High temperature ground connection

Details High temperature ground connection High temperature ground connection

1999-12-03

2001-03-06

Picard, Leo P. (Department: 2835)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S688000, C361S719000, C174S016300, C174S051000, C165S080200, C165S185000, C200S289000, C200S547000

Reexamination Certificate

active

06198631

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to wiring devices and more particularly to heat generating wiring devices, such as light dimmers, and even more particularly to improved ground terminals for such devices.
BACKGROUND OF THE INVENTION
Some wiring devices, such as light dimmers, generate substantial heat during operation. A 1000 watt light dimmer can, under certain operating conditions, generate temperatures exceeding 100° C.
Electrical code requirements limit the temperatures of certain exposed wiring devices, such as dimmers. With a few exceptions, portions of dimmers that are exposed to the occupants of buildings or houses cannot exceed 60° C. under normal operating conditions. Even inaccessible portions of wiring devices have temperature requirements. In order to avoid damaging the insulation on building wiring, no portion of a dimmer more than ¼″ from the main heat sink can exceed 75° C. This rule protects the insulation of field wiring, which routinely comes into contact with portions of light dimmers during installation.
A particular problem relates to the heat generated at an electrical component such as a triac. This is dealt with in prior art by mounting it far from the circuit board to which it is electrically connected.
A further problem relates to the control of the temperature of the ground strap. Since the ground strap is physically connected to the main heat sink, it tends to rise too close to the heat sink temperature. Various techniques are employed to reduce the temperature of the ground strap, such as physically locating it on the opposite side of the device from the heat generating components, usually scrs or triacs, but these techniques impose design limits on the devices that are undesirable.
SUMMARY OF THE INVENTION
We have developed a new construction for a ground terminal for a heat generating wiring device such as a light dimmer that overcomes the problems of the prior art. Rather than attempting to limit the temperature of field accessible portions of the ground terminal of a light dimmer, we have developed a construction that limits the accessibility of the ground terminal, so that higher temperatures can be tolerated.
In accordance with one aspect of the invention, a wiring device such as a dimmer includes a heat sink in thermal connection with a heat generating component such as a triac, so that the generated heat is dissipated over the entire area of the heat sink.
In accordance with another aspect of the invention, the device includes a ground strap which is integrally formed with the heat sink.
In accordance with another aspect of the invention, the device includes a ground terminal that is physically isolated from field wiring by a non-thermally conductive, and preferably non-electrically conductive housing. The housing completely encloses the ground strap except for providing access to the ground terminal at the connection point where a terminal screw is threaded through the ground terminal. The ground screw is recessed to prevent physical contact with field wiring, thus the wiring insulation is protected from being overheated by the heat generated at the ground terminal.
In accordance with another aspect of the invention, the non-thermally conducting housing includes a hole sized to receive the ground wire, so that it can be secured to the ground terminal with the ground terminal screw.
In accordance with another aspect of the invention, the non-thermally conducting housing includes a hole sized to receive the electrical conductor of a field wire, but sufficiently small to prevent the insulation of the field wire from being received by the hole. The insulation is thereby kept away from contact with heat sources within the housing.


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