Mounting arrangement for neutral bus in switchgear assembly

The neutral cross bus in a switchgear assembly formed from two sets of side-by-side cabinets includes first and second neutral buses for the respective sets of cabinets. Each neutral bus is made up of a stack of flat conductors oriented horizontally in a main section extending across the cabinets of the set and vertically in a terminal section confronting the terminal section of the other neutral bus. The vertically oriented terminal sections are easily bolted together despite their limited accessibility when the two sets of cabinets are installed side-by-side. The flat conductors of the neutral cross bus are supported in their horizontal main sections by spaced supports formed by planar members with spaced horizontal slots set on edge and mounted by end flanges. The multiple flat conductors of neutral runbacks are interleaved with the flat conductors of the main sections of the cross bus and are supported by partitions having an opening sized to accommodate the maximum number of runback conductors with the remaining portion of the opening blocked by spacers interlocked with each other and the edges of the opening when less than the maximum number of flat runback conductors are used.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to switchgear assemblies for electric power 
distribution systems. More particularly, it relates to the neutral bus of 
such switchgear assemblies and arrangements for mounting such neutral bus 
within the cabinet of the assembly and connecting such neutral buses of 
adjacent units. 
2. Background Information 
Switchgear assemblies for electric power distribution systems include 
electrical apparatus housed in metal cabinets with associated conductors 
including bus bars and cabling for connecting the electrical apparatus in 
appropriate locations within the distribution system. Typically, the 
electrical apparatus includes switching devices such as circuit breakers 
or network protectors which provide protection, disconnect switches for 
isolating parts of the distribution system and transfer switches for 
connecting the distribution system to alternative power sources. The 
electrical apparatus can also include instrumentation such as metering 
equipment. 
The associated conductors typically include a set of rigid multi-phase 
buses extending transversely through the cabinet. This set of rigid 
transverse buses usually includes a neutral bus, although in most 
installations in the United States the neutral is not switched. 
Many installations require multiple cabinets arranged side by side, each 
with a transverse set of rigid buses. It is common to assemble several 
cabinets as a unit for shipping with a common set of buses extending 
transversely through the unit. Such practice requires that the set of 
transversely extending buses in adjacent units be connected in the field. 
As the rigid buses extend through the middle of each cabinet, it is not 
easy to make such connections, especially in the case of the neutral bus 
which is typically fabricated as a stack of elongated flat conductors set 
on edge and horizontally spaced. The splice connection between the neutral 
buses in adjoining units is made by a set of short sections of flat 
conductor interleaved between and secured to the two sets of flat 
conductors by bolts. This requires the manipulation of a number of small 
parts in restricted space. 
The conductors provided within each cabinet include runbacks for the phase 
and neutral conductors which extend rearward into another compartment for 
connection to cabling forming a second set of buses to which the 
electrical apparatus is connected. The neutral runbacks are also 
fabricated as a stack of elongated, flat conductors set on edge and 
horizontally spaced which butt against the side of the rearmost conductor 
of the transverse neutral bus. Such a joint requires electrically 
conductive spacers between the flat conductors of the transverse bus and 
associated fasteners. Again, this requires manipulation of a number of 
small parts, although such joints are usually made during assembly at the 
factory. 
There is room for improvement therefore in the neutral bus and its 
mountings within switchgear. 
SUMMARY OF THE INVENTION 
The present invention offers such improvements by providing a switchgear 
assembly which includes first and second sets of switchgear cabinets 
positioned side by side, a first neutral bus having a main section 
extending transversely through the first set of switchgear cabinets and a 
first terminal section transverse to the main section. Similarly, the 
second neutral bus has a main section extending transversely through the 
second set of switchgear cabinets and generally axially aligned with the 
main section of the first neutral bus. The second neutral bus also has a 
second terminal section transverse to its main section and confronting the 
terminal section of the first neutral bus. Fastener means secure the 
terminal sections of the two buses together in surface to surface contact. 
Preferably the terminal sections of the two neutral buses have aligned 
apertures and the fasteners comprise bolts extending through the 
apertures. In addition, the main sections of the neutral buses preferably 
extend horizontally and the terminal sections extend substantially 
vertically. 
As a further aspect of the invention, the transverse neutral bus comprises 
a stacked plurality of elongated flat conductors. Preferably, the 
elongated flat conductors in the main sections of the neutral bus are 
spaced apart while they are in contact in the terminal sections. Again, 
preferably, the elongated flat conductors in the main sections are 
oriented in substantially horizontal planes while the flat conductors in 
the terminal section extends in substantially vertical planes. 
In a particularly advantageous arrangement, the cabinets have forward, 
middle and rear compartments with the main sections of the neutral buses 
extending transversely through the middle compartments. At least one of 
the neutral buses includes in at least one of the compartments a neutral 
runback bus comprising a number of elongated flat conductors interleaved 
with and extending rearward toward the rear compartment from the main 
section. 
