Shop Practice with Electrical Code:
Voltage Drop and Short Circuit
Calculation Residential Single
Phase System
Jayson Bryan E. Mutuc, REE, RME
BSEE-PUP
Voltage Drop
2.10.2.1 (a) (1) FPN No. 4:
To
provide reasonable efficiency
of operation of electrical
equipment, branch-circuit
conductors should be sized to
prevent a voltage drop not to
exceed three percent. In
addition, the maximum total
voltage drop on both feeders
and branch circuits should
not exceed five percent.
Voltage Drop Calculation
Voltage Drop Calculation:
%VD =
IR
Voltage Supply (V
3
)
x100%
where:
I – line current, amperes
R – line ac resistance, ohms
Purpose of Short Circuit Calculation
The purpose of short circuit calculation is to know the rating the
interrupting capacity of the overcurrent protective device
In circuit breaker there are 3 important parameters when it comes to
residential design,
ampere trip, ampere frame and interrupting rating
Ampere trip
– the current rating the circuit breaker set to trip
Ampere frame
– insulation housing for maximum long time current
available in physical
Interrupting Rating
– the highest current at rated voltage that a device
is intended to interrupt under standard test conditions.
Analogies to Short Circuit Condition
Normal Current Operation
Short Circuit Condition with Inadequate
Interrupting Rating
Analogies to Short Circuit Condition
Short Circuit with Adequate
Interrupting Rating
