Bulkhead gland assembly

To facilitate installation of cables through bulkheads and other surfaces and to provide electrical protection to apparatus connected to such cables, an assembly comprising electrically conductive blocks (6) clamped in a frame (2) is provided. The mounting blocks 6, each formed of two parts for fitting round a continuous cable length include ribs (11) adapted to grip the sleeving of the cable and an extended rib (10) for contacting screening of the cable. In use, the frame (2) is welded to a bulkhead or other conductive (earthed) element. A section of insulation is removed from the cable and on clamping of the assembly the blocks (6) are compressed together forcing ribs 10 to contact respective screens. Thus any induced electro-magnetic pulses on the cable screens are provided with a low-resistance leakage path.

The present invention relates to a bulkhead gland assembly and in 
particular to such an assembly arranged to provide a reduction in the 
effects of severe electro-magnetic pulses. 
It is known that atmospheric nuclear explosions can cause a high-energy 
short term electro-magnetic pulse. Such a pulse may cause an induced pulse 
to travel on screening of transmission cables which is likely to cause 
severe damage to connected equipment such as radar apparatus, radio 
transmitter and receiver equipments and other monitoring devices. 
To reduce the effect of such electro-magnetic pulses it is necessary for as 
much of the energy of the pulse as possible to be dissipated before 
reaching connected equipments. It is known to provide conductive 
assemblies where cables pass through the bulkhead of a ship, the 
assemblies having metallic members which contact the screens of cables 
passing through the assembly to effect connection of the screens to a 
large conductive surface to effect earthing. 
It is also known that to maintain the integrity of the surface through 
which cables pass the gland assembly should be substantially gas and water 
tight. Suitable gas tight and/or water tight and/or fire retardant frame 
assemblies are described in for example UK Specification No: 2040107, U.S. 
Pat. Nos. 3,489,440 and 3,282,544. 
It is an object of the present invention to provide an improved bulkhead 
gland assembly which is gas and water tight and which has the required 
high conductivity. 
According to the present invention there is provided a bulkhead gland 
assembly comprising a rigid electrically conductive frame for attachment 
to a bulkhead, a plurality of block members each of which includes an 
aperture to permit fitting of a cable, cable retaining means to grip a 
sheath of a fitted cable and means to contact a screen of such a cable, 
said plurality of block members being formed of a resilient electrically 
conductive material, and said frame having clamping means to locate and 
retain said members. 
Preferably each of said block members comprises at least two parts whereby 
the member may be fitted around a continuous length of cable. 
Said cable retaining means may comprise a plurality of ribs extending 
inwardly of said aperture and said contact means may comprise an elongate 
rib extending inwardly of said aperture and having greater depth than said 
retaining ribs. 
Said resilient electrically conductive material may have a silicon rubber 
base incorporating carbon fibres and nickel granules in predetermined 
proportions. 
The carbon fibres may be metal coated fibres in chopped lengths of 
approximately six millimeters and forming approximately four to five 
per-cent by weight of the finished material. 
The material may be derived from approximately twenty-four percent by 
weight of liquid silicone rubber, fifty percent by weight of five micron 
nickel granules, four percent by weight of chopped carbon fibres and 
twenty-two percent by weight of fifteen micron nickel granules. 
Spacing block members of the resilient electrically conductive material may 
be provided to fill unused space in the frame. 
The block members may be arranged in a plurality of rows within the frame, 
the or each pair of rows being separated by a block retaining means 
arranged to prevent accidental removal of the block members. 
Said block retaining means may be an H section member having arms extending 
either side of said frame. The block retaining member may be of stainless 
steel for example. 
The clamping means may include a plate member having a chamfered edge 
adapted to co-operate with a radius edge of the frame member on tightening 
of said clamping means to assist location and compression of said block 
members.