As another aspect of the invention, the cabinets include a plurality of 
supports for the neutral buses each of which comprises a planar member 
having spaced apart slots through which the plurality of elongated flat 
conductors extend. Preferably, the planar members have terminal flanges 
for mounting them in spaced relation in the cabinets. With the elongated 
flat conductors of the main sections of the neutral buses oriented in 
horizontal planes, the planar members of the supports are oriented in 
vertical planes with the slots extending horizontally to support the flat 
conductors in vertically stacked, horizontal planes. Preferably, the 
planar members are electrically conductive but magnetically nonpermeable 
to minimize eddy current heating and the effects of the large magnetic 
forces generated by a short circuit. A suitable material for the planar 
members of the supports is stainless steel. 
Partitions through which the stacked elongated flat conductors of the 
neutral bus extend comprise a planar part mounted substantially 
perpendicular to the neutral bus and having an opening sized to receive 
neutral buses with any number up to a predetermined number of flat 
conductors. The partition also includes removable spacers blocking off the 
opening around the elongated flat conductors. Spacers can be provided 
between the flat conductors of the neutral bus when spaced apart as well 
as between the conductors and the opening in the partition. In a preferred 
embodiment, the flat conductors have a selected thickness and the spacers 
have a width substantially equal to this thickness. The spacers are 
stackable to block the opening when the plurality of elongated flat 
conductors is less than the predetermined number. The spacers are made 
stackable by overlapping flanges extending along mating surfaces. 
Preferably, these overlapping flanges are provided by longitudinal tongues 
along one mating edge and a longitudinal groove along another mating edge. 
Also, preferably, the spacers engage the planar part adjacent the edges of 
the opening. This connection can be provided by a mounting tongue on one 
of the ends of the spacers and the edge of the opening, and a mounting 
groove on the other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates a piece of switchgear 1 incorporating the invention. 
This piece of switchgear 1 includes a metal cabinet 3 having a front 
compartment 5, a rear compartment 7 and a middle compartment 9. The front 
compartment houses electrical switching apparatus such as circuit 
breakers, network protectors, disconnect switches or transfer switches 
(not shown). In addition, instrumentation such as metering equipment 
(again, not shown) can also be housed in the front compartment 5. This 
electrical apparatus is housed in cells each of which has a front opening 
door 11. 
The middle compartment 9 of the metal cabinet 3 houses a cross bus system 
13 which includes phase buses 15 (only one shown) and a neutral bus 17. 
The phase buses 15 are connected (not shown) to a set of risers or 
vertical buses 19 which can be engaged by the electrical apparatus (not 
shown) in the front compartment 5 through stab conductors 21. The 
electrical apparatus is also connected to phase runbacks 23 which extend 
through the middle compartment 9 into the rear compartment 7. As the 
neutral is generally not switched in the United States, the neutral bus 17 
is not connected to the electrical apparatus in the front compartment. 
However, the neutral bus 17 does have neutral runbacks 25 which extend 
into the rear compartment. The phase runbacks 23 and neutral runback 25 
are connected in the rear compartment 7 to cabling (not shown) which forms 
feeder bus systems each with phase conductors and a neutral conductor. 
Typically, multiple pieces of switchgear 1 shown in FIG. 1 are joined 
together to form a switchgear assembly 27 such as that shown in FIG. 2. 
This switchgear assembly 27 includes a first set 29.sub.1 of three of the 
switchgear cabinets 3.sub.1, 3.sub.2, and 3.sub.3 and a second set 
29.sub.2 of the switchgear cabinets 3.sub.4, 3.sub.5, and 3.sub.6. While 
in the instant case the switchgear assembly 27 includes six cabinets, they 
are assembled in the factory as the two sets 29.sub.1 and 29.sub.2 of 
cabinets which are shipped to the field and then joined together to form 
the sixth cabinet assembly. Each set of three cabinets has a neutral bus 
17.sub.1 and 17.sub.2 extending across all three cabinets of the set 
29.sub.1 and 29.sub.2. The first neutral bus 17.sub.1 of the first set 
29.sub.1 and the second neutral bus 17.sub.2 of the second set 29.sub.2 of 
switchgear cabinets are then joined in the field to provide a common 
neutral bus for the assembly 27. 
Turning to FIG. 3, it can be seen that the first neutral bus 17.sub.1 is 
assembled from a plurality, in the example four, flat conductors 31.sub.1. 
In the main section 33.sub.1 of the neutral bus 17.sub.1 the flat 
conductors 31.sub.1 are oriented in horizontal planes and stacked 
vertically. The bus 17.sub.1 has a terminal section 35.sub.1 which extends 
transversely to the main section 33.sub.1 and therefore is oriented 
vertically. In the terminal section 35.sub.1 the conductors 31.sub.1 are 
in contact with one another. 
The second neutral bus 17.sub.2 is also formed from a stack flat conductors 
31.sub.2 which in a main section 33.sub.2 are oriented horizontally and 
spaced apart vertically, and which in a transversely extending terminal 
section 35.sub.2 extend vertically and are in contact with one another. 
In the field, the two sets 29.sub.1 and 29.sub.2 of three switchgear 
cabinets 3 each are positioned side-by-side with the main sections 
33.sub.1 and 33.sub.2 of the neutral bus bars 17.sub.1 and 17.sub.2 in 
longitudinal alignment. This brings the confronting terminal portions 
35.sub.1 and 35.sub.2 into surface to surface contact as shown in FIG. 4. 
