Patent Description:
Recent changes to the NEC will require GFCI protection in certain commercial areas that can be considered wet locations, and which may involve loads that are beyond the ratings of GFICs shown above. One example is commercial kitchens where heating loads will require three phase power and amperage of 60A and above. Three phase power supplies comprise one type of multiphase power phase power supply and include three power lines having AC phases that are <NUM> degrees apart and a neutral line that is common to all three phases.

North Shore Safety, a Tecmark Company, of Mentor, Ohio sells a three phase ground fault circuit interrupter under the trademark "LineGard. " Upon the detection of a ground fault, the LineGard triggers a "contactor" which disconnects the three phase power lines from the load. A similar device is made by Littlefuse of Chicago, Illinois under the trademark "Shock Block. " Neither of these devices are capable of disconnecting the neutral line from the load.

Contactors are often used as power switches for high-power multiphase systems such as HVAC, refrigeration, heating, and commercial kitchens. When tripped, they open a triple pole, single throw switch to disconnect the load from the power lines. Contactors do not disconnect the neutral line from the load.

Contactors are heavy-duty, high performance switches and tend to be relatively expensive. Furthermore, once tripped, contactors require power in order to remain open. Examples of commercially available contactors are the XMC0 series of "Definite Purpose Contactors" sold by Hongfa of Xiamen, China.

When contactors are used in GFCI of the prior art, power must remain available for the GFCI to both power its control circuitry and the contactor, even after a ground fault is detected. This not only consumes energy, but it also leads to potential inadvertent opening of the contactors switches in the event of a power failure. Even more dangerous is a "brown-out" situation, where there is insufficient voltage available to keep the contactor switches open even though there is a ground fault detected, creating a potential hazard.

These and other limitations of the prior art will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.

Prior art which relates to this field can be found in document <CIT>, disclosing a three-phase ground fault circuit interrupter (GFCI). The three-phase GFCI device may include contactors, a contactor control module configured to cause the contactors to close during normal operation of the GFCI device and open based on receiving a fault signal, a current detection module, a transient suppression module, a miswire detection module, a ground-fault test module, a ground load detection module, and a fail-safe module. In some examples, the GFCI device may include the stated modules in accordance with the UL 943C standard.

Further prior art can be found in document <CIT>, disclosing a ground fault circuit interrupter (GFCI). In the GFCI, a leading power factor circuit is connected to a secondary winding of a GFCI differential transformer to permit a magnetic circuit to respond to pulsating DC signals. Provision is made by a diode connected to earth for continuing to provide GFCI protection in the event of an open neutral lead, with a timing circuit to prevent current flow to the ground lead until current flow in the neutral lead is completely discontinued. Various types of circuit interrupting devices, such as a circuit breaker or a power contractor, may be selectively utilized, and a test switch is provided.

Example embodiments of a multiphase ground fault circuit interrupter utilize a plurality of latching relays associated with a corresponding plurality of power line inputs to disconnect the power lines from a load when a ground-fault is detected. In a further embodiments, an additional latching relay is used to disconnect the neutral line from the load.

Objects are achieved by what is defined in the appended independent claims. Advantageous modifications thereof are set forth in the appended dependent claims.

An advantage of using multiple latching relays rather than a contactor is that, once they are tripped, no power is required for the control circuitry to maintain an open state for the relay switches. Therefore, even if power is wholly lost or reduced (e.g. in a brown-out situation), the tripped relays will remain open until reset.

Another advantage of using multiple latching relays rather than a contactor is that the cumulative cost of the latching relays tends to be considerably less that than that of a single, high power contactor.

An advantage of using an additional latching relay to disconnect the neutral line from the load is that additional safety is provided in, for example, ground-neutral fault situations.

These and other embodiments, features and advantages will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.

Several example embodiments will now be described with reference to the drawings, wherein like components are provided with like reference numerals. The example embodiments are intended to illustrate, but not to limit, the invention. The drawings include the following figures:.

In <FIG>, an example multiphase ground fault circuit interrupter <NUM> includes a first phase power line input <NUM>, a second phase power line input <NUM>, a third phase power line input <NUM>, a neutral line input <NUM>, a controller circuit <NUM> having a relay control output <NUM>, a first phase latching relay <NUM> having a first phase switch input <NUM> coupled to the first phase power line input <NUM> and a first phase relay control input <NUM> coupled to the relay control output <NUM> of the controller circuit, a sensor <NUM> having a core <NUM> and a sensor pickup <NUM> coupled to the controller circuit <NUM>, and a first phase load wire P1 coupled to a first phase switch output <NUM> of the first phase latching relay <NUM> and passed through the core <NUM>. A neutral latching relay <NUM> has a neutral switch input <NUM> coupled to the neutral line input <NUM> and a neutral latching relay control input <NUM> coupled to the relay control output <NUM> of the controller circuit <NUM>. A neutral load wire N is coupled to a neutral switch output <NUM> of the neutral line latching relay <NUM> and extends through the core <NUM>.

