Series Circuit Measurements Be Accurate, Be Safe By David Rainey Navaid Lighting Associates, Inc.

Types of Test Equipment Required Accuracy of Test Equipment How to Determine if Your Equipment is Accurate Safety and Proper Procedures for Making Measurements

Test Equipment Requirements Maintaining series circuits requires more diversity and accuracy of test equipment. Series circuits operate at potentially high voltages and are prone to develop shorts and opens. Troubleshooting these problems requires an advanced knowledge of ohmmeters, insulation resistance testers and Amp Probes.

Make accurate measurements at low current 2.8 – 6.6 amps Be able to accurately measure non-sinusoidal waveforms Make accurate measurements of insulation resistance Provide the ability to accurately measure photometric output of lights especially for CAT II and CAT III operations

Class Style Step Nominal output amperes (A) root mean square (RMS) Allowable range (A RMS)   1 3 6.6 6.5 - 6.70 2 5.5 5.4 - 5.6 4.8 4.7- 4.9 5 6.50 - 6.70 4 5.2 5.1 - 5.3 4.1 4.0- 4.2 3.4 3.30 – 3.50 2.8 2.7 – 2.9 20.0 19.7 - 20.30 15.8 15.5 - 16.1 12.4 12.1 - 12.7 10.3 10.0 - 10.6 8.5 8.2 - 8.8

Accurate (true RMS) Equipment that doesn’t quite agree

Could One of These be the Culprit?

Swapping Clamp-on Devices Moves the Inaccurate Reading

Accuracy +or- 2% Accuracy +or- 3% +/-0.4A

Comparison of Current Readings on Circuit Between Two Instruments 6.37 Amps 6.63 Amps Low Accuracy Clamp-on Device Comparison of Current Readings on Circuit Between Two Instruments

6.60 Amps 6.63 Amps High Accuracy Device As Shown Previously, Accuracy of Measurement Depends on Accuracy of Clamp-On Accessory Used

Verifying Accuracy by Direct Measurement Method

!!CAUTION!! SERIES CIRCUIT CONSTANT CURRENT REGULATORS ARE CAPABLE OF DEVELOPING EXTEMELY HIGH AND LETHAL VOLTAGES. THE FOLLOWING INFORMATION IS PRESENTED FOR EDUCATIONAL PURPOSES ONLY. MEASUREMENTS OF VOLTAGES IN SERIES CIRCUITS SHOULD NOT BE ATTEMPTED. NEVER UNDER ANY CIRCUMSTANCES ATTEMPT TO MAKE DIRECT VOLTAGE MEASUREMNTS OF AIRPORT LIGHTING SERIES CIRCUITS.

10 FAA L-850C Runway Edgelight Fixtures and 200 Watt transformers Demonstration of the Behavior of Voltage in Airport Lighting Series Circuits 10 FAA L-850C Runway Edgelight Fixtures and 200 Watt transformers

105 + 105 = 210 watts 210 x 10% = 21 watts 210 + 21 = 231 watts 231 x 10 = 2310 watts P/I = E 2310 watts / 6.6 amps = 350 volts

Measuring Voltage at Output of Regulator

Jumpers with Portion of Insulation Removed for In-Circuit Voltage Measurements

Measuring Voltage to Ground

Measuring Voltage Drop Across Each Transformer

Voltage Proximity Detectors These are popular, but do not use to detect an energized series circuit!

Questions? Comments?