README.md

Main list of projects

Electrical Safety Talk For Factory Electricians and Control Technicians

This was the conversation I had with all new electricians that I supervised regardless of their previous experience.

Topics Covered

• Equipment Grounding For Electric Shock Protection
• The Dangers Of Voltage Gradients on Land, In Salt Water, and In Fresh Water
• System or Earth Grounding To Protect Equipment From Electromagnetic pulses Associated With Nearby Lightning And Power Surges
• Lightning Rods For Protection Against Direct Lightning Strikes
• Bonding For Fire Protection
• Understanding Causes of Arc Flash Explosions

As a controls technician, you are now an electrician.
In this role you will be:

• Wiring electrical devices that you and your coworkers are going to use,
• Doing some testing on live 480 volt circuits,
• Advising your coworkers how to stay safe during their work around electrical devices.

A full understanding of the topics discussed in the following video will help ensure your safety and the safety of everyone who depends on you.

At your earliest convenience you need to watch the video at:
https://youtu.be/mpgAVE4UwFw?si=8LH7m4NESoRNMt5p

The presenter is a legend in the industry and he is very funny.
I hope you enjoy the video.

When watching the video it is understood that:

• A “fault” is when a voltage carrying wire is touching the metal chassis of a machine.
• “Clearing a fault” means causing a circuit breaker to trip.

As you watch the video I want you to look for the answers to the following questions that I wrote out for you. Please read the questions first and then watch the video. Don’t read the answers, just read the questions. Most of the questions below are addressed in the video – some are not, but please give all of these questions some thought. Then we will discuss them together. This is not a test. I already know that you are very knowledgeable and highly intelligent. This is just a discussion to help ensure your safety.

• In the circuits you service, where are the electrons going? (Hint: It’s not the ground.)

  • The electrons are always going back to the power source from which they came.
  • This will be the transformer in the case of AC power in a cabinet.
  • This will be the VFD in the case of a motor.
  • This will be the power supply in the case of DC power.
  • The electrons will take any available path but they are always going back to the power source.

• Which organ in your body is it most important to protect from electric shock?

  • It’s the heart. Even a tiny amount of electric current through the heart will cause defibrillation and almost certain death.

• When testing live circuits, why do electricians work with one hand behind their back?

  • This prevents electric current from passing through the heart by way of the hands.
  • Still, even with one hand behind the back electric current can go from one hand, through the heart and back to the power source by way of legs, hips or torso if you are leaning on the machine chassis.
  • This is why electrically insulated gloves must be worn when working around live power.

• If you are holding a 480 volt copper wire in your bare hand while wearing electrically insulated boots and not touching anything else, will you get electrocuted or feel a shock?

  • Your body will now be at 480 volts but there is no path back to the power source for the electrons.
  • With no path back to the power source, there is no electric current moving through your body.
  • So no, you won’t feel any shock and you are not being electrocuted but you are in danger. Now is not the time to touch the chassis or anything else connected to the neutral terminal of the transformer. If you do, then you will become a wire and current will pass through your body. If the current passes through your heart then you will likely die.

• What would happened if you are holding a 480 volt copper wire in your bare hand while wearing electrically insulated boots and not touching anything but then touch that same hand to a metal chassis which is grounded to the neutral lead of the 480 volt transformer?

  • You would burn your hand as electric current passes from the wire, through your hand to the chassis.

• What would happen if you are holding a 480 volt copper wire in your bare hand while wearing electrically insulated boots and not touching anything but then touch your other hand to a metal chassis which is wired to the neutral lead of the 480 volt transformer?

  • Now you are dead.
  • Electric current has passed through your heart and caused defibrillation.

• What would happen if you are holding a 480 volt copper wire from phase A in your bare hand while wearing electrically insulated boots and not touching anything but then touch a 480 volt wire from phase B or C with your other hand?

  • Again, you are dead.
  • Because phases A, B, and C are always at different voltages at any given instant, current will flow through your heart and you will die.

• What would happen if you are holding a 480 volt copper wire from phase A in your bare hand while wearing electrically insulated boots and not touching anything but then touched another 480 volt wire from phase A with your other hand?

  • In this case both wires have the same voltage at any given instance, so your body is at 480 volts but no current is flowing.
  • So you are not dead but you are in great danger.
  • This is not a good time to lean on the machine chassis.
  • In fact wise electricians maintain their balance and never lean on machines.
  • And of course wise electricians always wear electrically insulated gloves.

• How do you make an electrical circuit safe to touch?

  • You disconnect the circuit from the voltage supply.

• What makes a circuit breaker trip?

  • A large amount of current passing through the breaker will cause it to trip.

• What is the Equipment Grounding Conductor (the green wire) for?

