April 2004 Issue

®	April-May 2004

IN THIS ISSUE: (CLICK TITLE TO READ ARTICLE)

Electrical Utilities, Part I . . . John Mittendorf
Self-survival Basics . . . Will Trezek
Water on Hot Steel . . . Francis Brannigan
Are You Studying for the Written? . . . Raul Angulo

More Water! . . . Brett Graves
Covering the Rear . . . Phil De Mik
The Role of Incident Commanders at Structure Fires . . . Raymond Orozco

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Questions and Answers
with Tom Brennan

Photo Lessons
with Tom Brennan

Gordon Graham
Column

Of all of the modern priorities that fireground personnel are responsible for, and/or must have a working knowledge of, none is more challenging than electrical hazards. Interestingly, electrical hazards often fall into the category of “out of sight, out of mind,” yet an inadvertent encounter with electricity has the capability to instantly create a “bad hair day”! To better understand the concept of electricity, it is essential to have a basic understanding of the following basic terms:

ALTERNATING CURRENT (AC) — Current flows first in one direction then in the opposite direction at 60 cycles a second. It is this pulsation that makes it difficult to let go of energized equipment.

AMPERAGE — The quantity of electrons moving through a conductor. When considering the effects of amperage and voltage on humans, amperage is primarily responsible for injury and death. The flow of electrons can be compared to the flow of water (gpm).

CIRCUIT — The path of electric current, starting from a source (generator, alternator, battery, etc.), and returning back to the source. If a person completes a circuit by touching both ends of a broken wire, the person can become a conductor and electricity may flow through the person’s body, causing an injury.

CONDUCTOR — A material (copper, aluminum, etc.) that contains and freely allows the movement of electrons. A conductor can be compared to a hose line that contains the flow of water.

DIRECT CURRENT (DC) — Direct current flows in one direction only as there are no cycles as in alternating current. Contacting this type of energy results in repulsion and can result in items being thrown.

DISTRIBUTION SYSTEM — Electricity is transmitted through conductors (lines) in overhead (towers and poles) and underground systems.

ELECTRON — A negatively charged particle of an atom. The flow of electrons in a conductor constitutes electric current. An electron can be compared to a drop of water.

HIGH VOLTAGE — Most utility companies consider any voltage over 600 volts as high voltage, although voltages over 750 volts are usually identified with the familiar yellow high voltage placards that are normally mounted on power pole crossarms. All lines should be considered high voltage and energized unless identified otherwise.

RESISTANCE — The quality of an electric circuit, measured in ohms, that resists the flow of current. This can be compared to friction loss in a hose line.

VOLTAGE — The property of electricity that is responsible for moving electrons through a conductor. The 1.5 volts in a battery is not detrimental to the human body, but 120 volts in a common outlet can be fatal. Voltage can be compared to pressure that is used to move water.

WATT — A measure of consumed power, determined by multiplying the amperage of a circuit by its voltage. This is the unit of electricity that is metered and sold by utility companies.

Electric power is generated and transmitted to municipalities from many sources. The transmission and distribution of electricity is accomplished as follows:

TRANSMISSION LINES (115,000 to 1,000,000 volts) — Electricity can be transmitted to municipalities on transmission lines that carry 115,000 to 1,000,000 volts, or, if generated locally, leaves generating plants at 13,800 volts and is increased to 230,000 volts by step-up transformers. It is then carried throughout a municipality by transmission lines on metal or concrete towers.

SUB-TRANSMISSION LINES (34,500 volts) — Its next stop is a receiving station which is basically a step-down transformer. The incoming electricity is from 115,000 to 1,000,000 volts and then stepped down to 34,500 volts and sent on. These sub-transmission lines may go directly overhead or underground to large consumers at 34,500 volts or travel to a distribution station which will step the electricity down from 34,500 volts to 4,800 volts.

PRIMARY DISTRIBUTION LINES (4,800 volts) — The 4,800 volts is then sent through primary distribution lines either underground to a vault (and then specific consumers), or overhead on power poles where it may be stepped down again and delivered to consumers through secondary distribution lines. It is important to remember that 4,800 volts can be more dangerous to personnel than 34,500 volts. In some municipalities, 4,800 volts can be an ungrounded system which uses relays to clear faults and isolate trouble in distribution lines. If a problem (short, etc.) is detected, appropriate relays will open (which removes power from a problem line) and automatically reset in varying amounts of time. Therefore, to unsuspecting personnel, an apparent dead wire can suddenly become a live wire when relays automatically reset.

SECONDARY DISTRIBUTION LINES (480/240/120 volts) — The 4,800 volts in primary distribution lines can be stepped down to 480, 240, or 120 volts and delivered to consumers through secondary distribution lines.

TRANSFORMERS — Transformers are used to either reduce or increase voltages as necessary. During operation, a transformer can generate a significant amount of heat which must be minimized to prevent damage to a transformer. The cooling methods generally used are air and oil. Oil-cooled transformers can present a hazard from flammability and the potential presence of PCB's in the cooling oil. Transformers are generally mounted above ground on poles, on the ground on concrete pads (referred to as padmount transformers), or underground in vaults.

With a basic understanding of definitions and distribution systems, let’s briefly consider another important subject — how to determine the approximate voltage that may be encountered (at an incident) to develop appropriate operations (if any).

The voltage of a conductor cannot be consistently and accurately determined by considering the following common factors:

The best method to determine the approximate voltage of conductors is by the SIZE of insulators and DISTANCE between the insulators. The higher the voltage the larger the size of insulators and the greater the distance between conductors. To fully understand this statement, take some time and look at the lines and insulators in your area. If necessary, ask your local power company for a few tips. If you understand this concept, it is relatively easy to determine voltages that you may encounter.

Although the primary side (input) of transformers that are normally encountered by suppression personnel is generally 34,500 or 4,800 volts, the secondary side (output) can have a multitude of different voltages. Identification of secondary voltages can be accomplished as follows:

In our next article, we will look at several methods that can be used to eliminate an electrical service to a structure and then consider specific electrical hazards and their remedies.

This article was adapted from Truck Company Operations, by John Mittendorf, published by Pennwell. Click here to purchase.