The disclosure relates generally to terminal block modules having a pair of electrical terminals for connecting electrical lines, and in particular to feed-through terminal block modules, and to terminal blocks assembled from the feed-through terminal block modules.
Current transformers are attached to the respective lines of a three-phase power line and connected to system relays that can take the power line off-line in the event of a fault condition.
When it is necessary to disconnect the current transformers from the relays for system maintenance, each current transformer positive must be shorted to the current transformer negative (or to ground) to prevent current transformer damage. The current transformers may be attached to a shorting block that protects the current transformers by enabling the current transformers to be shorted to neutral or ground when disconnected from the relays.
Shorting blocks however may expose arcing potentials. Protective gear is worn by maintenance personnel to reduce the risk of electrical shock when accessing the shorting block to disconnect or reconnect the current transformers.
There is a need then for an improved shorting block that reduces the risk of electrical shock to maintenance personnel.
Disclosed in embodiments is a feed-through terminal block module and terminal block formed from multiple feed-through terminal block modules. The terminal block in embodiments is a shorting block usable to protect current transformers while reducing the risk of electrical shock to maintenance personnel.
A feed-through terminal block module in accordance with the disclosure includes first and second electrical terminals, a first current bar, and a second current bar, the terminals and current bars in a terminal housing. The first current bar permanently electrically connects the first and second terminals. The second current bar is space away from the first current bar and is normally not electrically connected to the first current bar.
The first current bar includes a first contact portion of the module. The second current bar includes a second contact portion of the module and a third contact portion of the module.
The terminal housing has an opening aligned with the first and second contact portions that receives a contact plug inserted into the housing. The contact plug includes an electrical contact that, when fully inserted into the terminal housing simultaneously engages the first and second contact portions and thereby electrically connects the first current bar and the second current bar.
The entire electrical contact of the contact plug may be inside the terminal housing before making electrical contact with the first current bar to reduce the risk of inadvertent electrical shock of a user.
A number of feed-through terminal block modules may be placed side by side to form a feed-through terminal block. The terminal housing of the disclosed feed-through terminal block module further includes an additional opening or openings for a bridge pin or bridging current bar to engage and electrically connect the third contact portions of adjacent modules of the terminal block.
Other objects and features of the disclosure will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawing sheets illustrating one or more illustrative embodiments.
The terminal housing bottom wall 14, housing top wall 16, housing end wall 18, and housing end wall 20 together define an interior volume of the housing. Disposed in the interior of the terminal housing 12 is a first electrical terminal 24, a second electrical terminal 26, a first current bar 28, and a second current bar 30.
The first electrical terminal 24 is spaced apart from the second electrical terminal 26. The electrical terminals are located on opposite ends of the housing. The terminal housing has openings (not shown) which enable connecting external wires to the terminals. The illustrated terminals are screw terminals. In other embodiments other types of electrical terminals are used, including leg spring terminals, cage terminals, insulation-piercing terminals, and the like.
The first current bar 28 includes a feed-through portion 32 and a first contact portion 34 of the module 10. The first contact portion is permanently electrically connected to the feed-through portion.
The first current bar is formed of individual metal strips: a first metal strip 36 and a second metal strip 38. The metal strips are connected to one another and are electrically conductive with one another. The first metal strip forms the feed-through portion and the second metal strip including the first contact portion. The feed-through portion permanently connects the first electrical terminal 24 and the second electrical terminal 26 with one another. The first metal strip includes a first terminal end portion 40 and an opposite second terminal end portion 42 attaching the feed-through portion to the electrical terminals.
The first contact portion 34 is spaced away from the feed-through portion 32 towards the housing top wall 16. The first contact portion is formed on a free end of the second metal strip 38. The first contact portion is elastically displaceable and forms a resilient spring arm. The first contact portion includes a rounded contact nose 44.
The second current bar 30 is spaced away from the first current bar 28 towards the housing top wall 16. In the state of the module 10 shown in
The second current bar 30 includes a second contact portion 46 of the module 10 and a third contact portion 48 of the module 10. The second contact portion is formed on a free end of the second current bar. The second contact portion is elastically displaceable and forms a resilient spring arm. The second contact portion includes a rounded contact nose 50.
The contact nose 50 is aligned with the contact nose 44, the contact noses being aligned along a vertical axis as viewed in
The housing top wall 16 includes a through opening 52 that receives the contact plug inserted into the terminal housing. The terminal housing 12 includes an interior vertical wall 54 aligned with one side of the opening 52 that extends from below the opening 52 to near the feed-through portion 32. The lower contact nose 44 and the upper contact nose 50 each face the interior wall and are spaced apart from the wall by an air gap 56. The air gap extends along the vertical wall from the feed-through portion upwardly to the contact nose 44, upwardly beyond the contact nose 44 to the contact nose 50 and upwardly beyond the contact nose 50 to the upper end of the vertical wall. The vertical wall includes a pair of vertical ribs 58a, 58b extending the full height of the wall that extend into the air gap.
The third contact portion 48 is on an opposite end portion of the second current bar 30 spaced towards the end wall 20 from the first contact portion. The third contact portion is wider than the second contact portion and is shaped essentially as a flat plate that extends outwardly (in the direction perpendicular to the drawing sheet as viewed in
The material of the second current bar surrounding the through holes 60a, 60b and 62a, 62b define respective pairs of electrical contacts 64a, 64b, 66a, 66b (see
The housing top wall 16 defines a housing recess 68 that extends towards the third contact portion 48. The recess receives a bridge pin inserted into the terminal housing 12. The housing top wall at the bottom of the recess includes through holes aligned with the holes 60, 62 to receive a leg or legs of a bridge pin inserted into the terminal housing.
