E Light Safety, Training and Leadership Blog
What are the different forms and types of output relays?
Normally-open (or NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. This type of relay is also referred to as "Form A" or a "make" contact.
Normally-closed (or NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. This type of relay is also referred to as "Form B" or a "break" contact.
Change-over (or double-throw) contacts control two circuits: one normally-open contact and one normally-closed contact with a common terminal. This type of relay is also referred to as a "Form C" or "transfer" contact. It is also sometimes called a "break before make" contact. The converse, a "make before break" contact, is what is referred to as "Form D".
In addition to these naming conventions, there are other types of relays that are commonly encountered:
Single Pole Single Throw (SPST) - This type of relay has two terminals that can be connected or disconnected. Including the two terminals for the coil, this type of relays has four terminals in total. It is ambiguous whether the contact is normally-open or normally closed. The terminology "SPNO" and "SPNC" are used to resolve the ambiguity.
Single Pole Double Throw (SPDT) - A common terminal connect to either of two other. Including the two terminals for the coil, this type of relay has five terminals in total.
Double Pole Single Throw (DPST) - This type of relay has two pair of terminals. It is equivalent to two SPST relays actuated by a single coil. Including the two terminals for the could, this type of relay has six terminals total. The poles are also ambiguous; they can be normally-open, normally-closed, or one of each.
Double Pole Double Throw (DPDT) - This type of relay has two rows of change-over terminals. It is equivalent to two SPDT relays actuated by a single coil. Including the two for the coil, this type of relay has eight terminals.
Quadruple Pole Double Throw (QTDP) - These relays can also be referred to as Quad Pole Double Throw or 4PDT. This relay consists of four rows of change-over terminals and is equivalent to four SPDT relays actuated by a single coil or two DPDT relays. In total, there are fourteen terminals that comprise the coil.
Ground Fault Monitoring in Grounded AC Systems
Most electricians are very familiar with a current transformer based ground fault current relay due to their understanding of how a GFCI circuit breaker or receptacle works. Even non technical personnel encounter them on a daily basis in public rest rooms protecting a wall outlet in a wet area. Ground Fault Protection, sometimes also called GFI protection, works the same way except it is for services. The purpose of Ground Fault Protection is to monitor services for faults to ground and open the main breaker. Ground Fault Circuit Interuption in 120 volt circuits at receptacles and circuit breakers differs from Ground Fault Protection in one key way. GFCI protection is primarily designed to protect personnel from electric shock. Ground Fault Protection is not designed to protect people from electric shock, instead it is designed to protect the system and equipment from the effects of ground faults. Although the two types of protection differ in their purpose, they work in with same operating theory.
The operating theory behind the relay is as follows. A current transformer (CT) or “donut” is placed around the power wires leading to the protected load. It is important that hot and neutral wires are fed through the CT. This goes for both, single phase and three phase systems. One might come across a three phase system without a neutral, feeding a pump or an industrial motor. In this case the three phases only will be fed through the CT. Basic rule for three phase systems: If the neutral is being carried out to the load, feed it through the CT. If the neutral is not being used, then it may be left as is.
The current transformer will always read zero current in a healthy system even under a full load condition. In accordance to Kirchhoffs laws, Incoming and Outgoing currents will cancel each other out. Assume a 10A load connected to a 480/277VAC system. 10A will be fed from the source into the load, therefore 10A will have to return from the load back to the source. The CT will measure both simultaneously since it is placed around all conductors. The values were randomly chosen. Below is what the CT would see at a specific moment in time:
In accordance with the attached schematic: 10A - 5A -5A= 0A for a healthy system
Figure 1 Attached and Named Guideline 7: The grounded system with single ground fault and GF relay
A ground fault (for this example, 1 A) will divert some of the current from the arrangement and bypass the CT via the ground wire, a frame or the building ground and return back to the source.
The new equation for the CT is now: 10A - 5A - 4A = 1A; 10 A go into the load, 9 A return to the source via the phase L2 and L3 and 1 A returns to the source via the ground wire. The CT will step the current (1A) down and forward it to the Ground Fault Relay (GFR). The GFR will then alarm when its set point has been increased. The GF relay in combination with a zero sequence CT will work in resistance grounded systems as well. It will run into its limitations in circuits where wave form modifying equipment, such as Variable Frequency Drives (VFDs) or rectifier components are installed. A more advanced technique is employed for DC circuits as well as circuits with variable frequency drives.
