CT70 V7.0 09/10
8
Test 5: Impedance (Z) Measurements
The impedance measurement capability of the CT70 is used to check Hot and Neutral
impedance when voltage drop measurements are too high (greater than 5%). To determine
where the problem is, measure the impedances and analyze the data as follows:
•
If one impedance measurement is exceedingly higher than the other then the
problem is with the conductor that shows the higher impedance.
•
If both impedances are high the problem could be an undersized conductor, a
faulty load, or poor connections.
Ground impedance should be less than 1
Ω
, preferably in the 0.25
Ω
region to ensure that
the ground conductor can safely return current when necessary.
Surge suppressors require good grounding to adequately protect against transient voltages.
Note: A small amount of current is applied to the ground conductor during impedance
measurements and can trip a GFCI circuit.
High Impedance Troubleshooting Suggestions
Problems Likely
Causes
Probable Solutions
High hot and/or neutral impedance
(Limit: 0.048
Ω
/ ft of 14 AWG wire)
Excessive loading
Redistribute loads
High hot and/or neutral impedance
(Limit: 0.03
Ω
/ ft of 12 AWG wire)
Undersized wiring
Check code and rewire if
necessary
High hot and/or neutral impedance
(Limit: 0.01
Ω
/ ft of 10 AWG wire)
High resistance connection
in the circuit or at the panel
Locate bad connection and
rewire or replace
High Ground impedance (Limit: 1
Ω
for personal protection)
Undersized wiring
Check code and rewire if
necessary
High Ground impedance (Limit:
0.25
Ω
for equipment protection
High resistance connection
in the circuit or at the panel
Locate bad connection and
rewire or replace
