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Ground Circuits: Part 8

Measuring dual battery ground electron current engine OFF — engine RUN
Wednesday, September 27, 2017 - 07:00
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Understand Current Clamps
The current clamp is used to measure the electron current in one wire at a time, the preferred method, but it can also be used to measure more than one wire at a time provided the direction of electron current in each wire is known. Our illustration below shows that the current clamp must be connected to a voltmeter. The current clamp develops 1 mV for each amp of electron current flowing through the wire. The voltmeter indicates the number of millivolts which indicates the number of amps flowing.

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To illustrate this concept, we have selected Figure 2-42 from our book “Vehicle Electrical Troubleshooting SHORTCUTS:” Measuring electron current in two wires at the same time.

Figure 2-24 from "SHORTCUTS"

In Example #1 the current clamp algebraically adds the two currents flowing in the same direction indicating the sum:

+5 (+) +15 = 20 and indicates the sum is 20 A.

In Example #2 the current clamp algebraically adds the two currents flowing in opposite directions indicating the difference:
-5 (+) +15 = 10 A and indicates the difference is 10 A.

We employ this feature of a current clamp to measure the electron current in the battery negative cables when the battery has a dual ground cable to determine how much electron current is recharging the battery.

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