U.S. patent number 3,849,090 [Application Number 05/351,010] was granted by the patent office on 1974-11-19 for electrostatic precipitator.
This patent grant is currently assigned to Electrohome Limited. Invention is credited to Cassius D. Remick.
United States Patent |
3,849,090 |
Remick |
November 19, 1974 |
ELECTROSTATIC PRECIPITATOR
Abstract
An electrostatic precipitator is modified so that the amount of
energy that is dissipated when an arc-over occurs between any two
adjacent collector plates thereof is reduced. The positive
collector plates of the electrostatic precipitator are connected to
a positive bus bar by means of resistors. These resistors
preferably are in the form of a resistive cement. When an arc-over
occurs between two adjacent collector plates, the resistors prevent
the charges on the other capacitors constituted by other adjacent
collector plate pairs from being dissipated via the arc-over.
Inventors: |
Remick; Cassius D. (Waterloo,
Ontario, CA) |
Assignee: |
Electrohome Limited (North
Kitchener, Ontario, CA)
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Family
ID: |
26885878 |
Appl.
No.: |
05/351,010 |
Filed: |
April 13, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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190211 |
Oct 18, 1971 |
3727380 |
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Current U.S.
Class: |
96/86; 96/58;
439/65; 29/830 |
Current CPC
Class: |
B03C
3/66 (20130101); B03C 3/72 (20130101); Y10T
29/49126 (20150115) |
Current International
Class: |
B03C
3/66 (20060101); B03C 3/34 (20060101); B03C
3/72 (20060101); B03c 003/47 (); B03c 003/12 () |
Field of
Search: |
;55/143,145,154,146,136,137,138,139,142,141,140,156,155,157,126,151
;317/11R,11B,11C,11CC,11CM,11D,242,256,257,258,261
;339/17R,17LM,17M,267R,277R,278R ;29/155.5X,624 ;174/68.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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752,474 |
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Oct 1952 |
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DT |
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37-15989 |
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Dec 1963 |
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JA |
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163,097 |
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May 1955 |
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AU |
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848,446 |
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Sep 1960 |
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GB |
|
Primary Examiner: Talbert, Jr.; Dennis E.
Attorney, Agent or Firm: Sim & McBurney
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of copending application
Ser. No. 190,211, filed Oct. 18, 1971, now U.S. Pat. No. 3,727,380.
Claims
What I claim is:
1. In an electrostatic precipitator an improved arrangement for
supporting and electrically connecting the collector plates thereof
comprising two spaced apart printed circuit boards, a plurality of
collector plates stacked in spaced apart relationship one above the
other and extending between said printed circuit boards and
supported thereby, said printed circuit boards having a plurality
of slots extending therethrough, said collector plates having tabs
extending therefrom, said tabs extending into said slots, at least
two bus bars adapted for connection to two terminals of a DC power
supply at different DC potentials, one of said bus bars being on
one of said printed circuit boards and the other of said bus bars
also being on one of said printed circuit boards, every other one
of said collector plates being electrically connected via at least
certain of said tabs thereof to said one bus bar, a plurality of
isolating resistors, said isolating resistors being electrically
connected between said other bus bar and the remaining ones of said
collector plates and being of sufficient magnitude, upon occurrence
of an arc-over between two adjacent ones of said collector plates,
to inhibit discharge of the capacitors constituted by other
adjacent pairs of collector plates via said arc-over, said
isolating resistors being constituted by electrically resistive,
resilient cement adhered to said printed circuit board carrying
said other bus bar and electrically connecting said remaining ones
of said collector plates via at least certain of said tabs thereof
to said other bus bar, said certain tabs of said remaining
collector plates extending through certain of said slots that are
physically spaced apart from said other bus bar, whereby said
electrically resistive, resilient cement bridges the spaces between
said certain tabs of said remaining collector plates and said other
bus bar, said electrically resistive, resilient cement also being
adhered to said certain of said tabs of said remaining ones of said
collector plates and extending over the slots through which the
last-mentioned tabs extend and thereby inhibiting rattling of said
last-mentioned tabs.