A critical change to the 2017 NEC now requires that the GFP for services must be tested at the time of installation. This has been a requirement for some time now but the new change limits the type of test to a current injection test only now. This means that we will have to plan in advance because current injection testing can not be done if the line side feeders are terminated. We will have arrange for the testing, have it completed and do our feeder terminations.
From Chris Hartzel: There were a few of us who had some question about the most recent homework that was due yesterday. We felt some of the answers were not correct. Here's an example: Q. What is the primary purpose of the grounded conductor? A. Provide a second voltage without a second transformer B. Connect the grounded conductor to a single reference point, the earth C. Provide a low resistance path for fault current to get back to the overcurrent protective device to ensure that it trips and opens the circuit to stop the fault current D. Ensure that fault current is transferred into the earth and dissipated.
Excellent question Chris. This is one of the things that often causes confusion with electricians. It goes to the heart of grounding theory and practice. The grounded conductor's primary purpose is to provide a second voltage without a second transformer. For example, in a single phase system like a house, the grounded conductor is tapped into the center of the secondary winding on the transformer and allows you to get 240 volts between the secondary ungrounded conductors and 120 volts from either of the secondary ungrounded conductors to the grounded conductor. The same is true if a three phase wye system, where the grounded conductor is connected to the end point of each of the transformers allowing 208V between any of the ungrounded conductors and 120V between an ungrounded conductor and the grounded conductor. In situations where a second voltage is not needed, we don’t utilize a grounded conductor. For example, in a three-phase motor or feeding a three phase transformer. We simply run three ungrounded conductors and an equipment grounding conductor to those systems because we don’t need a second voltage there.
In order for this transformation and use of the grounded conductor to work properly, it must be connected in such a way that it has a solid, common reference point. Otherwise the transformation is unstable. For this reason we have to connect the grounded conductor to the earth and do it in a way that we ensure it will not be undone in the future.
In order to do this we use the grounding electrode system which is compromised of grounding electrodes and grounding electrode conductors. This system is used to connect the grounded conductor to earth at the main service or on the secondary side of three phase transformer where a new grounded conductor is created.
The third and final part of the grounding system is the equipment grounding conductor. This was added in the 1950s because our use of the grounded conductor to give us a second voltage also created a safety issue. It made the earth a potential return path for current back to its source. In order to keep fault currents from using the earth as a potential path, we began connecting the electrical devices and equipment and metal parts of buildings that were close to electrical equipment to a common conductor and bringing that conductor back to the main service and at that point connecting it all together with the grounded conductor and the grounding electrode system. That way, in the event of a fault, some small amount of fault current will still utilize the earth as a return path but the majority of the fault current will use the equipment grounding conductor as a return path and get the majority of that fault current to the overcurrent protective device and trip it.
I hope that helps. Please feel free to call me with any questions.
The NEC requirements pertaining to grounding have always been a mystifying segment of the Code. Why do we ground electrical systems and what function is it intended to achieve? What is the intended function of equipment grounding conductors? What systems are required by Code to be grounded? What is the purpose of the grounded conductor (Commonly and often mistakenly called the Neutral)
The first questions asked about grounding usually are: What is the purpose of grounding an electrical system to mother earth or something that serves in place of earth, and how much current can soil (earth) conduct?
A very common response is that the purpose of connecting a current-carrying conductor to ground is so that the fuse will blow or the circuit breaker will trip when the hot leg faults to ground. Wrong! The proof is when you intentionally take an ungrounded conductor and stick it in the earth while connected to a 15-ampere circuit and nothing happens. The amount of current that flows is in the milliampere range, which is why the earth alone cannot serve as the sole equipment grounding conductor or fault current path. The earth is a very poor conductor. Another common misunderstanding is that the purpose of the equipment grounding conductor is to direct fault currents into the ground. This is also wrong. In fact, it has the opposite purpose. By connecting the grounded conductor to earth to stabilize the voltage and provide a second voltage at the transformer, we have made the earth a potential return path for fault current. The purpose of the equipment grounding conductor is to direct fault currents along a low resistance fault path back to the source so that the overcurrent protection can sense the fault and open the circuit. In other words, it is to prevent fault currents from using the earth as a fault current return path.
One of the most important items in comprehending the requirements for grounding is to know the terminology and definitions provided in Article 100, Definitions. The terminology and definitions provided in Article 100 are specific to the Code and have very precise meanings. There is a big difference between grounded conductor and grounding conductor.
