrons.This is a VERY important concept to understand.Ground / Earth WireNow lets add in the third wire, variously called:Ground / grounding conductor or wireEquipment grounding wireSafety groundEarth / earthing wire conductor or wireProtective earth / PEIn some world areas some of these (and other) terms have different meanings. We can’t possibly go into all of those technical details here for the meaning of words in all world areas.For my purposes here I will simply call it the ground wire.Grounded US-Based Residential Systems in More DetailLets make our diagram a little more technical and more accurate.This is the way residential power systems in the US are generally wired. Although some of the details are different in other world areas, the grounding concepts are similar.In the diagram above (remember this is a US system):The secondary of the transformer is center-tapped, that is, in addition to the wire connections on either side of the transformer windings a connection is made to the center of the transformer secondary winding (labeled X0 in the diagram above).At the transformer that center tap is connected to earth ground via a stout wire and a ground rod or plate. Thus the name of the system - a grounded power system.The conductors that exit the transformer (called X1 and X2 in the diagram above) are the “Hot” conductors. The conductor exiting the transformer from the transformer center tap (called X0 in the above diagram) is called the “neutral’” conductor. The neutral is also sometimes called the “grounded conductor” because it is grounded and carries current in its normal operation - not to be confused with the ground wire. (In its normal operation, the ground wire does not carry current - at least in theory.)If voltage is measured from X1 to X2 in the diagram it will read a nominal 240 volts AC - so that is how we get 240 volts in the US. (Also see the diagram below).If voltage is measured from X1 or X2 to X0 (hot to neutral) a nominal 120 volts AC will be measured. This is how we get 120 volts in the US.The two hot conductors plus the neutral conductor go to the electric meter, then on to the circuit breaker box (in some cases with a disconnect switch or switches in the circuit).At the circuit breaker box each hot wire goes through a circuit breaker before going on to its load - a receptacle, light or whatever. (In the US, the circuits from the final circuit breaker to the load are called a branch circuits.)The neutral wire from the transformer is connected to a neutral “bus bar” in the circuit breaker box where the returning neutral conductors (colored white in the US) from the various branch circuit loads are wired to.Also in the circuit breaker box is a ground bus bar. The ground wires (in the US the ground wire may be bare metal, green or green with yellow stripe(s) insulation) that are run to receptacles /sockets, switches etc. all return and get wired to this ground buss bar in the circuit breaker box.The neutral and ground buss bars are “bonded” together (electrically connected together) in the circuit breaker box. This is the one and only point in the electrical system, under normal operation, that the neutral and ground are allowed to connect.A connection is made from the neutral / ground bus in the circuit breaker box to various grounds, including one or a number of rods driven into the ground and the metal water piping system. There are many details associated with what must be done here and what can’t be done here - which are way beyond the scope of this answer. (References are given at the end for those who are interested.)It is important to have at least a general overall understanding of the diagram above. If you don’t - please re-read my notes and ask questions if you have any. By asking questions that will allow me to understand areas that are not clear and to reword them or add more diagrams.Voltage on the Neutral ConductorSo we now know that the neutral conductor is grounded at the circuit breaker box. Is there a voltage on the neutral conductor, and if so what is that voltage?With the neutral being grounded its voltage to earth should be zero, but this is forgetting the voltage drop across the length of the neutral wire from the load to the ground connection at the circuit breaker box - that voltage drop being caused by the current flowing along the neutral.Lets look at an example. Lets say you have a run of 50 feet of #14 AWG copper wire from the load to the ground connection at the circuit breaker box, operating a hair dryer at 15 amps load. Per my reference manual (2017 NEC Table 8) the resistance of 50 feet of #14 AWG solid copper wire is 0.15 Ohms. Using Ohm’s Law to solve for voltage, 0.15 Ohms x 15 amps = 2.3 volts on the neutral conductor at the receptacle, which is a safe voltage.There are situations where a neutral conductor may be at a significantly higher and potentially hazardous voltage level. So never trust that a neutral conductor is safe - always test a neutral with a non-contact voltage tester just as you would a hot wire.Ground Fault in