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(11) | EP 0 188 046 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | By-pass unit |
| (57) An electrical by-pass unit, for use with residual current devices (RCD) to permit
testing of equipment receiving its electrical supply from a circuit controlled by
an RCD, comprising a rigid, electrically-insulating body (19, 20), adapted for releasably
secure attachment to an RCD and incorporating within the body one or more electrical
conductors (1, 2), which are inaccessible to touch when the by-pass unit is attached
to the RCD, and are adapted to safely electrically connect respective input and output
terminals of the RCD. |
[0001] This invention relates to electrical by-pass units, and particularly to such units which are suitable for use with earth leakage circuit breakers and similar devices known under the general title "Residual Current Devices" (hereinafter referred to as an "RCD") to permit testing of equipment receiving its electrical supply from a circuit controlled by an RCD.
[0002] An RCD is designed to detect any imbalance between the current in the "live" line and that in the "neutral" line of a circuit. Such an imbalance is normally due to current leaking to earth, and to safeguard against such earth leakage being through a human body, the RCD is designed to break the circuit very quickly, typically in the order of 20 milliseconds, following detection of the current imbalance.
[0003] When a new electrical installation is completed and commissioned, one of the tests that is done to establish the integrity of the earth circuit is the earth loop impedance test. This test involves plugging a testmeter into a socket in the circuit under test, and, using a specially designed feature of the meter, current is allowed to pass from the live pin to the neutral pin of the socket. A simultaneous computation of voltage and current gives a reading on the meter of the earth loop inpedance in ohms. Unfortunately, if the circuit under test includes an RCD, the testing procedure has the effect of artifically creating a fault in the circuit, which is sensed by the RCD, and the trip-out of the RCD breaks the circuit before a reading can be obtained on the meter. Tt is therefore impossible to carry out the earth loop impedance test in the normal manner, and to do the test properly, the RCD has to be physically removed, and replaced by a link, in order for the circuit to remain live during the test.
[0004] Removing RCD's, replacing them with links, performing the earth loop impedance test, removing the links and replacing the RCD's is a time consuming and inconvenient procedure, which is preferably avoided if possible. One alternative procedure is to by pass the RCD for the period of the test, using a short, insulated lead with a heavy duty "crocodile" clip at each end, to connect the imput and output terminals of the RCD. The use of such simple connectors is clearly, in itself, a somewhat hazardous procedure, and the present invention provides a completely safe and convenient device for bypassing an RCD while the earth loop impedance test is carried out.
[0005] Thus, according to the invention there is provided a by-pass unit for a residual current device comprising a rigid, electrically-insulating body, adapted for releasably secure attachment to a residual current device and incorporating within the body one or more electrical conductors which are inaccessible to touch when the by-pass unit is attached to the residual current device, and are adapted to safely electrically connect respective input and output terminals of the residual current device.
[0006] In a preferred embodiment of the invention, the by-pass unit includes a screw or screws which is or are adapted to co-operate with the like-threaded sockets on the RCD, which in normal use secure a protective cover thereto, thus enabling the by-pass unit to be easily releasably secured to the RCD.
[0007] In a further preferred embodiment each conductor of the by-pass unit comprises a linear bar or strap conductor bearing essentially perpendicularly at either end a spring-loaded terminal, adapted to contact electrically with the respective input and output terminals of an RCD.
[0008] Preferably, the by-pass unit is generally U-shaped, and is adapted to fit closely over the projecting body part of an RCD. It is also convenient for the insulating body of the by-pass unit to be formed in two parts, enabling the bar conductors to be sandwiched between them. The spring-loaded terminals are accommodated in appropriate bores within the two "legs" of the U-shaped body.
[0009] It is preferred that the insulating body of the by-pass unit be fabricated of plastics insulating material, for example polyvinyl chloride, poly(methyl methacrylate), or polypropylene, and that the conductors be of copper, brass or other conventional electrically conducting metallic material.