  • It causes the circuit breaker to trip in the event that a hot wire touches the chassis.
  • The Equipment Grounding Conductor provides a low resistance path from the chassis back to the power source.
  • This forces a high current to flow through the circuit breaker when a hot wire touches the chassis which causes the breaker to trip.
  • Once tripped, the voltage is removed from the circuit and the chassis becomes safe to touch.
  • It may take a moment for the circuit breaker to trip. During this time the chassis is hot.

• Why do we try to make the Equipment Grounding Conductors (the green wires) large in diameter and short in length?

  • This keeps the resistance of the Equipment Ground Conductor as small as possible.
  • Small resistance means maximum current is going through the circuit breaker so that it will trip in the shortest amount of time.

• What is the Effective Ground Fault Current Path?

  • This is the name given to the low resistance path back to the power source which is provided by the Ground Fault Conductor.
  • The Effective Ground Fault Current Path is what causes the circuit breaker to trip when a hot wire touches the chassis of a machine.

• Why do we never remove the grounding prong from an electrical plug?

  • Removing the grounding prong would break the Effective Ground Fault Current Path from the chassis back to the power source.
  • So now when a hot wire makes contact with the chassis the circuit breaker will not trip.
  • The chassis will maintain the same voltage as the hot wire.
  • In other words, the chassis will become hot.
  • If you were to lean on this chassis then you would become hot.
  • And if you reach out and put your hand on another piece of equipment or railing which has an Effective Ground Fault Current Path back to the power source then current will flow through your heart and you will likely die.

• What is it called when we install an Equipment Grounding Conductor to the metal chassis of a machine at one end and the neutral lead of a transformer at the other end?

  • This is called “Equipment Grounding”.

• What is an Equipment Ground and why is it used?

  • Equipment Grounding causes the circuit breaker to trip in case a hot wire touches the metal chassis of a machine.

• What is a “System Ground” or “Earth Ground” and why is it used?

  • A System Ground or Earth Ground is made when the neutral terminal from a transformer is connected by a wire to a metal rod which is driven into the earth.
  • This allows transformer and motor windings to dissipate voltage spikes caused from Electromotive Pulses (radio waves) which result from lightning strikes in the area.
  • Dissipating these voltage spikes protects the insulation around the wires in the transformer and motor windings.

• What is the difference between an Earth Ground and an Equipment Ground?

  • An Earth Ground, or System Ground, is a wire going from the neutral terminal of a transformer to a rod which is driven into the ground.
  • An Earth Ground protects motor and transformer windings from electromagnetic pulses caused by nearby lightning
  • An Equipment Ground is a wire going from the metal chassis of a machine to the neutral terminal of a transformer.
  • An Equipment Ground protects people from electric shock by causing the circuit breaker to trip when a hot wire touches the chassis of a machine.

• What is a “Common Ground” or “Common Wire” and why is it used?

  • A Common Ground is used in single phase AC and in DC applications.
  • It carries current back to the power source after it has dropped all its voltage across a load.
  • The neutral side of all loads driven by a power source will meet at this node which is why these are called the Common Wires or a Common Ground.
  • The Common Wire is usually white in both AC and DC applications.
  • The “Common Wire” is really a branching tree of wires all connected to the neutral side of a DC power supply or AC transformer. But since they are all connected together, they are thought of as single Common Wire.
  • Do not confuse the Common Ground with the Equipment Ground nor the Earth Ground discussed previously.

• Why should only fault current be allowed on an Equipment Ground but not working current?

  • The Common Ground (not the Equipment Ground) is for working current making its way back to the power source after dropping its voltage across a load.
  • The Equipment Ground is reserved only for Fault Current. This is current caused by a rogue hot wire which has come into contact with the metal chassis of a machine. This is the current which trips the circuit breaker.
  • Since we don’t want the chassis to carry current and since the Equipment Ground (green wires) make contact with the chassis, we don’t allow working current on the Equipment Ground wires. Working current is reserved for the white Common Wires.

• What is “Bonding” and why is it used?

  • Bonding is electrically joining all metal parts of a building structure including water pipes together by wire and joining all these by wire to rods driven into the ground.
  • This is done to protect against arcing between metal parts of a building when nearby lightning strikes cause electromotive pulses in the building.
  • This is for fire protection.
  • Without the bonding these pulses would cause arcs which might pass through combustible materials to cause a fire.
  • Machinery is not usually bonded to a building because the same voltage spikes in the building which create arcs can destroy solid state electronic equipment.

• What would happen if you touched a 120 volt wire to a rod driven into the ground?

  • It would create a voltage gradient in the earth starting at 120 volts and dissipating to zero volts as distance increases from the rod.
  • The dissipation with distance is not a linear function. Most of the voltage is dropped near the rod.
  • So if you step near the rod with one bare foot and step away from the rod with the other bare foot then you have a 120 volt potential between your feet which could kill you.
  • Touching a 120 volt wire to a grounding rod would not likely draw enough current to trip a circuit breaker so the gradient in the earth near the wire would remain energized. This is an accident waiting to happen. This is why Equipment Grounding is so important when Earth Grounding machinery.

