Surge protection device

A surge protection device for protecting an electric power system from excessive voltage surges, including those caused by direct lightning strikes. Metal oxide varistors are wired between each incoming 115 volt power line and ground and between the two power lines. The varistors connect with the power lines on the user side of the main circuit breakers. The varistors are normally nonconductive but become conductive when excessive voltages are present on the power lines. Then, short circuits are established through the varistors to protect downline equipment. The varistors are embedded in a pliable filler material which fills a rigid polymeric shell. In the event of a direct lightning strike, the surge protector is destroyed sacrificially and the pressure resulting from the failure is relieved through the opposite ends of the shell.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates in general to the protection of electrical and 
telephone equipment from damage caused by excessive voltage surges. More 
particularly, the invention deals with a surge detector which protects 
entire electrical and telephone circuits from both ordinary surges and 
extreme voltage surges such as those caused by a direct lightning strike. 
Surge protector and surge arrestors have long been used for the protection 
of electrical equipment from the erratic power surges or spikes that occur 
from time to time in electrical distribution systems. Each surge protector 
typically serves one electrical device which is deemed to be particularly 
important to protect, usually because of its expense or the severe 
problems that can result from the equipment being taken out of service. 
Ordinarily, the surge protector is wired in series with a fuse or circuit 
breaker and acts to absorb voltage spikes in order to prevent them from 
possibly damaging the equipment served by the protective device. The fuse 
of circuit breaker is relied upon to protect both the surge protector and 
the electrical equipment from overloads and other extreme conditions. 
There are numerous problems with this conventional approach to the handling 
of voltage surges. Perhaps most importantly, it is recognized that 
conventional surge protectors are unable to effectively handle extreme 
transient voltage conditions such as those caused by a direct lightning 
strike to the power lines. Voltage of this magnitude are applied to the 
electrical equipment before the fuse or circuit breaker can operate to 
open the circuit, and destruction and other extreme damage to the 
equipment can result. Even in situations where the surge protector is 
effective, it is able to protect only the single appliance which it 
serves, and other appliances and the electrical system in general remain 
unprotected 
It is thus apparent that there is a need for an electrical surge protector 
which acts to protect entire electrical systems and telephone systems and 
all appliances they serve from ordinary voltage spikes and also from the 
destructive effects caused by extreme transient conditions such as the 
surge voltages resulting from direct lightning hits. It is the primary 
goal of our invention to meet that need. To our knowledge, there have been 
no surge protectors available in the past capable of handling extreme 
voltage conditions, and there have likewise been no surge protectors 
available for the protection of the entire power or telephone systems of a 
residence, small business or light commercial establishment. 
In accordance with our invention, metal oxide varistors serve to protect 
electrical systems and telephone circuits from voltage surges. The 
varistors are housed in a rigid polymeric shell which is mounted within 
the fire rated fuse box or circuit breaker box already present in the 
building served by the surge protector. The varistors are connected with 
the incoming power lines or telephone lines on the user side of the main 
circuit breakers or fuses. Connection of the surge protector with the 
electrical or telephone system is simple, and all connections are located 
within the enclosed fuse box or circuit breaker box. 
The varistors are nonconductive when normal voltages are applied to the 
electrical or telephone circuit to provide power to the downline 
electrical or telephone equipment. However, when voltage spikes occur at 
levels above normal voltage levels, the varistors become immediately 
conductive and establish short circuits which divert the spikes from the 
downline equipment. In the event of extreme voltage levels such as those 
caused by lightning striking the power or telephone lines, the varistors 
accept all of the incoming power in the short circuit mode in order to 
protect the downline equipment long enough to permit the fuse or circuit 
breaker to open the circuit. The application of extreme voltages to the 
varistors causes them to fail sacrificially but only after they have 
functioned long enough to open the fuse or circuit breaker in order to 
protect the electrical or telephone equipment from destructive effects of 
the extreme voltage. The construction of the shell and the embedding of 
the varistors and related components in a pliable, nonflammable filler 
material within the shell minimizes the potential hazards resulting from 
catastrophic failure of the surge protector in extreme conditions.

Referring now to the drawing in more detail, numeral 10 generally 
designates a surge protection device constructed in accordance with the 
present invention. The surge protection device 10 has a rigid plastic 
shell 12 which forms a housing for three varistors 14, 16 and 18 which 
serve as the functional components of the surge protector. The shell 12 
has a tubular wall and initially open opposite ends 20 and 22. The shell 
21 can be constructed of any suitable fire rated material and is 
preferably formed from rigid pvc pipe. 