A contact plug 70 designed to selectively electrically connect the second current bar 30 with the first current bar 28 is shown in
The plug electrical contact 82 continues to maintain electrical contact with the upper contact nose 50 as the plug moves from its position shown in
The plug contact then makes contact with the first contact portion 34 and elastically deflects the first contact portion away from the housing vertical wall 54. The contact nose 44 makes reliable swiping electrical contact with the plug electrical contact 82. The spring force generated by the elastic deflection of the first contact portion and pressing the contact nose 44 against the plug electrical contact maintains that reliable electrical contact between the contact plug and first contact portion.
As shown in
As illustrated in
Multiple feed-through terminal block modules 10 can be used to form a terminal block such as the modular feed-through terminal block 110 shown in
Described below are illustrative uses of feed-through terminal blocks formed from multiple modules 10. The illustrated terminal blocks utilize the contacts 64a, 64b to bridge adjacent pairs of modules. The contacts 66a, 66b could be used instead, or a mix of contacts 64, 66 could be used. Contacts 64, 66 not used for bridging may be used for connecting test probes or the like into circuits connected to the terminal blocks.
Each transformer C is connected by respective transformer lines L1, L2, and L3 to the electrical terminals of a respective module 10B, 10C, 10D. The transformer lines L1, L2, L3 extend to relays (not shown) in a conventional manner.
The shorting block 110S is shown in
If desired, a contact plug 70 may be inserted into the module 10A that connects all the second current bars 30 of the shorting block 110S to ground or neutral during normal operation of the current transformers C.
Instead of individual bridge pins 86 to bridge adjacent pairs of modules, a ganged bridge pin having a sufficient number of electrically connected individual legs can be used to bridge the modules. For example, the ganged bridge pin 92 shown in
In
A ganged bridge pin having three electrically isolated pairs of electrically connected legs can also be designed to short the pairs of modules.
This design of a feed-through terminal block eliminates the need for externally exposed bridge pins, and the design of the individual modules 10 can be modified to eliminate external access to the holes 60a, 60b. Access to the other through holes 62a, 62b of the module may be retained if desired.
In a modification of the shorting block 114S, the module 10A is dedicated for attaching to a ground line. The second current bar 30 of the module 10A is permanently connected to the first current bar 28 as shown in broken lines in
The module 210 includes a fourth contact portion 212 of the module and a third current bar 214 that includes a fifth contact portion and a sixth contact portion of the module 210. The first electrical terminal 24 and the second electrical terminal 26 are spaced further apart from one another and the terminal housing 12 is widened to contain the third current bar 214.
The fourth contact portion 212 is part of the first current bar 28 and is formed from a third metal strip 216 connected to the first metal strip 36. The third metal strip 216 is identical to the second metal strip 38 but is disposed on the first metal strip mirror-symmetric on an opposite side of a vertical plane extending between the contact noses of the first and fourth contact portions. The contact noses of the first contact portion and the fourth contact portion 212 are spaced apart and separated by an air gap when the contact portions are unstressed.
The third current bar 214 is identical to the second current bar 30 but is disposed in the terminal housing 12 mirror-symmetric along the vertical axis with the second current bar 30. The third current bar 214 includes a fifth contact portion 218 like the second contact portion 46 and a sixth contact portion 220 like the third contact portion 48. The contact noses of the second contact portion 46 and the fifth contact portion 218 are disposed immediately adjacent one another. Alternatively, the contact noses can be separated by an air gap or could press against one another utilizing spring force.
The housing opening 52 is centered over the contact noses of the second contact portion 46 and the fifth contact portion 218. The top wall 16 of the terminal housing 12 is mirror symmetric about a vertical plane extending along the contact portions mirror axis to define a recess 222 like the recess 68 for providing external access to the contacts of the sixth contact portion 220.
The module 210 is designed to successively receive a contact plug such as the contact plug 70 inserted through the housing opening 52 first between the second and fifth contact portions and then between the first and fourth contact portions. When fully inserted the contact plug electrically connects the first current bar with both the second and third current bars. The plug elastically deflects the contact portions to provide swiping reliable electrical contact between the plug contacts and the contact noses of the contact portions as previously described. Because the contact plug is received between and squeezed between succeeding pairs of contact portions that assist in guiding the contact plug into the housing, the vertical wall 54 found in the module 10 is eliminated in the module 210.
The contact plug 70 has opposed first plug electrical contact 82 and second plug electrical contact 84 as previously described. The plug electrical contact 82 sequentially electrically connects with the contact noses of the first current bar 28 and second current bar 30 as previously described with respect to the module 10. The plug electrical contact 84 electrically sequentially connects with the contact noses of the first current bar 28 and the third current bar 214 in a like manner.
The illustrated feed-through terminal blocks are not intended to be limiting. Terminal blocks may be made of a different number of feed-through terminal block modules than the illustrated terminal blocks. The terminal block modules may be designed for mounting on a different mounting structure. Terminal blocks may be designed to have a mix of internal and external bridging.
While one or more embodiments have been disclosed and described in detail, it is understood that this is capable of modification and that the scope of the disclosure is not limited to the precise details set forth but includes modifications obvious to a person of ordinary skill in possession of this disclosure, including (but not limited to) changes in contact nose shape, material selection, size, operating ranges (temperature, current capacity, and the like), environment of use, and also such changes and alterations as fall within the purview of the following claims.
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Marathon Special Products, Product Data Sheet, Nov. 7, 2007, 3 pages. |