• What would happen if you touched a 120 volt wire to the metal chassis of a piece of equipment which has a System or Earth Ground but no Equipment Ground?

  • A voltage gradient would form around the grounding rod but not enough current would flow into the earth to trip the circuit breaker.
  • As a result the metal chassis would remain hot at 120 volts.
  • The ground at the grounding rod would also be hot at 120 volts and a voltage gradient would spread out from the grounding rod.
  • If you were to touch the hot machine with one hand and touch another Equipment Grounded machine with the other hand then current would pass through your heart and you would likely die.
  • If you have bare feet with one foot near the grounding rod and another foot further away from the grounding rod then your feet would be at different voltages and current would flow through your body and you could die.
  • If you were to touch the hot machine while standing on the ground with bare feet then electrical current would pass through your heart as it travels from hand to foot and you would likely die.

• What would happen if you touched a 120 volt wire to a metal chassis which is Equipment Grounded?

  • In this case the circuit breaker would trip and nothing bad would happen.

• Does an Equipment Grounded chassis protect you from electric shock in the event that a hot wire touches the metal chassis?

  • Yes it does.

• If so, how does the protection work?

  • The Equipment Ground Conductor provides an Effective Ground Fault Current Path. This causes a large amount of current to flow through the circuit breaker which causes it to trip. Now the hazardous voltage has been removed from the circuit.
  • There is an erroneous notion that the Equipment Ground Conductor keeps the chassis at zero volts when it comes in contact with a hot wire. This notion is false. The chassis will remain hot until the circuit breaker has tripped. All the voltage must be dropped across the resistance of the Equipment Ground Conductor and the windings of the transformer. The neutral terminal of the transformer will be at zero volts but the machine chassis at the other end of the Equipment Ground Conductor will remain hot until the circuit breaker trips.

• Does Earth Grounding a chassis protect you from electric shock in the event that a hot wire touches the metal chassis? If not, then why not?

  • No it does not. Earth grounding only protects the insulation of motor and transformer windings from high voltage spikes caused by electromotive pulses from nearby lightning strikes.
  • The earth does not draw enough current through the rod to trip the circuit breaker. So the machine chassis, the ground wire, the ground rod, and even the earth near the rod remains hot.
  • If you were to touch the metal chassis then you would become hot – that is you would carry the same voltage as the chassis. If you were to then make contact with any conductor which is Equipment Grounded or if you were to make contact with the earth then current would pass through you and you would likely die.

• If System Ground or Earth Ground does not protect people from electric shock then why is it used?

  • Earth grounding protects the insulation of motor and transformer windings from high voltage spikes caused by electromotive pulses from nearby lightning strikes.

• What types of devices should be System/Earth Grounded?

  • Any devices that have windings such as motors and transformers act as antennae for the Electromotive Pulses (radio waves) created by nearby lightning strikes.
  • This creates high voltage spikes within the windings that break down the insulation of the wires that make up the windings.
  • Eventually you get short circuits within the windings and that makes the motors and transformers useless.
  • Providing a System or Earth Ground allows the voltage spikes to dissipate into the earth without harming the windings.

• What types of devices should not be System/Earth Grounded?

  • Digital electronic equipment should not be System or Earth Grounded.
  • This is because you don’t want the voltage spikes picked up by transformer and motor windings to fry your delicate digital electronic circuits.

• Does System/Earth Grounding protect equipment from a direct lightning strike on a building?

  • No, a direct lightning strike on a building will do enormous damage no matter if there is a System/Earth Ground or not.
  • System/Earth Grounding only protects motor and transformer windings from Electromotive Pulses (radio waves) generated by nearby lightning strikes.

• What is a Lightning Rod and how is it different from System/Earth Grounding?

  • A lightning rod is a structure that goes over and around a building but is not connected to it. The idea is to draw lightning into the rod, away from the building, and into the ground.
  • A lightning rod protects the building from a direct lightning strike whereas a System/Earth Ground protects motor and transformer windings from radio wave pulses which are generated by nearby lightning.

• What would happen if you accidentally connected the hot 120 volt lead from shore power to the common bus bar in a fiberglass boat and connected the common wire from shore power to the 120 volt bus bar in the boat?

