Appendix: Loop And Cable Condition Test; Lineal Conductor Resistance And Inductance; Insulation Resistance - 3M Drive-Thru G5 Installation Manual

3M™ Drive-Thru System Model G5

10. Appendix: Loop and Cable Condition Test

Measure loop inductance/resistance for each order point, recommend replacement in comments section if needed. You must conduct two
separate tests on the Inductance Loop to determine its condition:
A. Lineal Conductor Resistance and Inductance
This test measures the Resistance and the Inductance of the loop conductor or wire at the Basestation.
Procedure
To measure the inductance and resistance of the loop wire, use test equipment such as an LCR meter (Inductance [L], Capacitance [C],
and Resistance [R]).
A reading of 1.2 for resistance and 100–120μH (or 20μH / wire turn) for inductance are acceptable measurements that reflect good wire
condition.
B. Insulation Resistance
In addition to the factors mentioned above, ice, water, frost, etc. can contribute to changes in the conductor's resistance. However,
measuring the conductor's resistance alone may not provide a complete picture, as it does not account for insulation leakage to the
ground/earth. Insulation leakage can be checked by utilizing a Megohm meter (or a Megometer or Megger Meg Out, in industry parlance)
capable of testing up to 500 megohms (500 million ohms).
In this test, a DC voltage is applied to the loop wire to check for insulation damage that may cause a short circuit when normal power is
applied. The Meggers have settings capable of delivering anywhere from 500–1000 volts through the loop. DO NOT apply more than
500 volts for this test or you may damage the insulation. The cable's insulation is rated at 600 volts.
Procedure
1. Disconnect the loop wires from the loop detector so the loop is floating.
2. Place one of the meter leads to the loop wire and the other to the ground/earth.
Resistance above 20 megohms
Resistance below 20 megohms
Resistance less than 10 megohms
66
Acceptable
Loop wire insulation has been damaged.
Loop integrity is questionable.
Loop wire must be replaced.
Installation Instructions G5 - Revision C, September 2019