Voltage indicating coupling for metal conduit systems

A voltage indicating coupling for metal conduit systems to indicate the presence or absence of voltage on a wire enclosed by a section of electrical conduit for a grounded AC power distribution system. Through the use of two opposing rectifiers the National Electrical Code requirement that the entire metal conduit system be grounded is met. The voltage indicating coupling comprises a liquid crystal display (LCD), a static suppression resistor, two opposing rectifiers for grounding purposes, a plastic block housing and two clamping screws with corresponding wire terminals. At least one “hot” conductor enclosed by the section of electrical conduit is capacitively coupled to the conduit creating a complete circuit through the liquid crystal display (LCD), the static suppression resistor and the opposing rectifiers. The path around the circuit is completed by a ground connection on the grounded part of the conduit system, and the ground connection at the transformer.

BACKGROUND OF THE INVENTION

1. National Field of Invention

One version of the voltage indicator is intended for single-phase and three phase AC voltage detection on 90-277 volt (with respect to ground) rms wires enclosed in metal conduit as is used in grounded AC power distribution systems as is common in the United States.

2. International Field of Invention

Another version of the voltage indicator is intended for single-phase and three phase AC voltage detection on 90-277 volt (with respect to ground) rms wires enclosed in metal conduit as is used in grounded AC power distribution systems as is common outside the United States.

3. Reasons for Utility of Invention

This invention shows that voltage is present on at least one wire of possibly several that are enclosed in a section of metal conduit of various possible sizes. The electrically isolated section of conduit is grounded to the rest of the metal conduit system through two opposing rectifiers which will electrically break down if a “hot” wire grounds to this semi-grounded section of the conduit.

1. Device can be mounted anywhere during initial installation in metal conduit system where there are two or more feet of exposed metal conduit.

2. Device doesn't physically damage the enclosed wiring.

3. Circuit breaker or fuse may be tripped or blown at main panel.

4. Incandescent light bulb filament may be burned out.

5. Ground fault circuit interrupter may be tripped.

6. Receptacle may be controlled by a light switch.

7. The circuit breaker panel is at a remote location.

8. The load may be burned out or defective.

9. The load may consist of a heating or cooling device that would take several minutes to know if turned on.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, the invention is designed to show whether the semi-grounded conduit section is enclosing at least one “hot” conductor. When at least one enclosed conductor is “hot” the liquid crystal display (LCD)26shows “ON.” The invention comprises a plastic coupling block34on which is mounted a liquid crystal display26that is in parallel with a static suppression resistor22and also in parallel with two series connected opposing rectifiers18,20. One of the two liquid crystal display (LCD)26leads is connected through a terminal lug, spring32and metal screw37to the end of a section of metal conduit. The second of the two liquid crystal display (LCD)26leads is connected through another terminal lug, spring32and metal screw37to the end of another section of conduit. With the use of two of these plastic couplings, a section of conduit at least two feet in length can be electrically isolated from the other sections of grounded conduit in the conduit run.

In accordance with a second aspect of the invention, the opposing rectifiers at each end of the semi-grounded section of conduit provide a path to ground in the unlikely event that a “hot” conductor should make electrical contact with the semi-grounded metal conduit section. One of the two rectifiers in this event will short out since the reverse voltage of the rectifiers is lower than the voltage applied to the “hot” conductor.

REFERENCE NUMBERS IN DRAWINGS

10Grounded metal conduit section (1)12Semi-grounded metal conduit section (1)13Grounded metal conduit section (1)14A “live” 90VAC-277VAC wire (one or more)16A main transformer (8,000-12,000 volt primary)(90VAC to 277VAC secondary) (1)17A voltage indicating coupling as an entire unit (1)18A low voltage rectifier (1)20A low voltage rectifier (1)22A static suppression resistor (1)26A two digit liquid crystal display (LCD) (1)29A hole for inserting a conduit end in (2)32A spring with a terminal lug on it (2)34A plastic rectangular block (1)35Screw mounting holes in phenolic board (2)37Conduit clamping and terminal metal screws (2)38Electrical tape spirally wrapped around (2 or moreper conduit section) semi-grounded metal conduitsection40Metal conduit strap (2 or more per conduit section)