In addition, the meaning of commonly used words and what they are meant to signify in the context of the requirement depends upon the rationale that generated the requirement. For example, the term sole as used throughout Article 250 of the NEC, means singularly, by itself, alone. For example, the earth alone cannot serve as the ground-fault return path; there must be a conductor of some type that provides a low impedance ground-fault path from the fault to the power source.
Now, letès discuss some of the most commonly used terms when explaining grounding.
Grounded: This is when something is connected to mother earth, or to some conducting body that serves in place of the earth, such as the steel frame of a high-rise building on a concrete footing, metal conduit, metal electrical enclosures, or equipment grounding conductors. It can be achieved intentionally or accidentally. For example, when an electrical system is grounded, a designated current-carrying conductor is intentionally connected to earth. An example of an accidental ground is when the conductor insulation is damaged and the metal meets the earth, or a conducting material that is in contact with the earth.
Grounded conductor: This is the system or circuit conductor that is intentionally connected to earth or something serving in place of the earth. Grounding of an electrical system is achieved by connecting a current-carrying conductor to a grounding electrode system. This conductor provides a second voltage at the source without having to provide a second transformer. For example, in a single-phase system at a residence in North America, there is typically 240 volts available at the secondary winding of the transformer. A residence requires both 240 volts and 120-volt circuitry. By attaching a conductor to the mid-point of the windings on the secondary, we can achieve 120V between either of the end winding conductors and the mid-point winding conductor. We also must stabilize this system and ensure that we always get the same voltage. To do that, we connect the mid-point winding conducting to the earth. Therefore, we refer to the conductor as the grounded conductor.
Grounding conductor: This is the conductor used to connect equipment or the grounded circuit of a wiring system to the grounding electrode or multiple electrodes.
Grounding electrode conductor: This is the conductor used to connect the grounding electrode(s) to the equipment-grounding conductor, to the grounded conductor, or to both. This connection can be at the service, at each building or structure where supplied from a common service, or at the source of a separately derived system. In other words, this is the main conductor that ties the grounded conductor to earth.
Equipment grounding conductor: This is the conductor used to connect the non-current-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor, the grounding electrode conductor or both. This connection can be made at the service equipment or at the source of a separately derived system.
Grounding electrode(s): These are the devices that serve to make physical contact between the grounding electrode conductor and the earth. Only specified items can serve as grounding electrodes, such as a metal underground water pipe, metal frame of a building or structure, concrete encased bars or rods, a bare copper conductor of a specific length and cross-sectional are, rods and pipes of a specific diameter and length, and steel or iron plates.
Grounding electrode systems: Where more than one of the above grounding electrodes exists on the premises, they must all be bonded together with an appropriate sized conductor to form the grounding electrode system.
Separately derived system: This is a premises wiring system whose power is derived from batteries, solar photovoltaic system, a generator, transformer, or converter windings, and that has no intentional, direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.
Why Ground the System?
The following discussion pertains to service supplied systems, as opposed to separately derived systems. There are several reasons for connecting one of the current-carrying conductors of the electrical system to the earth or to some conductive element that is effectively connected to earth. See Section 250.4(A)(1).
1. System grounding countries, stabilized the voltage relative to earth or to grounded objects. The voltage measured between an ungrounded conductor (the live wire) and earth or grounded objects will always be the same value. In North America, we utilize two different voltages for our electrical circuitry. Typically, 240-120V, 208-120V or 480-277V. The grounded conductor is used to provide the lower and second voltage in each system.
2. If the utility lines or service drop conductors receive a lightning strike, an effective ground on one of the current-carrying conductors will cause the voltage to be pulled down to earth potential (minimum voltage differential), thereby reducing the shock hazard to personnel and the fire hazard to buildings or structures.
3. Since low voltage and high voltage conductors are installed on the same poles, damage to the supporting members might cause contact between high and low voltage conductors. Where transformers are installed, there exists the likelihood that there can be insulation failure between the primary and secondary windings. Having one of the systems grounded will pull the voltage down to the potential of the earth.
4. Grounding the system reduces the stress on electrical insulation. For example, in a grounded three-phase, four-wire, 480 wye connected system, the maximum voltage stress applied to the system is 277 volts relative to earth or a grounded object. However, if the system is ungrounded, the voltage could be 480 volts or greater under a ground-fault situation.
5. An additional ground-fault return path is provided, although it is not the main path for operating the overcurrent device.
