Introduction

1. The effects of Smart Meters on GFCI Outlets Caroline Storm, Simon Donahue, David Wetz, Advisor Department of Electrical Engineering, The University of Texas at Arlington, Arlington, Texas 76019 Abstract Smart Meters have recently been deployed on a wide scale. These devices has proven to be successful, but there is still much that is unknown about how they impact the devices around them. One such device, is a ground fault circuit interrupter, or GFCI. A GFCI is a residual-current device that disconnects itself from an applied load when it detects in an imbalance of current. Typically, GFCIs are required in electrical installation where water may interfere with electronics. Under the construction pole setup conditions electrical contractors in North Texas have been experiencing repeated and uncontrollable GFCI tripping events, absent of the presence of water or leakage current, which were believed to be caused by interference with the RF transmissions from the Smart Meter located in very close proximity, typically within 0.5 m, to the GFCI. The goal of this research was to find out if the was actually the case and if so how to prevent it. Results Test 1: Source of energy The first test was to discover whether the energy was being radiated and then pick-up by the hot and neutral lines versus being conducted from the sense board. This was done by reading the voltage across the differential transformer in two different set ups: 1. The GFCIs’ power was supplied directly from the Smart Meter 2. The GFCIs’ power was supplied from a uninterrupted power supply (UPS), effectively isolating them from the Smart Meter Figure 2. GFCI differential transformer Voltage under no trip conditions. It spikes around 900 mV Figure 3. GFCI differential transformer connected directly to the Smart Meter during a trip event. Spiking around 1.25 V Figure 4. GFCI connected to a UPS during a trip event. Spiking around 1.60 V Test 2: How to mitigate the effects 2.1 Distance Knowing that the problem came from radiated energy, rather then conducted through the transmission lines, we wanted to see if the problem could be solved by moving the Smart Meter father away. Given the construction pole set up the Smart Meter and GFCIs could not be moved more then 15 inches away. We took measurements over 1 inch intervals and found very little difference. Figure 5. GFCI transformer voltage during a no trip conditions. Spike around 702 mV Figure 6. GFCI at 12 inches during trip event. Spike around 704 mV. Enough to cause the GFCI to trip. Figure 7. GFCI at 15 inches during trip event. Spike around 703 mV. Still enough to cause the GFCI to trip. These graphs demonstrate that given the 15 inch constraint of the construction power poles the problem cannot be solved by physical separation of the Smart Meter from the GFCIs. • Summary and conclusions • One of the more important things to note is that the power line going from the smart meter to the GFCI outlet box is acting as an antenna. This means the orientation of the wire has a profound effect on the frequency of tripping. However, due to the difficulty in finding an orientation to stop the tripping, and keeping the wire in that orientation, a better solution needed to be found. We propose the use of ferrite beads on the GFCI end of the power line. By effectively suppressing all the energy form the Smart Meter RF communications the extra functional tripping is eliminated. A test was run for 56 hours and found that this measure effectively stopped the tripping. It is an easy, cheap solution which can be implemented on already installed construction pole set ups. Differential voltage-no trip conditions Introduction Smart Meters use wireless RF to transmit data to the main HUB. It has been observed within the laboratory and at construction sites, that these transmissions interfere with GFCI outlets, producing problems for those using these two devices in close proximity. There have been no reported causes of this interference in homes where the Smart Meters are located a considerable distance away from the GFCI outlets. Instead the concern comes from installations on construction poles where the proximity between the meter and the GFCI is within 0.5 m. There are three likely sources of interference between the GFCI and the smart meter. First, direct coupling with the differential transformers inside the GFCI. Second, radiative coupling in the hot or neutral line to the GFCI. Thirdly, conductively interference into the GFCI’s electronic sense board from the Smart Meter PCP. The goal of this research is to establish the reason for the faulty trips and to find a cheap and easily implementable solution to mitigating them. Literature cited ‘Smart meter deployments continue to rise,’ U.S. Energy Information Administration, July 7, 2013. Z. Zhang, W-J. Lee, D.A. Wetz, B. Shrestha, J. Shi, A. Jackson, H. Honang and J. Fielder, ‘Evaluation of the Switching Surges Generated during the Installation of Legacy and ‘Smart’ Electric Metering Equipment,’ Proceedings of the 48th Industrial & Commercial Power Systems Technical Conference, Louisville, Kentucky, May 20 – 24, 2012. G. Mezei " An Investigation of Radiofrequency Fields Associated with the Itron Smart Meter " Electric Power Research Institute, 2010 Technical Report, Dec. 2010 W.D. Ford and R.G. McCormack, ‘Investigation of Ground Fault Circuit Interrupter,’ Technical Report E92, September 1976, Construction Engineering Research Laboratory. Powered off Smart Meter-trip conditions Materials and methods For all our tests we used a combination of the following equipment. Agilent 4403B spectrum analyzer LeCroyWavesurfer 24Xs Oscilloscope, with the probes hooked up to the differential transformers APC Smart-UPS 1500VA B-field probe Modified and unmodified GFCIs Figure 3. Test set up. The oscilloscope and spectrum analyzer are out of the picture Background Eaton has been doing similar work and found that isolating the hot and neutral lines from the field was enough to control, and stop, the tripping events. Effectively showing the tripping was not being caused by direct coupling with the transformers. Powered off UPS-trip conditions Acknowledgments We thank David Wetz for technical support. Simon Donahue was the masters student whom worked with me on this project. He provided much of the technical knowledge and instruction NSF Grant EEC-1156801 For further information Please contact caroline.storm@mavs.uta.edu