DETAILED DESCRIPTION

FIGS. 2A and 2Bshow the device in detail. A liquid crystal display26, a static suppression resistor22and two opposing rectifiers18,20are all connected in parallel and mounted to a phenolic circuit board. The phenolic circuit board is attached to plastic coupling block34by means of two machine screws35. The plastic coupling block34has two different diameter round holes in it just large enough to accommodate the two conduit ends. The bore size of the middle of the plastic block34is slightly smaller than the outside diameter of the conduit ends so that the two ends of the conduit do not touch each other physically or electrically. Conduit clamping screws37provide both an electrical and mechanical connection to each conduit end. Spring32provides a pressing against of a terminal lug that attaches wires to liquid crystal display26. The entire device is denoted by reference number17.

FIG. 1gives a schematic diagram of the complete circuit loop of the voltage indicating coupling when it is used in conjunction with a second voltage indicating coupling. The coupling is always intended to be used in pairs. A main transformer16supplies an AC voltage potential with respect to ground of 90-277 volts r.m.s. This potential goes through at least one “hot” wire14through the semi-grounded section of conduit12. A person having ordinary skill in the art can understand this circuit if the person understands capacitive coupling. Capacitors pass AC while blocking DC. A capacitor is formed by the “hot” conductor14, and the semi-grounded metal conduit section12with air and insulation on the conductor being the dielectric of the capacitor. This capacitive coupling energizes the liquid crystal display (LCD)26with grounded conduit section13being the return path to the main transformer16.

The static suppression resistor22provides a dummy load to absorb any stray signals from energizing the liquid crystal display26. The two opposing rectifiers18,20provide a path to ground for the semi-grounded conduit in the unlikely event that a “hot” conductor should “ground out” on an inside wall of the semi-grounded conduit section. The opposing rectifiers have a lower reverse voltage rating than the voltage supplied by the “grounded out” “hot” conductor which means that the reversed rectifier of the pair will be shorted closed permanently. This means that the circuit breaker or fuse will be tripped that protects the “grounded out” “hot” conductor. In order for the semi-grounded conduit section to be operable again as a voltage indicator, the “grounded out” conductor will need to be replaced along with the phenolic circuit board assembly on the voltage indicating coupling that has the shorted out rectifier18,20.

FIG. 3shows a semi-grounded section of conduit12that is not directly connected to conduit sections10or13. The “on” display is shown as if at least one of the wires enclosed in the semi-grounded section of conduit is “hot.”

FIG. 4Ashows two voltage indicating couplings making for a semi-grounded conduit section12. In this figure since the “on” display is energized, at least one of the enclosed wires is “hot.”

FIG. 4Bshows how to keep the semi-grounded conduit section12from being fully grounded when using conduit mounting straps40. A layer of electrical tape38is spirally wrapped over the conduit12at the point of the metal conduit strap40.

FIG. 5shows a block diagram for an overhead door circuit. In the diagram the individual links between each block represent actual runs of metal conduit with17indicating where a pair of voltage indicating couplings could possibly be installed. In the preferred usage of the invention each section of semi-grounded conduit represents a section of metal conduit two feet in length.

FIG. 6shows a block diagram for an irrigation pump in a field as a second usage example of the voltage indicating couplings.

SUMMARY, RAMIFICATIONS AND SCOPE

Accordingly, the reader will see that the national and international versions of the voltage indicating coupling for metal conduit systems of this patent application provides a convenient and inherently simple method for the determination of at least one AC potential on wiring enclosed by the semi-grounded conduit. A summary of the reasons for the usefulness of this invention was included in the “Reasons for Utility of the Invention” section.

Possible ramifications of this invention include but are not limited to making the couplings in the form of type C condulets to be placed in the conduit system. The coupling could be made out of many types of insulating materials. Although the description above contains certain specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of the currently preferred embodiment.