Patent Application
20070086141
1. Field of the Invention
This invention pertains generally to power systems and, more particularly, to power systems employing surge suppression. The invention also relates to surge suppression apparatus and, more particularly, to surge receptacle apparatus.
2. Background Information
With the wide use of computers and other relatively expensive electronic equipment, users, such as, for example, homeowners, are protecting their investments with “surge strips” (e.g., without limitation, apparatus including an extension cord and one or more electrical receptacles or outlets providing surge suppression, such as, for example, MOV-based over-voltage protection) or “surface receptacles”. Unfortunately, the present design of these surge strips or surface receptacles may cause significant ground current to flow whenever significant surge suppression, such as, for example, significant over-voltage clamping, occurs. This ground current, in turn, may cause what appears to be nuisance tripping of upstream GFCI or AFCI/GFCI circuit breakers.
There is a safety concern with the expanded use of ground fault protection. For example, known transient voltage surge suppressor (TVSS) cord-connected devices use voltage clamping devices with equal clamping voltage ratings from line-to-neutral and from line-to-ground. With such a design, under line-to-neutral surge conditions in, for example, a residential installation, surge fault current will be conducted equally from line-to-neutral and line-to-ground. This ground fault current in the ground conductor will cause a perceived nuisance tripping of ground fault protective devices when no true ground fault condition exists. The user, such as a homeowner, may well be tempted to remove the ground fault protection in order to eliminate the perceived nuisance tripping. This is a substantial safety concern. In a residential installation, where the neutral is bonded to the grounding impedance, line-to-ground TVSS protection may introduce voltages on the ground conductors instead of limiting them during line transient events. This has the potential to create unsafe ground voltages instead of reducing them.
The switching of capacitors for line voltage regulation purposes has been identified as a source of frequent transients (e.g., several times a week) creating twice the peak line voltage (see, for example, IEEE C62.41-1991).
The grounding conductor is a non-current carrying conductor per NEC § 250 “Grounding and Bonding” (2005). NEC § 250.4 (A) states that a purpose of grounding is to “limit the voltage imposed by lightning line surges”. This section also specifies that grounding of electrical equipment is intended to be non-current carrying. NEC § 250.6 “Temporary Currents Not Classified as Objectionable Currents” describes acceptable currents in the grounding conductors as including temporary currents in the grounding conductors resulting from accidental ground faults or resulting from the grounding conductors doing their protective function as being not objectionable.
Accordingly, there is room for improvement in power systems and surge receptacle apparatus.
These needs and others are met by the present invention, which provides a surge receptacle apparatus that substantially reduces nuisance trips of upstream interrupters with ground fault protection.
In accordance with one aspect of the invention, a power system for a power circuit including a line conductor, a neutral conductor and a ground conductor comprises: a circuit interrupter structured to provide ground fault protection for the power circuit; and a surge receptacle apparatus powered through the circuit interrupter, the surge receptacle apparatus comprising: a line terminal electrically interconnected with the line conductor, a neutral terminal electrically interconnected with the neutral conductor, a ground terminal electrically interconnected with the ground conductor, a number of outputs electrically interconnected with the line terminal, the neutral terminal and the ground terminal, and a surge suppression circuit comprising: (a) a first surge suppression device electrically connected between the line terminal and the neutral terminal and including a first voltage rating, a second surge suppression device electrically connected between the neutral terminal and the ground terminal and including a second smaller voltage rating of about 30 VRMS to about 50 VRMS, and generally no over-voltage protection device between the line terminal and the ground terminal other than the series combination of the first and second surge suppression devices, or (b) a third surge suppression device electrically connected between the line terminal and the neutral terminal and including a third voltage rating, a fourth surge suppression device electrically connected between the neutral terminal and the ground terminal and including a fourth voltage rating which is about equal to the third voltage rating, and a fifth surge suppression device electrically connected between the line terminal and the ground terminal, the fifth surge suppression device including a fifth voltage rating which is about 30 VRMS to about 50 VRMS greater than the third and fourth voltage ratings, wherein a limited energy line-to-neutral fault between the line terminal and the neutral terminal or a limited energy line-to-ground fault between the line terminal and the ground terminal above a first predetermined magnitude will produce a ground fault current in the ground conductor sufficient to trip the circuit interrupter, and wherein a limited energy line-to-neutral fault between the line terminal and the neutral terminal or a limited energy line-to-ground fault between the line terminal and the ground terminal below the first predetermined magnitude and above a second predetermined magnitude, which is less than the first predetermined magnitude, will produce a ground current in the ground conductor insufficient to trip the circuit interrupter.
