[rabbit73]

Leakage Current Tests of Equipment Used for CECB Calibration

When I was calibrating an Apex DT502 signal strength bar with a SLM (Signal Level Meter) I noticed a slight shock when I touched ground and the equipment case. Because I didn't want to use, or pass on, dangerous equipment I tested the equipment that I was using for calibration with my Simpson 229 Leakage Current Tester.
Apex #1: 22 VAC, 52 µA (micoamperes)
Apex #4: 21 VAC, 50 µA
Apex #1 & #4 together: 30 VAC, 100 µA (note that the leakage currents add)
2 Audiovox PLV16081 8" TV/Monitors: 21 VAC, 24 µA each
CM 0747 Power Supply/Inserter for CM 7777, plug inserted correctly: ~1 VAC, ~1 µA
CM 0747 Power Supply/Inserter for CM 7777, plug inserted reversed: 14 VAC, 33 µA
Sony KDL22L5000 TV: 24 VAC, 52 µA
Sadelco 719E SLM with AC Adapter/Charger: ~1 µA
Radio Shack 15-1115 Preamp with AC Adapter: ~1 µA

Leakage current tests must be made under 4 conditions: power on and off with plug normal, power on and off with plug reversed. With the exception of the CM 0747, all equipment gave the same readings under the 4 conditions. The 0747 has a 3.3 Meg resistor from ground to one side of the line, presumably to drain a static charge from the coax shield , which explains the difference in leakage current readings.

The Apex boxes and the 8" TVs have switchmode power supplies that have higher leakage currents. The AC adapters for the SLM and the RS preamp use a transformer adapter which has good isolation from the AC line.

CONCLUSIONS:

All pieces of equipment tested are safe to use individually as per the guidelines in the Simpson manual and other standards. However, when other equipment is connected, the leakage currents add as demonstrated by connecting the two Apex boxes together. This means that when pieces of equipment that have 2-wire power cords are connected together, even when the polarized plugs are correctly inserted, it is advisable to ground the cabinets and coax. Before I grounded the interconnected equipment that I was using, the AC voltage to ground was 40 volts, and the total measured leakage current was about 200 µA.

I originally bought the Simpson tester because of three close calls. One was because of my carelessness, the other two were because of the stupidity of others.

Many years ago a neighbor asked me to help him connect his new TV. He was having trouble because the polarized 2-wire plug wouldn't go into the AC receptacle, so he filed down the wider prong (neutral). I asked him why he hadn't just turned the plug around so that the wider prong would go into the longer slot. He looked at the outlet, looked at the plug, and then looked at me and said: "Oh."

Best regards,
rabbit
January 12, 2010; revised June 24, 2015