[0010] In order that the invention may be fully understood, a particular embodiment will now be described, by way of example only, with reference to the accompanying drawings, in which:-
Figures 1 and 2 show, separately, the two insulating parts of the by-pass unit, in perspective view;
Figure 3 is a perspective view of the conductor parts by the by-pass unit;
Figure 4 is a cross-section of the by-pass unit, in the plane A-A of Figure 1, when in operating position on an RCD, in this example a four pole unit made by Wylex Ltd.;
Figure 5 is a top view of the by-pass unit in operating position on an RCD;
Figure 6 is a front view of the by-pass unit in operating position on an RCD;
Figure 7 is a side view of the retaining screw, for securing the by-pass unit to the RCD.
[0011] The by-pass unit comprises:
(a) one or more conductors (1) each consisting of an electrically conducting metal bar (2), of such material and of such cross-sectional area as to comply with official regulations as shall from time to time be in force, and bearing near each end a terminal post (3,4) of similar material, each terminal post bearing a terminal cap (5,6) also of similar material, which is a tight, sliding fit on the terminal post, and is adapted to slide thereon against the resistance of a helical spring (7,8) mounted over each terminal post;
(b) a cover plate (10) of electrically insulating plastics material, in one surface of which are provided our parallel channels (11, 12, 13, 14) adapted to receive the metal bar portions (2) of four conductors (1), and in approximately the centre of which is provided an aperture (15) to accomodate the on-off switch (50) and test button (51) of an RCD, when the by-pass unit is operatively attached thereto;
(c) a U-shaped member (20), also of electrically insulating plastics material, comprising a base plate (34) and two arms (22, 23), in which are provided:
(i) in the base plate (34) an approximately central aperture (21) corresponding to the aperture (15) in the cover plate (10);
(ii)in each arm (22, 23) four bores (24-27 and 28-31 respectively) extending completely therethrough, of similar cross-section to the terminal posts (3,4) and terminal caps (5,6) of the conductors, and so positioned that when the by-pass unit is assembled and operatively secured to an RCD, the terminal caps (5,6) contact respective pairs of terminals on the RCD; each spring-biassed terminal cap (5,6) is retained within its respective bore (24-31) by means of a collar (9) which abuts a narrower terminal portion (45) of the said bore;
(iii)in each arm (22, 23) an additional bore (32,33) adapted to accommodate a screw (40) for securing the by-pass unit to the RCD by means of the screw sockets which in normal use secure a protective cover to the RCD; and
(iv)in the base member (34) of the U-shaped member (20), screw holes (35, 36 and 37,38 - not shown) to accommodate screws for holding together the U-shaped member (20) and the cover plate (10) with conductors (1) in position, the screws being secured through the screw holes (35-38) into corresponding threaded sockets (16-19) in the cover plate (10).
(d) two securing screws (40) each comprising a shank (41) adapted to pass lengthwise through a bore (33, 34) in a side arm (22,23) of the U-shaped member, and terminating at one end in a knob (42) and at the other end in a threaded portion (43) adapted to screw into the socket on an RCD which in normal use secures a protective cover thereto, and bearing near the threaded end a circlip or similar retaining clip (44) to retain the screw (40) in the side arm (22, 23) of the U shaped member (20).
[0012] The by-pass unit is assembled by placing a conductor (1) in each channel (11 to 14) of the cover plate (10), placing the U-shaped member over the terminal posts and terminal caps so that they are accommodated in the bores (24-31) and securing the U-shaped member to the cover plate with an appropriate adhesive.
[0013] In operation, when it is desired to carry out an earth loop impedance test in a circuit containing an RCD, the protective covers are first removed from the terminal connections of the RCD, and the by-pass unit according to the present invention is secured over the body of the RCD (60), by screwing the screws (40) into the threaded sockets (63) of the RCD which in normal use secure the protective covers thereto, thus electrically connecting each pair of imput and output terminals (61,62) of the RCD through a conductor (1) of the by-pass unit. The RCD is then effectively by- passed, and the earth loop impedance test can be carried out in normal manner. When the test is completed, the by-pass unit is unscrewed from the RCD, and the protective covers are replaced, so that the RCD is then again capable of performing its intended function.