Prostat SureTest PGT-61-164, Operation Manual, Page: 9 / 16

PGT-61-164 SureTest Circuit Analyzer
8
ASCC
1
= Line Voltage (V
HN
)/ (Hot Ω + Neu Ω )
ASCC
2
= Line Voltage (V
HN
)/ (Hot Ω + 1/(1/ Neu Ω + 1/Grd Ω )
Impedance (Z) Measurements
If the voltage drop measurement exceeds 5%, analyze the hot and neutral impedances. If one is
significantly higher than the other, the problem is with the conductor with the much higher
impedance. Then, check all connections on that conductor back to the panel. If both impedance
appear high, the source can be undersized wire for the length of run, a bad device, or poor
connections at the pigtails, devices, or panel.
The ground impedance measured should be less than 1 ohm as a rule of thumb to ensure that
fault current has a sufficient path back to the panel. IEEE states the ground impedance should
be less than 0.25 ohms to ensure the ground conductor can safely return any fault current which
could damage equipment on the circuit. Surge suppression systems require a good ground to
adequately protect equipment from transient overvoltages. Note that a small amount of current
is applied to the ground conductor to accurately measure its impedance. By the inherent nature
of this test, a GFCI protected circuit will trip unless the device is temporarily removed from the
circuit.
Troubleshooting Tips – Impedances
Measurement
Expected
Result
Problem
Possible
Causes
Possible
Solutions
<0.48 Ω /foot of
14 AWG wire
Too much load
on branch circuit Redistribute the
load on the
circuit
<0.03 Ω /foot of
12 AWG wire
Undersized wire
for length of run Check code
requirements
and rewire if
necessary
Hot and Neutral
Impedance
<0.01 Ω /foot of
10 AWG wire
High Conductor
impedance
High resistance
connection within
the circuit or at
the panel Locate high
resistance
connection/
device and
repair/replace
< 1 Ω to protect
people
Undersized wire
for length of run Check code
requirements
and re-wire if
necessary
Ground
Impedance
<0.25 Ω to
protect
equipment
High ground
impedance
High resistance
connection within
the circuit or at
the panel Locate high
resistance
connection/
device and
repair/replace