2. An electrostatic precipitator as claimed in claim 1 wherein the
ones of said collector plates electrically connected to said one
bus bar are electrically connected thereto via electrically
conductive resilient cement adhered to said printed circuit board
carrying said one bus bar and also adhered to said certain of said
tabs of the last-mentioned collector plates and extending over the
slots through which said certain of said tabs of the last-mentioned
collector plates extend and thereby inhibiting rattling of these
tabs.
3. An electrostatic precipitator as claimed in claim 2 wherein the
slots through which said certain of said tabs of the last-mentioned
collector plates extend also pass through said one bus bar.
4. An electrostatic precipitator as claimed in claim 2 wherein said
collector plates have additional tabs other than said certain tabs,
said additional tabs being electrically disconnected from said bus
bars, and electrically insulating resilient cement adhered to said
additional tabs, extending over the slots through which said
additional tabs extend and also adhered to the portions of said
printed circuit boards surrounding the slots through which said
additional tabs extend to inhibit rattling of said additional
tabs.
5. An electrostatic precipitator as claimed in claim 4 wherein said
bus bars are both on the same printed circuit board, said
additional tabs and the slots through which said additional tabs
extend are located between said bus bars and said electrically
insulating resilient cement is adhered to the portion of said same
printed circuit board that is located between said bus bars.
6. An electrostatic precipitator according to claim 5 wherein said
electrically insulating resilient cement also is coated over and
adhered to said electrically conductive resilient and said
electrically resistive resilient cements.
7. An electrostatic precipitator as claimed in claim 4 wherein
there are two of said one bus bars and two of said other bus bars,
one of each being located on each of said printed circuit boards,
said additional tabs and the slots through which said additional
tabs extend being located between the bus bars on the respective
printed circuit boards and said electrically insulating resilient
cement being adhered to the portions of said printed circuit boards
located between said bus bars thereon.
8. An electrostatic precipitator as claimed in claim 7 wherein said
electrically insulating resilient cement also is coated over and
adhered to said electrically conductive resilient and said
electrically resistive resilient cements.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to electrostatic precipitators of
the kind adapted to remove particles such as dust, smoke and pollen
from the air or other gas being passed through the precipitator.
More specifically, this invention relates to that portion of an
electrostatic precipitator construction which involves the mounting
of the collector plates thereof and electrical connections
thereto.
In the operation of an electrostatic precipitator, air or other gas
containing particles such as dust, pollen, etc., is caused to pass
through two zones, an ionizing zone and a collection zone.
Ordinarily the ionizing zone is characterized by a plurality of
positively charged parallel wires, while the collection zone
contains a series of alternately arranged positive and negative
plates between which the air must pass. Normally, particles that
have become positively charged in the ionizing zone are collected
on the negative plates in the collection zone. However, some of the
positively charged particles may pick up more electrons then they
require to become neutral, in which case they become negatively
charged and then are attracted to the positive plates.
In the copending patent application referred to hereinbefore there
is disclosed an electrostatic precipitator construction in which
the several components thereof are so designed that their assembly
is simple and does not require elaborate or expensive equipment.
More specifically, the electrostatic precipitator includes two,
spaced-apart, parallel printed circuit boards. Between the printed
circuit boards extend a plurality of parallel, alternately arranged
positive and negative collector plates, these plates being provided
with tabs that conductively engage bus bars on the printed circuit
boards that are connected to the positive and negative terminals
respectively of a suitable power supply. A third bus bar also is
provided on each printed circuit board and also is connected to the
positive terminal of the power supply. This third bus bar
conductively engages an electrically conductive, tension-providing
ionizing wire support on which the ionizing wire of the
electrostatic precipitator is mounted. With such an electrostatic
precipitator the third bus bar is directly connected to the
positive terminal of the power supply, which may be at +6,000 volts
DC, for example. The other positive bus bar also is connected to
the positive terminal of the power supply, as aforementioned, but
via a large resistor having a magnitude of about, say, 30 meg.