The terminal sections 35.sub.1 and 35.sub.2 have a number of aligned 
apertures 37.sub.1 and 37.sub.2 through which fasteners such as the bolts 
39 are passed to clamp the terminal sections 35.sub.1 and 35.sub.2 
together to form a common neutral bus 17 for the switchgear assembly 27. 
In the exemplary switchgear assembly 27, the terminal portions 35 extend 
vertically upward from the main sections 33. However, these terminal 
sections 35 could also extend vertically downward from the main sections 
33. Typically, the common neutral bus 17 is connected to an external bus 
system (not shown) only at one end, for instance, the left end as shown in 
the exemplary embodiment of FIG. 2. The other end, the right end in FIG. 
2, is terminated within the cabinet 3.sub.6. 
The flat conductors 31 are supported and fixed in spaced vertical alignment 
by a number of neutral bus supports 41 spaced along the neutral bus 17 in 
each compartment. As best seen from the far right of FIG. 3, each neutral 
bus support 41 includes a vertically oriented planar member 43 having 
spaced apart horizontal slots 45, one for each flat conductor 31. Mounting 
flanges 47 and 49 are provided on the ends of the planar member 43. The 
forward flanges 47 are secured to a cross-member 51 in the cabinet 3 by 
fasteners such as screws 52. The rear flanges 49 are secured to partitions 
53 (by fasteners 54) which also serve as barriers between the middle 
compartment 9 and rear compartment 7 through which the neutral runbacks 25 
extend. As best seen in FIG. 5, the neutral runbacks 25 are also formed as 
a stack of flat conductors 55. The neutral runbacks 25 are substantially 
perpendicular to the neutral cross bus 17 and are easily connected 
therewith by interleaving of the flat conductors 55 and 31. The number of 
flat conductors 55 in the runbacks 25.sub.1 -25.sub.4 depend upon the 
requirements of the feeder circuit of which they are a part. For exemplary 
purposes only, it is shown in FIG. 5 that the neutral runbacks 25.sub.1 
-25.sub.4 have five, four, three and two flat conductors 55, respectively. 
Whatever the number of conductors 55, they are secured to the conductors 
31 by bolts 57. As will be noticed, the flat conductors 55 of the neutral 
runbacks are not spaced apart along their length but are offset by bends 
adjacent the cross bus 17 for interleaving between the spaced apart 
conductors 31. Alternatively, the conductors 55 of the runbacks 25 can 
remain spaced apart as they extend into the rear compartment 7. 
As mentioned, the partitions 53 support the neutral runbacks 25 and also 
form a barrier between the middle and rear compartments 9, 7. In order to 
accommodate the variations in the number of flat conductors 55 in the 
neutral runbacks 25, and yet provide an effective barrier, the partitions 
53 have a through opening 59 (see FIGS. 5 and 6) which is sized to 
accommodate up to the predetermined maximum number of the flat conductors 
55. For neutral runbacks 25 having less than this predetermined number of 
flat conductors, removable spacers 61 are provided to block off the unused 
portion of the through opening 59. Preferably, the spacers 61 are 
vertically sized to be substantially equal to the thickness of the flat 
conductors 55 such that they replace the flat conductors 55 on a 
one-to-one basis. 
The spacers 61 are made stackable by overlappable flanges including the 
flanges 63 which form a longitudinally extending tongue 63 extending along 
a top mating surface 65 and a downwardly extending pair of flanges which 
form a longitudinally extending groove 67 on a bottom mating surface 69. 
As illustrated in FIG. 7, the longitudinally extending tongue 63 and 
groove 67 mate to stack the spacers 61. 
The spacers 61 are secured within the partition 53 by a horizontally 
extending tongue 71 at the bottom of the through opening 59 which engages 
the groove 67 in the bottom surface 69 of the bottom spacer 61. In 
addition, the spacers 61 have vertically extending grooves 73 at each end 
which slide onto and engage vertically extending tongues 75 on the side 
surfaces of the through opening 59. Alternatively, the spacer 61 could 
have vertically oriented tongues at each end which would engage vertically 
oriented grooves in the sidewalls of the opening 59. Also, if the flat 
conductors 55 of the neutral runbacks 25 remain spaced apart throughout 
their length, the spacers could be sized to extend between each of the 
spaced apart flat conductors 55. 
The neutral bus supports 41 for the neutral bus bar 17 can be fabricated 
from electrical conductive sheet material as the positions 41 and cross 
members 51 on which the supports 41 are mounted are electronically 
insulative. Preferably, this sheet material has a low magnetic 
permeability to minimize eddy currents and the effects of the magnetic 
flux generated by the high currents of short circuits. A suitable material 
is stainless steel. 
While specific embodiments of the invention have been described in detail, 
it will be appreciated by those skilled in the art that various 
modifications and alternatives to those details could be developed in 
light of the overall teachings of the disclosure. Accordingly, the 
particular arrangements disclosed are meant to be illustrative only and 
not limiting as to the scope of invention which is to be given the full 
breadth of the claims appended and any and all equivalents thereof.