Chapter 11 Electrical Utilities Flashcards
What is the definition of high voltage?
Anything over 600 volts
What are the four types of lines used to conduct electricity?
Transmission, subtransmission, primary distribution, and secondary distribution
What is the pprimary function of a transformer?
Transformers are used either to reduce or increase voltages as necessary.
What is the best method to determine the approximate voltage of conductors?
The size of the insulators and the distances between them
What are the three primary ways to eliminate the electrical service to a structure?
Depend on local Utility companies, shut off the service, and cut the drip loops
Why shouldn’t you pull a meter to eliminate the electrical service?
A meter can flash or explode, live line connectors will be exposed, and the meter may have been bypassed
What are the three types of main power disconnects?
Fused pullout, circuit breaker, and lever
Should suppression personnel enter electrical rooms marked “high voltage” to curtail the flow of electricity?
No. ONly appropriate utility company personnel should enter these areas to curtail the flow of electricity
What is the only practical way to ascertain the distribution of electrical power within complex occupancies?
Preplanning with qualified building engineers
What is a UPS room, and what are its specific hazards?
Uninterrupted power supply rooms. The hazards are potential acid spills, vapors from charging batteries, and bare bus bars
Electricity can be transmitted to municipalities on lines of how many volts?
115,000 volts to 1 million volts
Subtransmission lines carry what voltage?
34,500 volts
Primary distribution lines carry what voltage?
4,800 volts
Secondary distribution lines carry what voltage?
480 volts, 240 volts, 120 volts
Why can 4,800 volts be more dangerous than 34,500 volts?
An apparently dead wire can suddently become live when relays automatically set
Where can transformers be located? (3)
Above ground on poles
On the ground on concrete pads
Underground in vaults
What is considered high voltage and requires marking with “high-voltage” signs
750 volts and above
Subtransmission line (34,500 volts) insulators are how long?
12-22 inches
Primary distribution line (4,800 volts) insulators are how long?
4-6 inches
Secondary distribution line (480, 240, 120 volts) are how long?
2-3 inches
Transmission line (115,000 to 1,000,000 volts) insulators can be how long?
4 feet to 14 feet long
Where are Subtransmission transformers usually located?
Normally mounted on a platform between poles
What is the safest and most effective method to prevent injury from electric shock?
eliminate all electrical service to a structure
If it is necesary, how should a meter be removed?
Do not pull outward. pull upward towards the source of supply, then out
What is the minimum tools and equipment required when cutting electrical conductors?
Turnouts
Eye protection
Gloves–Rubber or leather
Axe, Wire cutters, hot stick
When cutting drip loops, do not cut wires that carry what voltage?
How much wire do you leave?
over 750 volts
At least 6 inches
Describe a single-phase triplex service line.
two covered conductors and one bare conductor
Describe a three-phase triplex service line.
Three covered conductors and one bare conductor
Who’s responsible for any electrical hazard?
The first person that sees it
What should you always check for after eliminating electrical service to a structure?
Any additional electrical services that may have been overlooked
Pad mount transformers can be classified into two classifications? What are they and what are their voltages?
Commercial stations (CS) 4,800 volts
Industrial stations (IS) 34,500 volts
What can you check power poles for to determin approx voltage?
High voltage signs
insulator size
Transformer markings
After cutting wires, what should you do to the cut wires to prevent other personnel from thinking that the wires are charged?
coil the wires
What is step potential?
stepping near or between energized wires on the ground can be electrocuted by this phenomenon
Pole-mounted transformers usually provide what?
voltage drop from 34,500 volts to 4,800 volts or
4,800 volts to 480/240/120 volts
What voltages can be encountered in street electrical vaults?
4,800 volts to 34,500 volts
What shape are the manhole covers that will usually indicate a vault?
square
Newer street lights with photoelectric cells are fed by how much voltage?
240 volts
Older street lights without photoelectric cells are fed by how many volts?
6,800 volts
What voltage do traffic lights operate on?
240 volts
Telephone line voltages can range from what?
45 volts to over 100 volts
What component of electricity is responsible for injury and death?
amperage