a Properly Grounded SystemsA ground fault is an unintentional connection between a hot conductor (voltage-carrying wire) and a ground. If left uncorrected, the current in a ground fault can potentially result in shock, electrocution or fire.The purpose of a ground wire is to protect in case of a ground fault. How does the ground wire accomplish this function?It does this by allowing sufficient current to flow along it to trip the circuit overprotection device for that circuit, which in the US for branch circuits is typically the 15 or 20 amp circuit breaker in the circuit breaker box.And we don’t just want the circuit breaker to trip - we want it to trip fast. Why fast? For a couple of reasons. First, a circuit breaker, unlike common understanding, does not trip to prevent excess current from flowing - it can’t do that. The current that flows in a ground fault is limited by a number of things (beyond what I want to get into here) - but which is basically controlled by Ohm’s Law and by the level of current supplied to the circuit under fault conditions (called short circuit current)The current in the ground fault is impacted by the resistance of the ground path back to its source - the transformer. (Actually it’s the impedance of the circuit and the available short circuit fault current, but that takes us to a level we don’t want to go to here).So if the overcurrent protective device does not protect by limiting the current flow, how does it protect? It does so by limiting the time that the fault current is available.Energy is watts per unit time - so if we minimize the time we minimize the available energy, and it is energy that generally causes damage at residential voltage levels, be that equipment damage or injury to a human. So we want the circuit breaker to trip as fast as possible (more on this below) to minimize the damage.Tripping a Circuit Breaker Quickly / Effective Ground Fault Current PathOur goal is to trip the circuit breaker quickly on a ground fault. How fast is “quickly” and how can we achieve this?My residence has GE circuit breakers, so I will talk about those. Other residential circuit breakers operate similarly, but not identically.Circuit breakers have what is called a “trip curve” - that is, a diagram that describes the relationship of current (in amps) that passes through any given circuit breaker versus time it takes that circuit breaker to clear the fault. If you know the brand and model number of your circuit breaker you will be able to find its trip curve on the manufactures web site.Below is the trip curve for GE circuit breakers of the type I have in my residence.I am not going to go into detail on these curves, other that to note a few things. One is that they have a tolerance range to them - an area where they may clear the fault or may not. This tolerance is due to manufacturing and other issues. On the diagram above that tolerance area is shown in green.Another point is that there are two parts to the curve, one part that is slower in acting - which acts on lower levels of current, and another portion that is called the “instantaneous trip region” where the circuit breaker operates more quickly.(The circuit breaker has different mechanisms that trip on different current levels and at different speeds. Looking at the diagram below, one can see the “Bimetal element” that acts on lower levels of current but at slower speeds and the “Magnetic element” that operates at higher current levels and at higher speeds - which is the “instantaneous trip” device in a circuit breaker.)The instantaneous trip portion of the curve is the horizontal green bar along the bottom of the graph. The green bar that extends upward from there is the trip at lower current levels that takes more time.If you want to learn more about trip curves look here: https://www.c3controls.com/wp-content/uploads/2018/05/c3controls-Understanding-Trip-Curves.pdf (https://www.c3controls.com/wp-content/uploads/2018/05/c3controls-Understanding-Trip-Curves.pdfWhat we want to have happen in a ground fault is to have the circuit breaker operate in its instantaneous region. Why? So that the circuit breaker can limit the amount of time the current is flowing - thus minimizing the resulting damage.How do we get the circuit breaker to trip in its instantaneous trip range? By having sufficient current (amps) pass through the circuit breaker. How much current is this? It varies by circuit breaker type, and can be determined from an engineering perspective by looking at the trip curve for the specific circuit breaker.Looking at the trip curves for my circuit breakers, they get into the instantaneous trip region with between 10 and 30 (or more) times their trip rating. For a 15 amp circuit breaker this is between 150 and 450 amps. So we want at least 150 amps to flow through the circuit breaker under ground fault conditions to allow the circuit breaker to trip quickly (in its instantaneous trip region) - thus limiting the time the current flows thereby limiting the damage caused by the release of electrical