Testing With A Dlro Low Resistance Tester; Using Current And Potential (Four Wire) Lead Sets - Megger DLRO10HD Guia Del Usuario

3. 2. 3 Testing with a DLRO low resistance tester.

As seen in this example, a DLRO or Ducter provides accurate results. By comparing similar connections
a number of potential hazards can be easily revealed:
1. Why is this lug 10 times higher than the other one on the same bolt?
2. This excessive resistance will cause heating which will waste energy and quickly develop into a fire risk.

3. 2. 4 Using current and potential (four wire) lead sets.

11 µΩ
Note: Cable length A to B >5 m, resistance >2.5 mΩ (approx)
The four wire method can be used in a similar way. However in this example the cable is quite long
meaning the overall resistance (A to B) would mean the instrument would use a higher resistance range
if Kelvin connections had been used, losing the ability to make accurate µΩ measurements.
The resistance measured on the four wire method will be between the P1 and P2 points only, providing
the instrument test current (C1 - C2) flows 100% through that connection (i e, there are no parallel
paths).
The measurement of each connection (Kelvin or four wire) will provide the same results as desired.
10
11 µΩ
4 µΩ
121 µΩ
1
4 µΩ
121 µΩ
P1
= 5.2 mΩ
C1
8 µΩ
11 µΩ
5.2 mΩ
2
A
C2
8 µΩ
3 µΩ
B
P2
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