ohms. This resistor serves to isolate the power supply from the
positive collector plates so as to protect the power supply in the
event of arc-overs occurring. Such arc-overs may occur between
adjacent positive and negative collector plates. As aforementioned,
the electrostatic precipitator includes a large number of adjacent
positive and negative collector plates, so each pair of adjacent
plates constitutes a charged capacitor, and these capacitors are
connected in parallel with each other. When an arc-over occurs
between any two adjacent collector plates of the electrostatic
precipitator, all of these capacitors discharge via the arc-over,
and this considerably amplifies the arc-over effect. This is
disturbing to any person who may be close to the electrostatic
precipitator as the amplified arc-over is accompanied by an audible
crackling sound similar to that which is head when a spark is
caused to jump a gap between two conductive terminals. Also
arc-overs of this type may result in damage being done to the
collector plates.
SUMMARY OF THE INVENTION
In accordance with the instant invention an electrostatic
precipitator of the general type disclosed in the aforesaid
copending application is modified in such a way that the amount of
energy that is dissipated when an arc-over occurs between two
adjacent collector plates is reduced. This is achieved by
connecting the positive collector plates to the positive bus bar by
means of resistors. These resistors preferably are in the form of a
resistive cement that is adhered to the printed circuit boards and
which extends between the positive collector plate bus bar and the
positive collector plates themselves, the length of the paths
between the positive collector plate bus bar and the positive
collector plates determining the magnitude of the resistors. With
such a construction the separate bus bar for the ionizing wire
support can be eliminated and the ionizing wire support connected
directly to the positive collector plate bus bar. Also the
previously used resistor between the positive collector plate bus
bar and the positive terminal of the power supply is eliminated.
When an arc-over occurs between two adjacent collector plates, the
aforesaid resistors greatly reduce the extent to which the charges
on the other capacitors are dissipated via the arc-over. In other
words, the capacitors formed by the pairs of adjacent oppositely
charged collector plates are resistively isolated from each
other.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention will become more apparent from the following
detailed description, taken in conjunction with the appended
drawings, in which:
FIG. 1 is a partly broken-away, partly exploded, perspective view
of an electrostatic precipitator construction embodying this
invention;
FIG. 2 is a partial elevation view taken at the line 2--2 in FIG.
1; and
FIG. 3 is a sectional view taken at the line 3--3 in FIG. 2.
Attention is now directed to FIG. 1, in which an electrostatic
precipitator 10 is seen to include an external rectangular frame
12, a plurality of collector plates 14, an ionizing wire 15, and
two protective screens 16 and 17. Two printed circuit boards 19 and
20 are also provided, one at either end of the collector plates 14,
and both arranged perpendicularly thereto.
As can be seen, the rectangular frame 12 is U-shaped in
cross-section having a main wall 22 and two perpendicular flanges
24. In the embodimemt shown, the frame 12 is in two L-shaped parts
manufactured of sheet metal, the flanges 24 being appropriately
notched at locations corresponding to the corners of the
electrostatic precipitator. Metal screws 26 or other suitable
attachment means are employed to secure the loose ends of the frame
12 together at the corners 28 and 29, as shown.
All of the collector plates 14 have the same length (the dimension
perpendicular to the plane of the printed circuit boards 19 and
20), but they are not all of the same width. The plates 14 are
preferably of aluminum or aluminum alloy. The plates 14 should have
substantially smooth and non-porous (i.e., relatively "closed")
surfaces so that collected dirt will be washed out easily and will
not have a tendency to adhere to the surfaces.
As seen in FIG. 2, the collector plates are arranged in repeating
sets of four. The uppermost set of four collector plates includes a
negative plate 30 of a width corresponding to the width of the
printed circuit board 19. Spaced apart from but immediately beneath
negative plate 30 and in parallel relation thereto is a positive
plate 32. The width of plate 32 is just over half that of negative
plate 30. Positive plate 32 is set slightly inwardly from the
left-hand edge of negative plate 30 and the printed circuit board
19. Next beneath the positive plate 32, and spaced-apart from but
in parallel relation thereto, is a negative plate 34, the left-hand
edge of which is aligned with that of the first negative plate 30.