Systems To Be Solidly Grounded (less than 50 V)
The NEC, in Section 250.20 22 identifies alternating current electrical systems and circuits that are required to be grounded. This section is broken down into four areas, (A) AC circuits of less than 50 volts, (B) AC systems of 50 volts to 1000 volts, (C) AC systems of 1000 volts and greater, and (D) separately derived systems.
Alternating current circuits operating at less than 50 volts are required to have one of their current-carrying conductors grounded under the following conditions.
1. Transformers supplied with at voltage in excess of 150 volts to ground and with a secondary voltage of less than 50 volts. The secondary must be grounded.
2. Transformers supplied from an ungrounded electrical system with a secondary voltage of less than 50 volts, one of the conductors on the secondary must be grounded. An example of this is a 3-phase, delta supply of greater than 150 volts to ground; the voltage to ground for an ungrounded delta system is the line-to-line voltage.
3. Circuits rated less than 50 volts that are run as overhead conductors, are required to have one of their circuit conductors grounded. This is to ensure that under accidental contact between high and low voltage conductors, as well as lightning strikes, the voltage will be pulled down to earth potential.
Systems To Be Solidly Grounded (50 to 1000 V)
The NEC in Section 150.20(B) identifies alternating-current systems that must be grounded where the voltage is 50 to 1000 volts as follows:
1. Where the system can be grounded so that the maximum voltage does not exceed 150 volts when measured from an ungrounded conductor to ground. A step down transformer that reduces the voltage from 240/480/550/ to 120 volts, regardless of whether it is a 2-wire or 3-wire secondary, must be grounded.
2. Any 3-phase, 4-wire, wye connected system in which the neutral is used as a current-carrying conductor must have the neutral grounded. Examples of some of the system voltages are 208Y/120, 480Y/277, and 600Y/347.
3. Circuits in systems other than those specified in (1) and (2) are allowed to be grounded, but they must follow the requirements in Article 250.
4. Anytime the premises wiring is supplied from a system that is intentionally grounded, the grounded conductor that is run to the premises wiring must be grounded again at the building or structure.
Where an installation is supplied from a 3-phase, 3-wire, wye ungrounded system, with a line-to-line voltage greater than 150 volts, it is not required to be grounded. However, it is good engineering design to ground the common point of the wye configuration at the transformer and route it to the premises wiring service equipment enclosure where it must be grounded again.
Which Conductor Do We Ground?
The conductor that must be grounded is based on the configuration of the supply system as follows:
1. Any two-wire system originating from the secondary of a two-wire transformer in which the voltage does not exceed 150 volts, either one of the conductors must be grounded. [Section 250.26(1)]
2. Any three-wire system originating from the secondary of a three-wire transformer in which the neutral is a current-carrying conductor common to the other two legs, the common or neutral conductor must be grounded. [Section 250.26(3)]
3. Any three-phase, four-wire, wye connected system in which the neutral is used as a current-carrying conductor, the common or neutral conductor must be grounded. [Section 250.26(3)]
4. Any three-phase, four-wire, delta connected system in which a common or neutral conductor is tapped from the center of one of the transformer windings that is connected between two phases, the common or neutral conductor must be grounded. [Section 250.26(5)]
Where Do We Make The Grounding Connection?
The installer or designer has the choice of where the grounding connection can be made, provided it is located within specific parameters. Remember one of the reasons for grounding that was mentioned earlier. Should an accidental contact between the high and low voltage system or a hit from a lightning strike occur, the ideal situation is that the voltage or lightning strike is directed to ground outside the building or structure. Therefore, the NEC allows a grounding connection to be made outside, on the load-side of the service drop near the weatherhead. Additionally, the connection can be made anywhere from the load-side of the service-point and the terminal or bus in at the service disconnecting means. The most common location for the grounding connection is in the main service disconnect enclosure [Section 250.24(A)(1)].
It is important to remember, do not make a grounding connection on the load-side of the service disconnect.
Takt Time – Cycle Time
There has been an interesting discussion thread on “Kaizen (Continuous Improvement) Experts” group on LinkedIn over the last few weeks on the differences between takt time and cycle time.
This is one of the fundamentals I’d have thought was well understood out there, along with some nuances, but I was quite surprised by the number (and “quality”) of misconceptions posted by people with “lean” and “Sigma” in their job titles.
I see two fundamental sources of confusion, and I would like to clarify each here.
