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General Electrical Safety

J.S. Held expands building consulting practice in Canada with the acquisition of SPECS.

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Electrical systems by nature are considered extremely dangerous to most human beings as these systems operate under conditions that are not seen, touched or felt unless it is by accident. The consequences of these accidents are sometimes catastrophic or fatal. Electricity is not a product that comes bottled and ready for use; it must be designed, installed, and maintained in a manner that makes it safe for human consumption or general use. The installations, maintenance, and inspections of electrical equipment is required by qualified personnel. Sometimes these tasks must be completed on live equipment due to the fact that many buildings and institutions require power to be on at all times. In the building consulting industry, we are required many times to enter buildings that have been damaged by any number of natural or human causations and it is imperative to understand the factors involved in keeping safe in these conditions.


This white paper is intended to cover general electrical safety information in relation to understanding electrical systems and best practices in being safe around electrical equipment. This is not an in-depth study of all requirements for electrical safety procedures and practices, but more of a general introduction in being safe around electrical systems. For more information on safety concerns and issues related to electricity overall, we recommend the Electrical Safety Handbook as an excellent resource.

The items for discussion relative to electrical safety will include the following topics:

• Electrical Dangers
• AC and DC Power
• Voltage Levels
• Personal Protective Equipment
• Understanding Electrical Circuits and Safety

Electrical Dangers

Anybody who encounters the International Safety Symbol for “Caution Risk of Electrical Shock” must know that electrical voltages are present that are capable of death to a human being.

The presence of the International Safety Symbol on any electrical equipment cover, panel door, or component means that only a qualified person should perform any necessary duties within electrical equipment. A qualified person, per the National Electrical Code (NEC), is defined as “one who has skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training to recognize and avoid the hazards involved”. [1]

SAFTETY WARNING: Removing the cover plate on any electrical item may expose you to dangerous voltages and extreme caution should always be practiced. Always treat electrical items as live unless you and your qualified person have tested them or have verified the power is off.

The three main hazards of working on, around, or near electrical equipment are shock, arc, and blast. Each of these hazards have many factors involved in being injured by any one of them, however there are protection systems, procedures, and mitigating resources available to keep you safe from all of them. Every working situation needs to be documented and considered using protective strategies that are published in most Arc Flash Hazard Study evaluations before any procedures are performed on live gear. Ultimately if equipment can be de-energized then it is typically the safest strategy of all. Again, refer to your safety handbook for tables and references for more on protective strategies to remain safe at all times.

AC and DC Power

Electrical energy is derived from different sources that produce differing wave lengths of power. One of the source types is an “alternating” means; as it alternates in relation to time. The other source type is a “direct” means; as it is directly proportional to time. Electricity is “current”.

So, in the simplest terms; AC is “Alternating Current” and it is derived from rotational sources such as generators, alternators, turbines, hydros, or any type of rotational mass. DC is “Direct Current”, it is typically derived from stored energy sources such as batteries, capacitor banks, power supplies, solar cells, or a rectified AC source. This is the most basic understanding of the two types of systems that will be encountered in any type pf building or structure.

Typical power systems within a building will involve AC systems from a utility source, while some types of buildings will have renewable or green energy sources from PV modules (solar), wind generators, and steam generators.

Some emergency systems are UPS (Uninterruptable Power System) which are made up of banks of batteries that are equivalent to the total load of the design capacity. CPS (Constant Power System) type emergency systems use a rotational mass (50,000 Lbs.+) that are connected inline with an electrical motor and a diesel engine system. Both of these systems derive power from a DC source and are transferred to AC power via one form or another to be used within the building circuits.

Emergency generators use a gas or diesel engine source typically to rotate an AC alternator that will produce voltage at the designed system capacity. Emergency electrical systems are designed to automatically transfer power during a utility power outage to the emergency source after the engine starts. There are specific regulations as to how these emergency systems must be labeled to warn qualified persons of all sources of power for safety concerns. The same warnings and information are required for solar photovoltaic and wind energy systems that produce power from sources other than the utility. You must be aware of all sources of power in any overall system.