In this example, multiphase ground fault circuit interrupter <NUM> further includes a second phase latching relay <NUM> having a second phase switch input <NUM> coupled to the second phase power line input <NUM> and a second phase relay control input <NUM> coupled to the relay control output <NUM> of the controller circuit <NUM>. A second phase load wire P2 is coupled to a second phase switch output <NUM> of the second phase latching relay <NUM> and extends through the core <NUM>.

With continuing reference to <FIG>, in this example a third phase latching relay <NUM> having a third phase switch input <NUM> coupled to the third phase power line input <NUM> and a third phase relay control input <NUM> coupled to the relay control output <NUM> of the controller circuit <NUM>. A third phase load wire P3 is coupled to a third phase switch output <NUM> of the third phase latching relay <NUM> and extends through the core <NUM>.

The number of power lines extending through the core <NUM> depends upon the requirements of a load <NUM>. For example, if load <NUM> only requires a single phase, only load wire P1 and neutral load wire N need to extend through the core <NUM>. As another example, if the load <NUM> requires all three phases, load wires P1, P2, P3 and N all extend through the core <NUM>. It will therefore be appreciated that the power provided to the load <NUM> can be one, two or three phases, in the present example.

The core <NUM> and sensor pickup <NUM> comprise an inductive current sensor which can detect current flowing on the wires that extend through the core. The core <NUM> is typically made from a high-nickel metal alloy and the sensor pickup comprises a number of winds of an insulated wire on the core surface. Inductive current sensors are well known to those of skill in the art. For example, in <CIT>, the disclosure of which is incorporated herein by reference, a device to measure current magnitude in a conductor coupled to an electrical device is disclosed.

It will be noted that in this example embodiment, the relay control output <NUM> and the relay control inputs <NUM>, <NUM>, <NUM> and <NUM> include separate Reset (R) and Set (S) lines carrying R and S signals, respectively. This is because the latching relays of this example will latch in a closed position in response to a reset signal on their R control inputs and will latch in an open position in response to a set signal on their S control inputs. In this example, suitable latching relays include the Power Latching Relay TOU80 series made by TE Connectivity, headquartered in Schaffhausen, Switzerland with worldwide offices. Other types of latching relays can also be used with other types of control inputs. For example, a latching relay with a single toggle control input can be used to toggle the latching relays between their open and closed positions.

More particularly, in this example, the relay control output of the controller circuit includes a Reset (R) output and a Set (S) output, the first phase relay control input includes an R input coupled to the R output and an S input coupled to the S output, and the neutral latching relay control input includes an R input coupled to the R output and an S input coupled to the S output, whereby the R output of the controller circuit resets both the first phase latching relay and the neutral latching relay, and the S output of the controller circuit set both the first phase latching relay and the neutral latching relay. Similarly, the R output of the controller circuit further resets the second phase latching relay and the third phase latching relay, and the S output of the controller circuit sets the second phase latching relay and the third phase latching relay.

The controller circuit <NUM> of this example includes a microcontroller (µC) <NUM>, a sensor test circuit <NUM>, an isolated alternating current to direct current (AC/DC) converter <NUM>, a state relay <NUM>, and a current limiting resistor <NUM>. The microcontroller <NUM> is coupled to the sensor pickup <NUM> and is operative to develop the set signal S upon the detection of a ground fault. The microcontroller <NUM> can be, for example, an NCS37010 Self Test With Lockout Ground Fault Circuit Interrupter sold by onsemi of Phoenix, Arizona.

The AC/DC converter <NUM> converts the AC voltage on first phase power line input <NUM> to a relatively low DC voltage, e.g. in the range of <NUM>-12VDC. The state relay <NUM> is a latching relay, preferably of the same type latching relays <NUM>, <NUM>, <NUM>, and <NUM>, and is controlled by the same set (S) and reset (R) relay control signals. When the state relay <NUM> is in a reset (R) state, the relay switch is closed and the microcontroller <NUM> is powered. When the state relay is in a set (S) state, the relay switch is open, and power is removed from the microcontroller. In consequence, upon a detection of a ground fault, all of the latching relays are set to an open state, and the only device of the controller circuit that is powered is the AC/DC converter <NUM>.

The multiphase ground fault circuit interrupter <NUM> is reset by activating a reset switch <NUM> to create the R signal, thereby resetting all of the latching relays and thereby repowering the system. A test switch <NUM> is also coupled to the microcontroller <NUM> to manually initiate a test of the system.

The sensor test circuit <NUM> includes a relay <NUM> and four diodes <NUM>, <NUM>, <NUM> and <NUM>. The relay is activated by the microcontroller <NUM> via a relay control line <NUM> to initiate a test of the sensor <NUM>. The relay <NUM> can be activated manually by test switch <NUM> or can be automatically activated on a periodic basis during operation by the microcontroller <NUM>. Diode <NUM> is coupled to the P1 line on the load side of core <NUM>, diode <NUM> is coupled to the N line on the load side of core <NUM>, diode <NUM> is coupled to the P1 line on the power side of the core <NUM>, and diode <NUM> is coupled to the N line on the power side of core <NUM>. When the relay <NUM> is activated, the diodes <NUM>, <NUM>, <NUM>, and <NUM> cause current to flow through the P1 line and the N line to simulate a ground fault condition. If the microcontroller <NUM> detects the simulated ground fault condition, the sensor <NUM> is operating properly. If the microcontroller <NUM> does not detect the simulated ground fault condition, the sensor is not working properly, and a set (S) signal is developed to trip the latching relays and remove power from the system.