energy (watt-seconds).How do we do this? By having an “effective ground fault current path.” This means the resistance (actually the impedance - but we are already way over our time allotment here) back to the current source be sufficiently low so that the required trip current can flow to cause the circuit breaker to trip in its instantaneous region.The actual engineering calculations get more complex than this, but simplistically using DC Ohm’s Law where resistance in Ohms = voltage / current, 120 volts / 150 amps = 0.8 Ohms. Although this calculation is not accurate for a number of reasons it does give one important learning. To be able to clear a fault quickly requires a path back to the source of the current (the transformer) of pretty low resistance (actually impedance - but again this is not meant to be an engineering dissertation).In a typical 15 amp circuit, will a #14 AWG copper wire be OK for this? I won’t bother you with the calculations, but basically as long as the #14 is less than 250 feet from the load to the circuit breaker box you should be OK. (Note - this is not a precise engineering calculation, just an example for our Quora purposes here.)If you want to be able to calculate this more accurately, Mike Holt Enterprises has a (free) app “Mike Holt’s Electrical Toolbox” that can easily calculate this and other things for you.Ground Return Path, Ground Rods and Water Pipe GroundingRemember where current in the circuit wants to go to? Not to earth - to its source, which in this case is the transformer.In the case of a ground fault (a hot touching something that is grounded) it does so by following the ground path(s) back to the source - the transformer.Some people believe the ground rod at the circuit breaker box, through the earth, to the ground rod at the transformer back to the neutral at the transformer provides an adequate ground fault current return path - but does it?Per Soars (reference at the end of this) - “A study of the fault current circuit … shows that it would be unlikely to have an impedance (from the transformer to the circuit breaker box - via the ground rod at the circuit breaker box, through the earth to the ground rod/plate at the transformer) of less than 22 ohms as the sum of all the impedances …” This includes situations where the water piping is tied into the ground system. Soars notes that this 22 ohms ground impedance number is an optimistically low number at best, and is largely a function of soil resistivity. (Soars has a lot more information on this topic for those interested.)So lets take a look at this using Ohm’s Law. 120 volts / 22 ohms = 5.5 amps. With a 15 or 20 amp fuse or circuit breaker it is obvious the overcurrent protective device will never trip, thus exposing metal in the ground fault path to potentially hazardous voltages and currents indefinitely.This is why it is unsafe and against the National Electrical Code (NEC - the electrical installation code used in all 50 states) to ground only to a ground rod.(I have heard a number of people state that one can change a non-grounded receptacle out for a grounded receptacle by simply driving a ground rod at a convenient location and connecting that to the ground terminal on the grounded receptacle, or connecting a ground wire to a nearby water pipe. Again - both would be unsafe for the reasons shown and a violation of the NEC.)In the US, having an “effective ground-fault current path” is a legal requirement per 2017 NEC 250.4(A)(5), and I suspect wiring installation codes around the world have a similar requirement.Here is what that section of the NEC says on this subject:“Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device … The earth shall not be considered as an effective ground-fault path.”But what about metal piping systems as an effective ground-fault current path? Like with ground rods, metal piping systems count on the resistivity of earth between the water pipe and the source (what is that again?) - and as we have already seen the earth does not provide that required low-impedance path to trip the overcurrent device.Purpose of Ground Rods / Grounding to Water PipesThen what is the purpose of these ground rods and their connection to earth?Per the National Electrical Code, specifically 2017 NEC 250.4(A)(1) it is to “limit the voltage imposed by lightening, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.”Note that nowhere does it mention anything about tripping overcurrent protective devices, limiting the time and energy available under ground fault conditions, or protecting equipment or people from the hazards associated with ground faults.