GFCI compatible system and method for activating relay controlled lines having a filter circuit between neutral and ground

#Transient voltages adversely affect power circuits. Many people mistakenly believe that most problems caused by transient voltages are the result of lightning strikes and black outs. However, the majority of the problems are the result of common mode noise (CMN). CMN occurs between the neutral line and ground line or between a hot line and a ground line. CMN has many causes including, but not limited to, computer power supplies and the starting and stopping of motors. CMN manifests itself as small voltage shifts in the ground line. Further, CMN can be viewed as a higher frequency signal that has been added to the fundamental frequency of the electrical signal. Typically this fundamental frequency is 60 [Hz] while the frequency of CMN can typically exceed 100 [kHz]. Since equipment on a typical electrical network share a common ground, such equipment on the electrical network sees these voltage shifts.

#CMN causes logic confusion in microprocessors, which is a common source of malfunctions in these devices. Microprocessors are binary devices that transmit and compute data using a series of ones and zeroes. A microprocessor views 5V with respect to ground as a one, while 0V with respect to ground, a zero. CMN can prevent the voltage seen by the microprocessor from reaching 0V. Thus the microprocessor will mistakenly read a zero as a one causing logic errors. Likewise, CMN can also prevent the voltage from reaching 5V and causing the microprocessor to mistakenly read a one as a zero. Such logic errors can lead to microprocessors misreading data, programs not functioning properly, and even system crashes.

#An early solution to filter out CMN was the isolation transformer. However, as power systems became more complex, CMN became more severe and isolation transformers became less economical. New power filtration circuits were developed as a more economical alternative to isolation transformers. An example of a power filtration filter is the Transformer Based Filter (TBF) developed by Smart Power Systems, Inc. Such power filtration circuits used inductors on the neutral line of the circuit and capacitors connected between the neutral and the ground to filter out CMN transient voltage spikes.

#FIG. 1 illustrates an exemplary electrical network including an electric supply, CMN source, CMN Suppressor and CMN Sensitive Device.

#FIG. 2A illustrates a CMN on a GFCI protected ground node.

#FIG. 2B illustrates an effect of a CMN on a signal not protected by a CMN suppressor.

#Described herein is a GFCI compatible system and method for activating relay-controlled lines having a filter circuit between neutral and ground. The following description is presented to enable any person skilled in the art to make and use the invention as claimed and is provided in the context of the particular examples discussed below, variations of which will be readily apparent to those skilled in the art. In the interest of clarity, not all features of an actual implementation are described in this specification. It will be appreciated that in the development of any such actual implementation (as in any development project), design decisions must be made to achieve the designers' specific goals (e.g., compliance with system- and business-related constraints), and that these goals will vary from one implementation to another. It will also be appreciated that such development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the field of the appropriate art having the benefit of this disclosure. Accordingly, the claims appended hereto are not intended to be limited by the disclosed embodiments, but are to be accorded their widest scope consistent with the principles and features disclosed herein.

#FIG. 1 illustrates an electrical network 100. In one embodiment, electrical network 100 can comprise an electrical supply 101, nodes 102, one or more CMN sources 103, one or more ground fault current interrupters (GFCI) 104, GFCI monitored nodes 105, a CMN suppressor 106, CMN suppressor monitored nodes 107, and a CMN sensitive device 108. Electrical supply 101 can provide power to devices on electrical network 100 over nodes 102. Nodes 102 can comprise a hot node, 102a, a neutral node 102b, and a ground node 102c. All or portions of lines 102 can be monitored by GFCIs 104. For purpose of this disclosure, GFCI monitored nodes 105 are power delivery nodes immediately downstream from GFCI 104. Each GFCI monitored node 105 can comprise a GFCI monitored hot node 105a, a GFCI monitored neutral node 105b, and a GFCI monitored ground node 105c. However, practically speaking, GFCI monitored ground node 105c can be the same node as ground node 102c. GFCI monitored nodes 105 can connect GFCI 104 to CMN suppressor 106. Also for purpose of this disclosure, CMN suppressor monitored nodes 107 are power delivery nodes immediately downstream from CMN suppressor 106. Each CMN suppressor monitored node 107 can comprise a CMN suppressor monitored hot node 107a, a CMN suppressor monitored neutral node 107b, and a CMN suppressor monitored ground node 107c. CMN suppressor monitored nodes 107 can connect CMN suppressor 106 to CMN sensitive device 108. CMN sensitive devices 106 can include, but are not limited to, computers, copy machines, point of sale terminals, self-checkout terminals, and automatic teller machines.

#CMN source 103 can receive power through nodes 102 or GFCI protected nodes 105. Examples of CMN sources 103 can include but are not limited to shredders, microwaves, ice machines, cappuccino machines, air conditioning units, refrigerators, elevators, and items with rectifier circuits. During operation, CMN source 103 can transmit CMN 109 back over nodes 102 or GFCI protected nodes 105. Further, CMN 109 can pass through GFCI 104 with little or no effect to CMN 109. CMN 109 can exist between hot node 102a and ground node 102c, neutral node 102b and ground node 102c, GFCI protected hot node 105a and GFCI protected ground node 105c, and/or GFCI protected neutral node 105b and GFCI protected ground node 105c. CMN suppressor 106 can substantially block CMN 109, allowing only a reduced CMN 110 to reach CMN sensitive device 108 over CMN suppressor monitored nodes 107.