The surge suppression circuit may comprise the third, fourth and fifth suppression devices, and the third and fourth voltage ratings may be about 130 VRMS.
The surge suppression circuit may comprise the first and second surge suppression devices and may generally have no over-voltage protection device between the line terminal and the ground terminal other than the series combination of the first and second surge suppression devices. The first voltage rating of the first surge suppression device may be about 130 VRMS.
As another aspect of the invention, a surge receptacle apparatus comprises: a line terminal; a neutral terminal; a ground terminal; a number of outputs electrically interconnected with the line terminal, the neutral terminal and the ground terminal; a first surge suppression device electrically connected between the line terminal and the neutral terminal, the first surge suppression device including a first voltage rating; a second surge suppression device electrically connected between the neutral terminal and the ground terminal, the second surge suppression device including a second voltage rating which is about equal to the first voltage rating; and a third surge suppression device electrically connected between the line terminal and the ground terminal, the third surge suppression device including a third voltage rating which is about 30 VRMS to about 50 VRMS greater than the first and second voltage ratings.
The first and second voltage ratings may be about 130 VRMS.
As another aspect of the invention, a surge receptacle apparatus comprises: a line terminal; a neutral terminal; a ground terminal; a number of outputs electrically interconnected with the line terminal, the neutral terminal and the ground terminal; a first surge suppression device electrically connected between the line terminal and the neutral terminal, the first surge suppression device including a first voltage rating; and a second surge suppression device electrically connected between the neutral terminal and the ground terminal, the second surge suppression device including a second smaller voltage rating of about 30 VRMS to about 50 VRMS, wherein the surge receptacle apparatus generally has no over-voltage protection device between the line terminal and the ground terminal other than the series combination of the first and second surge suppression devices.
The first voltage rating of the first surge suppression device may be about 130 VRMS.
The first voltage rating of the first surge suppression device may be about 80 VRMS to about 100 VRMS greater than the second voltage rating of the second surge suppression device.
The first surge suppression device may further include a first indicator circuit structured to indicate when the first fuse is open; and the second surge suppression device may further include a second indicator circuit structured to indicate when the second fuse is open.
The first surge suppression device may include a first fuse in series with a first metal oxide varistor, and the second surge suppression device may include a second fuse in series with a second metal oxide varistor. The first fuse may be electrically connected to the first metal oxide varistor at a node; the first surge suppression device may further include a resistor having first and second leads, a diode having an anode and a cathode, and a light having a first lead and a second lead; the first lead of the resistor may be electrically connected to the node; the second lead of the resistor may be electrically connected to the anode of the diode; the cathode of the diode may be electrically connected to the first lead of the light; and the second lead of the light may be electrically connected to the neutral terminal.
The second fuse may be electrically connected to the second metal oxide varistor at a node; the second surge suppression device may further include a resistor having first and second leads, first, second and third diodes each having an anode and a cathode, and a light having a first lead and a second lead; the first lead of the resistor may be electrically connected to the line terminal; the second lead of the resistor may be electrically connected to the anode of the first diode; the cathode of the first diode may be electrically connected to the anodes of the second and third diodes; the cathode of the second diode may be electrically connected to the first lead of the light; the second lead of the light may be electrically connected to the neutral terminal; and the cathode of the third diode may be electrically connected to the node.
A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the term “surge suppression” and variations thereof shall mean surge suppression, surge protection, over-voltage suppression and/or over-voltage protection. For example, a “transient voltage surge suppressor” (TVSS) is a device that attenuates (i.e., reduces in magnitude) random, high energy, short duration electrical power anomalies caused by, for example, electric utilities, atmospheric phenomena or inductive loads. Such anomalies may occur in the form of voltage and/or current spikes with a duration of less than about one-half of an alternating current (AC) line cycle. Such high energy power spikes may, otherwise, damage sensitive electronic equipment, such as computers, instrumentation or process controllers.
As employed herein, the term “surge suppression device” shall expressly include, and not be limited by, TVSSs, MOVs and other devices providing surge suppression.