<FIG> is a flow diagram of an example process <NUM> performed by the microcontroller <NUM>. Process <NUM> begins with a power-on <NUM> of the system, e.g. by either applying power to the system or resetting the system after a ground-fault has been cleared. Next, an operation <NUM> idles until the system passes initial power-up tests, after which the system is delayed in an operation <NUM> to allow the circuitry to settle. For example, operation <NUM> can provide a <NUM> delay. After the delay, an operation <NUM> determines if the sensor passes a self-test procedure. If not, the latching relays are tripped (e.g. by developing an S signal) to remove power from the system, and the process ends at <NUM>. If the sensor self-test is successful, an operation <NUM> determines if a relay test is enabled. If so, an operation determines if the relay test had failed and, if so, the process again ends at <NUM>. If operation <NUM> determines that the relay test was successful, an operation <NUM> disables the relay test so that it does not run again. That is, typically the relay test runs only once after power-up. Next, in an operation <NUM>, it is determined if a ground-neutral fault test is enabled. If so, an operation <NUM> determines if the ground-fault test was successful. If not, an operation <NUM> trips the latching relays to remove power from the system and the process ends at <NUM>. Next, an operation <NUM> determines if a ground fault is detected. If so, operation <NUM> again trips the latching relays and the process ends at <NUM>. If no ground fault is detected by operation <NUM>, an operation <NUM> determines if it is time to self-test the sensor. If not, operation <NUM> again tests for ground faults. If operation <NUM> determines that it is time to self-test the sensor, the process returns to operation <NUM>. An example time between periodic, automatic self-tests is about <NUM> minutes, although shorter and longer periods can also be used as determined by a self-test timer, typically implemented by the microcontroller.

<FIG> is a flow diagram of an example power test process <NUM> of <FIG>. The process begins at <NUM> and, in an operation <NUM>, it is determined if the power to the microcontroller (chip) <NUM> is good. If not, operation <NUM> idles until the microcontroller chip <NUM> is properly powered. Next, in an operation <NUM>, it is determined if the line voltage <NUM> is good. If not, the process returns to operation <NUM>. If operation <NUM> determines that the line voltage is good, operation <NUM> of <FIG> proceeds to make the aforementioned delay.

<FIG> is a flow diagram of an example self-test process <NUM> of <FIG>. The process begins at <NUM> and, in an operation <NUM>, the microcontroller <NUM> activates the test relay <NUM>. Next, in an operation <NUM>, a differential ground fault test is performed on the lines P1 and N. If an operation <NUM> determines that the ground fault test did not pass, the process continues with operation <NUM> of <FIG>, and if operation <NUM> determines that the ground fault test did pass, the process continues with operation <NUM> of <FIG>.

<FIG> is a flow diagram of an example relay test process <NUM> of <FIG>. The process begins at <NUM> and, in an operation <NUM>, all of the latching relays are tripped (e.g. set or opened). Next, in an operation <NUM> it is determined if a load voltage is available on P1. If yes, the relay test has failed, and the process ends at <NUM> of <FIG>. If no, the relay test was passed, and an operation <NUM> resets (e.g. closes) the latching relays and resets the self-test timer count to zero. Process control then returns to operation <NUM> of <FIG>.

Claim 1:
A multiphase ground fault circuit interrupter (<NUM>) comprising:
a first phase power line input (<NUM>);
a second phase power line input (<NUM>);
a third phase power line input (<NUM>);
a neutral line input (<NUM>);
a controller circuit (<NUM>) having a relay control output (<NUM>);
a first phase latching relay (<NUM>) having a first phase switch input (<NUM>) coupled to the first phase power line input and a first phase relay control input (<NUM>) coupled to the relay control output of the controller circuit;
a second phase latching relay (<NUM>) having a second phase switch input (<NUM>) coupled to the second phase power line input and a second phase relay control input (<NUM>) coupled to the relay control output of the controller circuit;
a third phase latching relay (<NUM>) having a third phase switch input (<NUM>) coupled to the third phase power line input and a third phase relay control input (<NUM>) coupled to the relay control output of the controller circuit;
a sensor (<NUM>) having a core (<NUM>) and a sensor pickup (<NUM>) coupled to the controller circuit;
a first phase load wire (P1) coupled to a first phase switch output (<NUM>) of the first phase latching relay and extending through the core;
a second phase load wire (P2) coupled to a second phase switch output (<NUM>) of the second phase latching relay and extending through the core; and
a third phase load wire (P3) coupled to a third phase switch output (<NUM>) of the third phase latching relay and extending through the core.