(Those interested in the topic of using metallic water piping systems as an electrical grounding means are referred to the very interesting article “Electrical grounding, pipe integrity, and shock hazard” - American Water Works Association Journal, ; July 1998Volume 90, Issue 7. https://www.researchgate.net/publication/239778042_Electrical_grounding_pipe_integrity_and_shock_hazard )Solid / “Bolted” Ground Faults & GFCIsThe types of ground faults we have been discussing so far are solid ground faults, also called “bolted” ground faults. In this type of fault there is a solid or “bolted” connection between a hot and a grounded object. But what if the connection is not solid - if it on only partial or weak connection? Such high resistance connections can occur if parts are corroded, or if there is another high resistance in the ground fault path - such as a human. In these cases the current will be insufficient to trip the circuit breaker and the hazard will remain, potentially resulting in fire or electrocution.Looking at the trip curve for my GE circuit breaker, a 15 amp circuit breaker will clear a 30 amp fault in between 17 and 120 seconds. For a 22 amp fault it will take between 50 and 500 seconds to clear the fault. These are sufficient times to potentially electrocute a person.How fast will my 15 amp circuit breaker clear a 16 amp fault? Never - that’s right, never! For faults of approximately 16 amps and less these 15 amp circuit breakers will never clear the fault.Enter GFCI’s (ground fault circuit interrupters). A GFCI is designed to trip in a specified length of time when the current from hot to ground exceeds 6 mA - 6 thousandths of an amp. This level was chosen to be inline with human physiology, electrocution levels and “let-go” current levels (levels of current that most people can let go of).Like with circuit breakers, GFCI’s can’t and don’t limit the current flow - current flow is a function of Ohm’s Law. Like with circuit breakers, GFCI’s are effective by limiting the length of time that the fault is present. And like with circuit breakers, GFCI’s operate on a current versus trip time curve (shown below).The theory behind the operation of a GFCI (ground fault circuit interrupter) is fairly simple. The difference between the current flow in the hot and the neutral conductors should be zero - all current that goes out on the hot conductor should return to the transformer on the neutral conductor. If other than zero that current must be going somewhere other than where it is intended to go to - which is to power the device.In a ground fault the current is flowing from hot to ground, thus the name ground fault - a fault where electrical current is flowing unintended to ground. One possible place that current might be going to is through the body of a person.In practice it is reasonably simple to construct a device that will trip on such a ground fault (reference the GFCI schematic diagram below):Measure the difference in current flow between the hot and neutral conductors. This is done with a current transformer (“Sensor” in the diagram below) through which the hot and neutral conductors pass. The output of the current transformer, under normal conditions, should be zero - as the current flow in the hot and neutral wires should be exactly the same. If a ground fault occurs (current flows from hot to ground, bypassing the neutral conductor) the difference in current flow between the hot and neutral conductors is non-zero, and the output from the current transformer will be directly proportional to that difference.Take the output from the current transformer and put it into electronic circuitry that can measure it and activate when the current exceeds a specified amount for a specified length in time. This current level and time is coordinated with safe levels of energy for the human body and is shown in the diagram and curve above.When the measured output from the current transformer exceeds the levels set in the electronics, the electronic circuitry activates a switch that opens the hot and neutral conductors, thus stopping flow of electricity and potentially saving a life.Unlike what some people believe, to properly and fully operate a GFCI does not require a ground wire. A glance at the internal schematic for a GFCI shows why this is the case. The ground wire provides no use in the function of the GFCI circuitry.Some incorrectly believe the internal Test function on a GFCI will not trip without the presence of a ground wire. This is incorrect - as studying the GFCI schematic indicates.However - if using an external GFCI tester with a GFCI that does not have a ground connection the external GFCI tester will not operate the GFCI. The external GFCI tester operates by placing a test resistor across the hot and ground wires. There being no ground wire no current flows, therefore the GFCI can not trip.Arcing Ground Faults & AFCI’sAFCI stands for arc fault circuit interrupter. AFCI’s trip on arcing faults.Many fires are started by arcing faults. There are various types of arcing faults:Parallel arcing faults - hot to neutral.Parallel arcing faults - hot to ground.Series arcing faults, such as loose screw terminals or other poor terminations or partially broken conductors.Arcing faults generate a lot of heat and high temperatures and therefore are especially dangerous in their ability to start fires.GFCI’s generally don’t react to arcing faults for a variety of reasons.Conventional circuit breakers and