Continuity Test Resistance Calculator

You can use this calculator to help determine effective thresholds for your wire tests. This calculator will help you estimate the maximum resistance of your Device Under Test (DUT), then add in resistance variations from wire length, temperature, diameter, fixturing, and tester accuracy.

Step 1: Find the DUT's Maximum Theoretical Wire Resistance

a) Set the units of measurement

All lengths in
All temperatures in
All resistance values in ohms
All wire gauges are AWG
All wire is copper

b) Calculate the Resistance of the Ideal DUT(Theoretical)

Wire in DUT
Length Gauge Note	___ ohms
Contact Mating Resistance (DUT to fixture):
At Point A: ohms Note	___ ohms
At Point B: ohms	___ ohms
Total Ideal Resistance of DUT (nominal)	___ ohms

c) Add Variation From Ideal for the DUT

Account for Resistance Increases from:
Wire Length Tolerance: % Note	___ ohms
Wire Diameters Per Twist Length: Note	___ ohms
Wire Resistance Tolerance: % Note	___ ohms
Temperature Deviation : ° Note	___ ohms
Total (In-Spec) Variance From Ideal	___ ohms
Estimated Max Resistance of a Good DUT	___ ohms

Step 2: Allow for Real-World Measurement Issues

Option 1 - Four-Wire
Add Resistance Variation If Using 4-Wire Measurement

Variance Due to 4-Wire Tester Measurement Error:
Tester Accuracy for 4-wire Measurement % (of reading)	___ ohms
Tester Resolution Error ohms	___ ohms
Total Variation Due to Tester (4-Wire Measurement)	___ ohms
Resistance From Wear of Mating Contacts ohms	___ ohms
Estimated Max Measured Resistance of a Good DUT (4-Wire)	___ ohms

Option 2 - Two-Wire
Add Resistance Variation If Using 2-Wire Measurement

Variance Due to 2-Wire Tester Measurement Issues: Fixturing wire from tester to:
Point A: Length Gauge	___ ohms
Point B: Length Gauge	___ ohms
Resistance of Fixture Wire (nominal)	___ ohms
Fixture Wire Variation (diameter/temperature)	___ ohms
Estimated Max Fixture Resistance	___ ohms
Tester Accuracy for 2-wire Measurement % (of reading)	___ ohms
Tester Resolution Error ohms	___ ohms
Total Variation Due to Tester (2-Wire Measurement)	___ ohms
Resistance From Wear of Mating Contacts ohms Note	___ ohms
Estimated Max Measured Resistance of a Good DUT (2-Wire)	___ ohms

Option 3 - A-620 Specification

A-620 Specification Class III Default Test Requirement	___ ohms

Results: Your Lowest Practical Test Resistance Threshold

We define the "lowest practical test specification" as the lowest resistance setting that passes "in-spec assemblies on in-spec test equipment." If you test at a setting lower than what is practical you will fail assemblies that were manufactured correctly.

A DUT with an ideal wire resistance of ___ ohms can have a resistance as high as ___ ohms and be correctly built and in spec. That increase in resistance comes from variations in wire length, conductor diameter, test temperature, and contact resistance. Taking into account the variations caused by test fixturing and tester accuracy the lowest practical test thresholds for that wire are:

When testing 2-wire use a threshold higher than ___ ohms.
When testing 4-wire use a threshold higher than ___ ohms.
The A-620 Class III Default Threshold is ___ ohms.

Cable and Harness Testers