The surge protection device 10 is intended for use in residential, small 
business and light commercial power systems and incoming telephone lines, 
and it is connected with the power system or telephone lines on the user 
side of the incoming fuses or circuit breakers. FIG. 3 illustrates 
schematically the manner in which the surge protector is electrically 
connected with the incoming power lines of a typical three wire electrical 
distribution system. 
The electrical system includes a pair of incoming 115 volt power lines 24 
and 26 and a neutral line 28. All of the incoming lines extend into an 
enclosed metal fuse box or circuit breaker box 30 which forms an enclosure 
for the electrical service distribution panel of the residence, small 
business or commercial establishment. The incoming hot lines 24 and 26 are 
provided with respective main circuit breakers 32 and 34 (or fuses) which 
serve as overload protectors and which likewise open the power circuits if 
a short circuit develops. The circuit breakers 32 and 34 are mounted 
within the box 30. Downline from the circuit breakers 32 and 34, the power 
lines 24 and 26 connect with branch circuits which service downline 
electrical equipment (not shown). 
As previously indicated, the varistors 14, 16 and 18 are contained within 
the shell 12, and the shell is mounted within the box 30. Varistor 14 has 
lead wires 14a and 14b connecting with its opposite sides. Wire 14a has an 
electrical connection 36 with a lead wire 18a leading from one side of 
varistor 18. Extending from connection 36 to line 24 is a conductor 38 
which connects with line 24 within the box 30 at a location between 
circuit breaker 32 and the downline equipment served by line 24. The other 
lead wire 14b connects at junction 40 with a lead wire 16a extending from 
one side of varistor 16. Extending from the connection 40 is a conductor 
42 which is connected at its opposite end with the neutral line 28 or with 
ground potential. The other two varistor leads 16b and 18b are connected 
at juncture 44 from which another conductor 46 extends to connection with 
power line 26. The connection between conductor 46 and power line 26 is 
located within the box 30 between the circuit breaker 24 and the downline 
equipment served by line 26. 
The wire connections 36, 40 and 44 are all soldered connections. 
Additionally, as shown in FIGS. 1 and 2, each of these wire connections is 
enclosed by a metal wire connector 48 which is crimped tightly on the 
connection. The soldered nature of the wire connections and the use of the 
mechanically crimped connectors 48 enhances the security of the wire 
connections and assures that they will not inadvertently fail. 
As shown in FIG. 2, a retainer ring 50 projects inwardly from the tubular 
wall of shell 12 into the cylinder chamber 52 presented within the shell 
for housing of the varistors and related components. Ring 50 is located 
near end 22 of the shell and may be secured to the shell wall by glue or 
in any other suitable manner. The ring 50 presents an annular shoulder 54 
which faces the opposite end 20 of the shell. A circular passage 56 is 
formed through the ring 50 in order to accommodate the conductor wires 38, 
42 and 46 which are insulated wires. The wires extend through end 22 of 
the shell and through passage 56 into the crimped wire connectors 48. 
The opposite end 20 of the shell is covered by a discoidal end plug or cap 
58. Preferably, the end cap 58 is connected with the interior surface of 
the shell wall by a bead of glue 60 which holds the end cap in place 
covering the end 20. The end cap prevents a screw driver or similar device 
from being extended into the shell to possibly create an electrical shock 
hazard. The glued connection 60 between the end cap and shell wall is 
intentionally a relatively weak connection so that it will fail and 
release the end cap 58 in the event of excessive pressure build up within 
the shell. The end cap 58 is then displaced from the end of the shell in 
order to relieve the pressure within chamber 52 before the pressure level 
rises sufficiently to fracture the shell wall. 
The wire connections 36, 40 and 44 are located between the varistors and 
the end cap 58, as are portions of the insulated wires 38, 42 and 46. The 
retainer ring 50 and particularly the annular shoulder surface 54 serves 
to retain the varistors and related components within the shell when a 
pulling force is applied to any of the wires 38, 42 or 46. The varistors 
are restricted from moving through the passage 56 when the wires are 
subjected to a pulling force applied within the limits specified by 
prevailing standards established by recognized testing organizations. 
The varistors, electrical connectors 48, lead wires and portions of the 
insulated wires 38, 42 and 46 are all embedded in a pliable filler 
material 62 which fills the chamber 52 formed within shell 12. The filler 
material is nonflammable and may conveniently be silicon rubber of a 
similar pliable substance treated with a suitable flame retardant. The 
pliable character of the filler material assists in the absorption of the 
extreme energy generated when the surge protection device 10 is destroyed 
sacrificially, while its nonflammable nature reduces the fire hazard. 