fuses don’t react to series arcing faults because there is no increase in current flow in the circuit. They don’t react to parallel arcing faults because the amount of additional current flow is relatively low - well below the current required to blow a fuse or trip a conventional circuit breaker.Common Causes of Arc FaultsAccording to the US Consumer Products Safety Commission, the most common causes of non-operational arc faults are:Staples piercing cable insulation in a wall, generally creating a parallel hot to ground arc fault.A nail or screw used to mount something to the wall (such as to hang a picture) penetrating a cable, creating a parallel hot to ground arc fault.Extension cords used inappropriately, such as under rugs or in a door jamb, typically resulting in a series arc fault.Wear and tear on appliance power cords, typically resulting in a series arc fault.Furniture pushed against the plug of an appliance cord creating stress that can damage insulation, typically resulting in a series arc fault.Arcing faults produce electrical waveforms that can be detected by AFCIs.Tamper-Resistant ReceptaclesTamper-resistant receptacles provide permanent, reliable automatic protection from sticking an object into a slot on a receptacle.An analysis of U.S. Consumer Product Safety Commission (CPSC) data over a 10 year period from 1991 to 2001 revealed that over 24,000 children under the age of 10 years old were treated in emergency rooms as the result of receptacle-related incidents.That’s an average of almost 7 children a day.These injuries ranged from minor electrical shocks and burns to more serious conditions. The injuries were caused mostly due to children sticking everyday household items into electrical outlets (receptacles). These items include paperclips, keys, hairpins, screws/nails, or even their fingers. Children are less resistant to electrical shock than adults as they have thinner skin and, among younger children, saliva is often present which promotes conductivity.Some preventative measures have been on the market for years, such as plastic outlet caps, but these are not used consistently. In fact, research conducted by Temple University Biokinetics Laboratory found that 47 percent of 4-year-olds studied were able to remove one brand of cap, and 100 percent of 2- and 4-year-olds could remove a second brand—in many cases within 10 seconds!Additionally, adults forget to reinsert the caps after receptacle use, thereby leaving no safeguard for the outlet.If you are interested in more recent data read the following fact sheet from the National Fire Protection Association: https://www.nfpa.org/-/media/Fil...Tamper-Resistant receptacles have been used in pediatric areas of hospitals for many years and have proven to be a reliable solution in preventing electrical injuries. A tamper-resistant receptacle functions the same as a standard receptacle but adds a built-in safety mechanism that prevents delivery of electricity to anything other than plug blades.Mechanical tamper resistant protection resists the insertion of foreign objects into the receptacle (See diagram below).The tamper-resistant shutters inside of the receptacle are designed to remain closed if an object is inserted into one side or the other of the receptacle.Tamper-resistant shutters will only open if two objects, such as the blades of a plug, are inserted at the same time using the same force, as is the case when a plug is inserted into an outlet.In contrast to plastic caps, the protection provided by a tamper-resistant receptacle is permanent, reliable, and automatic as it’s integral to the receptacle. There is no need to remember to insert or replace a plastic blocking cap.Putting It All TogetherHopefully you now have a better understanding of how the following provide a system that is essentially free of the hazards of electricity in US residential installations:an effective grounding systemovercurrent protective devices (fuses or circuit breakers)GFCI technologyAFCI technologytamper-resistant receptaclesReferencesThere are various references and resources available on the subject, many of them assuming the reader has a solid background in electrical theory (e.g. college textbooks and technical articles).There are two books that I believe anyone with a general knowledge of and interest in electricity can understand. They were written specifically for electricians and practicing electrical power system engineers in the US, but the information they contain I believe would be of interest to a much wider audience:Soars Grounding and Bonding - believed by some to be the bible on the subject.Mike Holt’s Illustrated Guide to Understanding the NEC Requirements for Bonding and Grounding.Of course anyone in the US who is involved with electrical installation will want a copy of the NEC.The National Electrical Code (NEC), also known as NFPA-70. Published every three years by the National Fire Protection Association, the most current edition (although not the edition enforced in your local jurisdiction) is the 2020 Edition.