The right-hand edge of negative plate 34 is positioned leftwardly
of the right-hand edge of positive plate 32. In fact, plates 32 and
34 are identical, but are reversed end-to-end. Thus they are both
of the same width. Next beneath the negative plate 34 is another
positive plate 36 identical to the first positive plate 32 and
aligned therewith. Thus, the right-hand edges of the plates 32 and
36 are aligned, while the left-hand edges of the plates 30 and 34
are aligned.
The same set of four plates is then repeated in the same sequence
beneath the first set described above. Thus, there is a plurality
of wide plates 30, and a plurality of narrow plates 32, 34 and
36.
As illustrated, each plate has two projecting tabs at each end
integral with the plate. In the embodiment shown in the drawings,
each plate has an integral contact tab and an integral support tab
at either end. Specifically, the upper negative plate 30 has a
contact tab 38 and a support tab 40, while positive plate 32 has a
contact tab 42 and a support tab 44. Negative plate 34 has a
contact tab 45 and a support tab 46, while positive plate 36 has a
contact tab 48 and a support tab 50. The repeating sets of these
four plates have identical tabs to those described immediately
above. For every plate, the contact tabs are longer than the
support tabs.
As seen in FIG. 1, printed circuit board 19 has a plurality of
spaced slots 52 along its left-hand edge for receiving the contact
tabs 38 and 45 of the negative plates 30 and 34, and has a
plurality of spaced slots 53 along its right-hand edge for
receiving the support tabs 40 of the wide negative plates 30. The
support tabs 46 of the narrow negative plates 34 are received in a
series of slots 55 shown in FIG. 1. A further series of slots 57
are adapted to receive the contact tabs 42 and 48 of the positive
plates 32 and 36, while a series of slots 58 are adapted to receive
the support tabs 44 and 50 of the positive plates 32 and 36.
Preferably, printed circuit board 19 is symmetrical about a
transverse mid-line, so that boards 19 and 20 can be identical, but
reversed end-to-end so that the bus bars to be described below
always are located on the outer face.
Each plate has integral, arcuate, raised ribs 60 aligned with the
pairs of tabs at its ends. Both ends of each plate are identical,
which means that the tabs occur in the same positions at either
end, and thus each raised rib 60 has a tab at either end. Because
each tab is, in effect, an extension of the raised rib, each tab is
also arcuate in crosssection. The arcuate nature of the tabs is
clearly seen in FIGS. 1 and 2. The purpose of the raised ribs 60 is
to add strength and rigidity to the collector plates.
Along its right-hand edge, printed circuit board 19 has a plurality
of cut-away indentations 62, one between each adjacent pair of
support tabs 40 of the wide negative plates 30. The indentations 62
are all substantially rectangular. Secured to the printed circuit
board 19 along the inner extremities of the cut-away indentations
62 is an electrically conductive bar 64 which has a plurality of
resilient, wire-supporting fingers 66 which extend alternately up
and down so that each finger has its end generally situated mid-way
of one of the cut-away indentations 62. The end of each finger,
whether an upwardly extending or downwardly extending finger, has a
V-notch which is adapted to receive ionizing wire 15. Each finger
is arcuately curved away from the printed circuit board 19, so that
when the wire 15 is tightly wound, it is maintained under tension
by the resilience of fingers 66. The bar 64 is soldered or
otherwise firmly conductively adhered to a printed bus bar 69 on
board 19.
Printed circuit board 19 also has another bus bar 67. In addition,
printed circuit board 19 has terminals 100 of conductive material
around each slot 57, the terminals being in the form of discrete
circles in the embodiment shown. As can be seen, bus bar 69 is
arranged vertically and has conductive fingers 101 that extend
between adjacent terminals 100. Bus bar 69 has a soldering
extension 69a at the top for soldering purposes. Bus bar 67 extends
down the left-hand edge of board 19 and links all of the spaced
slots 52 which are adapted to receive the contact tabs 38 and 45 of
the negative collector plates 30 and 34. Bus bar 67 also extends
across the upper extremity of board 19.
