Chapter 9 - Power Distribution Flashcards
When calculating voltage drop, a value of K = ____ is used to represent the specific resistance of a copper conductor circuit loaded to more than 50 percent of allowable carrying capacity.
K = 12
When calculating voltage drop, a value of K = ____ is used to represent the specific resistance of a copper conductor circuit loaded less than 50 percent of allowable carrying capacity.
K = 11
When calculating voltage drop, what value K is used for aluminum conductors 30 degree C (86 degree F)
K = 18
What can be a source of radiated interference?
- Proximity to interfering sources
- Missing or inadequate gaskets/enclosures
- Missing or inadequate bonding and grounding (earthing) system components
- Missing or inadequate device or cable shielding
What is a Class 1 electrical system?
A class 1 electrical system has no redundant capacity and only a single path. This system typically only has a UPS and generator sized at N capacity.
What is a class 2 electrical system?
A class 2 electrical system has redundant components, but only a single path. UPS and generator are typically sized at N+1.
What is a class 3 electrical system?
A class 3 electrical system has redundant components and multiple distribution paths so that one path can be shut down for maintenance without impacting the communications equipment.
What is a class 4 electrical system?
A class 4 electrical system is fault tolerant with redundant capacity components and multiple electrical distribution paths. The main difference between this and class 3 is that it is fault tolerant.
For Vented Lead-Acid (VLA) cell batteries, how often does the air in the room storing it need to be changed?
A minimum of 4 changes per hour is required due to the hydrogen gas being produced by the battery, which is explosive. Because of the gassing action, the water needs to be replenished at regular intervals to maintain a minimum level and ensure that the plates are totally immersed.
Power supplies should have a remote alarm contact that indicates when the unit fails. What are two types of remote alarm?
- Cabled remote: transmit power system alarms to another room or building within a relatively short distance
- Dialup remote: transmit alarms to a distant location usually over the telephone network
What is apparent power?
Apparent power is the product of measured voltage and measured amperage. The term measured is misleading, it’s basically calculated voltage and amperage. Apparent power doesn’t take into account inductive and capacitive reactance of a system. And would provide a value based on volt-amperes.
What is real power?
Real power is determined by incorporating the effects of the inductive and capacitive reactance of a system into the calculation of power, and is expressed in watts.
What is power factor?
Power factor is the ratio of real power to apparent power. It will always be one (unity) or less.
When designing cable runs for direct current (dc) power system, the bending radius must not be less than ___ times the overall diameter for unshielded power cables.
8 times