Voltage Levels

Electrical voltage is a term that most people understand about electrical equipment and its ratings. Voltage comes in many different shapes (wave forms) and sizes (high, medium, low) to suit everyone’s needs from basic residential uses to expansive manufacturing facilities.

Voltage is what completes the work task of an electrical system. Other terms for forces of energy include amperage, ohms, and watts. You need to know that these are all measurements of electrical energy - no matter if it is AC or DC power. Each of the measurements of power provides a different type of work force of energy. These forces, when impacted with the human body, can cause devastating injuries and/or death. For the purposes of this paper we will discuss where the different voltage levels are found and when to be aware of them.

Building Voltage Ranges: (Based on IEEE Standards)
• 1V to 50V is considered Extra Low Voltage
• 50V to 600V is considered Low Voltage
• 601V to 69,000V is considered Medium Voltage
• 69,000V to 800,000V+ is considered High Voltage & EHV (Extra High Voltage)

Extra Low Voltage: Voltage of 1V to 50V AC is considered Extra Low Voltage (ELV). Up to 100V DC is considered Extra Low Voltage. Extra Low Voltage Systems are Typically Used for:

Telecom and Datacom Systems, HVAC Control Wiring, Fire Alarm Wiring, CCTV, TV, Radio, Communication, Audio, Video, Security Wiring, Sound, Speaker System Wiring, Nurse Call, Clock/Bell System Wiring and Automation System Controls.

Danger: Any voltage above E 50V-AC can damage human skin

Low Voltage or LINE Voltage: Line Voltage typically refers to commercial/residential systems that are transformed at the utility power source and are provided at the following main voltages:

• Residential is usually 120/240 Volt - Single Phase Systems
• Light Commercial is usually 120/208/480 Volt - Three Phase Systems
• Heavy Commercial is typically 277/480/5000 Volt - Three Phase Systems

Single Phase systems derive their power from a 2-wire power circuit and three-phase systems derive their power from a 3-wire power circuit that provides 1.732 times more power than a single-phase system. This is why it is more compatible for commercial industrial applications.

Heavy Commercial or Industrial “Line” Voltage systems are typically transformed by equipment that is owned and maintained by the property or business owner. These larger power systems are typically provided in the following main voltages:

• Heavy Commercial is typically 277/480/5000 Volt - Three Phase Systems
• Industrial is typically 480/5000/12470/34000 Volt - Three Phase Systems

Medium Voltage: Medium voltage is typically a secondary utility power distribution system between 1kV to 69kV. DC voltages up to 100kV DC is considered medium voltage (k = add three 000). Medium voltage systems are typically used for:

• Substation secondary wiring systems
• Distribution transformers
• Residential transmission lines for utility distribution - power poles
• Commercial primary substations
• Motor Control Centers
• Large motor distribution/branch power circuits

DANGER: Any voltage above 120V-AC can cause death/DC Voltage is dangerous

High Voltage: High voltage is present at any primary utility power distribution point. Voltages from 36kV to 300kV are considered High Voltage. DC voltage up to 1000kV is considered High Voltage (k = add three 000). Primary voltage systems are typically used for:

• High tension power transmission lines feeding from:
• Hydro, Coal, Fuel Oil, Wind and Photovoltaic power systems

Understanding that voltages at this level are highly volatile power systems that require a qualified personal to have many additional hours of proper training and the use of proper power rated PPE to even come within what is known as approachable limits. Tools that are rated specifically for the voltages that are being worked on are required. Know these limits before ever attempting to approach these types of systems or components of these systems. No person without proper training and PPE should ever attempt to approach live gear in these voltage ranges. They are deadly.

DANGER: Voltage above 5kV-AC can literally jump across open air gaps

Personal Protective Equipment (PPE)

The specialized protective equipment for qualified persons is intended generally to protect eyes, face, head, body, hands and feet from the three general hazards of electrical danger (arc, shock, blast). All of these protective items have ratings for the systems being worked on. All pieces of the PPE are rated so that in the event of an arc fault explosion, the qualified person can walk away from such an event without harm.

