FLAMEPROOF ELECTRIC COUPLERS

RACCORD ELECTRIQUE A L'EPREUVE DU FEU

English Abstract

ABSTRACT
FLAMEPROOF ELECTRIC COUPLERS
A flameproof electric coupler includes at least
one metal contact 1 fixed in a bore in a support member
having a shoulder 2, 4 facing towards each of its ends.
The shoulder 2 is engaged by a shoulder 3 on the contact
and the shoulder 4 is engaged by a separate annular
member 5 which is secured against axial movement with
respect to the contact. This separate annular member 5
forms a flameproof leakage path with both the contact and
the support member. A substantial saving in overall
length can be achieved.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:-
1. A flameproof electric coupler including at least one
metal contact fixed in a bore in a support member having a shoulder
facing towards each of its ends, one of those shoulders being
engaged by a shoulder on the contact and the other being engaged by
a separate annular member secured against axial movement with
respect to the contact and forming a first flameproof leakage path
between itself and the contact and a second flameproof leakage path
between itself and the support member.
2. A flameproof electric coupler including at least one
metal contact fixed in a bore in a support member having a shoulder
facing towards each of its ends, the shoulder facing towards the
cable being engaged by a shoulder on the contact and the other
shoulder being engaged by a separate annular member secured against
axial movement with respect to the contact and forming a first
flameproof leakage path between itself and the contact and a second
flameproof leakage path between itself and the support member.
3. A flameproof electric coupler including a least one metal
contact fixed in a bore in a support member having a shoulder
facing towards the cable being engaged by a shoulder on the contact
and the other shoulder being engaged by a separate annular member
secured against axial movement with respect to the contact and
forming a first flameproof path between itself and the contact and
a second flameproof path between itself and the support member, the
first flameproof path being formed by a screw thread with either
five or more full threads or an axial length of 8 mm or more, and
the second flameproof path being formed by an unthreaded path at
least 12.5 mm long.
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Description

This invention relates to electric couplers of the flame-
proof type for use in mines, oil refineries and other environmentc
where explosive atmospheres may be encountered for connecting
cables to one another or to electrical equipment.
In such couplers i-t is frequently necessary to fix a
metal contact (with or without an insulating covering) in a bore i
an insulator or other support member in such a manner that the
creepage path through the bore meets the standards for flameproof
10 connection. This normally means that the creepage path must be
formed by a screw thread having a minimum of five full threads or
an axial length of at least 8 mm, or if unthreaded must have a
length of at least 12.5 mm and often longer to ensure that
concentricity requirements are satisfied. As it is usually
preferable for the contact to be fixed to a cable conductor befor~
being fixed in the support member, a threaded connection is usual]
ruled out, and the alternative of a path length of 12.5 mm or
higher may significantly increase the overall length and the
material cost of the complete coupling.
In accordance with the invention, a flameproof electric
coupler includes at least one metal contact fixed in a bore in a
support member having a shoulder racing towards each of its ends,
one of those shoulders (usually the one facing towards the cable,
when applicable) being engaged by a shoulder on the contact and t~
other being engaged by a separate annular member secured against
axial movement with respect to the contact and forming a first
flameproof leakage path between itself and the contact and a seco
flameproof leakage path between itself and the support member.
Preferably the flameproof path between the separate
30 annular member and the contact is formed by a screw thread wlth
~ither five or more full threacls or an axial lenyth of 8 mm or
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more, and the flame-proof path between the separate annular member
and -the support member by an unthreaded path at least 12.5 mm long.
With this arrangement an overall leng-th oE at leas-t 12.5 mm is
required for the provision of -the f]ameproof connection, but a
substantial part of -that length can overlap with the function part
of the contact (which is not possible when -the :~larneproof path is
formed directly between the contact and the support member).
Preferably the Elameproo:E path between the separate
annular member and the con-tact is formed by a screw thread with
10 either five or more full threads or an axial length of 8 mm or
more, and ~he flameproof path between the separate annular member
and the support member by an unthreaded path at least 12. 5 mm
long. With this arrangement an overall length of at least 12.5 mm
is required for the provision of the flameproof connection, but a
substantial part of that length can overlap with the function part
of the contact (which is not possible when the flameproof path is
formed directly between the contact and the support member).
In the accompanying drawings, Figure 1 shows a mounting
suitable for a socket contact of a 3.3kV 30A mining coupler in
20 accordance with the invention, and Figure 2 shows for comparison an
equivalent conventional design. In each case the mating pin
coupler enters from the right, and the cable is connected to the
left as seen in the drawing.
In each case the contact 1 engages a shoulder 2 on the
support member that faces to the let through a shoulder 3, and a
shoulder 4 on the support member is used to fix the contact 1 in
position. In the design according to the invention, the shoulder 4
is engaged by the separate annular member 5 with a flameproof path
oE ten full screw threads with -the contact and a flameproof path of
30 12.5 ~m or longer with the support member. In the conventional
design, the shoulder 4 is engaged by a si.mple nut 6 threa-led on the
con-tact, which serves no unc-tlon except to secure the contact in
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position, and the whole of the flameproof path length has to be
provided between the shoulders 2 and 4.
In this particular design, a length saving of about 18 mm
results.
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