As seen in FIG. 1, board 19 also has a number of spaced circular
apertures 70 in which spacing members 72 are adapted to be
received. Each spacing member 72 has a conically flared portion 73
and a reduced stem 74 adapted to be received snugly in circular
aperture 70. The purpose of the spacing members 72 is to maintain a
desired spacing between the frame 12 and the printed circuit board
19. The spacing members also give support in case the unit is
dropped on its side. Printed circuit board 19 has, at either end,
two extensions 76 which are adapted to be received in slots 78
provided therefor in frame 12. The registry of the extension 76 in
the slots 78 accurately locates the boards 19 and all of the
collector plates with respect to the frame 12.
It will be understood, of course, that board 20 is the same in all
respects as board 19 and has the same components mounted
thereon.
As seen in FIG. 3, each of the tabs, whether contact tabs or
support tabs, have a small shoulder 80, the purpose of which is to
space the main bodies of the collector plates from the printed
circuit boards 19 and 20.
The assembly of the electrostatic precipitator of this invention
will now be described.
Firstly, the different collector plates and two printed circuit
boards are assembled so that the different tabs register with the
appropriate slots, as shown in the figures. The two printed circuit
boards would be identical, but reversed. In other words, one is the
mirror image of the other. That is, the far printed circuit board
20 in FIG. 1 would have the indentations 62 at its right-hand edge
as seen in FIG. 1, but would have the bar 64, with its arcuate
resilient fingers 66, located on the far side of the board as
viewed in FIG. 1. Bar 64 and fingers 66 also would be reversed, in
the sense that fingers 66 would be arcuately curved away from the
collector plates on the far side of the electrostatic precipitator
as viewed in FIG. 1. It is not necessary that both printed circuit
boards 19 and 20 have bus bars 69 and 67, although this is
desirable because of the resulting advantage of uniformity.
It will be appreciated from what follows that it would be possible
also to have one of the bus bars on one of the printed circuit
boards and the other on the other printed circuit board. For
example, the bus bar 67 could be located on printed circuit board
19, while bus bar 69 could be located on printed circuit board 20.
In the embodiment shown, however, it will be assumed that bus bars
67 and 69 are located on both printed circuit boards 19 and 20.
When the collector plates and the printed circuit boards have been
assembled in the required arrangement, the contact tabs 38, 42, 45
and 48 of all of the collector plates are crimped over as seen in
FIGS. 1 and 2. This crimping can be done manually or by machine.
The support tabs 40, 44, 46 and 50, are left uncrimped.
It will be appreciated that for two reasons it is highly desirable
to have the two vertical rows of crimped contact tabs separated
from each other by the greatest possible distance. The first reason
is, of course, to reduce the risk of electric arc-over between the
bus bars, these being at a high potential difference when the
precipitator is in use. The second reason is that the spread-apart
crimping locations hold the two printed circuit boards 19 and 20
tightly against the collector plates while subsequent operations,
now to be described, are performed. If both lines of crimped
contact tabs were close together along one edge of the printed
circuit boards 19 and 20, it would be possible to pull the "free"
edge of each board away from the collector plates, which is very
undesirable. To achieve separation of the two rows of crimped
contact tabs, the support tabs for the negative plates are all to
the right of the negative contact tabs, while the support tabs for
the positive plates are all to the left of the positive contact
tabs.
After tabs 38 and 45 have been crimped over as shown in FIG. 2,
both the tabs and associated bus bar 67 are masked by the
application of a coating of an electrically conductive, resilient
cement. This coating prevents arcs between bus bar 67 and the
crimped contact tabs 38 and 45 to minimize radio interference
arising from arcing. Because of its resilient nature, cement 82
also serves to minimize rattling.
In accordance with the instant invention, bus bar 69 is isolated
from each positive collector plate 32, 36 by means of a resistor.
In the embodiment of the invention shown this is achieved by
applying a coating of conductive but electrically resistive,
resilient cement 82a over each of fingers 101 and terminals 100.