Basic day to day work clothing worn by an electrician or person working near electrical equipment should be constructed of flame retardant cotton or synthetic-cotton blended materials which have long sleeves for full arm protection, long pants for leg protection and fiberglass style protective toed leather boots. The boot soles should also not contain any metal or metallic studs that hold the sole onto the boot. Only leather sewn or glued sole type boots should be worn in energized equipment areas.

Arc Flash clothing and full suits have an arc rating that is measured in Cal/cm2 (CAL). These materials are typically manufactured from flame resistant materials such as NOMEX®, KEVLAR®, and KERMEL®.

Flash suits are rated in the same manner and have more of the same materials in them. Typically, with medium and high voltage power equipment the requirement is for a full flash suit which includes the coveralls being worn underneath.

The National Fire Protection Association (NFPA) code 70E regulates the different categories of arc fault clothing and the requirements for how much to wear and when.

Each of the category levels of protection have different voltage ratings for leather coverings and rubber insert type gloves also. These gloves have a procedure for required testing before every use to verify the integrity of the insulation.

As with the protective equipment, clothing and gloves that are utilized for medium and high voltage type work, the hand tools and power tools are also voltage rated for the types of systems being worked on. All tools from screw drivers to cutters, testing equipment and handling sticks are all rated for the MV and HV systems to which they are used.

It is imperative to always wear the proper PPE and use the proper tools for each type of voltage system in order to work safely and prevent accidents and/or injuries.

Understanding Electrical Circuits and Safety

A circuit is an electrical path of current flow from a source to a single load or multiple loads. There are many parts of circuits; i.e. main, sub, feeder, distribution, branch, etc. but they all provide the same result to bring electrical energy from one source to another.

An electrical circuit is essentially a path in which the currents flows from one point to another, which is usually from positive to negative or vice versa. Therein, there are three essential parts to an electrical circuit; the power circuit is the positive side of a circuit which is usually identified as (+) or positive. This part of the circuit is fed from a power source, typically a circuit breaker in the main panel, and is fed to the positive side of all the loads within the circuit. Power is always a colored wire and each voltage system uses differing color patterns. For 120/240 volt systems, it is usually black, red and blue. For 277/480/600 volt systems the colors are usually brown, orange and yellow for the positive wires.

The second part of the circuit is the neutral circuit which this is the negative side of a circuit and is identified as (-), NEG, negative, or neutral. This is also fed from the power source and is terminated on a neutral bus bar within the distribution panel. Typically, there is a bonding wire or screw that interconnects the neutral and ground bus bars as these negative systems interact with each other. Neutral circuit wires are also colored for the systems they serve; 120/240 is typically white and 277/480/600 volt systems are typically grey.

The third part of the circuit is the ground circuit which is always identified with a symbol such as one those shown in the attached pdf, or GRND or GROUND. The wire sheath is typically colored green, green with yellow stripe or is a bare wire.

When electrical current is flowing, it is always searching for a circuit to be completed from a POSITIVE (+) power point to a NEGATIVE (-) point. Electrical shock occurs when the human body becomes the conductive path in that circuit of energy being transferred from one point to another.

The minimum current a human can feel depends on the current type (AC or DC) as well as frequency for AC. A human body can feel at least 1 ma (milliamp) of AC at 60 Hz, while at least 5 mA for DC. At around 10 milliamperes, AC current passing through the arm of a 68-kilogram (150 lb.) human can cause powerful muscle contractions; the victim is unable to voluntarily control muscles and cannot release an electrified object.[5] This is known as the "let go threshold" and is a criterion for shock hazard in electrical regulations.