  • There is great danger but it is not immediately obvious.
  • Since the common bus bar in the boat is connected to the boat's equipment ground, and since all metal parts of the boat also bonded to the equipment ground, then all the metal parts of the boat would become hot at 120 volts.
  • But since all the metal parts are at the same 120 volts and since the fiberglass hull does not conduct electricity there is no where for current to flow
  • So someone standing in the boat could touch the metal items and also become hot at 120 volts but would not suffer a shock because no current can flow when everything is at the same 120 volts.
  • The boat would appear to work fine because AC equipment runs even when the hot and common leads are reversed.
  • However, there is great danger
    • Voltage Gradients In the Water
      • Since all metal parts are bonded to the equipment ground and since the equipment ground is connected to the common bus bar, the propeller shaft and other metal parts are hot at 120 volts.
      • This makes the water close to the propeller hot at 120 volts and creates a voltage gradient in the water as you get further away from the boat.
      • Anyone swimming near the boat will become paralyzed by voltage gradient and drown.
      • The effect of voltage gradients are much much worse in fresh water than in salt water because fresh water is much less conductive to electricity.
    • Touching Something Metal On The Boat While Touching Something Metal On Shore
      • If a person on the boat is touching a metal handrail with one hand which is bonded to the hot equipment ground on the boat and then touches something metal on shore which has a proper equipment ground fault path back to the neutral terminal of the transformer then current would flow through the heart and the person would likely die.
    • Electrolysis will put a hole in the boat and sink it.
      • Since metal parts in the water are hot at 120 volts, electrolysis is highly accelerated and metal parts will corrode in only a few days. This will cause holes to open up below the water line and the boat will sink.

• What are Arc Fault, Arc Flash, and Arc Blast?

  • Arc Fault is an electric arc which forms between two hot wires of different phases or between a hot wire and a neutral wire.
  • When an Arc Fault occurs, there’s a massive electrical explosion.
  • Both Arc Flash and Arc Blast are separate byproducts of that electrical explosion.
  • The Arc Flash is the light and heat from the explosion
    • Arc flash can ignite clothing and burn the skin of anyone within a few feet.
    • Arc Flash can also melt metal, cause lung and eyesight damage and even lead to hospitalization or death
  • The arc blast is a pressure wave that follows.
    • These can be strong enough to throw a fully grown technician to the ground or cause additional equipment damage.
    • Arc blasts can cause damage to your hearing or brain functions.
    • The blast can also cause loose equipment, tools, machinery, debris, and molten metal to go flying which can cause further damage or injury.
  • The destruction is devastating and often deadly.

• What causes Arc Fault?

  • Touching a tool or test probe to the electrical cables, bus bars, or surfaces of different voltages at the same time.
    • When a technician is using a metal tool inside a live electrical cabinet there is the risk of touching a hot wire or hot bus bar and a neutral bus bar or a bus bar of a different voltage phase at the same time.
    • This creates a short circuit and sparks which startle the technician and causes him/her to pull back the tool.
    • As the technician pulls back, an arc of superheated plasma forms between the tool and the wires. This is the Arc Flash. The Arc Blast is the explosive pressure wave that follows.
    • For this reason it is wise to avoid any maintenance of live electrical cabinets.
    • Sometimes troubleshooting and taking electrical measurements can only be done when the electrical cabinet is live.
    • If you must work in a live electrical cabinet then:
      • Suit up in Arc Blast gear which is rated for the available amperage of a blast.
      • Use electricians tools which are insulated as much as possible to prevent accidentally bringing metal the metal tool in contact with two surfaces of different voltages at the same time.
      • Set up boundaries to keep your coworkers out of danger.
  • Dust, Corrosion, or loose wires are present in an electrical cabinet when throwing a switch or opening the cabinet door.
    • If dust, corrosion, or loose wires are present when moving the switch of an electrical disconnect then an arc may form causing an explosion in the electrical cabinet.
    • When throwing the main disconnect in an electrical cabinet one should always:
      • Suit up in Arc Blast gear which is rated for the available amperage of a blast
      • Stand to the side of the cabinet door as you throw the switch or open the door so that you will not be directly in front of the explosion.
      • Set up boundaries to keep your coworkers out of danger.
  • Voltage transients (spikes), resulting from switching reactive loads or lightning strikes. - Spikes can happen at any time. - So always wear Arc Blast gear which is rated for the available amperage of a blast when working in a live electrical cabinet.

• What is Available Arc Fault Current?

  • This is the resistance of the electrical cables or bus bars going back to the transformer multiplied by the voltage on the cables.
  • This value is used to determine what type of blast gear the electrician should be wearing when throwing disconnect switches or when opening live electrical cabinets.

• What do short thick cables or the presence of bus bars tell us about Available Arc Fault Current?

  • Short cables have low resistance. Thick cables have low resistance. Bus bars have low resistance.
  • Cables and bus bars which are both short and thick have even lower resistance.
  • Let this be a warning: When you see thick electrical cables or bus bars of any size you should understand that there will be enough Available Arc Fault Current to create a massive Arc Blast
  • Take appropriate precautions.