Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Casings
Reexamination Certificate
1999-06-15
2001-09-18
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Casings
C324S129000, C324S107000, C324S149000, C324S127000
Reexamination Certificate
active
06291986
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to current measurement and, more particularly, to an apparatus that provides convenient access for current measurement of conductors within an electrical enclosure.
BACKGROUND OF THE INVENTION
Electrical enclosures that house circuitry for receiving and distributing electrical power and for otherwise housing various electrical components are well known. For example, in residential and industrial settings, electrical enclosures are used as load centers (e.g., fuse boxes) or electrical disconnects to distribute power from a central power distribution transformer to one or more circuits. These enclosures house fuses, circuit breakers, ground fault interrupters, and other electrical components. In industrial environments, electrical enclosures are used not only for power distribution, but also to house equipment-specific electronics such as fuses, relays, transformers, motor controllers, logic circuitry, power supplies and the like. In general, most any piece of industrial equipment will include a separate enclosure that receives facility power and distributes it in accordance with equipment demands. While the present invention is applicable to most any electrical enclosure, for the sake of brevity it will be discussed with reference to these equipment-specific enclosures.
Electrical enclosures generally comprise a box having an open side or face providing access to the enclosure interior. Mounted within the box are various electrical components as already mentioned above. Electricity is provided to the box by one or more conductors, distributed to the various electrical components therein, and ultimately routed to the specific circuits/conductors that supply the equipment.
During use, the open side of the enclosure is partially or completely covered by a cover panel or door. The panel prevents contact between foreign objects (hands, tools, etc.) and the electrical components within the box. To further protect personnel from potential electrical shock, the panel is designed to prohibit casual opening. That is, it is typically fastened or secured to restrict unauthorized access.
With industrial equipment, it is often necessary to measure the load or current drawn by specific equipment (or specific circuits within the equipment). In fact, facility maintenance personnel often measure current draw of various machines on a periodic basis to determine the operational status or to predict potential problems before they occur. For example, an electric motor will often exhibit a gradual increase or decrease in current draw as the driven equipment wears. By monitoring the current load, technicians can anticipate motor and equipment life and schedule replacement prior to failure. In addition to routine maintenance, current measurement is also used to diagnose malfunctioning equipment.
Of the various devices used to measure electrical current, the hook-on or clamp-on ammeter probably enjoys the most widespread use. Hook-on ammeters of the type having a hook-shaped magnetic core probe that hooks around a current-carrying wire, cable, or conduit are well known. The magnetic core probe of the ammeter reacts with the magnetic field generated by the current flowing through the wire. Since the intensity of the magnetic field is directly proportional to the current, the ammeter may be calibrated to provide an accurate current reading. Hook-on ammeters are often preferred over other current measuring methods as they are simple to use and do not require breaking the wire casing or otherwise contacting the conductor. Nonetheless, hook-on ammeters do require access to the individual conductor.
Unfortunately, in order to access the current-carrying conductors, it is generally necessary to gain access to the enclosure. The same cover panel which was beneficial in preventing unauthorized access to the enclosure now becomes a impediment. Depending on the number of enclosures in a given facility and the frequency with which current measurements are taken, the time spent removing and reinstalling enclosure cover panels can be substantial.
In addition to the time burden of removing the panel, other problems exist. For example, removing the panel may require momentarily shutting down the equipment. This can introduce significant delays in equipment usage depending on the start-up procedure required thereafter. Furthermore, to test current draw, the equipment must be operating. That is, the enclosure is “live” during testing such that the technician is exposed to high voltage conductors. Because of the potential danger involved in dealing with high voltage systems, local or facility regulations may limit enclosure access to licensed electricians.
Still yet another problem experienced by technicians is the isolation of the particular conductor to be measured. Industrial enclosures typically have numerous conductors and, even when the desired conductor is clearly labeled, it must be adequately isolated or separated from the others to permit coupling of the hook-on ammeter.
Accordingly, what is needed is an apparatus for use with an electrical enclosure that permits quick, efficient current measurement of one or more circuits within the enclosure without actually requiring entry therein.
SUMMARY OF THE INVENTION
A conduit apparatus for measuring electrical current is provided herein. In one embodiment, the apparatus comprises a conduit enclosure having at least one open side and one or more non-magnetic conduits extending through a portion of the enclosure. The conduits are accessible through the open side and each conduit is adapted to receive a single electrical conductor.
A method of measuring the current in a conductor contained within an electrical enclosure is also provided. In one embodiment the method comprises providing an electrical enclosure having a box with a series of walls defining an interior. The box further includes at least one electrical conductor therein. The electrical enclosure also has a conduit apparatus having at least one non-magnetic conduit accessible from outside the box wherein the conduit is adapted to receive the electrical conductor therein. The conduit apparatus additionally comprises a conduit enclosure having one or more surfaces which isolate the conduit from the interior of the box. The method further includes attaching a hook-on ammeter to the conduit and measuring the current with the ammeter.
An electrical enclosure is also provided. In one embodiment, the enclosure comprises a box having a series of walls defining an interior and having one side that defines an opening wherein the box is adapted to receive one or more electrical conductors. The enclosure further includes: a panel which selectively covers the opening; and a conduit apparatus. The conduit apparatus has at least one non-magnetic conduit accessible from outside the box wherein the conduit is adapted to receive the electrical conductor therein. The conduit apparatus also includes a conduit enclosure having one or more surfaces which isolate the conduit from the interior of the box.
Advantageously, the present invention provides an apparatus for use with an electrical enclosure which provides convenient access for current measurement of circuits within the enclosure. In particular, the apparatus provides adequate access for a hook-on ammeter without requiring entry into the enclosure itself. Any number of independent conductors may be measured simply by providing a corresponding conduit through which the conductor passes. Because entry into the enclosure is not required, the time required to complete the current measuring process is minimized. Furthermore, risk of electrical shock is also reduced as external measurement reduces or eliminates exposure to high voltage components.
REFERENCES:
patent: 1101210 (1914-06-01), Potter et al.
patent: 3753049 (1973-08-01), Plummer
patent: 4001804 (1977-01-01), Irving
patent: 4004221 (1977-01-01), Wilson
patent: 4616177 (1986-10-01), McClain et al.
patent: 5072848 (1991-12-01), Pipis et al.
Amprobe's Catalog—Clamp-Ons
Brown Glenn W.
Hamdan Wasseem H.
Schwegman Lundberg Woessner & Kluth P.A.
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