The current may, if it is high enough and is delivered at sufficient voltage, cause tissue damage or fibrillation which can cause cardiac arrest; more than 30 mA of AC or 300 – 500 mA of DC at high voltage can cause fibrillation. A sustained electric shock from AC at 120 Volts, 60 Hz is an especially dangerous source of ventricular fibrillation because it usually exceeds the let-go threshold, while not delivering enough initial energy to propel the person away from the source. However, the potential seriousness of the shock depends on paths through the body that the currents take. If the voltage is less than 200 V, then the human skin is the main contributor to the impedance of the body in the case of a macro shock — the passing of current between two contact points on the skin. The characteristics of the skin are non-linear however. If the voltage is above 450–600 V, then dielectric breakdown of the skin occurs. The protection offered by the skin is lowered by perspiration, and this is accelerated if electricity causes muscles to contract above the let-go threshold for a sustained period of time. [2]

To alleviate the possibility of these electrical shock occurrences, most all electrical systems, equipment, appliances, etc. are now grounded by means of the National Electrical Code (NEC) requirements by all manufacturers. That means they have a ground wire installed that takes any metal parts of the chassis to earth ground. In this manner, if there is any malfunction of the power circuit to the equipment then it will go directly to earth ground; immediately short-out the circuit and trip the source power breaker.

Visual understanding of electrical circuiting is very simply done by identifying the color coding on wiring and then matching them to the components, devices and equipment to know that a gold or brass color is always the power circuit, silver or chrome is the neutral circuit, and green is the ground circuit. All devices are color-coded for Power, Neutral and Ground per the NEC.


This white paper provides only the most basic rules to stay safe and return home from your normal work duties uninjured and ready to enjoy your family. The ultimate goal of safety is not to constrict your working ability, but to make your ability to work in the safest way possible in the most dangerous of conditions.

All things great and small need to be taken into consideration when dealing with electricity as it cannot be seen before it can cause serious injury. In many situations where inspections are made on damaged building structures, be very aware of your surroundings and the condition of the electrical systems when entering a building full of water or debris.

• Ask yourself - Is the power on or off?
• If the power is ON, has there been any damage to the electrical systems that could make them unsafe to enter or approach with absolute certainty of your safety?
• Be AWARE of what type of system voltages are around you; AC -DC low, medium or high voltage systems
• Always treat all electrical circuits, devices and equipment as live if unknown.
• Do Not OPEN any electrical equipment covers or plates. This should be completed by a licensed, qualified electrician at all times.
• Never approach live open gear or equipment on an inspection site: Proper PPE is required at all times no matter how safe someone else may believe you are.
• When working with somebody else, even a qualified person, electrician, engineer or manufacturer, make sure you understand what they are doing as they are doing it. If you feel it is unsafe, it is your responsibility to take action and discuss a safe way to accomplish the task. Your life is just as close to the danger as theirs and you are responsible for your own well-being.
• If photos are needed, let the qualified person perform that for you. Photography can be dangerous around live open gear.
• Understand all the dangers around you before you perform any work. Take the time to complete an ARC-FLASH study of the area and your surroundings and it may just save your life and everyone around you.

SAFETY WARNING: Removing the cover plate on any electrical item may expose you to dangerous voltages and extreme caution should always be practiced. Always treat electrical items as live unless you and your qualified person have tested them or have verified the power is off.

[1] National Electrical Code Reference; NFPA 70 2014 Definitions Article 100 “Qualified Person” Page 70-33
[2] Clifford D. Ferris, Electric Shock, chapter 22.1 in Jerry C. Whitaker (ed.) The Electronics Handbook, CRC Press, 2005, ISBN0-8493-1889-0, pp. 2317-2324


This publication is for educational and general information purposes only. It may contain errors and is provided as is. It is not intended as specific advice, legal, or otherwise. Opinions and views are not necessarily those of J.S. Held or its affiliates and it should not be presumed that J.S. Held subscribes to any particular method, interpretation, or analysis merely because it appears in this publication. We disclaim any representation and/or warranty regarding the accuracy, timeliness, quality, or applicability of any of the contents. You should not act, or fail to act, in reliance on this publication and we disclaim all liability in respect to such actions or failure to act. We assume no responsibility for information contained in this publication and disclaim all liability and damages in respect to such information. This publication is not a substitute for competent legal advice. The content herein may be updated or otherwise modified without notice.

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