In use, the surge protector 10 protects the downline equipment on the power 
lines 24 and 26 (or incoming telephone lines) from damage caused by 
voltage surges. The surge protector is connected with the power system in 
the manner shown in FIG. 3, and the varistors 14, 16 and 18 are 
nonconductive at the voltage levels normally applied to lines 24 and 26 
for operation of the downline appliance and equipment. However, when a 
voltage spike appears on the power system at sufficient magnitude, the 
varistor to which the voltage is applied becomes conductive and 
establishes a short circuit. For example, if a voltage spike appears on 
line 24 at sufficient magnitude to make varistor 14 conductive, a short 
circuit is established from line 24 through line 38, connection 36, lead 
wire 14a, varistor 14, lead wire 14b, connection 40 and line 42. This 
short circuit prevents the voltage spike from affecting the downline 
equipment. Varistor 14 reverts to the conductive state as soon as the 
voltage spike passes. Normally, the short circuit will not be established 
long enough to cause the circuit breaker 32 to open. 
Similarly, application of a voltage spike to the other power line 26 makes 
varistor 16 conductive and establishes a short circuit which protects the 
downline equipment served by line 26. When the potential between lines 24 
and 26 is sufficient to make the third varistor 18 conductive, it 
establishes a short circuit between the two power lines and thus protects 
downline equipment served by 230 volt power. 
In the event that lightning directly strikes the power transmission lines 
to cause extreme transient conditions on lines 24 and 26, the varistors 
are able to draw all of the transient power through the short circuits 
they establish and to maintain the short circuits through the varistors 
for a sufficient time to permit the circuit breakers 32 and 34 to open. 
Thus, prior to opening of the circuit breakers, the varistors prevent the 
extreme voltage condition on the power lines from damaging the downline 
equipment, and the circuit breakers protect the equipment once they have 
opened. 
Application of extremely high voltages such as caused by direct lightning 
strikes to the varistors causes the varistors to be subjected to extreme 
forces which result in sacrificial failue of the surge protector 10. The 
extreme power levels applied to the varistors mechanically rupture the 
varistors and create explosive forces within the shell 12. The forces are 
absorbed partially by the pliable filler material 62 which fills shell 12. 
The filler material presses against the end cap 58 and causes the glued 
connection 60 to fail, thereby releasing the end cap and relieving the 
pressure generated internally of the shell by the destruction of the 
varistors. Release of the pressure in this fashion normally prevents the 
wall of shell 12 from fracturing. 
Additionally, since the electrical connections covered by connector 48 are 
located between the sacrificial varistors and the end cap 58, the pressure 
is applied to the lead wires of the varistors and the wires 38, 42 and 46, 
causing elongation of the wires which partially absorbs the energy 
released during rupture of the surge protection package. The wires are 
stretched until they snap or the pressure subsides, whichever occurs 
first. The result is either a reduction in the force resulting from 
destruction of the package or prevention of the end cap 58 from releasing 
in some cases. 
Since the pressure resulting from destruction of the varistors is relieved 
through both ends of the shell 12, the shell wall normally does not 
fracture but instead only the end cap 58 and the soft filler material 62 
is forced out of the shell. The filler material is soft enough to prevent 
significant damage, and the small end plug 58 is confined to the enclosed 
circuit breaker box 30 in which the device is contained so that damage to 
surrounding objects is minimized. Additionally, fire hazards are minimized 
because of the nonflammable nature of all components of the surge 
protector and its enclosure within the fire rated circuit breaker box. 
It should be noted that the surge protector is equally suited for use in a 
two wire electrical system and also in connection with incoming telephone 
lines. In either of these cases, the surge protector would include only a 
single varistor connected on one side with the incoming power line or 
telephone line on the user side of the circuit breaker. The other side of 
the varistor would be connected to effect a short circuit in the event of 
a voltage surge at a level sufficient to make the varistor conductive, 
thereby protecting the downline electrical or telephone equipment. In the 
case of telephone lines, the increasing use of computers and other 
sophisticated and expensive electronic equipment directly on the telephone 
network makes it increasingly important to provide the telephone system 
with protection such as that afforded by our surge protector. 
It should also be noted that the surge protector can be used in a three 
phase power system and will be connected for each phase in substantially 
the same manner desribed herein. 
From the foregoing, it will be seen that this invention is one well adapted 
to attain all the ends and objects hereinabove set forth together with 
other advantages which are obvious and which are inherent to the 
structure. 
It will be understood that certain features and subcombinations are of 
utility and may be employed without reference to other features and 
subcombinations. This is contemplated by and is within the scope of the 
claims. 
Since many possible embodiments may be made of the invention without 
departing from the scope thereof, it is to be understood that all matter 
herein set forth or shown in the accompanying drawing is to be interpreted 
as illustrative and not in a limiting sense.