Although takt time and cycle time are terms used in manufacturing, I have added comments concerning construction, as the same principles apply to us. Please always keep in mind that the primary risk to manufacturing is materials. The primary risk to construction is labor. When manufacturing talks about just in time delivery, they are referring to materials. When we in construction talk about just in time delivery, we are talking about labor.
“Cycle Time” has multiple definitions.
Most of the definitions of cycle time apply to manufacturing, however, cycle time can also be applied to construction. “Cycle time” can mean the total elapsed time between when a customer places an order and when he receives it. This definition can be used externally, or with internal customers. This definition actually pre-dates most of the English publications about the Toyota Production System.
It can also express the dock-to-dock flow time of the entire process, or some other linear segment of the flow. The value stream mapping in Learning to See calls this “production lead time” but some people call the same thing “cycle time.”
In early publications about the TPS, such as Suzaki’s New Manufacturing Challange and Hirano’s JIT Implementation Manual, the term “cycle time” is used to represent what, today, we call “takt time.” Just to confuse things more, “cycle time” is also used to represent the actual work cycle which may, or may not, be balanced to the takt time.
We also have machine cycle time, which is the start-to-start time of a machine and is used to balance to a manual work cycle and, in conjunction with the batch size, is a measure of its theoretical capacity.
“Cycle time” is used to express the total manual work involved in a process, or part of a process.
And, of course, “cycle time” is used to express the work cycle of a single person, not including end-of-cycle wait time.
None of these definitions is wrong. The source of confusion is when the users have not first been clear on their context. Therefore, it is critically important to establish context when you are talking. Adjectives like “operator cycle time” help. But the main thing is to be conscious that this can be a major source of confusion until you are certain you and the other person are on the same wavelength.
In construction we use the definition of cycle time as the total manual work time in a process. For example, if we determine that the it will require 8-man hours to install 200 feet of EMT conduit. The cycle time is determined by determining the number of feet of conduit that must be installed each man minute. 8 hours is 480 minutes. 200 feet of conduit divided by 480 minutes is .4 feet per minute on the average. The cycle time would be .4 feet per man minute. This would be the what we expected to happen on this project for this task. Please keep in mind this is not a general rule but determine for a specific task.
Takt time is often over simplified which leads to confusion.
The classic calculation for takt time is:
Available Minutes for Production / Required Units of Production = Takt Time
This is exactly right. But people tend to get wrapped up around what constitutes “available time.” The “pure” definition is usually to take the total shift time(s) and subtract breaks, meetings, and other administrative non-working time. Nobody ever has a problem with this.
So let’s review an example of what we have really done here. For the sake of a simple discussion, let’s assume a single 8 hour shift on a 5 day work week. There is a 1/2 hour unpaid lunch break in the middle of the day, so the workers are actually at the project. “at work” for 8 1/2 hours.
So we start with 8 hours:
8 hours x 60 minutes = 480 total minutes
But there is a 10 minute start-up process in the morning, two 10 minute breaks during the day, and 15 minutes shut-down and clean up at the end of the shift for a total of 45 minutes. This time is not production time, so it is subtracted from “available minutes”:
480 – 45 = 435
A very common mistake at this point would be to subtract the 30 minute lunch break. But notice that we did not include that time to start with. Subtracting it again would count it twice. In construction this is somewhat greater due to the placement and availability of latrines on large construction projects and other considerations.
No employee works 8 hours per day on a large construction site. Let’s analyze:
1. Daily safety briefing and JHA review: 5 minutes
2. Daily stretch and flex- 8 Minutes
3. Break time – 15 minutes
4. Latrine breaks- 3 x 5 minutes- 15 minutes
5. Cleaning up at the end of the day- 15 minutes
None of this is accounting for looking for materials, looking for tools, looking for information that the supervisor failed to provide the crew. Just taking into account the items above you have a total of 58 minutes. Therefore your 480 minutes of production time in one day is reduced to 422 minutes.
Lets continue the example using the original of 435 minutes.
So when determining takt time, we would use 435 minutes as the baseline. Lets suppose we needed to produce 50 units / day, then the takt time would be:
435 available minutes / 50 required units of production = 8.7 minutes per unit
Note that you can just as easily do this for a week, rather than a day.
435 minutes x 5 days = 2175 total available minutes
2175 available minutes / 250 required units of production still equals 8.7 minutes
All of this is very basic stuff, and I would get few arguments up to this point, so why did I go through it?
Because if you were to run this construction project, at a 8.7 minute takt time, you will come up short of your production targets. You will have to work overtime to make up the difference, or simply choose not to make it up which is rarely an option.
