Taking cathodic protection current measurements at junction boxes and electrical connections.
- Clamp on current meter.
- Digital multi-meter.
- Selection of calibrated shunts.
- Low resistance connecting conductors and clips.
16.1.1. At the transformer rectifier.
16.1.2. Clamp the current meter around the positive DC cable and note the reading on the meter.
16.1.3. Switch the transformer rectifier off and note that the clamp on meter has returned to zero. If it has not, and can be adjusted, it should be re-set to zero and repeat
16.1.4 Note the value.
NOTE. Clamp on current meters can require calibrating before each use, and a small calculation to establish the value of the current. This should be practiced with currents of a known value before going to site. Each instrument has the manufacturers procedure guide for its own use, and these should be followed and practiced.
16.2.1. Switch the transformer rectifier off.
16.2.2. Disconnect the positive pole DC.
16.2.3. Re-connect the positive pole DC through a 1 Ohm shunt.
16.2.4. Switch the transformer rectifier back on.
16.2.5. Connect the high resistance voltmeter probes to each end of the shunt and note the reading in millivolts and then in microvolts.
16.2.6. Re-instate the transformer rectifier to it's original status.
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