Safety light socket

Details Safety light socket Safety light socket

2003-02-25

2004-08-31

Duverne, J. F. (Department: 2839)

Electrical connectors

With guiding means for mating of coupling part

Lamp or electron tube socket or base

Reexamination Certificate

active

06783383

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
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BACKGROUND OF THE INVENTION
There are a number of different light bulb styles. One particular style is sometimes called a “candelabra” style and includes those standard type light bulbs as the C7, C9, and T50. For convenience, “C7/C9” will be used to designate all candelabra-style lights. The C7 and C9 types they are probably the most popular types of candelabra-style lights for use in holiday lighting, night lights, and decorative lighting systems for homes, restaurants, outdoor events, theme parks, holiday lighting of parks, towns, cities, etc. These bulbs are the small- and medium-sized screw type, threaded bulbs.
The outdoor use of C7/C9 lighting for holiday events, decoration and extravaganzas has steadily increased every year since the mid 80's. The popularity of the larger C7/C9 lamps was very high in the 50's, 60's and 70's when these lamps were used on the interior trees, exterior trees, bushes, and on the home exterior, until the price of electricity suddenly and rapidly increased, making everyone aware of power consumption. As a result, outside holiday decorations declined to almost nothing for years. The larger C7/C9 style, in particular, fell out of favor due to its high power consumption. Gradually, however, more and more holiday decorators started using the more energy efficient miniature light sets, which became very popular since the early 80's because they used 30+% less power.
During the mid 80's, special, for profit, seasonal lighting displays started appearing everywhere. The lack of exterior home decorating created a very profitable business as families wanted to go see lighting displays, once free on homes, now available for a charge in special parks. These parks began using a mix of C7/C9 and miniature light sets and as the parks grew, more and more of them started changing over to the C7/C9 as a primary light source due to the fact that the C7/C9 sets operated electrically in parallel and therefore failed less often compared to the miniature light sets which operated electrically in series. A series lamp failure could mean that half of the lights on a display could go out at one time from the failure of just a single lamp, whereas, the failed lamp in a parallel system would not have this effect on the remaining lamps. The series approach also made trouble-shooting the failed light displays a very difficult task. As most of the miniature lamps are wrapped around metal frames to hold the display's shape, trouble shooting “sniffer” tools developed to find the burned out lamp in a series set were prevented from working properly.
As these light display companies grew larger and larger, the requirement for dependability also grew, so more and more of the displays have been converted over to the C7/C9 sets. The popularity of the C7/C9 sets in the displays has now effected the designing public, so more and more homes are again using the C7/C9 style light sets, especially outdoors as these sets are much stronger and more durable, however, the C7/C9 sets do have their own unique set of problems and dangers. Firstly, the C7/C9 sets operate electrically in parallel and are powered by 120VAC. C7/C9 light sets are fused at 5 and 7 amps when using energy efficient lamps. If a lamp is missing, however, then the lamp socket is open, exposing 120V AC at 5-7 amps. This amperage is easily enough to kill a grown adult. The socket is also large enough for a child to insert a finger into it or for a small bush limb to work its way into the socket. In either of these cases the outcome of such a contact be dangerous and possibly fatal; also, they can cause an electrocution or a fire as a to a limb.
In one of these sockets, there is a two-part center (AC Line) terminal. The upper portion of this terminal (namely, the part that contacts the lamp) is a special copper alloy and is slightly bent upwards with one end bent downward towards the bottom of the socket to form a switch contact. Under the downward-bent part is the second part of this two-part terminal. The second terminal is made of brass and pierces the electrical wire under it. When a lamp is screwed into the socket, the center contact of the lamp engages the center terminal of the socket, compressing the downward-bent part of the terminal until it comes into contact with the energized second part of the terminal under it. Then the lamplights. However, this approach has several problems, and that often cause the lamps to fail to light.
Secondly, in order to reduce the manufacturing cost of the new C7/C9 sets, manufacturers are using molded plastic sockets rather than a metal screw base internal to the design. The threads molded in the socket are molded in sections, usually two, and only cover about 50% of the internal surface of the lamp base. The threaded sections are separated by cavities where there are no threads. One of these cavities has a thin, flat piece of metal (brass) running up the cavity, perpendicular to the threads. This metal bar contacts the threaded conducting base of the lamp by contacting the tips of the threads on the lamp as the bulb is screwed into the socket.
There is in the industry, especially due to price sensitivity, a considerable lack of uniformity in lamp base diameters and length. When a lamp is replaced with another lamp made by another manufacturer, it may not fit properly. If this replacement lamp is a little smaller in diameter then the lamp that it replaced, the quality of the electrical contact with this metal strip is poor at best, so lamp failure is immediate or inevitable. When a larger diameter lamp is screwed into the socket, it compresses this metal strip and, because this metal strip is made of brass, there is no return memory, so it stays compressed. This worsens the contact problems with other replacement lamps, plus the inability to get the lamp tight in the socket means that it will loosen more rapidly, failing even sooner.
The reduction of thread surface area reduces the ability of the socket to properly hold the lamp. Likewise, because the socket is plastic, and the C7/C9 lamps radiate so much heat, the sockets are constantly expanding and contracting. This expansion/contraction cycle is enhanced by the fact that most C7/C9 lamps hang downward, with the base directly in the path of the thermal given off by the bulb in the socket. This thermal coupled with normal temperature changes loosens the lamp via these expansion/contraction cycles. As the lamp loosens, the electrical contact fails first, then, especially outdoors, the loose lamp condition worsens from the wind and weather conditions swinging and moving the lamps, plus the expansion/contraction cycle. Everyone has attempted to replace a bad lamp at home only to find, when tightened, the lamp turns back on, that it was not burned out but only loose. This loosening happens in a full metal socket in doors, in an environment of constant temperature—imagine what a plastic socket does when exposed to dramatic temperature changes, especially if the lamps are hanging upside down, which is the normal case regarding C7/C9 lamps due to their weight and simple fastening system.
Thirdly, still further cost cutting forces the manufacturer to use a very inexpensive method for connecting the metal conductors in the socket to the appropriate power lines. Electrical connection is achieved by forming the bottom of the socket terminals into spear pointed shapes which stick out of the bottom of the socket far enough to “pierce” the wire insulation and to make contact with the copper wire within, then a ‘snap in’ socket bottom is attached securing the wires to the socket. Nearly all of the C7/C9 sets use AWG 20, multi-strand wire. The plastic insulation is typically 2.4 mm in diameter, so the copper core being 20 AWG is very small in diameter compared to the plastic insulation. When the vinyl insulation is extruded

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