PowerPoint ® Presentation Chapter 1 PLC Electrical Safety Programmable Logic Controllers PLC Safety...

PowerPoint® Presentation

Chapter 1PLC Electrical Safety

Chapter 1PLC Electrical Safety

Programmable Logic Controllers • PLC Safety • Electrical Properties • Grounding • Force and

Disable Safety Considerations • Electrical Noise Suppression • Static Electric Charges • Electrical

Safety • Personal Protective Equipment • Lockout/Tagout • Inspecting a PLC System •

Chapter 1 — PLC Electrical Safety

PLC system programming is viewed by various devices that connect to micro-sized PLCs (8 to 10 inputs and outputs) or to large-sized PLCs that control thousands of inputs and outputs.


Improperly installed and/or maintained PLCs can overheat, leading to fire or explosion.


An advantage of a PLC controlling a process is that a PLC can be programmed and reprogrammed as process conditions change.


An electric shock results anytime a body becomes part of an electrical circuit.


Possible effects of electrical shock include the heart and lungs ceasing to function, and/or severe burns where the electricity (current) enters and exits the body.


Current is the amount of electrons flowing through an electrical circuit and is measured in amperes.


Voltage is the amount of electromotive force in a circuit and is measured in volts.


Resistance is the opposition to the flow of electrons and is measured in ohms.


Grounding provides a direct path for unwanted fault current to travel to earth without causing harm to technicians or equipment.


Building grounding, equipment grounding, and electronic equipment grounding are used to create a safe working environment for technicians.


Building grounding ensures that there is a low impedance (low resistance) grounding path for fault current (electrical short or lightning) to earth ground.


Equipment grounding prevents electrical shock when a person comes in contact with electrical equipment or exposed metal of machinery.


Electronic equipment grounding is used to provide a quality ground for electronic systems to enable better communication (less noise) with PLCs, process control equipment, and other facility operations.


Ground resistance measurements are taken on grounding conductors used with service entrances, transformers, utility transmission, and communication (control circuit) grounds.


PLC force and disable commands are used during system start-up and for troubleshooting.


Electrical noise enters a PLC system through input devices, output components, and power supply lines.


To prevent false signals from entering a PLC, input and output lines must cross at right angles (90°) and not run parallel to each other.


A shielded cable uses an outer conductive jacket (shield) to block electromagnetic interference from the inner, signal-carrying conductors.


Snubber circuits are used to suppress voltage spikes in PLCs.


Depending on the PLC application, an enclosure with a cooling unit can be required.


Article 500 of the NEC® classifies hazardous locations according to the properties and quantities of the hazardous material that may be present.


Electrical safety rules aid in the prevention of injuries from electrical energy sources.


PLC safety begins with a sufficient number of emergency stops and a master control relay that removes power to the inputs and outputs of the PLC and stops all motion of the machine(s) or process.


Personal protective equipment includes items that protect a technician from electrical and other hazards.


Arc-flash protective clothing made of Nomex®, Basofil®, and/or Kevlar® fibers must be used when working with live high-voltage electrical circuits.


The National Fire Protection Association (NFPA) specifies boundary distances that vary depending on voltage.


Protective helmets are identified by class of protection. For example, Class E protective helmets protect against high-voltage shock and burns.


Eye protection must be worn to prevent eye or face injuries caused by contact arcing, radiant energy, or flying particles.


Ear protection is worn to prevent technician hearing loss caused by electrical systems, machinery, power tools, and HVAC equipment.


Rubber insulating gloves have color-coded labels that represent voltage ratings for specific applications.


Rubber insulating gloves must be air tested before each use and when there is cause to suspect damage.


Insulated rubber-soled shoes are typically worn during electrical work to aid in the prevention of electrical shock.


Lifting an object with the legs reduces the possibility of a back injury.


When carried on the shoulder by one person, objects such as conduit must be transported with the front end down.


Rubber insulating matting aids in protecting a technician from electrical shock when working on energized electrical circuits.


Lockout/tagout kits contain reusable danger tags, tag ties, multiple lockout hasps, magnetic signs, and information on lockout/tagout procedures.


Lockout devices resist chemicals, cracking, abrasion, and temperature changes and are available in colors to match American National Standards Institute (ANSI) pipe colors. Lockout devices are sized to fit standard industry equipment.


A proper inspection of a PLC ensures safe control of an electrical system.


Proper grounding is important in PLC applications. Improper grounding can lead to interference (noise) being induced into PLCs, which can cause output devices to be falsely turned ON and put personnel and equipment at risk.

PowerPoint ® Presentation Chapter 1 PLC Electrical Safety Programmable Logic Controllers PLC Safety...

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