US 1783062 A
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Patented Nev. 25, 1930 UNITED STATES HENRY TRENCHAM, on
ELECTRIC swrrcn Application filed December 10,1923. Serial no. 679,720.
My invention relates to improvements in electric switches and particularly to switch gear for use in places where the atmosphere may be charged with explosive gases or particl'es, as for instance in mines. 1
My invention is particularly applicable to switch gear of i the truck or draw-out type, although not limited thereto. In this type of switch gear the main circuit is first 1o broken at a set of circuit breaker or switch contacts usually located within a chamber carried by the truckmember, and upon withdrawing the truck or movable switching member a movable contact or plug is disengaged from a fixed contactor socket connected. to the supply circuit or bus bars, the plug and socket arrangement thus acting. as an isolatingswitch. In high tension alternating current circuits it often happens that a static? spark may be formed at these latter contactswhen the truck member is'withdrawn, due to the capacity of the switch gear when the main circuit is broken, thusthe sur rounding gases may be ignited.
The object of my invention is to provide a switch of the plug and socket type which may be used without danger in places where the surrounding atmosphere contains explosive gases. Another object of my invention is to provide means whereby the live terminals in the truck type of switch gear are protected when the truck member is withdrawn without theaddition of specialban riers, covering doors or the like.
According to my invention freedom from danger of igniting explosive gases surrounding the switch is obtained by providing the switch. with a comparatively long tight fitting sleeve of insulating material which is secured at one end preferably to the socket member of the switch and makes a long snug fit with the plug member so that when the two contact members separate as in opening the circuit the spark which may follow will be confined within the sleeve and any explosion of gas that may occur between the contactswill not be communicated to the exterior.
My invention will be better understood by reference to the accompanying specification P E OFFICE.
RUISLIP, ENGLAND, ASSIGN'OR T0 GENERAL ELECTRIC COM IANY, A CORPORATION OF NEW YORK and drawings and its scope will be pointed out in theappended claimsr Figure l is a side elevationof a switchof the truck type showing the stationary contactsof the isolating plug and socket switch in cross section; Fig. 2 shows in crosssection portions of the stationaryand movable contacts of Fig. 1 separatedyand Fig. 3 shows in cross section portions of a modified form of'contacts. g V Referring now to the drawings; lrepresents-thefixed frame ofthe switch carrying isolatingsocket terminals 2and 3 arranged in the compartments l. These terminals are i electrically connected respectively to the bus bar -5- and lead Arranged upon the terminals are insulating sleeves 7 which in this 1 case are-shown occupying most of the avail:
able space in the isolating compartments and which are of a length suflicient to still cover the plugs after they break contact with the sockets. Themovable frame or truck indi cat-ed by 8 carries the plug contacts 9 which are mounted in sleeves 1O fixed to the movableframe. f Upon withdrawal of thetruck a distance just sufficient to cause the plug and socket contact members to separate a static spark might passbetween those contacts but *it would be confined to the small space between the contacts and 'within the sleeve, and any explosion of gas therein would also be con fined thereto since the temperature of the ex- ,ploded gas would be reducedbelow the ignition point in escaping between the plug and the end of? the socketcontact 11 the insulating sleeve 14 is provided with an internal annular groove 16 to collect anyparticles of dust or dirt ormetal which might otherwise stick to theinside of the sheath and reduce the insulation properties of the switch when the contacts are first separated.
In the open position of an isolating switch according to the invention the sheath may be of sutficient length so that the plug contact remains in the hole and is not entirely withdrawn. Preferably however the plug contact will be withdrawn clear of the sheath to avoid any possibility of leakage.
It will also be seen that the sheath of insulating material itself serves as a barrier to isolate or protect the live fixed terminal when the truck member is withdrawn.
lVhat I claim as new and desire to secure 5 by Letters Patent ot' the United States, is 1. An electric switch particularly adapted for use in an explosive atmosphere comprising cooperating plug and socket contact members, and an elongated insulating sleeve se- 9 cured at one end to one of said members, said end being thereby closed, said sleeve and the other of said members being adapted to make a relatively long, closely fitting, sliding contact with each other after the contact mem 5 bers are separated to cool below their ignition point gases expelled upon explosions occurring within said sleeve at the separation of the contacts.
2. In truck-type switch gear, isolating contacts particularly adapted for-usein an explosive atmosphere comprising cooperating plug and socket contact members, an elongated insulating sleeve secured atone end to said socket member, said end being thereby )5 closed, said sleeve and plug being adapted to make a relatively long, closely fitting, sliding contact with each other after the contacts are separated from each other to open the circuit, whereby an elongated enclosed 40 space is formed between the separating contacts to prevent communication of explosions occurring within said sleeve due to arcing between said contacts to the surrounding atmosphere.
3. An electric switch particularly adapted for use in an explosive atmosphere comprising cooperating plug and socket contact members, an insulating sleeve secured-t0 and having one end closed by said socket member,
00 said sleeve extending beyond the end thereof to make a relatively long close fit with said plug member after the contact members are separated, the extending portion of said sleeve having a bore substantially equal to that of the socket member and having. an internal peripheral groove adjacent the end of said socket member.
In witness whereof, I have hereunto set my hand this 30th day of November, 1923.