Facility Electrical Design Flashcards
(16 cards)
Describe Ampacity
The maximum current in amperes that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.
Enemy of our electrical components
Heat
What is a conductor?
Current carrying material
The UFC limits conductors to no smaller than…
12 Gauge
Wires smaller than this must be copper
6 Gauge
Define what equipment ratings correlate to
equipment ratings correlate to the magnitude of current that will cause heat damage
As a conductor size increases, ____________increases
Ampacity
What is the maximum voltage drop per the UFC?
5%
What causes voltage drop in a system?
heat from current moving along conductors
1st purpose of electrical grounding
to provide a low impedance path for ground faults, resulting in high levels of fault current that will trip an OCPD (Over Current Protective Device)
2nd purpose of electrical grounding
To limit voltages imposed by lightning and surges
3rd purpose of electrical grounding
To establish a stable reference for all normal voltages
What factors influence voltage drop?
Current, nominal voltage, conductor impedance, circuit length
What does a service transformer do?
to step the voltage down from distribution voltage to utilization voltage
Overcurrent Protective Device (OCPD) sizing criteria
Circuit Load < OCPD Rating <= Circuit Ampacity
3 Sources of Overcurrent
Overload (25A on 20A), Short Circuit (current along a low impedence path), Ground Fault (Current is going where it shouldn’t)