Cement 82a not only serves the same function as cement 82 but
provides a highly resistive path between each finger 101 and each
adjacent terminal 100. The magnitude of the resistive path may vary
widely but preferably is in the range of 1 to 30 meg. ohms. In any
event, the value of the resistors so formed should be such that
when an arc-over occurs between an adjacent positive and negative
collector plate, the charge that is stored in the capacitors that
are constituted by the other positive and negative collector plates
is prevented from contributing to the arc-over. Thus, by way of
example, the application of cement 82a creates a 30 meg. ohm
resistor between bus bar 69 and each positive collector plate, so
that from an equivalent circuit point of view the collector plates
of the precipitator can be represented by a plurality of series
circuits each including a capacitor and a resistor with the series
circuits being connected in parallel with each other, whereas in
the electrostatic precipitator disclosed in the aforementioned
copending application the equivalent circuit is that of a plurality
of capacitors connected in parallel.
As the aforesaid resistors now are effectively connected between
bus bar 69 and each positive collector plate, there is no longer
any necessity to provide a 30 meg. ohm isolating resistor between
terminals 69a of bus bar 69 and the positive terminal of the power
supply (not shown). The required isolation of the power supply and
the collector plates is achieved by the resistors connected between
fingers 101 and terminals 100. This being the case, terminal 69a
can be and in practice is directly connected to the positive
terminal of the power supply which may be at, say, +6,000 volts DC.
The fact that no 30 meg. ohm resistor is connected between the
positive terminal of the power supply and terminal 69a also means
that bar 64 can be and is electrically connected to bus bar 69
eliminating the previously required separate external connection
between bar 64 and the positive terminal of the power supply. It
will be understood, of course, that bus bar 67 is directly
connected to the negative or grounded terminal of the power
supply.
Preferably cement 82 and 82a is a carbon-filled silicon rubber
cement which not only exhibits satisfactory resistive properties,
but will withstand the vibration of the collector plates caused by
air flow for an extended period of time. One material which has
been found satisfactory as cement 82 and 82a in the electrostatic
precipitator according to this invention is known as "Dow-Corning
Silastic 735 RTV" (trade mark).
Following the application of cement 82, 82a, a further coating 84
of non-conductive (insulative) resilient material may be applied
over the entire board 19 and 20 except for the bars 64. This
coating 84 entirely covers the projecting support tabs of the
collector plates, as well as the earlier coatings of cement 82,
82a. It also covers the spacing members 72 and anchors them in
place. The non-conductive, resilient coating 84 prevents arc-overs
across the surface of the board, and prevents rattling at the
support tabs. One material which has been found satisfactory for
coating 84 is "Dow-Corning 145" (trade mark) protective coating.
This material does not dry rigid and therefore can withstand
vibrations. FIG. 2 shows only cement 82, 82a. The non-conductive
coating is seen in section in FIGS. 1 and 3.
After the plates and printed circuit boards have been assembled as
above described, ionizing wire 15 can be wrapped sinusoidally about
the fingers 66. The wrapping of the ionizing wire can take place
prior to the application of the two coatings, if desired. It should
be understood, however, that the arrangement of ionizing wire 15
and its supports are not relevant to the instant invention, which
is directed to the collector plate mounting and electrical
connection arrangements. The ionizing wire and its supports might
even be in a separate part of the precipitator.
It also should be noted that even though cements 82, 82a may be the
same material, there is nothing inconsistent in referring to cement
82 as conductive and cement 82a as resistive, since resistive
material is conductive to some degree. Cement 82 is not required to
exhibit any degree of resistivity and could be a "perfect
conductor" if such were possible. In practise the amount of it that
might find its way between bus bar 67 and tabs 38 and 45 is such
that a very low resistance path is provided. On the other hand, the
length of the path between each finger 101 and each terminal 100 is
considerably greater providing a path having high resistance.
In the appended claims, the expression "printed circuit board" is
intended to cover any plate-like element of stiff, non-conductive
or insulative material which is capable of receiving a printed
circuit or bus bar on one surface. "Board" is here used in its
broadest sense, and is not limited to wood, wood products or
cellulosic materials.
* * * * *