As employed herein, the term “surge receptacle apparatus” shall expressly include, and not be limited by, “surge protector strips,” “surge strips,” “power surge strips,” “surge receptacles,” “wall-mounted surge receptacles,” “wall-mounted surge protectors,” “surface receptacles” and other devices structured to receive an AC source of power, provide surge suppression for such AC source of power, and output such surge suppressed AC source of power to a number of AC output(s).
As employed herein, examples values of VRMS are nominal values and example ranges of VRMS values are nominal ranges, all of which are understood to further have nominal manufacturing tolerances (e.g., without limitation, about ±10%). As a non-limiting example, as disclosed and claimed herein, a range of about 30 VRMS to about 50 VRMS, covers, for example, nominal manufacturing tolerances of about ±10% and, thus, covers the range of about 27 VRMS to about 55 VRMS.
An example surge protector strip includes a power input (e.g., without limitation, a power cord), a housing, one or more surge suppression devices (e.g., without limitation, an EMI/RFI filter), and a plurality of AC power outputs (e.g., without limitation, outlets; receptacles). Such a surge protector strip may also include none, some or all of a power switch, a resettable circuit breaker that automatically turns-off in the event of a power overload, and a power indicator.
A wall-mounted surge receptacle includes a power input (e.g., without limitation, terminals structured to engage a three-conductor AC power circuit), a body structured to engage a wall-mounted receptacle box and receptacle cover, one or more surge suppression devices, and one or two AC power outputs (e.g., without limitation, female three-terminal AC outlets or receptacles).
A wall-mounted surge protector includes a power input (e.g., without limitation, a male three-prong plug structured to engage a female three-terminal AC outlet or receptacle), a housing, one or more surge suppression devices, and a plurality of AC power outputs (e.g., without limitation, female three-terminal AC outlets or receptacles). Such a wall-mounted surge protector may or may not include a power indicator light.
Referring to
Although MOVs 34,36,38 are shown in
The line terminal 28, the neutral terminal 30 and the ground terminal 32 are disposed on a three-terminal plug 40. The terminals 28,30,32 are respectively electrically connected to a line conductor 42, a neutral conductor 44 and a ground conductor 46 of a power cord 48.
The surge strip 22 of
In this example, the first MOV 50 includes a first voltage rating, the second MOV 52 includes a second smaller voltage rating of about 30 VRMS to about 50 VRMS, and the surge strip 22 generally has no over-voltage protection device between the line terminal 42 and the ground terminal 46 other than the series combination of the MOVs 50,52. For example, the MOV 38 of
The first voltage rating of the first MOV 50 is about 130 VRMS.
The first voltage rating of the first MOV 50 is about 80 VRMS to about 100 VRMS greater than the second voltage rating of the second MOV 52.
The surge strip 24 of
In the first MOV failure indicator circuit 58, the first fuse 54 is electrically connected to the first MOV 50 at node 76. One lead of the resistor 64 is electrically connected to the node 76 and the other lead of the resistor 64 is electrically connected to the anode of the diode 66. The cathode of the diode 66 is electrically connected to the anode the LED 62 and the cathode of the LED is electrically connected to the neutral conductor 44 and, thus, the neutral terminal 30.
For the second MOV failure indicator circuit 60, the second fuse 56 is electrically connected to the second MOV 56 at node 78. One lead of the resistor 68 is electrically connected to the line conductor 42 and, thus, the line terminal 28. The other lead of the resistor 68 is electrically connected to the anode of the first diode 70, while the cathode of the first diode 70 is electrically connected to the anodes of the second and third diodes 72,74. The cathode of the second diode 72 is electrically connected to the anode of the LED 62. The cathode of the third diode 74 is electrically connected to the node 78, in order to provide a path for current through the resistor 68 and the fuse 56 when the MOV 52 has not failed. Although the single LED 62 is employed, the circuits 58,62 may employ separate lights or LEDs (not shown).
The example neutral-to-ground and line-to-neutral MOV voltage ratings of the surge strip 24 are selected in order that, for example, a one-cycle 240 V, limited energy (e.g., without limitation, supplied through a 2 Ω source impedance) line-to-neutral surge will not cause a perceived nuisance tripping of an upstream ground fault protective device, such as GFCI 26 of
As a non-limiting example, for the surge strips 20,22,24 of
While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