Referring to FIG. 1, the assembly comprises a frame 1 attached to a 
backplate 2 by welding for example. The frame 1 and backplate 2 are 
manufactured from metal such as stainless steel for example, the backplate 
2 being provided for attachment to a bulkhead by welding or bolting to 
ensure a good electrical contact with the bulkhead. 
The frame 1 has an opening at one end which is closed by a clamping member 
4 acting on a clamp plate 3 to compress and retain blocks 5, 6 held in the 
assembly. 
Each of the blocks 5 and 6 is in practice two half-blocks, the blocks 5 
acting as spacer members and the blocks 6 including an aperture 7 through 
which a cable may pass. 
The clamping member 4 is held in place by four bolts 8 which fit threaded 
apertures (not shown) in the frame 1. 
As thus far described, the assembly is similar to some of the known 
assemblies previously mentioned. However, in the present invention the 
blocks 5 and 6 are formed from a resilient, electrically conductive 
material such that, when compressed, the blocks due to their resilience 
form a water tight and gas tight seal between cables (not shown) passing 
through the apertures 7 and the frame 1. It will be appreciated that, in 
use, the assembly also provides fire retardance. 
On assembly, each cable passing through the bulkhead has a section of 
insulation stripped from it to expose an area of the cable screening 
layer. The exposed cable screen is then contacted by a segment of its 
respective block 6 (as described hereinafter with reference to FIG. 3) to 
ensure a good electrical contact between all the cable screens, through 
the blocks 5 and 6, the frame 1, the backplate 2 and the bulkhead to 
provide a low resistance path for dissipation of induced electro-magnetic 
pulses. 
As has been mentioned the blocks 5 and 6 require both resilience and good 
conductivity. One suitable block material is based on silicone rubber with 
the addition of nickel granules and chopped carbon fibres, the material 
being prepared by the following method: 
A base of twenty-four percent by weight of the required final product of 
liquid silicone rubber is used. To this base fifty percent by weight of 
five micron nickel granules is added and mixed. 
The silicone rubber and nickel mix is poured over four percent by weight of 
carbon fibres which are in chopped lengths of approximately six 
millimeters and mixed to produce a material having a plastic consistency. 
Finally twenty-two percent by weight of fifteen micron nickel granules is 
added to the material and mixed to produce a granular material which may 
be moulded to form the desired block shapes. 
It is here noted that metal coated carbon fibres may be used in the mixture 
and that the percentage figures given are approximate and some slight 
variation in the percentages is permissible. In practice it has been 
established that a finished material having 4.33% by weight of carbon 
fibres gives desired resilience, strength and conductivity parameters. 
Referring again to FIG. 1, to prevent dislodging of individual blocks 
within the matrix when assembled stainless steel `H` section plates 9 
which extend either side of the frame 1 are provided between each row of 
the blocks 5 and 6. This helps to ensure that if a longitudinal force is 
applied to one of the cables, the blocks 5 and 6 are retained in position 
by the arms of the H section. 
Referring now to FIG. 2, the basic components are essentially the same as 
the corresponding components of the gland of FIG. 1. However, it will be 
noted that the backplate 2' is circular. Providing the circular backplate 
2' avoids significant electrical stress factors at corner points of a 
backplate such as that shown in FIG. 1. 
Turning now to FIG. 3 the construction of the blocks 5 and 6 of FIG. 1 may 
be seen. Each of the blocks 5 and 6 comprise two identical parts, an upper 
and a lower part which, in the case of the blocks 6 facilitates fitting a 
cable through a bulkhead without necessitating cutting and rejoining of 
the cable. It will be appreciated that the blocks 5 do not need to be 
separable and may be moulded in a single piece. 
The block 6 in which the aperture 7 is provided has inwardly extending 
annular ribs 11 which grip sleeving of a fitted cable, and an inwardly 
extending annular portion 10 which is arranged to contact the screen of 
the fitted cable. 
The construction and operation of the plates 9 may also be seen. 
In use, when the baseplate 2 is attached to a bulkhead through which cables 
are to pass, the gland is assembled first by placing one of the H section 
plates 9'" into the base of the framework 1 and inserting the lower halves 
6' of the first layer of blocks into the upper part of the H section 
plate. A short length of insulation is stripped from the cable to be 
fitted to expose a length of the screening wire of comparable size to the 
length of the annular portion 10. 
The upper halves 6" of the first layer of blocks 5, 6 are now fitted 
followed by a further H section plate 9". Other layers of blocks 5,6 
interspersed by plates 9 are fitted in similar manner until the framework 
is full. The clamp plate 3 and clamping member 4 are fitted above the 
assembled blocks and tightened down using the screws 8. 
It will be noted that, on tightening down of the clamping member 4, the 
blocks 5,6 are slightly compressed causing the ribs 11 to grip the 
sleeving of inserted cables and the portions 10 to contact the exposed 
screens of the inserted cables. Any air gaps between the blocks also tend 
to be eliminated which helps to prevent flames spreading through a 
bulkhead in the event of fire. 
A feature of the present invention is the construction of the clamp plate 3 
which has a wedge shaped rear edge 12 adapted to co-operate with a 
radiussed edge 14 of the backplate 2. Thus, when the gland is assembled, 
the wedge 12 is positioned under the radius 14. A front lip 15 of the 
clamping member 4 acting on the front edge of the clamp plate 3 will force 
the wedge 12 further under the radius 14 as the screws 8 are tightened. 
This facilitates assembly of the gland since it is not necessary for the 
entire depth of the clamp plate 3 to be manually forced under the edge of 
the backplate 2 in the first instance and ensures electrical continuity 
between the plate 3 and the backplate 2 when the unit is assembled. 
It will be appreciated that, while as herein described, the assembly is 
particularly suited to use at a bulkhead of a ship or aircraft for 
example, the gland may also be used in walls of screened rooms. The unit 
may also be located in walls of unscreened rooms provided that a good 
earthing contact, such as through reinforcing metalwork of concrete walls, 
is available. 
Many advantages of the gland of the present invention in regard to water 
and gas tightness and fire retardant effects for example in addition to 
conductivity and ease of assembly will be realised.