Why? Because there are always problems, and problems disrupt production. Those disruptions come at the expense of the 435 minutes, and you end up with less production time than you calculated. Some times these issues are outside of our control. When this happens, we need to track these and submit them as change order requests. Often times, these disruptions are our fault. Many times we prevent our crews from doing their jobs and be productive because we fail to provide them with 100% of the Tools, Material and Information that they need to complete the task. They then have to stop producing and go find what they need to complete.
One mistake supervisors make on a regular basis is that that they estimate the amount they can produce in a single day based on 8 hours of production, even though they can not work their crews for 8 hours.
Also remember that other things happen that we have to deal with that are in the contract that we can not recoup. Such as weekly required safety meetings for the entire job site, and OSHA inspection, the GC closes off an area for a hazard, etc. I could go on with a myriad of examples gathered from real sites, but you get the idea.
Here is what is even worse, though.
If you expect operators to do their daily equipment checks, when do you expect that to happen?
Do you truly expect your crews to stop work if they determine a safety or quality issue until it is corrected? How are you to account for these stoppages?
All of these things take time away from production.
The consequence is that the leadership – the ones who have to deal with the consequences of disrupted production – will look at takt time as a nice theory, or a way to express a quota, but on a minute-by-minute level, it is pretty useless for actually pacing production.
All because it was oversimplified.
If you expect people to do something other than produce all day, you have to give them time to do it.
Let’s get back to the fundamental purpose of takt time and then see what makes sense.
The Purpose of Takt Time
Here is some heresy: Running to takt time is wholly unnecessary. Construction projects operate just fine without even knowing what it is.
What those projects lose, however, is a fine-grained sense of how things are going minute by minute. Truthfully, if they have another way to immediately see disruptions, act to clear them, followed by solving the underlying problem then they are as “lean” as anyone. So here is the second heresy: You don’t NEED takt time to “be lean.” ( LEAN: The removal of everything that does not add value to the final product)
What you need is some way to determine the minimum resource necessary to get the job done and a way to continuously compare what is actually happening vs. what should be happening, and then a process to immediately act on any difference. This is what makes “lean” happen.
Takt time is just a tool for doing this. It is, however, a very effective tool. It is so effective, in fact, that it should be considered a fundamental although it is mostly overlooked in construction. I made the above statements to get you to think outside the box for a minute.
What is takt time, really?
Takt time is an expression of demand normalized and leveled over the time you need to produce. What takt time does is make demand appear level across your working day.
This has several benefits.
First, is it makes calculations for planning really easy through even a complex flow. You can easily determine what each and every task and crew must be capable of. You can determine the necessary speeds of crews. You can look at any process and quickly determine the optimum number of people required to make it work, plus see opportunities where a little bit of change or improvement will make a big difference in productivity.
More importantly, though, takt time gives your team members a way to know exactly what “success” looks like for each and every task. All you have to do is tell them up front and then they can tell throughout the day if they are meeting the goal or not.
This gives your team members the ability to let you know immediately if something is threatening required output. Put another way, it gives your entire team the ability to see quickly spot problems and respond to them before little issues accumulate into working on Saturday.
The key point here is that to get the benefit, you have to have a takt time that actually paces production. It has to be real, tangible, and practically applied on the project. Otherwise it is just an abstract, theoretical number which no one cares about.
The second big advantage is that it allows to you better plan and forecast your work. You can determine what it will really take to complete and also be able to defend that and explain to your project manager. You can also be more realistic in your forecasting so that when you say it will take three men, two weeks to accomplish this task, you will most likely be able to make the goal and also track it daily and make adjustments if need be.
You can also use this data to determine places where you can increase the productivity of your crews, and therefore increase the profitability. For example, what if you were to determine a takt time using the example earlier and determined that it worked out that you needed to produce at .4 feet per man minute. Now, what if you were to talk to the crews and ask them for ideas on how to increase to just .5 feet per man minute. If you were to accomplish that you would then produce .5 x 422= 211 feet per shift, per man. That is an 11% increase in productivity. Carried over a project, that could be significant.
Finally if disruptions do cause shortfalls to the required output, you have to make it up sometime. If you are constrained from running overtime (and many operations are for various reasons), then your only alternative is to build a slight over speed into your takt time calculation. You can also use the tracking that you have done to demonstrate the disruption and perhaps request either a schedule extension cost increase change order.